Effects of photoperiod on formation of oestradiol-17 beta in the dove brain.

The effects of photoperiod and castration on brain aromatase activity have been examined using an in-vitro radioassay. Formation of oestradiol-17 beta was lower in the preoptic area of male Barbary doves on a short daylength (6 h light:18 h darkness) than in males on a long daylength (14 h light:10 h darkness). This was a specific effect of photoperiod which did not influence aromatase activity in the anterior or posterior hypothalamic areas, and was not accompanied by changes in hormone-sensitive vocal behaviour. Production of 5 beta-dihydrotestosterone, 5 beta-androstane-3 alpha, 17 beta-diol and 5 alpha-dihydrotestosterone by the preoptic area did not differ between birds on long or short days. Therefore, a short photoperiod does not appear to influence other pathways of androgen metabolism. In contrast to the effects of photoperiod, castration reduced oestradiol formation in both preoptic and hypothalamic areas. Intramuscular injection of testosterone propionate (TP) in intact males on short days did not restore the pattern of distribution of aromatase activity seen in males on long days. Preoptic aromatase activity was, however, restored by TP in castrated birds. We conclude that a short photoperiod influences both the activity of aromatase and the inductive effect of testosterone on enzyme activity in the preoptic area, which is known to be associated with the behavioural action of oestrogen in the dove. Photoperiod is likely to act both through changes in circulating androgen and by a direct action on preoptic cells.