CORTICAL INHIBITORY POSTSYNAPTIC POTENTIALS AND STRYCHNINIZATION

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Abstract
Three types of inhibitory postsynaptic potentials, IPSPs, (evoked by stimulation of the cerebral peduncles, evoked by stimulation of intralaminar thalamic nuclei, or "spontaneously" occurring) were studied in cortical neurons in the cat before and after topical strychninization. This procedure would result in a depression of all types of IPSPs in most cells; often after depression to zero, the IPSP was replaced by a depolarizing potential which increased in amplitude with time. Resting membrane levels were unaltered by strychninization. Whenever reliable determinations could be obtained (and specifically in the case of antidromic inhibition) the depolarizing potentials were characterized by the same latency, time to peak amplitude, and duration as the replaced IPSP. The possibility that these depolarizing potentials might represent pre-existing EPSPs are discussed. An alternative hypothesis is offered, whereby strychnine would actually convert IPSPs to depolarizing potentials. This could occur through a "damaging" effect on the subsynaptic membrane thereby removing the restriction on the movement of larger ions, principally Na, during the action of the inhibitory transmitter. This mechanism could explain both the decrease and "reversal" of IPSPs induced by strychnine.

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