Presynaptic and long-lasting postsynaptic inhibition during penicillin-induced spinal seizures.

In experiments on seven cats we tested the hypothesis that the epileptogenic effect of penicillin (PCN) on the spinal cord is mediated by a reduction of presynaptic inhibition. PCN-induced spinal hyperactivity was not associated with changes in either the presynaptic inhibition of extensor monosynaptic reflexes by conditioning volleys in flexor muscle nerves, or in evoked dorsal root potentials. Long-lasting inhibition of monosynaptic reflexes by repetitive cutaneous nerve volleys, shown by intracellular recording to be associated with prolonged inhibitory postsynaptic potentials (IPSPs), was also not changed by PCN. Antagonism of either pre- or postsynaptic spinal inhibition is not a necessary condition for induction of spinal seizures by PCN.