Modifications induced by neonatal steroids in reproductive organs and behavior of male rats.

112 3-day-old male Sprague-Dawley rats were injected neonatally with .01, .1, 1, 10, 100, or 1,000 μg of estradiol benzoate (EB), 10,000 μg of testosterone propionate (TP), or sesame oil; they were subsequently examined for testicular, penile, and accessory organ development. Sexual behavior was evaluated during therapy with fluoxymesterone (FM) and then with TP. EB in dosages greater than 1.0 μg delayed testicular descent, reduced the size and hormone responsiveness of reproductive organs, and decreased sexual behavior in a dose-dependent manner. The 10,000 μg dosage of neonatal TP delayed testicular descent and reduced sexual behavior to levels near those of the 10–200 μg EB groups, but it produced no significant penile or accessory organ changes. Neither reduced peripheral organ development nor inhibited neonatal testicular secretions fully explain reductions in male behavior following large dosages of neonatal TP. Neonatal androgen may reduce the responsiveness of CNS neurons governing male sexual behavior after being converted to estrogen or by directly altering steroid receptor systems. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)