NEUR0007: Lecture and Textbook Notes

Contents
INTRODUCTION TO ELECTRICITY ............................................................................................................................................................ 9
ELECTRICITY ................................................................................................................................................................................................. 9
CONDUCTORS........................................................................................................................................................................................... 9
INSULATORS ............................................................................................................................................................................................. 9
CIRCUITS TOPOLOGY.............................................................................................................................................................................. 10
RESISTANCE IN SERIES .................................................................................................................................................................... 11
RESISTANCE IN PARALLEL ............................................................................................................................................................. 11
THE VOLTAGE DIVIDER.................................................................................................................................................................... 11
CAPACITANCE............................................................................................................................................................................................ 11
Factors affecting capacitance .......................................................................................................................................................... 11
Capacitance in parallel....................................................................................................................................................................... 12
Capacitance in series .......................................................................................................................................................................... 12
DIRECT AND ALTERNATING CURRENT ......................................................................................................................................... 12
TIME DEPENDENT CIRCUITS: RC CIRCUIT ................................................................................................................................... 12
ELECTRICAL MODEL OF A CELL ........................................................................................................................................................ 13
ELECTRICAL EQUIVALENT CIRCUIT OF A NEURONAL CELL BODY................................................................................... 13
Nernst Equation: .................................................................................................................................................................................. 14
METHODS OF MEASURING ION CHANNELS ...................................................................................................................................... 15
QUESTIONS ................................................................................................................................................................................................. 15
ION CHANNELS ......................................................................................................................................................................................... 15
METHODS OF TESTING ION CHANNEL THEORY ........................................................................................................................ 15
METHODS OF DETERMINING AMINO ACID SEQUENCE OF ION CHANNEL .................................................................... 16
1. CLONING BY PROTEIN PURIFICATION (Na+ channels) ............................................................................................ 16
2. POSITIONAL CLONING (K+ channels) ............................................................................................................................... 17
3. CLONING BY SEQUENCE HOMOLOGY ............................................................................................................................... 17
ION CHANNEL STRUCTURED INFERRED FROM SEQUENCE ................................................................................................. 18
STRUCTURE OF SODIUM CHANNELS.......................................................................................................................................... 18
STRUCTURE OF POTASSIUM CHANNELS .................................................................................................................................. 18
MEASURING CURRENT FLOW: PATCH CLAMPING THE MEMBRANE ............................................................................... 19
ORIGIN...................................................................................................................................................................................................... 19
PURPOSE ................................................................................................................................................................................................. 19
METHOD .................................................................................................................................................................................................. 19
MAIN FINDINGS ................................................................................................................................................................................... 19
TECHNIQUES ......................................................................................................................................................................................... 19
CONFIGURATIONS .............................................................................................................................................................................. 20
MEASURING CURRENT FLOW: VOLTAGE-CLAMPING THE MEMBRANE......................................................................... 22
PATCH CLAMP RECORDING OF SINGLE CHANNELS ............................................................................................................ 24
USE OF HETEROLOGOUS EXPRESSION SYSTEMS ...................................................................................................................... 24
XENOPUS OOCYTES ............................................................................................................................................................................ 25
EXPRESSION OF MUTANT CHANNELS ....................................................................................................................................... 25
CRYSTALLISATION STUDIES ............................................................................................................................................................... 26
LIMITATIONS WITH MUTAGENESIS EXPERIMENTS ........................................................................................................... 26
PROKARYOTIC POTASSIUM CHANNEL ...................................................................................................................................... 26
STOICHIOMETRY ...................................................................................................................................................................................... 27
PROBABILITY OF OPENING / OPEN PROBABILITY................................................................................................................... 27
PROBABILITY OF OPENING (VG) .................................................................................................................................................. 27
OPEN PROBABILITY OF Na+ CHANNELS (p. 54 of Cellular and Molecular Neurophysiology)........................... 28
PROBABILITY OF OPENING (LG) .................................................................................................................................................. 29

