Sensitization of sexual behavior in ovariectomized rats by chronic estradiol treatment

The ovariectomized (OVX) rat treated with estradiol benzoate (EB) is used to elucidate neuroendocrine mechanisms of sexual behavior. Chronic behavioral and pharmacological manipulations can be confounded by rising baselines, since females are behaviorally more sensitive to repeated EB injections. The literature lacks a systematic examination of chronic effects of EB administered alone to the sexually experienced OVX rat. Long-Evans rats were repeatedly treated (8 tests) with s.c. injections of 2, 5, or 10 mu g EB at different time intervals (4 or 8 days). Female sexual behaviors as well as receipt of mounts, intromissions and ejaculations from the male were observed in the unilevel 4-hole pacing chamber. The effects of adrenalectomy (ADX) and strain (Long-Evans vs. Wistar) were also assessed. Long-Evans OVX rats treated with 5 mu g EB every 8 days showed persistently low levels of sexual behavior. Sensitization was most robust following 10 mu g LB at 4-day intervals. Very few sexual behaviors were ever induced by 2 mu g EB. ADX did not affect the development of behavioral sensitization by 10 mu g EB. Therefore, to achieve a low steady state of sexual behaviors in sexually experienced Long-Evans OVX rats 5 mu g of EB administered every 8 days is optimal, whereas a persistently high level of sexual behaviors is induced with 10 mu g EB administered every 4 days. OVX Wistar rats are behaviorally more sensitive to EB. Behavioral sensitization to EB may serve as a mechanism to optimize reproductive success. (C) 2013 Elsevier Inc. All rights reserved.