| Abstrakt: |
Growth hormone (GH) secretion in the rat is sexually dimorphic, due, at least in part, to differences in the activity of growth hormone-releasing hormone (GHRH) neurons in the hypothalamus. Galanin (GAL), a small peptide that stimulates GH secretion in humans and rats, is coexpressed in GHRH neurons of the adult rat and this coexpression is sexually dimorphic. We investigated the changes in GAL coexpression in GHRH neurons over development in both sexes by performing double-label in situ hybridization on coronal sections from the brains of male and female 10, 25 and 70 day old rats. For GHRH and GAL mRNAs, we used cRNA probes labeled with digoxigenin and 35S-UTP, respectively. GAL mRNA levels were measured by counting autoradiographic silver grains over individual GHRH mRNA-positive cells. The results, in grains/cell (±SE) are summarized above. GAL mRNA coexpression was significantly dimorphic at all ages. To lest the hypothesis that this sexual dimorphism is related to plasma testosterone levels, we measured GAL mRNA levels in GHRH neurons of intact (I), castrated (C), and castrate plus testosterone (T)-replaced male rats. Castration reduced GAL message levels and T replacement prevented this reduction (73±6 (I), 58±4 (C), and 77±5 (C+T) grains/cell).Conclusion: GAL mRNA expression is sexually dimorphic in rats over development and this dimorphism is likely due, in part, to the presence of T in the male. |
