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Mechanisms and consequences of action potential burst firing in rat neocortical pyramidal neurons
Author(s) -
Williams Stephen R.,
Stuarty Greg J.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.00467.x
Subject(s) - bursting , depolarization , neuroscience , electrophysiology , action potential , soma , postsynaptic potential , dendritic spike , biophysics , axon , membrane potential , chemistry , excitatory postsynaptic potential , synaptic potential , biology , inhibitory postsynaptic potential , receptor , biochemistry
1 Electrophysiological recordings and pharmacological manipulations were used to investigate the mechanisms underlying the generation of action potential burst firing and its postsynaptic consequences in visually identified rat layer 5 pyramidal neurons in vitro.2 Based upon repetitive firing properties and subthreshold membrane characteristics, layer 5 pyramidal neurons were separated into three classes: regular firing and weak and strong intrinsically burst firing. 3 High frequency (330 ± 10 Hz) action potential burst firing was abolished or greatly weakened by the removal of Ca 2+ ( n = 5 ) from, or by the addition of the Ca 2+ channel antagonist Ni 2+ (250‐500 μm; n = 8 ) to, the perfusion medium. 4 The blockade of apical dendritic sodium channels by the local dendritic application of TTX (100 n m ; n = 5 ) abolished or greatly weakened action potential burst firing, as did the local apical dendritic application of Ni 2+ (1 m m ; n = 5 ). 5 Apical dendritic depolarisation resulted in low frequency (157 ± 26 Hz; n = 6 ) action potential burst firing in regular firing neurons, as classified by somatic current injection. The intensity of action potential burst discharges in intrinsically burst firing neurons was facilitated by dendritic depolarisation ( n = 11 ). 6 Action potential amplitude decreased throughout a burst when recorded somatically, suggesting that later action potentials may fail to propagate axonally. Axonal recordings demonstrated that each action potential in a burst is axonally initiated and that no decrement in action potential amplitude is apparent in the axon > 30 μm from the soma. 7 Paired recordings ( n = 16 ) from synaptically coupled neurons indicated that each action potential in a burst could cause transmitter release. EPSPs or EPSCs evoked by a presynaptic burst of action potentials showed use‐dependent synaptic depression. 8 A postsynaptic, TTX‐sensitive voltage‐dependent amplification process ensured that later EPSPs in a burst were amplified when generated from membrane potentials positive to ‐60 mV, providing a postsynaptic mechanism that counteracts use‐dependent depression at synapses between layer 5 pyramidal neurons.