Histamine in the brain of insects: A review

Histamine is the neurotransmitter of photoreceptors in insects and other ar thropods. As a photoreceptor transmitter, histamine acts an ligand-gated ch loride channels. Another type of histamine receptor has been indicated in t he insect central nervous system by binding pharmacology. This receptor is similar to the mammalian H 1 receptors, which are G-protein coupled and thu s utilize a second messenger system. The distribution of histamine-immunore active (HAIR) neurons has been studied in a few insect species: cockroaches , locust, crickets, honey bee, blowfiies, and in Drosophila. In addition to its presence in photoreceptor cells, histamine is distributed in a rather small number of neurons in the insect brain. Many of these neurons have ext ensive bilateral arborizations that innervate several distinct neuropil reg ions, notably in the protocerebrum Some patterns of histamine distribution are seen in all the species. On the other hand, the number and morphology o f neurons differ between the studied species, and several major neuropils ( central body, antennal lobes, mushroom bodies) are supplied by HAIR neurons in some species, but not in others. Thus it appears that there are some sp ecies-specific functions of histamine and on others that are preserved betw een species. Some of the histaminergic neurons may constitute wide field in hibitory systems with functions distinct from those of neurons containing g amma-amino butyric acid (GABA). Novel data are presented for Drosophila and the cockroach Leucophaea maderae and a comparison is made with published d ata on other insects. Microsc. Res. Tech. 44:121-136, 1999. (C) 1999 Wiley- Liss, Inc.