,IV CURVE........................................................................................................................................................................................................... 31
I-V RELATIONS OF A SQUID AXON.................................................................................................................................................... 31
STRUCTURE AND MOLECULAR BIOLOGY OF ION CHANNELS .................................................................................................. 32
FAMILIES OF ION CHANNELS ............................................................................................................................................................. 33
Common functional modules between different families ................................................................................................... 33
MAIN GROUPS OF ION CHANNELS ................................................................................................................................................... 33
1. Gated ............................................................................................................................................................................................... 33
2. Non gated ...................................................................................................................................................................................... 34
MEMBRANES, IONS, AND CHANNELS ............................................................................................................................................. 34
SIGNALLING IN THE NERVOUS SYSTEM ........................................................................................................................................ 34
FUNCTIONAL FEATURES OF VGIC .................................................................................................................................................... 35
CHANNEL GATING ................................................................................................................................................................................... 35
VOLTAGE SENSOR (S4 segment): ................................................................................................................................................. 36
THE INACTIVATION DOMAIN ............................................................................................................................................................. 38
o N-type inactivation .................................................................................................................................................................... 38
o P-type inactivation .................................................................................................................................................................... 39
o C-type inactivation .................................................................................................................................................................... 39
POTASSIUM CHANNEL INACTIVATION ..................................................................................................................................... 39
SODIUM CHANNEL INACTIVATION ............................................................................................................................................. 41
THE PORE DOMAIN ............................................................................................................................................................................ 42
CALCIUM IN CHANNEL ACTIVITY ..................................................................................................................................................... 43
Neuronal activities regulate channel activities via calcium ............................................................................................... 43
DIVERSITY IN STRUCTURE AND FUNCTION OF ION CHANNELS........................................................................................ 43
MAJOR CLASSES OF VOLTAGE-DEPENDENT ION CHANNELS ......................................................................................... 44
CALCIUM CHANNELS ......................................................................................................................................................................... 44
POTASSIUM CHANNELS.................................................................................................................................................................... 44
DISEASES ASSOCIATED WITH ION CHANNEL DYSFUNCTION ............................................................................................. 45
HOW TRANSMITTERS MEDIATE CHANNEL OPENING ............................................................................................................ 45
COUPLING TO TRIMERIC G PROTEIN ......................................................................................................................................... 45
INTERACTION WITH Gβγ SUBUNITS .......................................................................................................................................... 45
CONVERGENCE OF SECOND MESSENGER ON SAME CHANNEL ..................................................................................... 45
ION PERMEATION .................................................................................................................................................................................... 46
MAIN OBSERVATIONS ....................................................................................................................................................................... 46
EVIDENCE FOR ION BINDING SITE(S) ........................................................................................................................................ 46
EVIDENCE FOR MULTIPLE ION BINDING SITES .................................................................................................................... 46
CRYSTALLOGRAPHIC EVIDENCE OF MULTIPLE IONS IN A PORE.................................................................................. 46
ION SELECTIVITY ..................................................................................................................................................................................... 46
ION SELECTIVITY OF Ca2+ CHANNELS...................................................................................................................................... 47
ION SELECTIVITY FOR Na+ CHANNEL ....................................................................................................................................... 47
KEY MOLECULAR DIFFERENCES BETWEEN VG CALCIUM AND SODIUM CHANNELS .......................................... 47
ION CHANNEL DISTRIBUTION ........................................................................................................................................................... 47
K+ CHANNELS TARGETED TO AXONS AND DENDRITES ................................................................................................... 47
Ca2+ CHANNEL DISTRIBUTION .................................................................................................................................................... 48
BACKPROPOGATION............................................................................................................................................................................... 48
BIOELECTRICITY I ........................................................................................................................................................................................ 49
EXAMPLE QUESTIONS............................................................................................................................................................................ 49
GENERAL DISTRIBUTION OF IONS ACROSS A CELL ................................................................................................................. 49
DIFFUSION POTENTIAL......................................................................................................................................................................... 50
ELECTRIC POTENTIAL DIFFERENCE ............................................................................................................................................... 50

