Generalized convulsions induced by pentylenetetrazol in the cat: participation of forebrain, brainstem, and spinal...

The respective capabilities of forebrain, brainstem, and spinal cord to generate seizures in response to intravenous pentylenetetrazol (PTZ) were determined in intact, precollicular, and spinal cord transected (C2-C3) cats. Threshold doses for the induction of generalized EEG seizures were similar, approximately 26 mg/kg, in all groups, but only in intact cats was this associated with generalized clonic convulsions. In cats with precollicular transection, in spite of an unchanged EEG seizure threshold, induction of convulsions required on average 63 mg/kg of PTZ. They consisted of generalized tonic contractions. In cats with spinal cord transection, convulsions began with a mean dose of 167 mg/kg of PTZ. They consisted of bilateral, frequently asynchronous jerks, although tonic contractions were also observed. These experiments show widespread central nervous system (CNS) sensitivity to PTZ, and demonstrate that (a) ictal EEG activity in the forebrain, normally associated with clonic convulsions, may occur independently from brainstem influence; (b) clonic convulsions in intact cats likely originate from the forebrain with little contribution from the brainstem; and (c) the brainstem and spinal cord can induce tonic and predominantly clonic seizures, respectively, at PTZ levels exceeding those required to induce seizures in intact cats.