Influence of environmental events immediately after birth on postnatal testosterone secretion and adult sexual behavior in the male rat.

A rise in plasma testosterone (T) levels occurs in male rats during the first 2 hr after birth which is of importance for the process of sexual differentiation. To study the influence of environmental factors on the postnatal T surge and sexual development, newborn male rats were subjected to various treatments immediately after cesarean delivery including cooling, ether anesthesia, and mother-infant separation. In adulthood, the animals were observed for masculine and feminine sexual behavior. Males anesthetized at 0 hr showed elevated levels of feminine sexual behavior and impaired masculine sexual behavior. Pups subjected to cooling or mother-infant separation showed slightly prolonged intromission latencies, but otherwise normal levels of feminine sexual behavior. Significantly elevated plasma T levels were found in intact pups 2 hr after birth but not in pups subjected to cooling or ether anesthesia. Significantly higher levels of T were observed in pups subjected to cooling 4 hr after birth, suggesting a delay of the T surge. The most pronounced impairing effects were seen in the defeminization process, but the masculinization process also is affected by ether anesthesia. It was concluded that ether anesthesia immediately after birth may permanently interfere with the sexual development by suppressing the neonatal T surge.