BIOSYNTHESIS OF STEROIDS IN THE CENTRAL NERVOUS SYSTEM OF AMPHIBIANS

摘要

Distribution and activity of steroid producing enzymes have been studied in the central nervous system (CNS) of the frog Rana ridibunda. Cell bodies containing 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD)-like immunoreactivity were exclusively observed in the preoptic nucleus, the dorsal infundibular nucleus and the dorsal aspect of the ventral infundibular nucleus. Identification of astrocytes with antisera raised against GFAP, and oligodendrocytes with antisera against galactocerebroside revealed that 3 beta-HSD is expressed in frog neurones. Biochemistry showed that hypothalamic slices can convert pregnenolone into Delta-3-ketosteroids including progesterone (P) and 17-hydroxyprogesterone (17OH-P); these steroids likely serve as precursors for other neurosteroids. This is the first immunocytochemical localisation of 3 beta-HSD in the brain and the first evidence for neurosteroid biosynthesis in a nonmammalian vertebrate.