XXXX may directly influence gonadotropin-releasing hormone gene expression in the @entity35 hypothalamus.

@entity35 @entity22345 @entity1176 @entity1810
In vitro studies using immortalized GT1 cells suggest that hypothalamic astrocytes employ @entity1810 to directly regulate the secretion of @entity1176 , the neurohormone that controls sexual maturation and adult reproductive function. However, whether such astrocyte- @entity1176 neuron signaling occurs in vivo is not clear. In the present study, we used in situ hybridization and immunohistochemistry to determine whether astrocytes and @entity1176 neurons express the molecular components necessary to set in motion communication processes involving @entity1810 signaling. Double-labeling experiments showed that astrocytes in the male @entity35 preoptic region (POA) expressed @entity1810 mRNA and that @entity1176 perikarya were often found in close association with @entity1810 mRNA-expressing cells. In addition, @entity1176 neuronal cell bodies in the POA expressed both type II TGFbeta receptors (TGFbeta-RII), which selectively bind TGFbeta, and @entity22345 , one of the primary transducers of TGFbeta signaling, suggesting that they are fully capable of responding directly to @entity1810 stimulation. Consistent with this hypothesis, incubation of POA explants with @entity1810 caused a significant, dose-dependent decrease in @entity1176 mRNA expression in individual neurons. This effect was observed within 1 h after @entity1810 -treatment and was inhibited by addition of the soluble form of TGFbeta-RII to the incubation medium. In contrast, whereas both @entity1810 and TGFbeta-RII mRNAs were abundantly expressed in both glial cells and capillaries in the median eminence, the projection field of @entity1176 neurons, TGFbeta-RII immunoreactivity was mainly restricted to the processes of tanycytes and did not colocalize with @entity1176 -immunoreactive fibers. This observation supports previous in vivo studies showing that @entity1810 is unable to directly modulate decapeptide release from @entity1176 nerve terminals. Thus, astrocyte-derived @entity1810 may directly influence @entity1176 expression and/or secretion in vivo by acting on the perikarya, but not the terminals, of @entity1176 neurons.
