Expression of activin and follistatin in the rat hypothalamus - Anatomicalassociation with gonadotropin-releasing hormone neurons and possible role of central activin in the regulation of luteinizing hormone release

The central role of activin in the regulation of the reproductive axis rema ins largely unexplored, Evidence suggests that activin may play a role in c ontrolling gonadotropin-releasing hormone (Gn RH) release. We assessed pote ntial neuroanatomical associations between activin- and GnRH-neuronal syste ms via examination of the distribution of activin PA-subunit and activin bi nding protein (follistatin) protein and mRNA signals relative to GnRH neuro ns in the adult rat brain. Activin beta A-subunit-immunostained fibers were distributed throughout the hypothalamus and GnRH-positive perikarya, and f ibers were in close association with beta A-subunit-immunoreactive fibers, Follistatin mRNA-expressing cells were also identified throughout the hypot halamus with GnRH fibers often observed juxtaposed to follistatin cell bodi es. Colocalization of either the beta A-subunit or follistatin within GnRH neurons was not detected. The functional significance of central activin in the regulation of the reproductive axis was also demonstrated. The intrace rebroventricular infusion of rh-activin A significantly increased luteinizi ng hormone, but not follicule-stimulating hormone, serum levels in adult ma le rats. Taken together, the present results support an interaction between activin and GnRH neuronal systems in the rat hypothalamus, and suggest act ivin may act within the brain to regulate the reproductive axis.