H-3 AUTORECEPTORS AND MUSCARINIC ACETYLCHOLINE-RECEPTORS MODULATE HISTAMINE-RELEASE IN THE ANTERIOR HYPOTHALAMUS OF FREELY MOVING RATS

To investigate the modulation of histamine release by autoreceptors an d heteroreceptors, the rat anterior hypothalamus was superfused throug h a push-pull cannula with agonists or antagonists of histamine and ac etylcholine muscarinic receptors. Superfusion with the H-3 receptor ag onist (R)-alpha-methylhistamine inhibited, while superfusion with thio peramide (H-3 antagonist) enhanced histamine release. Superfusion with carbachol (a mixed M(1), M(2), M(3) agonist) inhibited the release of histamine. The release of endogenous histamine was enhanced on superf usion with atropine (a mixed M(1), M(2), M(3) antagonist). The M(3) mu scarinic antagonist 4-diphenylacet-oxy-N-methylpiperidine enhanced the release rate of histamine. It is concluded that in the anterior hypot halamus the release of endogenous histamine is modulated by H-3 autore ceptors. Moreover, acetylcholine released from cholinergic neurons als o modulates the release of histamine via M(1) and/or M(3) heterorecept ors.