The effect of clonidine on adrenal sympathetic nerve responses to mechanical, noxious and innocuous stimulation of the skin in rats

Abstract The effect of clonidine on the reflex responses of the adrenal sympathetic nerve to mechanical stimulation of the lower chest skin was studied in anesthetized CNS intact and spinalized rats. Clonidine (3–120 μg/kg i.v.) administration resulted in a dose-related decrease in spontaneous adrenal efferent nerve activity in both CNS intact and spinalized rats. In CNS intact rats, noxious pinching caused a reflex increase in adrenal nerve activity while innocuous brushing caused a reflex decrease. In both cases, clonidine reduced the reflex response in a dose-dependent manner. In spinalized rats, both noxious and innocuous stimulation caused reflex increases in adrenal nerve activity, and clonidine produced a similar dose-dependent decrease in these responses as seen in CNS intact animals. The similar dose-response relationships for adrenal nerve tone or reflex response in CNS intact and spinalized animals suggest, although not conclusively, that at least some of clonidine's effects in CNS intact animals may be mediated at the spinal level.