Regional distribution of glutamic acid decarboxylase (GAD₆₅ and GAD₆₇) mRNA in the hypothalamus of male rhesus macaques before and after puberty

Glutamic acid decarboxylase (GAD) is the rate-limiting enzyme in the γ-aminobutyric acid (GABA) biosynthetic pathway, and is coded for by two mRNAs, GAD₆₅ and GAD₆₇. Using in situ hybridization, we examine the distribution pattern of both GAD mRNAs in the hypothalamus and thalamus of prepubertal and adult male rhesus macaques. Qualitatively, GAD₆₅ and GAD₆₇ mRNAs showed a similar wide, but highly specific distribution pattern, supporting the view that GABAergic neurons play an important role in modulating neuroendocrine function. However, no quantitative difference in the intensity of hybridization signal was detected between prepubertal and adult animals in any of the hypothalamic or thalamic nuclei. Therefore, although GABAergic neurons are anatomically well-placed to control the secretion of gonadotropin-releasing hormone (GnRH) in primates, it is unlikely that the onset of puberty and the associated increase in GnRH secretion is triggered by a change in GAD gene transcription.