Immunohistochemical localization of hydroxysteroid sulfotransferase and sulfatase in the brain of Rana esculenta tadpoles

Sulfation plays a major role in regulating the active concentrations of a variety of biologically important molecules, including steroids, catecholamines and peptides. Sulfation is also important in the detoxification of many xenobiotics. Hydroxysteroid sulfotransferase (HST) catalyses the biosynthesis of sulfated steroids in classical steroidogenic glands as well as in other organs including the CNS. Immunocytochemical mapping of HST in the brain of the adult frog Rana esculenta as well as HST bioactivity have shown the expression of HST-immunoreactive material in neurons of the telencephalon and diencephalon. In the present study we describe the immuno-localization of HST and the conjugated steroid enzyme sulfatase (S) in the brain of Rana esculenta tadpoles, sampled at five stages of development: VIII-XII, XIII-XV, XVI-XVIII, XIX-XX and XXI-XXV (following Taylor and Kollros, 1946). For each stage, six specimens were anesthetized and fixed in Bouin's fluid for histological and immunohistochemical studies. Paraffin sections were cut at 5 µm in either the sagittal or frontal plane. Immunoreactive fibers for both HST and S were detected starting from stage VIII-XII. At this early stage, HST-positive fibers were seen in the glomerular layer and in the basal rombencephalon. Immunoreactive fibers for both HST and S were found in the accessory olfactory bulb starting from stage XIII-XV. Immunoreactive neurons for S were observed in the periventricular region of the diencephalon from stage XVI-XVIII. These data suggest that regulation of sulfation of hydroxysteroids occurs in the frog brain at an early stage of development.