Exposure to male siblings facilitates the response to estradiol in sexually naive female prairie voles.

Female prairie voles undergo induced estrus, and require both physical contact with males and exposure to male urine to become reproductively active. This study attempted to determine if physical contact with males enhanced female response to estradiol. Two groups of sexually naive females were tested. One was reared without any exposure to males after weaning, and the other was reared with sibling males to 60 days of age. Sibling males were used because females avoid direct contact with the urine of related males, allowing for the establishment of a group of females that experienced physical contact in the relative absence of exposure to male pheromones associated with urine. Females were then subcutaneously injected with 0.5 microg estradiol benzoate once a day for 7 days. Sexual receptivity was tested with novel adult males 48 h and 168 h after the first injection. There was a significant difference between the treatment groups, with 10% of sexually naive females reared without sibling males displaying lordosis compared to 70% of females raised with sibling males. The results indicate that exposure to sibling males significantly increased a female's behavioral response to estradiol.