THE ENDOZEPINE TRIAKONTATETRANEUROPEPTIDE DIAZEPAM-BINDING INHIBITOR[17-50] STIMULATES NEUROSTEROID BIOSYNTHESIS IN THE FROG HYPOTHALAMUS

Neurons and glial cells are capable of synthesizing various bioactive steroids, but the neuronal mechanisms controlling neurosteroid-secreti ng cells are poorly understood. In the present study, we have investig ated the possible effect of an endogenous ligand of benzodiazepine rec eptors, the triakontatetraneuropeptide [17-50] (TTN), on steroid biosy nthesis in the frog hypothalamus. Immunohistochemical studies revealed that most hypothalamic neurons expressing 3 beta-hydroxysteroid dehyd rogenase/Delta(5)-Delta(4)-isomerase also contained peripheral-type be nzodiazepine receptor-like immunoreactivity. Confocal laser scanning m icroscopic analysis revealed that the peripheral-type benzodiazepine r eceptor-immunoreactive material was located both in the cytoplasm and at the periphery of the cell bodies. By using the pulse-chase techniqu e, TTN was found to stimulate the conversion of [H-3]pregnenolone into various steroids, including 17-hydroxypregnenolone, 5 alpha-dihydrote stosterone and 17-hydroxyprogesterone, in a dose-dependent manner. The peripheral-type benzodiazepine receptor agonist Ro5-4864 mimicked the stimulatory effect of TTN on the formation of neurosteroids. The peri pheral-type benzodiazepine receptor antagonist PK11195 significantly r educed the effect of TTN on neurosteroid synthesis, while the central- type benzodiazepine receptor antagonist flumazenil did not affect the formation of neurosteroids evoked by TTN. These data indicate that TTN stimulates the biosynthesis of 3-keto-17 alpha-hydroxysteroids in fro g hypothalamic neurons through activation of peripheral-type benzodiaz epine receptors likely located at the plasma membrane level. (C) 1997 IBRO. Published by Elsevier Science Ltd.