Expression and activity of 3 beta-hydroxysteroid dehydrogenase Delta(5)-Delta(4)-isomerase in the rat Purkinje neuron during neonatal life

Recently, we demonstrated that cytochrome P450 side-chain cleavage enzyme ( P450scc) occurs in the rat cerebellar Purkinje cell after differentiation a nd remains during neonatal development and into adulthood. 3 beta-Hydroxyst eroid dehydrogenase/Delta(5)-Delta(4)-isomerase (3 beta HSD) is also an ess ential enzyme for progesterone biosynthesis not only in peripheral steroido genic glands but also in the nervous system. In the present study, therefor e, the expression of 3 beta HSD in the rat cerebellum was investigated duri ng neonatal development and in the adult. RT-PCR analysis showed that the e xpression of 3 beta HSD messenger RNA (mRNA) in the cerebellum was higher a t 7-14 days of age than at other times. Biochemical studies together with H PLC analysis revealed that cerebellar slices at 10 days of age converted pr egnenolone to progesterone, suggesting enzymatic activity of 3 beta HSD. Th is conversion was significantly reduced by trilostane, a specific inhibitor of 3 beta HSD. A specific RIA indicated that progesterone concentrations i n the cerebellum were higher at 3 and 10 days of age than at 60 days of age . The progesterone level in the cerebellum was significantly higher than th at in plasma at 10 days of age. In contrast, the concentrations in both cer ebellum and plasma at 3 and 60 days of age were similar. In the present stu dy, the site of 3 beta HSD mRNA expression in the cerebellum was further ex amined in neonatal and adult rats using in situ hybridization. The cerebell ar expression of 3 beta HSD mRNA was obscure at 3 days of age, whereas inte nse expression occurred in Purkinje cells and external granule cells throug hout the cerebellum at 10 days of age. 3 beta HSD mRNA was also expressed i n Purkinje cells and granule cells at 60 days of age, but a restricted expr ession was observed along the cerebellar meninges. These results suggest that the steroidogenic enzyme 3 beta HSD as well as P 450scc are expressed at least in the cerebellar Purkinje cell. The expressi on of 3 beta HSD, however, may increase for a limited period around 10 days of age, unlike P450scc.