Repeated electroconvulsive shock attenuates clonidine-induced hypoactivity in rodents.

Clonidine administration at low dose produces hypoactivity in both rats and mice, probably by stimulation of presynaptic alpha 2-adrenoceptors in the brain. This behaviour is antagonised by yohimbine pretreatment but is unaffected by pretreatment with prazosin. An electroconvulsive shock (ECS) given once daily for 10 days markedly attenuated the hypoactivity in both species when tested 24 h after the final shock. The attenuation in mice was not found after either a single ECS or 10 subconvulsive shocks. Ten ECS did not alter the hypoactivity response produced by (+/-)-propranolol in mice. Clonidine administration decreased rat brain MOPEG-SO4 concentrations. A single ECS given daily for 10 days abolished this decrease. These results suggest that repeated ECS causes a subsensitivity of alpha 2-adrenoceptors in the brain and that these receptors may be located presynaptically.