, FACTORS INDUCING ION MOVEMENT THROUGH MEMBRANE .......................................................................................... 50
MEMBRANE POTENTIAL (Vm)........................................................................................................................................................... 51
WHY ARE NEURONS ELECTRICALLY POLARISED? .............................................................................................................. 51
RESTING MEMBRANE POTENTIAL.............................................................................................................................................. 51
RECORDING THE RESTING POTENTIAL.................................................................................................................................... 52
EXPERIMENTALLY DEPOLARISING THE MEMBRANE ........................................................................................................ 53
EXPERIMENTALLY HYPERPOLARISING THE MEMBRANE ............................................................................................... 53
RESTING POTENTIALS OF DIFFERENT NEURONS ............................................................................................................... 53
FACTORS RESPONSIBLE FOR GENERATION AND MAINTENANCE OF RESTING POTENTIAL: ......................... 54
SELECTIVE PERMEABILITY ................................................................................................................................................................. 54
RELATIONSHIP WITH EQUILIBRIUM POTENTIAL ............................................................................................................... 54
GOLDMAN-HODGKIN-KATZ EQUATION .................................................................................................................................... 55
EQUILIBRIUM POTENTIAL ................................................................................................................................................................... 57
HYPERPOLARISATION ...................................................................................................................................................................... 57
DEPOLARISATION ............................................................................................................................................................................... 57
NERNST EQUATION............................................................................................................................................................................ 57
REVERSAL POTENTIAL (Vr) AKA NERNST POTENTIAL ......................................................................................................... 58
DIFFERENCE WITH EQUILIBRIUM POTENTIAL .................................................................................................................... 58
POTASSIUM CHANNELS.................................................................................................................................................................... 58
NEURONAL IONIC CURRENTS ............................................................................................................................................................ 59
DETERMINING CELL’S ELECTRICAL PROPERTIES .................................................................................................................... 59
MEMBRANE AT REST EQUIVALENT ELECTRICAL CIRCUIT .................................................................................................. 59
BIOELECTRICITY II ....................................................................................................................................................................................... 61
NEURON EQUIVALENT ELECTRICAL CIRCUIT ............................................................................................................................ 61
ELECTRICAL EQUIVALENT TO MEMBRANE ONLY PERMEABLE TO K+ ..................................................................... 63
Ohms Law: ................................................................................................................................................................................................... 63
DRIVING FORCE ........................................................................................................................................................................................ 64
VOLTAGE AND TIME-DEPENDENT ION CURRENTS ................................................................................................................. 64
FACTORS INFLUENCING POSTSYNAPTIC INTEGRATION....................................................................................................... 65
SPECIFIC CAPACITANCE................................................................................................................................................................... 65
HOW MEMBRANE POTENTIAL CHANGES WITH INJECTION OF CURRENT .............................................................. 66
SYNAPTIC TRANSMISSION EVENTS................................................................................................................................................. 67
PASSIVE ELECTRICAL PROPERTIES OF NEURONS.................................................................................................................... 67
MEASURING PASSIVE ELECTRICAL PROPERTIES OF NEURONS.................................................................................... 68
ELECTRICAL CONSTANTS OF A NEURON AND SIGNAL INTEGRATION ........................................................................... 68
THE LENGTH SPACE CONSTANT ....................................................................................................................................................... 69
DECREMENT .......................................................................................................................................................................................... 69
THE TIME CONSTANT 𝝉......................................................................................................................................................................... 70
SUMMATION............................................................................................................................................................................................... 70
SPATIAL SUMMATION....................................................................................................................................................................... 71
TEMPORAL SUMMATION ................................................................................................................................................................. 72
WHICH SIGNALS INTEGRATE IN TEMPORAL AND SPATIAL SUMMATION ............................................................... 72
INTERACTIONS BETWEEN SYNAPTIC INPUT AND A BACK-PROPAGATING AP .......................................................... 72
THE ACTION POTENTIAL .......................................................................................................................................................................... 74
EXAMPLE QUESTIONS............................................................................................................................................................................ 74
DIFFERENT TYPES OF AP’s IN EXCITABLE CELLS ..................................................................................................................... 74
PHASES ......................................................................................................................................................................................................... 75
MAIN CHARACTERISTICS ..................................................................................................................................................................... 76
IONIC MECHANISMS OF THE AP........................................................................................................................................................ 78
GATING OF CHANNELS DURING Na+ DEPENDENT AP ....................................................................................................... 79

