Histaminergic neuron system in the brain: distribution and possible functions.

Recent immunocytochemical studies have identified the histaminergic neuron system in the brain. In the rat brain, histaminergic neuronal cell bodies are located in the tuberomammillary nucleus in the posterior hypothalamus, while histaminergic fibers are distributed in almost all regions of the brain. Similar distributions of histaminergic neuronal cell bodies and fibers have been reported in the brains of other mammals and nonmammalian vertebrates. As expected from the widespread distributions of the efferent fibers, the central histaminergic neuron system seems to be involved in multiple functions in the brain. The results of intracerebral injection of histamine and administration of alpha-fluoromethylhistidine (FMH), which depletes brain histamine level, suggest that the central histaminergic system may modulate feeding, drinking and sexual behaviors, sleep-wakefulness and circadian rhythm, neuroendocrine and cardiovascular controls and thermoregulation.