Immunocytochemical localization and biological activity of hydroxysteroid sulfotransferase in the frog brain

Biosynthesis of the neuroactive steroids pregnenolone sulfate (Delta(5)PS) and dehydroepiandrosterone sulfate (DHEAS) is catalyzed by the enzyme hydro xysteroid sulfotransferase (HST), which transfers the sulfonate moiety from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) on the 3-hydroxy site of ster oids. Although high concentrations of Delta(5)PS and DHEAS have been detect ed in the rat brain, the anatomical localization of HST in the CNS has neve r been determined. Using an antiserum against rat liver HST, we have invest igated the distribution of HST-like immunoreactivity in the CNS of the frog Rana ridibunda. Two populations of HST-immunoreactive neurons were observe d in the hypothalamus, and several bundles of positive nerve fibers were vi sualized in the telencephalon and diencephalon. Incubation of frog brain ho mogenates with [S-35]PAPS and [H-3]pregnenolone yielded the formation of se veral H-3,S-35-labeled compounds, including Delta(5)PS and testosterone sul fate. When [H-3]dehydroepiandrosterone and [S-35]PAPS were used as precurso rs, one of the H-3,S-35-labeled metabolites coeluted with DHEAS. Neosynthes is of [H-3]Delta(5)PS and [H-3]DHEAS was reduced significantly by 2,4-dichl oro-6-nitrophenol, a specific inhibitor of sulfotransferases. The present s tudy provides the first immunocytochemical mapping of HST in the brain. Our data also demonstrate for the first time that biosynthesis of the highly p otent neuroactive steroids Delta(5)PS and DHEAS occurs in the CNS of nonmam malian vertebrates.