, EXPERIMENTAL FINDINGS ............................................................................................................................................................. 79
CALCULATING CONDUCTANCE FROM VOLTAGE CLAMP DATA ......................................................................................... 80
DETERMINING THE CONDUCTANCE OF A CHANNEL ......................................................................................................... 81
MEAN OPEN TIME OF A CHANNEL ................................................................................................................................................... 82
K+ vs Na+ ..................................................................................................................................................................................................... 82
SIMILARITIES ........................................................................................................................................................................................ 82
DIFFERENCES ....................................................................................................................................................................................... 82
SHAPE OF THE AP .................................................................................................................................................................................... 82
PROPAGATION OF AN AP ..................................................................................................................................................................... 83
FACTORS AFFECTING PROPAGATION ....................................................................................................................................... 83
ACTIVE TRANSPORT IN THE NERVOUS SYSTEM ............................................................................................................................ 85
QUESTIONS ................................................................................................................................................................................................. 85
INTRODUCTION ........................................................................................................................................................................................ 85
POWER .......................................................................................................................................................................................................... 85
Na+/K+-ATPase......................................................................................................................................................................................... 86
Ca2+-ATPase .............................................................................................................................................................................................. 86
NEUROTRANSMITTER TRANSPORTERS........................................................................................................................................ 87
DIVERSITY OF NEUROTRANSMITTER TRANSPORTERS .................................................................................................... 87
STRUCTURE AND FUNCTION IN NEUROTRANSMITTER TRANSPORTERS ................................................................ 87
ION-COUPLED ACTIVE TRANSPORT ................................................................................................................................................ 87
Na+/Ca2+ EXCHANGER ......................................................................................................................................................................... 87
TERMINATION OF NEUROTRANSMISSION................................................................................................................................... 88
pH REGULATION....................................................................................................................................................................................... 88
REVERSAL OF ATPases .......................................................................................................................................................................... 88
H+-ATPases ............................................................................................................................................................................................ 88
HOW NEURONES COMMUNICATE – GAP JUNCTIONS ................................................................................................................... 89
QUESTIONS ................................................................................................................................................................................................. 89
TYPES OF CELL-CELL JUNCTION ....................................................................................................................................................... 89
ADHERING JUNCTIONS: Desmosomes........................................................................................................................................ 89
TIGHT JUNCTIONS ................................................................................................................................................................................... 90
GAP JUNCTION ........................................................................................................................................................................................... 91
DISCOVERY OF ELECTRICAL COUPLING ................................................................................................................................... 91
ELECTRICAL VS CHEMICAL SYNAPSES .......................................................................................................................................... 92
FEATURES OF GAP JUNCTIONS ..................................................................................................................................................... 93
COMPOSITION OF GAP JUNCTIONS ............................................................................................................................................. 94
FUNCTIONS OF GAP JUNCTIONS................................................................................................................................................... 94
LEVELS OF ORGANISATION ............................................................................................................................................................ 94
GAP JUNCTIONS GATED BY TRANSJUNCTIONAL VOLTAGE ............................................................................................. 95
..................................................................................................................................................................................................................... 95
OTHER FACTORS GATING GAP JUNCTION CHANNELS ....................................................................................................... 95
BLOCKING GAP JUNCTION CHANNELS ...................................................................................................................................... 95
MEASURING GAP JUNCTION CHANNEL ION SELECTIVITY ............................................................................................... 96
GAP JUNCTIONS IN THE HEART.................................................................................................................................................... 96
BIOCHEMICAL COUPLING – WHAT GOES THROUGH GAP JUNCTIONS ........................................................................ 96
GAP JUNCTIONS AND CALCIUM WAVES.................................................................................................................................... 97
MODULATION OF GAP JUNCTIONS .............................................................................................................................................. 98
GAP JUNCTIONS IN CONNECTING GLIAL CELLS ......................................................................................................................... 98
ASTROCYTES ......................................................................................................................................................................................... 98
OLIGODENDROCYTES AND SCHWANN CELLS ....................................................................................................................... 98
LEPTOMENINGEAL CELLS ............................................................................................................................................................... 99
HEMIJUNCTIONS ...................................................................................................................................................................................... 99

