抄録
Somatostatin is widely distributed in the central nervous system and the periphery, and is implicated in neuronal survival or neurogenesis. The number of somatostatin neurons is sexually dimorphic in the human or rat bed nucleus of the stria terminals. In the rat, one of the most prominent brain sex differences is found in the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA), and which is significantly larger in the male than in the female. The difference also depends on the gonadal-steroid milieu during the critical period. In the present study, a transient, sex-specific transcription of somatostatin gene was detected by in situ hybridization in the rat SDN-POA, during the establishment of sex difference. On postnatal day 1 (day of birth), somatostatin mRNA was detected in the SDN-POA of both sexes. On days 8 through 35, the area of somatostatin mRNA-positive cells was significantly larger in males than in females. In males, the area attained its maximum size on day 15 and diminished gradually thereafter. In females, the area did not change in size during this period. On day 60, expression of somatostatin mRNA was low and not different between sexes. As with Nissl staining and calbindin immunohistochemistry, somatostatin mRNA hybridization on day 15 revealed a reversal of the sexual dimorphism in the size of the SDN-POA in males that had been neonatally orchidectomized or females given estrogen as pups. Sex-specific, transient transcription of the somatostatin gene may causally relate to the estrogen-dependent organization of the SDN-POA. [J Physiol Sci. 2008;58 Suppl:S14]
