Interaction of androgens and estrogens in the control of sexual behavior in male Japanese quail

Neuroanatomical distribution of testosterone-metabolizing enzymes in the Japanese quail

We describe a very sensitive and precise assay which allows one to study the metabolism of testosterone (T) in small brain nuclei dissected out according to the method of Palkovits and Brownstein. With this method, the neuroanatomical distributions of aromatase, and 5 alpha- and 5 beta-reductase activities were studied in adult male quail (Coturnix coturnix japonica). The different enzymes show different neuroanatomical distributions. Production of estradiol-17 beta (E2) was highest in the sexually dimorphic nucleus preopticus medialis (POM). We showed previously that the preoptic aromatase activity is higher in male than in female quail. As the POM is a central and very large structure within the preoptic area, the present results suggest a relationship between the neuroanatomical and the biochemical sex differences. By contrast, the production of 5 alpha-DHT was highest in the lateral hypothalamic area (LHY), the bed nucleus of the pallial commissure (BPC) and the lateral septum (SL). The 5 beta-reductase activity was highest in the lateral septum and in the ventral part of the archistriatum (AV). Moreover, there was a rostral to caudal decrease in 5 beta-reductase activity in the hypothalamus.

Central and peripheral metabolism of 5 alpha-dihydrotestosterone in the male Japanese quail: biochemical characterization and relationship with reproductive behavior

An in vitro radioenzymatic assay and purification procedure by thin-layer chromatography were used to study the metabolism of dihydrotestosterone (DHT) into 3 alpha- and 3 beta-androstanediols by the brain and cloacal gland of Japanese quail. Kinetic studies showed that these 2 metabolites are produced in a linear fashion with respect to time of incubation for up to 15 min but that they continue to accumulate for up to 4 h. The maximum velocity of these reactions is high (nmol/mg protein/15 min), but the affinities of the enzymes for DHT are low (in the microM range). The enzymatic activities are not evenly distributed in the brain: they are high in the tuberal hypothalamus and lobus parolfactorius but low in the preoptic area and anterior hypothalamus. Enzyme activities are not markedly affected by treatment of the birds with either testosterone or DHT. The activity of these enzymes is lower in the preoptic area and tuberal hypothalamus of DHT-treated birds which display female-directed sexual behavior than in the same brain areas of birds which are sexually inactive. We discuss the relationships between this reductive metabolism of DHT and the activational effects of the steroid on sexual behavior.

Effect of the injection solvent on steroid activity

The effects of testosterone, 5 alpha-dihydrotestosterone, and androstenedione on cloacal gland and sternotracheal muscle growth and on luteinizing hormone plasma levels were studied in Japanese quail. The steroids were given to the animals in daily intramuscular injections and were dissolved either in propylene glycol or in ethanol:saline (1:1). The three steroids had significant effects on the responses which were measured, but the magnitude of this effect was clearly related to the type of vehicle in which the steroids were dissolved. Furthermore there was a significant interaction between the effects of solvents and of steroid; for example, testosterone was much less androgenic than 5 alpha-dihydrotestosterone when dissolved in propylene glycol, but both had similar effects when dissolved in ethanol:saline. The effects of the mode of administration of different steroids on a given physiological response should be taken into consideration.

Effects of metabolism inhibitors, antiestrogens and antiandrogens on the androgen and estrogen induced sexual behavior in Japanese quail

The relative contribution of androgenic and estrogenic metabolites of testosterone to the activation of sexual behavior was studied in Japanese quail by using inhibitors of testosterone metabolism, antiestrogens and antiandrogens. These compounds were tested in castrated birds whose sexual behavior had been activated by silastic implants of testosterone (T) or daily injections of testosterone propionate (TP) or diethylstilboestrol (DES). The aromatase inhibitor ATD only depressed T-induced behavior when injected at high doses and the 5 alpha-reductase inhibitor, 4MA was inactive in this respect. The antiestrogens, tamoxifen (TAM) and nitromifene citrate (CI-628) strongly depressed sexual behavior but they also drastically reduced the crowing behavior which is typically androgen-dependent which throws some doubts on the specificity of their action. The antiandrogens, flutamide and cyproterone acetate (CA), only had limited inhibitory effects on the copulatory behavior but similarly decreased only marginally the crowing. As they strongly depressed the cloacal gland growth, it can be ascertained that they were injected in sufficient amounts and their lack of action on crowing questions the ability of these compounds to inhibit brain processes even when they are androgen-dependent. Taken together with the results of previous experiments which tested the behavioral effects of the testosterone metabolites, the present data confirm the implication of both androgenic and estrogenic metabolites of testosterone in the activation of behavior. Their interaction remains, however, poorly defined and its understanding will probably require the identification of the biochemical processes which in the brain mediate the behavior.