Testosterone-induced brain aromatase is sexually dimorphic

Area of Science:

• Neuroendocrinology
• Behavioral Endocrinology
• Avian Reproduction

Background:

• Testosterone (T) significantly influences behavior, but its effects differ between sexes.
• Estradiol (E2) is crucial for activating male sexual behavior in many species.
• Hypothalamic aromatase activity, responsible for T to E2 conversion, shows sex-specific differences in quail.

Purpose of the Study:

• To investigate the reasons behind the differential sensitivity of male and female quail to testosterone's behavioral effects.
• To examine the role of hypothalamic aromatase activity and its conversion efficiency in sex differences in T sensitivity.
• To test the hypothesis that limited E2 production in the female hypothalamus contributes to their insensitivity to T.

Main Methods:

• Comparative analysis of testosterone's behavioral effects in male and female quail.
• Measurement of hypothalamic aromatase activity, including Vmax and Km, in both sexes.
• Assessment of 5 alpha-reductase induction by T in the anterior hypothalamus.

Main Results:

• Female quail demonstrated lower sensitivity to the behavioral effects of testosterone compared to males.
• Hypothalamic aromatase activity was induced more efficiently by testosterone in males (higher Vmax) than in females, with similar Km values.
• Testosterone induced 5 alpha-reductase in the anterior hypothalamus of both male and female quail.

Conclusions:

• The lower efficiency of hypothalamic aromatase in females limits the production of behaviorally active estradiol (E2).
• This reduced E2 production in the female hypothalamus is a likely cause for their insensitivity to testosterone's behavioral effects.
• While both sexes exhibit 5 alpha-reductase induction, the key difference lies in the T to E2 conversion pathway.