Effects of clonidine and naloxone on the dopamine levels in the rat mediobasal hypothalamus measured by in vivo voltammetry.

Abstract

We examined the effect of alpha 2-adrenergic stimulation on dopamine (DA) levels in the mediobasal hypothalamus (MBH) by means of in vivo voltammetry in the rat. Intravenous (i.v.) injection of an alpha 2-agonist, clonidine (15 micrograms/100 g b.wt.) caused a decrease of MBH DA levels (76 +/- 3% of basal levels). Pretreatment with phenoxybenzamine (500 micrograms/100 g b.wt.i.v.), an alpha-antagonist, blunted the decrease of MBH DA levels induced by clonidine. Naloxone (125 micrograms/100 g b.wt.i.v.), an opioid antagonist, blunted the decrease of MBH DA levels induced by clonidine. These results suggest that alpha 2-adrenergic mechanisms may inhibit the tuberoinfundibular dopaminergic (TIDA) system through the activation of the endogenous opioid system.