Phylogeny of histamine in vertebrate brain

Measurement of histamine and its metabolizing enzymes in a variety of chordate species indicated that histamine and histamine methyltransferase were present in brain of all vertebrate species with a recognizable brain structure. Diamine oxidase was absent in mammalian brain but was present in brain of lower vertebrates. Histamine levels were especially high in amphibia and fish brains, in which the phylogenetically newer parts of the brain were less well-developed. In the spiny dogfish (as in mammals), brain histamine levels were highest in the midbrain regions. In contrast to brain, histamine levels were low in muscle, skin and intestine of all aquatic species.