Potentiation by yohimbine of pentylenetetrazol-induced seizures in rats: role of alpha 2 adrenergic receptors.

10 mg/kg yohimbine significantly reduced the latency to the first convulsion of rats treated with 90 mg/kg pentylenetetrazol (PTZ) and markedly increased the number of animals showing generalized strong clonic seizures and dying within 1 h. All the animals treated with 20 mg/kg yohimbine and PTZ died with 1 h after repeated episodes of strong generalized clonic seizures. Yohimbine's ability to cause tonic seizures and mortality in rats given 70 mg/kg s.c. PTZ was reduced by pretreatment with clonidine (0.5 mg/kg i.p.). Strong clonic seizures of animals treated with yohimbine + PTZ were less affected by clonidine treatment. It thus appears that yohimbine potentiates PTZ-induced seizures through an action on alpha 2 adrenoreceptors, although other mechanisms, e.g. serotonergic ones, seem to contribute to yohimbine's effect.