Modulatory mechanisms of cyclic AMP-stimulated steroid content in rat brain cortex

The modulation of cyclic AMP dependent neurosteroidogenesis was studied in minces prepared from the cerebral cortex of adult rat. Forskolin or dibutyryl-cyclic AMP enhanced pregnenolone and progesterone production in a time and dose-dependent manner. The forskolin effect was mimicked by the cyclic AMP phosphodiesterase inhibitor isobutyl-methyl-xanthine, but not by the adenylate cyclase inactive forskolin analogue 1,9,dideoxy-forskolin. 4'-Chloro-diazepam, a high affinity ligand for the mitochondrial diazepam binding inhibitor (DBI) receptor, also elicited a time dependent increase in steroidogenesis. The forskolin and the 4'-chloro-diazepam stimulated pregnenolone increase was prevented by preexposing the rat brain cortical minces to 1-(2-chlorophenyl)-N-methyl-N-(1-methyl-propyl)-3-isoquinoline carboxamide (PK 11195), a high affinity ligand for the mitochondrial DBI receptor endowed with antagonistic properties. The protein synthesis inhibitor cycloheximide prevented the forskolin and 4'-chloro-diazepam stimulation of pregnenolone formation. In brain cortical minces of adrenalectomised/orchiectomised rats dibutyryl-cyclic AMP increased both pregnenolone and progesterone formation, while forskolin only increased progesterone. These data show that cyclic AMP enhances brain steroidogenesis by acting on a labile protein substrate which interacts with the mitochondrial DBI receptor.