cgp-36742 and Seizures

In Wistar rats with spontaneous non-convulsive absence epilepsy, absence seizures were dose dependently suppressed by intraperitoneal administration of the GABAB receptor antagonists CGP 36742, 50-400 mg/kg, and CGP 56999, 0.25-0.75 mg/kg, and by bilateral microinjections of the same compounds into the lateral nuclei of the thalamus. In rats susceptible to audiogenic seizures, intraperitoneal administration of both GABAB receptor antagonists, at doses which suppressed absence seizures, facilitated the elicitation of sound-induced tonic seizures. In non-epileptic control rats, intraperitoneal injections of higher doses of CGP 36742 (800-2400 mg/kg) and CGP 56999 (3-6 mg/kg) induced delayed clonic convulsions, which were suppressed by pretreatment with baclofen. c-Fos protein was expressed after GABAB receptor antagonist-induced seizures in the cortex, hippocampus, amygdala, perirhinal and piriform cortex. Intra-cortical and hippocampal microinfusion of both GABAB receptor antagonists produced focal seizures. In conclusion, GABAB receptor antagonists suppress non-convulsive absence seizures by blocking thalamic GABAB receptors, while they induce convulsions in cortical and limbic structures.

Topics: Animals; Brain; Epilepsy, Absence; GABA Antagonists; GABA-B Receptor Antagonists; Male; Organophosphorus Compounds; Phosphinic Acids; Proto-Oncogene Proteins c-fos; Rats; Seizures

Behavioral characteristics of seizures have age-dependent features, which suggests that effective treatment of seizures may be age-specific as well. In experiments that used the flurothyl seizure model, we examined the effects of several drugs that affect GABAergic neurotransmission in rats of various ages. Systemic administration of phenobarbital (PB, a drug that enhances GABAA receptor-mediated inhibition) was anticonvulsant in most age groups. In contrast, gamma-vinyl GABA (VGB, a drug that increases endogenous GABA levels and enhances both GABAA and GABAB receptor transmission) did not have anticonvulsant effects. Baclofen (a GABAB receptor agonist) was proconvulsant in 9-day-old rat pups, and anticonvulsant in 15-30-day-old rats and lost its anticonvulsant activity in 60-day-old rats. CGP 35348 (a GABAB receptor antagonist) was proconvulsant in developing rats but not in 60-day-old rats. A novel GABAB receptor antagonist, CGP 36742, was proconvulsant in 9- and 15-day-old rats but had no effects in 30- and 60-day-old rats. These results indicate that the effects of presumed GABAergic agents are not uniform across the age span. The differences may reflect age-dependent maturational changes of GABA receptor subtypes, differential action of the drugs on pre- and postsynaptic sites and possible non-GABAergic effects.

Topics: Age Factors; Animals; Anticonvulsants; Baclofen; Convulsants; Flurothyl; GABA Agents; GABA Agonists; GABA Antagonists; gamma-Aminobutyric Acid; Male; Organophosphorus Compounds; Phenobarbital; Rats; Rats, Sprague-Dawley; Receptors, GABA-A; Receptors, GABA-B; Seizures; Vigabatrin