, GAP JUNCTION-RELATED NEUROPATHOLOGIES ...................................................................................................................... 99
EPILEPSY ................................................................................................................................................................................................. 99
GLIAL CELLS AND HOMEOSTASIS OF THE EXTRACELLULAR SPACE ..................................................................................101
DISCOVERY ...............................................................................................................................................................................................101
CENTRAL GLIA: ..................................................................................................................................................................................101
PERIPHERAL GLIA ............................................................................................................................................................................101
METABOLIC CHARACTERISTICS OF GLIAL CELLS ...................................................................................................................101
ASTROCYTES ............................................................................................................................................................................................101
TYPES OF ASTROCYTES ..................................................................................................................................................................101
ROLES OF ASTROCYTES .................................................................................................................................................................101
ASTROCYTES MAINTAIN THE BBB.................................................................................................................................................102
ASTROCYTES REGULATE IONIC COMPOSITION OF EXTRACELLULAR FLUID ............................................................103
BUFFERING [K+]o VIA THE Na/K PUMP AND ION CHANNELS .....................................................................................104
SPATIAL BUFFERING .......................................................................................................................................................................105
ASTROCYTES IN THE NEUROTRANSMITTER CYCLE..............................................................................................................107
PREVENTING [GLUTAMATE]o REACHING NEUROTOXIC LEVELS ...............................................................................107
SYNAPTIC TRANSMISSION: PRESYNAPTIC MECHANISMS .......................................................................................................109
QUESTIONS ...............................................................................................................................................................................................109
EVENTS LEADING TO SYNAPTIC TRANSMISSION ..............................................................................................................110
RETICULAR THEORY VS NEURONE DOCTRINE ...................................................................................................................110
DISCOVERY OF SYNAPTIC TRANSMISSION ................................................................................................................................110
SOUP VS SPARK ..................................................................................................................................................................................111
EVIDENCE OF CHEMICAL SYNAPTIC TRANSMISSION ......................................................................................................111
EVIDENCE OF ELECTRICAL SYNAPTIC TRANSMISSION ..................................................................................................112
CHEMICAL VS ELECTRICAL TRANSMISSION .............................................................................................................................112
WHY CHEMICAL .................................................................................................................................................................................114
Ca2+ IN SYNAPTIC TRANSMISSION ...............................................................................................................................................114
SQUID GIANT SYNAPSE...................................................................................................................................................................115
TRANSMITTER RELEASE OCCURS RAPIDLY FOLLOWING CALCIUM ENTRY .........................................................118
TRANSMITTER RELEASE REQUIRES BINDING OF CALCIUM IONS..............................................................................118
MOLECULAR MACHINERY UNDERLYING VESICLE RELEASE .............................................................................................119
VESICLE HYPOTHESIS OF TRANSMITTER RELEASE .........................................................................................................119
NEUROTRANSMITTER RELEASE MECHANISMS..................................................................................................................119
KEY PROTEINS OF EXOCYTIC MACHINERY ...........................................................................................................................119
HOW IS NEUROTRANSMITTER RELEASE PROBABILITY REGULATED? ...................................................................120
SYNAPTOTAGMIN I IS A MAJOR CA2+ SENSOR FOR EXOCYTOSIS ..............................................................................120
QUANTAL NATURE OF SYNAPTIC TRANSMISSION .................................................................................................................121
TRANSMITTER RELEASE IS STOCHASTIC (random) .........................................................................................................121
TRANSMITTER RELEASE IS QUANTISED ................................................................................................................................121
EPPs and MEPPs.................................................................................................................................................................................121
EPPs are made up of multiple MEPPs .......................................................................................................................................122
MORPHOLOGICAL EVIDENCE FOR EXOCYTOSIS DURING SYNAPTIC TRANSMISSION ......................................123
CNS SYNAPSES AND QUANTA ......................................................................................................................................................124
RESPONSE TYPES AT SINGLE CNS SYNAPSES WITH DIFF #S OF RELEASE SITES ...............................................124
BASIC PRINCIPLES OF QUANTAL ANALYSIS AT CENTRAL SYNAPSES ......................................................................124
WHAT FACTORS DETERMINE TRIAL-TO-TRIAL VARIABILITY IN AMPLITUDE OF EVOKED SYNAPTIC
CURRENTS ............................................................................................................................................................................................129
DOCKED SYNAPTIC VESICLES......................................................................................................................................................129
SHORT-TERM HOMOSYNAPTIC PLASTICITY ..................................................................................................................................130
CHEMICAL SYNAPTIC TRANSMISSION .........................................................................................................................................130

