Localization of P450scc and 5 alpha-reductase type-2 in the cerebellum of fetal and newborn sheep

Prenatally, neuroactive steroids that modulate GABAergic activity may be sy nthesized de novo within the fetal brain. We have examined changes in immun oreactivity staining for the steroidogenic enzymes cholesterol P450 side-ch ain cleavage (P450scc), and 5 alpha-reductase type-2 in the cerebellum of l ate gestation (130-145 days gestation) fetal sheep and newborn lambs (1-4 w eeks of age). Both enzymes were predominantly localized in the Purkinje cel l body and dendrites of the fetal and newborn cerebellum, with weaker immun oreactivity in a few cells of the inner granular layer. P450scc immunoreact ivity was present in Purkinje neurons expressing either of the neuronal mic rotubule associated proteins MAP1b/5 or MAP2a/b, but was absent from GFAP a nd HNK-1 positive cells. Soma of Purkinje neurons were also immunopositive for 5 alpha-reductase type-2 in the fetuses, but expression decreased to ju st detectable levels in the 1-2 and 2-4 week old lambs. Both MAP1b/5- and M AP2a/b-positive Purkinje neurons showed 5 alpha-reductase type-2 expression in the fetus, whereas the residual 5 alpha-reductase staining in the newbo rn lamb was present only in MAP2a/b-positive Purkinje neurons. Allopregnano lone in the cerebellum decreased from 21.8+/-1.9 ng/g wet weight in fetuses at 140-145 days gestation to 6.7+/-0.5 ng/g in 2-4 week old lambs (P<0.05) . Thus, synthesis of neuroactive steroids from cholesterol is possible in c erebellar neurons in late gestation and persists into neonatal life, 5 alph a-reductase type-2 expression is greater in the fetus compared to the neona te, and allopregnanolone concentrations in the cerebellum decrease signific antly after birth. (C) 2000 Elsevier Science B.V. All rights reserved.