Effects of clonidine and naloxone on the dopamine levels in the rat mediobasal hypothalamus measured by in vivo voltammetry.
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.
Koshiyama
H
H
Department of Internal Medicine, Kyoto University Faculty of Medicine, Japan.
Kato
Y
Y
Shimatsu
A
A
Imura
H
H
D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D004563:Electrochemistry / Q000379:methods; D007033:Hypothalamus, Middle / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D010643:Phenoxybenzamine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
D010643:Phenoxybenzamine; D009270:Naloxone; D003000:Clonidine; D004298:Dopamine