Increased expression of forebrain GnRH mRNA and changes in testosterone negative feedback following pubertal...

Pubertal development is associated with increased activity of the gonadotropin releasing hormone (GnRH) neuronal system and rising gonadal steroid levels. The purpose of this study was to determine whether different circulating levels of testosterone affect GnRH mRNA and luteinizing hormone (LH) to the same degree prior to and following pubertal maturation. Pre- and post-pubertal male Syrian hamsters were gonadectomized and treated with timed-release testosterone pellets (0, 0.5, 1.5, or 2.5mg) for one week. Following treatment, three separate brain tissue dissections containing the majority of GnRH cell bodies, tenia tecta and medial septum (TT/MS), diagonal band of Broca/organum vasculosum of the lamina terminalis (DBB/OVLT), and preoptic area (POA), were analyzed for GnRH mRNA levels by RNase protection assay and terminal plasma luteinizing hormone concentrations were determined by radioimmunoassay. Pre-pubertal animals were more sensitive to testosterone negative feedback on LH. Conversely, the ability of testosterone to reduce GnRH mRNA was much greater after pubertal development. Specifically, GnRH mRNA in the TT/MS was considerably higher in adults, and testosterone reduced GnRH mRNA in a dose-dependent manner only in adults. These data indicate that although testosterone is a powerful suppressor of LH release before puberty, it does not have appreciable control over GnRH mRNA until after puberty. Furthermore, the pubertal increase in GnRH mRNA appears to occur via steroid feedback-independent mechanisms in the male Syrian hamster.