Histamine in the central nervous system: its role in circadian rhythmicity.

Histamine is an accepted neurotransmitter and/or neuromodulator in the central nervous system (CNS). Its neuronal system in the brain is well organized, with cell bodies localized in a small area of the posterior hypothalamus. Diverse biological actions of histamine are mediated via three classes of receptors termed H1, H2, and H3. The existence of other histamine receptor subtypes is likely in invertebrates or in birds. This article surveys basic data indicative of a neuroregulator role of histamine in the CNS; it also presents accumulating evidence suggesting that histamine may be related to circadian rhythmicity in the body.