Hybridization histochemical and immunohistochemical localization of inhibin/activin subunits and messenger ribonucleic acids in the rat brain

Inhibin and activin are best known as gonadal glycoprotein hormones but have a broad anatomical distribution. We previously described the central distribution ofinhibin/activin beta A- and beta B-subunit proteins in some neuronal cell bodies, fibers, and nuclei of the rat brain and reported a possible role for central activin in suckling-induced oxytocin secretion and corticotropin releasing factor release. In the present report, we mapped the detailed immunohistochemical localization of inhibin/activin alpha-, beta A-, and beta B-subunits throughout the rat brain to further clarify their central distribution. In addition, the localization and distribution of their corresponding mRNAs was assessed. The results are summarized as follows: 1) Both beta A- and beta B-subunit immunoreactivity are found in neuronal cell bodies in the nucleus of the solitary tract and the dorsal and ventral medullary reticular nuclei, and in fibers and terminals of known projection sites for these nuclei. 2) beta B-subunit immunoreactivity is localized in a group of perifornical neurons in the hypothalamus. 3) beta A-subunit immunoreactivity is present in discrete populations of neuronal cell nuclei scattered throughout the CNS. 4) mRNAs encoding each of the inhibin/activin subunits are expressed in all major brain regions as determined by S1 nuclease assay and in a variety of specific neuroanatomical sites as shown by in situ hybridization. The results suggest that central inhibin and activin proteins are produced in the brain where they may potentially serve inter- and intracellular functions in multiple systems.