Sexually dimorphic expression of glutamate decarboxylase mRNA in the hypothalamus of the deep sea armed grenadier, Coryphaenoides (Nematonurus) armatus

Glutamate decarboxylase (GAD), is a key enzyme in the central nervous syste m (CNS) that synthesizes the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) from glutamate, Our previous phylogenetic studies on the evolu tion of this enzyme indicates that there are at least two distinct forms: G AD65 and GAD67. They are the products of separate genes and probably derive from a common ancestral GAD gene following gene duplication prior to the e mergence of the teleosts more than 200 Myr ago. Furthermore, a third GAD-li ke molecule, GAD3, discovered in the armed grenadier, Coryphaenoides (Nemat onurus) armatus, is equally divergent from both GAD65 and GAD67. Specimens of C. (N,) armatus were collected by trawl at a depth of 4,000 m in the Por cupine Seabight (Northeastern Atlantic), and brains dissected and frozen fo r RNA extraction. All three GAD forms are found in the cerebellum, telencep halon and hypothalamus. Semiquantitative PCR analysis showed that males and females have similar levels of expression of GAD67 and GAD3 in the tissues studied. Independent of the sex examined, the levels of expression of GAD6 5 and GAD67 in the cerebellum were approximately half that in the telenceph alon. GAD3 levels were approximately 30% higher in the cerebellum than in e ither the telencephalon or hypothalamus. In contrast to GAD67 and GADS, hyp othalamic expression of GAD65 mRNA is 1.8 times higher (p < 0.05) in males than in females. These data indicate that the expression of GAD65, a key en zyme for the synthesis of GABA is sexually dimorphic in females and males o f C, (N.) armatus, Copyright (C) 2001 S. Karger AG. Basel.