Oxytocin, social factors, and the expression of conditioned disgust (anticipatory nausea) in male rats.

Disgust has been proposed to have evolved as a means to rid the body and mouth of noxious substances and toxins, as well as to motivate and facilitate avoidance of contact with disease-causing organisms and infectious materials. Nonemetic species, such as the rat, show distinctive facial expressions, including the gaping reaction, indicative of nausea-based disgust. These conditioned disgust responses can be used to model anticipatory nausea in humans, which is a learned response observed following chemotherapy treatment. As social factors play a role in the modulation and expression of conditioned disgust responses in rats, and the nonapeptide, oxytocin (OT), is involved in the modulation of social behavior, the present study examined the effects of an OT antagonist, L-368 899, on the development and expression of socially mediated conditioned disgust in male rats. When administered 10 min before testing in a distinct context (different from the original conditioning context), L-368 899 (5 mg/kg) significantly decreased gaping behavior in rats that were conditioned with a social partner. LiCl-treated rats administered L-368 899 before testing also showed decreased social initiations toward their social partner. These findings suggest that OT may play a role in the modulation and expression of socially mediated conditioned disgust in rats.