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Post‐inhibitory excitation and inhibition in layer V pyramidal neurones from cat sensorimotor cortex.
Author(s) -
Spain W J,
Schwindt P C,
Crill W E
Publication year - 1991
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 - 10.1113/jphysiol.1991.sp018489
Subject(s) - hyperpolarization (physics) , depolarization , inhibitory postsynaptic potential , tonic (physiology) , chemistry , neuroscience , electrophysiology , biophysics , membrane potential , biology , organic chemistry , nuclear magnetic resonance spectroscopy
1. The effect of conditioning pre‐pulses on repetitive firing evoked by intracellular current injection was studied in layer V pyramidal neurones in a brain slice preparation of cat sensorimotor cortex. Most cells displayed spike frequency adaptation (monotonic decline of firing rate to a tonic value) for several hundred milliseconds when depolarized from resting potential, but the cells differed in their response when pre‐pulses to other potentials were employed. In one group of cells, the initial firing rate increased as the pre‐pulse potential was made more negative (post‐hyperpolarization excitation). Adaptation was abolished by depolarizing prepulses. In a second group, the initial firing rate decreased as the pre‐pulse potential was made more negative (post‐hyperpolarization inhibition). Hyperpolarizing pre‐pulses caused the initial firing to fall below and accelerate to the tonic rate over a period of several seconds. A third group displayed a mixture of these two responses: the first three to seven interspike intervals became progressively shorter and subsequent intervals became progressively longer as the conditioning pre‐pulse was made more negative (post‐hyperpolarization mixed response). 2. Cells were filled with horseradish peroxidase or biocytin after the effect of pre‐pulses was determined. All cells whose firing patterns were altered by pre‐pulses were large layer V pyramidal neurones. Cells showing post‐hyperpolarization excitation or a mixed response had tap root dendrites, fewer spines on the apical dendrite and larger soma diameters than cells showing post‐hyperpolarization inhibition. 3. Other electrophysiological parameters varied systematically with the response to conditioning pre‐pulses. Both the mean action potential duration and the input resistance of cells showing post‐hyperpolarization excitation were about half the values measured in cells showing post‐hyperpolarization inhibition. Values were intermediate in cells showing a post‐hyperpolarization mixed response. The after‐hyperpolarization following a single evoked action potential was 20% briefer in cells showing post‐hyperpolarization excitation compared to those showing inhibition. 4. Membrane current measured during voltage clamp suggested that two ionic mechanisms accounted for the three response patterns. Post‐hyperpolarization excitation was caused by deactivation of the inward rectifier current (Ih). Selective reduction of Ih with extracellular caesium diminished post‐hyperpolarization excitation, whereas blockade of calcium influx had no effect. Post‐hyperpolarization inhibition was caused by enhanced activation of a slowly inactivating potassium current. Selective reduction of this current with 4‐aminopyridine diminished the post‐hyperpolarization inhibition. 5. Chord conductances underlying both Ih and the slow‐transient potassium current were measured and divided by leakage conductance to control for differences in cell size.(ABSTRACT TRUNCATED AT 400 WORDS)
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