CNS Stimulation and PGE2Release. III. Pentamethylenetetrazole-Induced Seizures

Abstract

Measurement of prostaglandin E2(PGE2) in the ventriculocisternal perfusate of the halothane anesthetized, artificially ventilated cat has revealed low but measurable levels of the prostanoid (64 ± 5 pg/min). Administration of pentamethylenetetrazole (PTZ) resulted in a rapid appearance of paroxysmal bursting, the magnitude and duration of which was dose dependent. During the 30-min interval after seizure initiation, PGE2secretion rates into the ventriculocisternal perfusate rose by five- to sevenfold. Though the initial rate of PGE2secretion correlated closely with the initial magnitude of bursting, there were significant differences, viz. the time courses. Thus, after a low dose of PTZ (200 mg/kg) the increase and return to normal of PGE2secretion was time locked with the onset and offset of seizures. In contrast, after high doses of PTZ (250 mg/kg i. v.), seizure activity returned to near baseline by 90 min, while the levels of PGE2 secretion remained elevated for periods in excess of 150 min. Pretreatment with clonazepam (CLP: 3 mg/kg i. v. infusion) blocked seizures otherwise induced by PTZ (250 mg/kg) and the increase in PGE2secretion. CLP administration 60 min after the initiation of seizures, blocked further seizure activity but did not alter the elevated secretion of PGE2. We thus believe these data jointly support the hypothesis that under intense paroxysmal bursting there is a change in neuronal state such that large stores of free fatty acids are available either because they have accumulated during the seizure because of a continued Ca2+influx or the presence of large and continuing concentrations of Ca2+accumulating in the cytosol secondary to energy failure.