Transient expression of the 5alpha-reductase type 2 isozyme in the rat brain in late fetal and early postnatal life.

The enzyme 5alpha-reductase plays a key role on several brain functions controlling the formation of anxiolytic/anesthetic steroids derived from progesterone and deoxycorticosterone, the conversion of testosterone to dihydrotestosterone, and the removal of excess of potentially neurotoxic steroids. Two 5alpha-reductase isoforms have been cloned: 5alpha-reductase type 1 is widely distributed in the body, and 5alpha-reductase type 2 is confined to androgen-dependent structures. In this study, the gene expression of the two 5alpha-reductase isozymes has been analyzed in fetal, postnatal, and adult rat brains by RT-PCR followed by Southern analysis. 5Alpha-reductase type 1 messenger RNA is always detectable in the rat brain [from gestational day 14 (GD14) to adulthood]. 5Alpha-reductase type 2 messenger RNA expression is undetectable on GD14, increases after GD18, peaks on postnatal day 2, then decreases gradually, becoming low in adulthood. This pattern of expression appears to be correlated with the rate of production of testosterone by the testis. The possible control by androgens of gene expression of the two isozymes has been studied in brain tissues of animals exposed in utero to the androgen antagonist flutamide; the sex of the animals was determined by genetic sex screening of the SRY gene located on the Y-chromosome. In the brain of male embryos, flutamide treatment inhibited the expression of 5alpha-reductase type 2; this effect was much less pronounced in females. Moreover, 5alpha-reductase type 2 gene expression in cultured hypothalamic neurons is highly induced by testosterone and by the phorbol ester 12-O-tetradecanoyl-phorbol-13 acetate. The transient, androgen-regulated, expression of 5alpha-reductase type 2 overlaps the critical period of development, which may be important for sexual differentiation of the brain and for the formation of anxiolytic/anesthetic steroids involved in the stress responses associated with parturition.