Receptors for clonidine in brain: insights into therapeutic actions.

Clonidine acts at specific receptor sites in the brain. These sites, i.e. adrenergic receptors, can be localized in the brain at the light-microscopic level by utilizing autoradiographic techniques. Autoradiographic studies revealed a striking differential distribution throughout the brain. These results provide an anatomical basis for understanding the actions of clonidine in the CNS. For example, the finding of high densities of alpha-2-receptors in the nucleus tractus solitarius and in the dorsal motor nucleus of the vagus is very likely related to its antihypertensive action. Also, the striking codistribution of alpha-2 receptors with opiate receptors in some areas could provide an explanation for the observation that alpha-2 drugs block opiate withdrawal.