The development of olfactory conditioned ejaculatory preferences in the male rat. I. Nature of the unconditioned stimulus.

We have demonstrated previously that repeated pairing of a neutral odor with copulation produces a subsequent conditioned ejaculatory preference (CEP) for a female bearing that odor. Here we examine the copulatory components that comprise the unconditioned stimulus (UCS). In Experiment 1, male Long-Evans rats were allowed to copulate with scented females for nine sessions in which they achieved two ejaculations, one ejaculation plus the first intromission following the postejaculatory interval (PEI), one ejaculation without a PEI, or five intromissions without ejaculation. Only the males that achieved two ejaculations or one ejaculation plus the PEI displayed significant CEP. In Experiment 2, males were allowed to remain in the presence of the scented female without access to her after different amounts of copulatory stimulation. Under these conditions, both one and two ejaculations, but not five intromissions, supported the development of CEPs. In Experiment 3, males were allowed to copulate to ejaculation with an unscented female followed by exposure without access to a scented female. This treatment also supported the development of CEP. These results indicate that ejaculation plus a PEI are necessary for the development of CEPs and that the female must be present during the PEI for this to occur. These findings indicate that events during the PEI are the critical components of the UCS for CEP development.