Anticonvulsant effects of clonidine mediated through central alpha2-adrenoceptors

The effects of centrally (0.3-30 ng/kg) and peripherally (0.01 microgram/kg-1.0 mg/kg) administered clonidine on PTZ-induced seizures was studied in rats. At low doses, dose-dependent decreases in the duration of seizures was observed but at higher doses the duration returned to control levels. Anticonvulsant activity was antagonized by yohimbine (100 microgram/kg i.p.) indicating alpha2-adrenoceptor involvement, whereas the second phase of the response was antagonized by prazosin (10 ng/kg i.c.v.) indicating that it involved alpha1-adrenoceptors.