, SHORT-TERM PLASTICITY .................................................................................................................................................................133
SYNAPTIC DEPRESSION ......................................................................................................................................................................133
CAUSES OF DEPRESSION................................................................................................................................................................134
MEASURING SYNAPTIC DEPRESSION ......................................................................................................................................134
MECHANISMS UNDERLYING SYNAPTIC DEPRESSION......................................................................................................134
SYNAPTIC FACILITATION ...................................................................................................................................................................135
CAUSE .....................................................................................................................................................................................................135
MEASURING FACILITATION .........................................................................................................................................................135
MECHANISMS UNDERLYING SYNAPTIC FACILITATION ..................................................................................................136
POTENTIATION .......................................................................................................................................................................................136
LONG-TERM SYNAPTIC PLASTICITY ..................................................................................................................................................138
LONG TERM POTENTIATION (LTP) ...............................................................................................................................................138
CRITICAL EVALUATION ..................................................................................................................................................................138
EVIDENCE OF ROLE OF NMDA RECEPTORS IN LTP ...........................................................................................................138
SUMMARY OF MECHANISM OF LTP ..........................................................................................................................................139
FEATURES OF LTP.............................................................................................................................................................................139
EVIDENCE OF LTP .............................................................................................................................................................................140
WHAT CHANGES IN LTP .................................................................................................................................................................141
PHASES OF DECAY OF LTP ............................................................................................................................................................141
PROPOSED MECHANISM FOR LTP .............................................................................................................................................142
POSTSYNAPTIC MECHANISMS UNDERLYING INDUCTION OF LTP .............................................................................142
aCaMkinase II ......................................................................................................................................................................................143
SILENT SYNAPSE (pg. 327 From Neuron to Brain) .............................................................................................................143
PRESYNAPTIC MECHANISMS UNDERLYING LTP ................................................................................................................144
LONG-TERM DEPRESSION .................................................................................................................................................................145
TYPES OF LTD .....................................................................................................................................................................................145
QUANTAL ANALYSIS AND DISTRIBUTION ..................................................................................................................................146
NEUROTRANSMITTERS ...........................................................................................................................................................................147
DIFFUSION AND REMOVAL OF TRANSMITTER FROM CLEFT ............................................................................................147
ACETYLCHOLINE ....................................................................................................................................................................................147
SYNTHESIS AND RELEASE ............................................................................................................................................................147
DIFFUSION AND REMOVAL FROM CLEFT ..............................................................................................................................147
GLUTAMATE .............................................................................................................................................................................................148
DIFFUSION AND REMOVAL FROM CLEFT ..............................................................................................................................148
GABA ............................................................................................................................................................................................................148
DIFFUSION AND REMOVAL FROM CLEFT ..............................................................................................................................148
GLYCINE .....................................................................................................................................................................................................149
DIFFUSION AND REMOVAL FROM CLEFT ..............................................................................................................................149
NEUROTRANSMITTER TRANSPORTERS......................................................................................................................................150
DIVERSITY OF NEUROTRANSMITTER TRANSPORTERS ..................................................................................................150
STRUCTURE AND FUNCTION IN NEUROTRANSMITTER TRANSPORTERS ..............................................................150
MODULATION OF SYNAPTIC TRANSMISSION ................................................................................................................................151
NEUROTRANSMISSION ........................................................................................................................................................................151
FAST OR SLOW ACTIONS ...............................................................................................................................................................151
NEUROMODULATION ...........................................................................................................................................................................152
WHO IS RESPONSIBLE FOR NEUROMODULATORY EFFECTS ........................................................................................153
MECHANISMS OF NEUROMODULATIONS ..............................................................................................................................154
GPCR ............................................................................................................................................................................................................154

