Abstract
Strong evidence now supports the view that histamine is a neuroregulator. This assertion is not easily refuted unless one invokes demands that have not been applied to analogous assertions that have been made for other biogenic amines, e.g. 5-hydroxytryptamine. Histamine has a nonuniform regional distribution in the brain of all species examined, the phylogeneti cally older regions of vertebrate brain showing higher levels (see reviews by Green 1970, Taylor 1975, Schwartz et a1 1979a, Hough & Green 1984). It sediments with synaptosomes (Carlini & Green 1963, Kataoka & DeRobertis 1967, Dismukes et a1 1974, Picatoste et aI 1977, Schwartz et al 1979a, Sperk et al 1981b, Almeida & Beaven 1981). The histamine synthesizing enzyme, histidine decarboxylase, has high specificity for histidine and is distinct from aromatic L-amino acid decarboxylase (Schwartz et a1 1970, Palacios et aI 1976). Histamine methyltransferase, the enzyme that metabolizes histamine in mammalian brain, has no other known endogenous substrate (Brown et aI 1959). The regional distribution in brain of the synthesizing enzyme is similar to the distribution of histamine (Schwartz et al 1979a), as are the distributions of the metabolites-both tele-methylhistamine (i.e. N<-methylhistamine), the immediate metabolite (Hough & Domino 1979a, Hough et al 198 1), and tele-methylimidazoleacetic acid (i.e. N<-methylimidazoleacetic acid), the metabolite of tele-methylhistamine (Khandelwal et al 1984). Histamine turns over in brain, and the turnover rates vary over 50-fold in different brain regions, correlating with the regional concentrations of histamine (Pollard et al 1974, Hough et al 1984a, Oishi et al 1984). Immunohistochemistry shows histaminergic fibers in many parts of the brain (Tran & Snyder 1981,
Published Version
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