Abstract

Although male rats are known to display greater unconditional sexual arousal and mating preference to copulate with a novel female compared to a familiar one, research has shown that males given repeated copulatory trials in bi-level chambers with a random almond-scented female develop a conditioned ejaculatory preference (CEP) for females bearing this odor cue. These findings suggest that male rats can learn to associate cues with sexual reward and display preferences for partners that bear those familiar cues. Examination of the effect of copulation in pacing chambers bisected by a divider that either had one hole or four holes at the bottom that only allowed the female to cross, revealed that in 1-hole pacing chambers, females spend more time away from the male than in 4-hole pacing chambers. Males copulating in 1-hole pacing chambers displayed longer ejaculation latencies than those in the 4-hole condition. Interestingly, when animals were changed environments, the differences in ejaculation latencies were maintained suggesting that the pattern of copulation in these males had become conditioned by their initial environment of copulation. An examination of the preferred environment of copulation showed that males prefer to copulate in 4-hole over 1-hole pacing chambers perhaps because males can achieve their optimal rates of copulation in 4-hole chambers. However, contrary to what would be expected, males trained to copulate in 4-hole pacing chambers, with the same almond-scented female at every trial, failed to develop CEP for their familiar female. Instead, it is the males that were trained to copulate in 1-hole pacing chambers that displayed CEP for their familiar female as opposed to the novel one. These findings suggest that copulation in environments in which the female withdraws away from the male for longer periods of time facilitate the development of CEP for a familiar scented female. An analysis of the components required for males to develop CEP for their familiar female revealed that copulation in 1-hole pacing chambers with the same female bearing an olfactory cue and of the same strain as their own are necessary conditions for males to display CEP for their familiar female. Examination of the brain areas involved in the development of CEP for a familiar female, using immunohistochemistry, demonstrated that males that developed CEP for their familiar female displayed significantly more Fos immunoreactivity in the ventral tegmental area (VTA) and in the arcuate nucleus of the hypothalamus (Arc). Pharmacological analyses of the neurochemical mechanisms important for the development of CEP showed that intact opioidergic, but not dopaminergic system, are necessary for the development of CEP in male rats. Examination of neural structures involved in the development of CEP revealed that the VTA and the Arc play an important role in the development of this preference. The present findings shed light on the effect of context on the development of male copulatory behavior and on the development of CEP for a familiar female and its underlying mechanism.