Abstract
Somatostatin, originally identified as a hypothalamic peptide that inhibits the secretion of pituitary growth hormone, is widely distributed in the central nervous system and the periphery, and is implicated in neuronal survival or neurogenesis. By using non-isotopic in situ hybridization histochemistry, we report here that somatostatin gene is expressed transiently in the central part of the rat medial preoptic nucleus, which coincides with the sexually dimorphic nucleus of the preoptic area (SDN-POA), during, but not after, 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. Throughout the observed period, Nissl staining and calbindin immunohistochemistry enabled visualization of the typical SDN-POA in the same region. Orchidectomy of males on day 1 decreased, and administration of estradiol benzoate to females (10 µg in 0.02 ml sesame oil) on days 1 through 10 increased the volume of somatostatin mRNA-positive areas which corresponded to the SDN-POA, when observations were made on day 15. Sex-specific, transient transcription of the somatostatin gene may causally relate to the estrogen-dependent organization of the SDN-POA. [J Physiol Sci. 2007;57 Suppl:S174]