, G PROTEINS .........................................................................................................................................................................................154
ION CHANNELS MODULATED BY G PROTEINS ....................................................................................................................155
INWARDLY RECTIFYING K+ CHANNELS REGULATED BY G PROTEINS ....................................................................156
EFFECTORS: ADENYLYL CYCLASES...........................................................................................................................................157
SECOND MESSENGERS.........................................................................................................................................................................157
TESTING 2ND MESSENGER MEDIATION OF NT EFFECTS ON ION CHANNELS ........................................................158
PROTEIN KINASES ............................................................................................................................................................................158
3 TYPES OF SECONDARY MESSENGER MOLECULES .........................................................................................................159
TURNOVER OF MEMBRANE PHOSPHOLIPIDS......................................................................................................................161
cAMP AS A SECOND MESSENGER....................................................................................................................................................163
TESTS TO DETERMINE IF RESPONSE IS MEDIATED BY Camp ......................................................................................163
2ND MESSENGER PATHWAYS – COMMON MECHANISMS OF NEUROMODULATION BY GPCRs ...........................164
1. AC/cAMP/PKA-dependent protein kinase system ....................................................................................................164
2. PLC-mediated turnover of membrane phospholipids leading to production of IP3, DAG and
arachidonic acid .................................................................................................................................................................................165
POSTSYNAPTIC MODULATION OF SYNAPTIC TRANSMISSION .........................................................................................165
PRESYNAPTIC MODULATION OF SYNAPTIC TRANSMISSION ............................................................................................167
SWITCH-ON MECHANISMS ...........................................................................................................................................................171
SWITCH-OFF MECHANISMS – TERMINATION......................................................................................................................171
SIGNAL TRANSDUCTION PATHWAYS ...........................................................................................................................................172
ADVANTAGES OF COMPLEX SIGNAL TRANSDUCTION CASCADES..............................................................................172
ENDOCANNABINOIDS ..........................................................................................................................................................................174
DOWN-REGULATION OF GPCRs ..................................................................................................................................................174
MODULATION OF SIGNAL ENCODING ..........................................................................................................................................175
SPIKE FREQUENCY ADAPTATION..............................................................................................................................................175
EFFECT OF SEROTONIN AND NA ON SPIKE FREQUENCY ADAPTATION..................................................................176
EXPLAINING THE EFFECT OF NA AND SEROTONIN ON SPIKE FREQUENCY ADAPTATION ............................176
NEUROMODULATION: LONG-TERM EFFECTS ..........................................................................................................................177
NEURONAL CALCIUM SIGNALLING.....................................................................................................................................................178
IMPORTANT FACTS AND FIGURES TO REMEMBER ...........................................................................................................178
THE CALCIUM SIGNAL.....................................................................................................................................................................178
CALCIUM HOMEOSTASIS ...............................................................................................................................................................179
ELEMENTS OF THE Ca2+ SIGNALLING TOOLKIT .....................................................................................................................179
ELEMENTS OF THE Ca2+ SIGNALLING TOOLKIT IN NEURONS .........................................................................................180
CALCIUM AS A SECOND MESSENGER ............................................................................................................................................180
CaMKinaseII .........................................................................................................................................................................................182
MEASURING INTRACELLULAR CALCIUM ...............................................................................................................................182
CALMODULIN IS THE CALCIUM SENSOR FOR GENE EXPRESSION ..................................................................................183
ON MECHANISMS ...................................................................................................................................................................................184
VOLTAGE-GATED CALCIUM CHANNELS .................................................................................................................................184
LIGAND-GATED, CALCIUM-PERMEABLE RECEPTORS ......................................................................................................185
INTRACELLULAR CALCIUM STORES.........................................................................................................................................185
INTRACELLULAR CALCIUM STORES – IP3 RECEPTORS – PLC PATHWAY ...............................................................185
RYANODINE RECEPTORS AND CALCIUM-INDUCED CALCIUM RELEASE (CICR) ..................................................187
INTRACELLULAR CALCIUM STORES.........................................................................................................................................188
CICR CAN GIVE RISE TO CALCIUM OSCILLATIONS .............................................................................................................188
OFF MECHANISMS .................................................................................................................................................................................189
CALCIUM BUFFERING......................................................................................................................................................................189
RE-UPTAKE ..........................................................................................................................................................................................189
EXTRUSION ..........................................................................................................................................................................................190

, FUNCTIONAL ASPECTS OF Ca2+ SIGNALLING ..........................................................................................................................191
HOW CAN WE DEMONSTRATE THE INVOLVEMENT OF Ca2+ IN A CELLULAR RESPONSE? ...........................191
CALCIUM SOURCE AND IT SUB-CELLULAR LOCALISATION MAKE A DIFFERENCE.............................................191
DYSFUNCTIONAL ASPECTS OF CALCIUM SIGNALLING .........................................................................................................193
FAMILIAL HEMIPLEGIC MIGRAINE (FHM).............................................................................................................................193
CALCIUM OVERLOAD IN NEURODEGENERATIVE DISEASES .........................................................................................193
OPTOGENETICS............................................................................................................................................................................................195
LEARNING OBJECTIVES .......................................................................................................................................................................195
QUESTIONS ...............................................................................................................................................................................................195
WHAT IS OPTOGENETICS ...................................................................................................................................................................195
CONTROLLING NEURONES WITH LIGHT................................................................................................................................195
DEVELOPMENT OF OPTOGENETICS ..............................................................................................................................................195
OPTOGENETIC CONTROL OF FIRING IN VITRO ...................................................................................................................195
OPTOGENETIC CONTROL OF FIRING EX VIVO .....................................................................................................................196
OPTOGENETIC CONTROL OF FIRING IN VIVO ......................................................................................................................196
TARGETING YOUR EFFECTS ..............................................................................................................................................................196
TEMPORAL AND SPATIAL PRECISION .....................................................................................................................................197
DELIVERING THE GENETIC CONSTRUCT ...............................................................................................................................197
CRE/LOX RECOMBINATION METHOD .....................................................................................................................................198
TARGETING SPECIFIC NEURONES ..................................................................................................................................................199
TARGETING SPECIFIC COMPARTMENTS .....................................................................................................................................200
LIGHT DELIVERY ....................................................................................................................................................................................201
APPLICATIONS OF OPTOGENETICS ...............................................................................................................................................201
CIRCUIT MAPPING (CRACM) ........................................................................................................................................................201
OPTOGENETIC CONTROL OF BEHAVIOUR..................................................................................................................................203
TRADITIONAL VIEW OF FEAR/ANXIETY RESPONSE ........................................................................................................203
ACTIVATION OF BLA-CeA REDUCES ANXIETY .....................................................................................................................203
CIRCUITRY REVEALED THROUGH OPTOGENETICS ...........................................................................................................204
TRADITIONAL VIEW OF FEEDING CONTROL .......................................................................................................................204
OPTOGENETIC CONTROL OF FEEDING ...................................................................................................................................204
CIRCUITRY CONTROLLING MATERNAL BEHAVIOUR .......................................................................................................204
BUILDING A FUNCTIONAL CONNECTOME..................................................................................................................................205
THE INFLUENCE OF A SINGLE NEURONE ..............................................................................................................................205
CURRENT ISSUES WITH OPTOGENETICS ....................................................................................................................................206
ONGOING EXPERIMENTS....................................................................................................................................................................206
MODIFICATION...................................................................................................................................................................................206
NEW ACTUATORS .............................................................................................................................................................................207

