Hypothalamic sites of progestin action on aggression and sexual behavior in female Syrian hamsters

The effects of intracranial implants of the synthetic progestin, promegestone (R5020), on aggression and sexual behavior were examined in female Syrian hamsters. Ovariectomized female hamsters showed high levels of aggression and no lordosis towards stimulus male and female hamsters, both prior to and after estradiol benzoate treatment. Forty-six hr after estradiol treatment (10 μg SC), 10% crystalline promegestone was applied bilaterally (27 ga cannulae) to the ventromedial hypothalamus. When tested 5-7 hr later, these animals had a significant reduction in the rate of attacks towards females, with no lordosis responding to a male. In contrast, promegestone in the caudal anterior hypothalamus activated low levels of lordosis, yet these females maintained high levels of aggression towards stimulus females. Females receiving promegestone in the rostral anterior hypothalamus, and control females receiving intracranial cholesterol, maintained high levels of aggression and no lordosis. Estradiol treatment alone enhanced pelvic movements in response to experimenter-applied perineal stimulation in a majority of females ( 18 22 compared with 4 22 prior to estradiol injection), with intracranial treatments having no further effect. These results indicate that progestins act on aggression and sexual behavior in female Syrian hamsters at different hypothalamic loci.