Histamine receptors in the brain.

In mammalian brain, neuronal histamine is likely to act as a neurotransmitter and is recognized by the two classes of histamine receptors (H1 and H2) previously characterized in peripheral organs. Cerebral H1 receptors can be selectively labeled by a tritiated antagonist mepyramine, in particulate fractions or in the living animal. Cerebral H1 receptors mediate the glycogen hydrolysis and the breakdown of inositol phospholipids elicited by the amine. They are indirectly involved in the histamine-mediated accumulation of cyclic AMP. All these biochemical responses mediated by H1 receptors are calcium-dependent. H2 receptors are coupled to an adenylate cyclase. In addition, a novel class of histamine receptors (H3) are presynaptic autoreceptors and modulate the release of neuronal histamine.