Changes of sex hormone-binding globulin/SHBG expression in the hypothalamo-hypophyseal system of rats during pregnancy, parturition and lactation.

Sex hormone-binding globulin (SHBG) is expressed in hypothalamic magnocellular neurons. High co-localization rates of SHBG with oxytocin have been observed in the hypothalamus, indicating that SHBG plays a role in pregnancy, parturition and lactation. Further studies have shown that hypothalamic SHBG expression is malleable to changing steroid conditions. In this study, we have examined SHBG levels in the supraoptic and paraventricular hypothalamic nuclei and in the posterior pituitary lobe of late pregnant, parturient and early lactating rats by IN SITU hybridization, immunocytochemistry, and ELISA. Immunocytochemical and biochemical analysis showed that the SHBG levels increased during late pregnancy in hypothalamic nuclei. During parturition, SHBG levels fell in the magnocellular nuclei but increased in the posterior pituitary lobe. SHBG levels increase again during lactation. At day six of lactation, there was no significant difference in SHBG levels compared to normal cycling female rats, which served as control in this study. IN SITU hybridization showed increased SHBG mRNA signal during late pregnancy. The highest SHBG expression was observed during parturition. Our data indicate that hypothalamic SHBG expression changes during pregnancy, parturition and lactation, parallel to ovarian steroid and co-localized OT levels. This may in part be linked to known steroid actions on synthesis and secretion of magnocellular hypothalamic peptide hormones, important for the control of parturition and lactation.

Expression of corticosterone-binding globulin in the rat hypothalamus.

We observed coexistence of corticosteroid-binding globulin (CBG) with vasopressin (VP) and oxytocin (OT) in magnocellular neurons in rat hypothalamus by combined immunoperoxidase staining and immunofluorescence. A portion of the supraoptic and of the paraventricular neurons showed double immunostaining of CBG with either VP or with OT. CBG staining was intensified by pretreating animals with colchicine to block axonal transport. CBG was also observed in widespread axonal projections throughout the lateral hypothalamus, the median eminence and the posterior pituitary lobe. Single ependymal cells and some of the endocrine cells in the anterior lobe contained specific CBG immunoreactivity. IN SITU hybridization of semithin sections with a synthetic oligonucleotide probe to CBG mRNA provided staining of magnocellular hypothalamic neurons, but not ependymal cells or anterior lobe cells. Western blots of CBG extracted by affinity chromatography from hypothalamus homogenates showed a band at approximately 50 kDa. Our observations indicate the intrinsic expression of CBG in peptidergic hypothalamus neurons in rat. The multiple locations of CBG-expressing neurons indicate multiple functional properties, probably exceeding the role of a mere steroid transporter. CBG is likely to be subject to axonal transport and secretion in a neuropeptide-like fashion, perhaps involved in neuroendocrine regulation, which may include stress responses.

Expression of corticosteroid-binding protein in the human hypothalamus, co-localization with oxytocin and vasopressin.

Corticosteroid-binding globulin, a specific steroid carrier in serum with high binding affinity for glucocorticoids, is expressed in various tissues. In the present study, we describe the immunocytochemical distribution of this protein in neurons and nerve fibers in the human hypothalamus. CBG immunoreactive perikarya and fibers were observed in the paraventricular, supraoptic, and sexual dimorphic nuclei in the perifornical region, as well as in the lateral hypothalamic and medial preoptic areas, the region of the diagonal band, suprachiasmatic and ventromedial nuclei, bed nucleus of the stria terminalis and some epithelial cells from the choroid plexus and ependymal cells. Stained fibers occurred in the median eminence and infundibulum. Double immunostaining revealed a partial co-localization of corticosteroid-binding globulin with oxytocin and, to a lesser extent, with vasopressin in the paraventricular and the supraoptic nuclei. Double immunofluorescence staining showed coexistence of these substances in axonal varicosities in the median eminence. We conclude that neurons of the human hypothalamus are capable of expressing corticosteroid-binding globulin, in part co-localized with the classical neurohypophyseal hormones. The distribution of CBG immunoreactive neurons, which is widespread but limited to specific nuclei, indicates that CBG has many physiological functions that may include neuroendocrine regulation and stress response.

Sexual dismorphism in rat oxytocinergic hypothalamic regions / Dimorfismo sexual en regiones hipotalámicas oxitocinérgicas de la rata

Oxytocin (OT), a nonapeptide of the hypothalamo-neurohypophyseal system is known to be important for milk ejection and uterus contraction in females and for erection and seminal emissions in males. These sex-specific functional properties imply differential distribution of OT in the hypothalamus. In the present study, complete series of vibratome sections of male and female rat brains were stained for OT with either immunoperoxidase or immunofluorescence in order to evaluate such sex differences. While no significant differences were found in the classical magnocellular nuclei, females had more OT neurons in the zona incerta and the retrochiasmatic portion of the supraoptic nucleus. In males, the lateral subcommissural nucleus and the lateral preoptic area contained significantly more OT perikarya. These sexually dimorphic locations of OT-expressing neurons may be the neuroanatomical correlates of known gender-specific functions of OT (AU)

La oxitocina (OT), un nonapéptido del sistema hipotálamo-neurohipopisario es conocido por ser importante en la eyección láctea y la contracción del útero en las hembras y en la erección y emisiones seminales en los machos. Estas propiedades funcionales específicas del sexo implican la distribución diferencial de OT en el hipotálamo. En el presente estudio fueron teñidas para OT series completas de secciones de vibratomo de cerebros de ratas machos y hembras bien con inmunoperoxidasa o con inmunofluorescencia para evaluar dichas diferencias sexuales. Aunque no se hallaron diferencias significativas en los clásicos núcleos magnocelulares, las hembras presentaron más neuronas de OT en la zona incerta y en la porción retroquiasmática del núcleo supraóptico. En machos, el núcleo subcomisural lateral y el área preóptica lateral contenían significativamente más pericarion de OT. Estas localizaciones sexualmente dimórficas de las neuronas que expresan OT pueden ser la correlación neuroanatómica de las funciones sexo-específicas de la OT (AU)