Paced mating behavior in female rats in response to different hormone priming regimens

A female rat will display a repertoire of behaviors during a sexual encount er with a male rat including sexually receptive (the lordosis response) and preceptive (hopping, darting) behaviors. In addition, when given the oppor tunity, a sexually receptive female rat will approach and withdraw from the male rat, controlling the timing of the receipt of mounts, intromissions, and ejaculations, a behavior known as paced mating behavior. The present ex periments tested the hypotheses (1) that progesterone regulates paced matin g behavior, and (2) that multiple hormone regimens used previously to induc e sexual receptivity have the same effect on paced mating behavior. Paced m ating behavior was assessed in sexually receptive ovariectomized female rat s after treatment with: (1) estradiol benzoate (EB; 30.0 mg/kg) followed by a range of doses of progesterone (P; 1.0-8.0 mg/kg), (2) two pulses of une sterified estradiol (E-2; 2.0 mu g/rat) followed by 1.0 mg/rat of P, and (3 ) EB alone (5.0 mu g/rat) for 6 days. No differences in sexual receptivity or in paced mating behavior were observed across doses of P (1.0-8.0 mg/kg) . In contrast, the number of hops and darts per min increased with the dose of P administered. E-2 + P administration resulted in slightly, but signif icantly, lower levels of sexual receptivity along with significantly longer contact-return latencies following an intromission in relation to the othe r treatment conditions. In addition, female rats exhibited fewer hops and d arts per min in response to E-2 + P than in response to EB + 8.0 mg/kg of P . The administration of EB alone for 6 days induced levels of receptivity a nd paced mating behavior indistinguishable from Pa + P, while eliciting sig nificantly fewer hops and darts per min than the Pa + 8.0 mg/kg P treatment condition. Hormone priming regimen had no effect on the percentage of exit s displayed during the paced mating tests in any experimental phase. Dose o f P had no effect on paced mating behavior in sexually receptive rats. In a ddition, P does not appear to be necessary for the display of paced mating behavior following long-term treatment with EB. In contrast, the pulsatile administration of E-2 + P induced a different pattern of paced mating behav ior in sexually receptive rats. (C) 1999 Academic Press.