Motor and electrical signs of epileptiform activity induced by penicillin in the spinal cords of decapitate cats.

Convulsive activity was induced in functionally decapitate cat preparations by topical and by systemic administration of toxic amounts of penicillin. The paroxysmal movement patterns and the electrographic signs of spinal seizure activity recorded from spinal ventral and dorsal roots and from the dorsal surface of the spinal cord are described. Paroxysms of interictal myoclonic twitching as well as tonic and clonic ictal seizures reminiscent of epileptiform convulsions of intact animals were seen in the absence of descending influences from the brain. Tonic seizures consisted of flexion--extension sequences; co-contraction of antagonistic muscles was the rule. Clonic activity consisted of rhythmic discharges at 4--6/sec, In dorsal roots, electrotonically conducted paroxysmal negative potential shifts as well as antidromically conducted trains of impulses were recorded. Ictal paroxysmal waves of the cord dorsum potential consisted of either biphasic positive--negative sequences or of purely negative waves. Diphenylhydantoin effectively controlled spinal seizures in the absence of a functioning cerebellum. Diphenylthiohydantoin changed the pattern of seizures, suppressing all ictal activity and greatly enhancing the amplitude and frequency of interictal bursts. Three different barbiturates suppressed seizure activity, but diazepam was ineffective, indicating that the site of its clinical anticonvulsant action may be supraspinal. Seizure activity, once induced, continued for up to 18 h. Intravenous administration of penicillinase abolished seizures indicating that their usual persistence is caused by the presence of the drug in the tissue, not by an irreversible biochemical lesion.