GnRH mRNA increases with puberty in the male Syrian hamster brain

Puberty in the male Syrian hamster (Mesocricetus auratus) is characterized by decreased responsiveness to testosterone mediated negative feedback, but the neural mechanism for this change remains elusive. We hypothesized that decreased inhibition of the gonadotropin-releasing hormone (GnRH) system results in increased neurosecretory activity, which includes an increase in GnRH gene expression. This study examined GnRH mRNA in male hamsters before and after puberty, and sought to determine if any increase in mRNA was specific to particular subpopulations of GnRH neurones. Brains were collected from 21-day-old prepubertal males (n = 5) and 56-day-old postpubertal males (n = 5). Alternate 10 microm coronal sections from fresh-frozen brains were collected throughout the septo-hypothalamic region, and 25% of those sections were processed for in-situ hybridization histochemistry using an 35S-riboprobe complementary to hamster GnRH. No differences were observed in the number of GnRH mRNA expressing cells in any region, but in the diagonal band of Broca (DBB)/organum vasculosum of the lamina terminalis (OVLT) there was a significant increase in labelling intensity (defined as area of the cell occupied by silver grains) in postpubertal males. A second analysis compared the frequency distributions of cells based on labelling intensity between prepubertal and postpubertal males. This analysis revealed significant differences between the two frequency distributions in all areas analysed (DBB/OVLT, medial septum (MS), and preoptic area (POA)). Furthermore, examining the distribution of cells in these regions revealed a shift to the right in the postpubertal population of cells, which indicated an increased number of GnRH neurones with greater labelling intensity. These data clearly demonstrate increased GnRH mRNA during puberty. Furthermore, they suggest that the previous observation of brain region specific pubertal decreases in GnRH-immunoreactivity only within the DBB/OVLT and MS but not the POA are not due to differential levels of GnRH gene expression, but could indicate increased release from these neurones during puberty.