The effect of polarizing currents on unitary Ia excitatory post‐synaptic potentials evoked in spinal motoneurones.

Abstract

Depolarizing and hyperpolarizing currents were applied to [cat] motoneurons in which unitary Ia EPSP [excitatory postsynaptic potentials] were evoked. The results concentrated on those EPSP which had time courses which were compatible with somatically located synapses. No reversal of these EPSP was observed. Depolarizing currents up to 150 nA simply reduced the peak amplitude. Hyperpolarizing currents caused little, if any, increase in the peak amplitude of the EPSP. The time course of decay became briefer as the membrane was hyperpolarized. Changes in decay time course of the EPSP which accompanied depolarization and hyperpolarization could be attributed to changes in membrane conductances, rather than to changes in synaptic current time course. The failure of the EPSP to increase with hyperpolarization was shown to be due to the failure of the synaptic current to increase, rather than to the shunting of anomalous rectification. Chemical and electrical transmission were discussed.