,INTRODUCTION TO ELECTRICITY
ELECTRICITY
- Movement of charge
- Carrier of charge in electrical circuits
- Ions carry charge across cell membrane
- Electrons and ions mostly obey the same rules

Information processing in the CNS results from the operation of channels and transporter proteins that enable
and regulate the movement of ions across membranes

CONDUCTORS
- Electrons in an atom are confined in orbits around the nucleus
- Electrons in the outer shells can move easily from atom to atom → transfer of charge → current flow
- Good conductors cannot store charges
E.g., copper wire, gap junctions

INSULATORS
- Electrons stay in their own orbital
- Good insulators can store charge
- Are usually molecules rather than elements
E.g., DNA sequence, rubber

Name Symbol Unit Equation Definition
Charge Q Coulombs Charge of 1 electron = 1.6 x 10-19C
1C = 1A x 1s Charge of 1 mole of univalent ions =
Faraday’s constant
Avogadro’s number x charge
on each ion
F = NAe0
= 6.022 x 1023 x 1.602 x 10-19
= 96,500 coulombs per mole
Current I Amperes (A) Flow of electrons or ions from one
1𝐶 𝑑𝑄 place to another
1𝐴 = 𝐼=
1𝑠 𝑑𝑡 The rate of change of charge with
time
1 Ampere = flow of 1 Electron flow = negative → positive
coulomb of charge in 1 electrodes while current flow =
second positive → negative electrodes
Charge of monovalent ion
= 1.6 x 10-19 coulombs
Potential Volts (V) Charge only moves if there is a
difference potential difference between 2 points
Resistance R ohm (Ω) V = RI For any given potential difference, the
I = GV current that flows through an element
of a circuit is determined by its
resistance
The ease with which a charge moves
through the conductor is a measure of
the resistance
current through a conductor between
two points is directly proportionate
to the voltage across two points
Conductance G Siemens (S) G = 1/R
Capacitance C Farad (F) C = Q/V Neuron = described by simple
electrical circuit

, 1F = capacitance of an 𝑑𝑉 Ionic gradients = battery in a
𝐼=𝐶
element that can store 1 C 𝑑𝑡 circuit
of charge given a 1 V Ion channel = conductance’s
potential difference inserted in the membrane
Cell membrane = capacitor

Amount of electric charge stored on a
conductor to a difference in electric
potential

Given 1C = 6.24 x 1018 charges and the current through a Na+ channel is 1 x 10-12 A, how many Na+ ions pass
through the channel if it stays open for 1 ms = 6000
1 Ampere = flow of 1 coulomb of charge in 1 second
Charge of monovalent ion = 1.6 x 10-19 coulombs
Current of one pA = 10^7 ions passing through the channel each second

Rate of ions passing through a channel




CIRCUITS TOPOLOGY
Elements of an electrical circuit can be arranged in series, in parallel, or in combination of both




Pump: battery
Water: electrons
Flow of water: electric current
Resistance: narrowing of the pipes

What factors determine how much water flows?
1. Voltage
2. Current
3. Resistance
4. Power