Appetitive olfactory conditioning in the neonatal male rat facilitates subsequent sexual partner preference

Pairing a neutral odor with a male rat's initial sexual experiences to ejaculation produces a subsequent conditioned ejaculatory preference (CEP) in which males ejaculate preferentially with receptive females that bear the odor relative to unscented receptive females. In 1986, Fillion and Blass reported that neonatal male rats exposed to a neutral lemon odor (citral) painted on their mother's ventrum while nursing ejaculated faster as adults with sexually receptive, citral-scented females compared to unscented receptive females. The present study examined whether the same odor paired with tactile reward in neonatal male rats would alter the subsequent expression of a CEP. Newborn Long-Evans male rats were separated from their mothers each day beginning on Postnatal Day 1 and placed into a Plexiglas cage that contained either unscented or citral-scented bedding (N = 8/group). During each trial, rats were stroked from head to toe with a soft, narrow paintbrush, after which they were returned to their mothers. Males were weaned at 21 days of age and housed in same-treatment pairs for an intervening 50 days. Following habituation to a large open field, males were presented with two sexually receptive Long-Evans females, one scented with citral, and the other unscented, for a 30-min test of copulation. Males in the Paired group copulated and ejaculated preferentially with the scented female whereas males in the Unpaired group showed no preference. Pairing a neutral odor with a reward state in infancy generates a preference in male rats to ejaculate with sexually receptive females bearing the same odor in adulthood.