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Oxytocin and direct reciprocity in rats
Tristan Tanchanco1, Ruth I Wood1
1Department of Integrative Anatomical Sciences, Keck School of Medicine at the University of Southern California, Los Angeles, CA 90033, USA.
Abstract:
Cooperation is an important dimension of social behavior in humans and animals. Reciprocal altruism provides an evolutionary basis for cooperation between unrelated organisms, but the neuroendocrine mechanisms driving these behaviors are not fully understood. The present study tested an operant model of direct reciprocity in male and female rats. Direct reciprocity is a sequential 2 × 2 game where rats alternate as Donor and Recipient to deliver and receive 1 sugar pellet (respectively) in repeated trials. Rats were tested in same-sex pairs, and we determined the effects of oxytocin (OT) and its antagonist (OTR-A) on cooperative responses. There was no baseline sex difference in cooperation (females: 25.2 ± 3.8%; males: 20.7 ± 3.1%), and pretreatment with OT (0.05-2 mg/kg) had no effect on the likelihood of the Donor to respond on behalf of their cagemate Recipient. In a similar manner, there was no difference in cooperation when rats were paired with an unfamiliar partner (p > 0.05). However, OTR-A had a sex-specific effect to reduce cooperative responses in females (to 11.1 ± 2.2%, p < 0.05), and increase the likelihood of defection after their partner defected (from 80.2 ± 4.1% to 87.8 ± 2.3%, p < 0.05). These findings align with recent studies suggesting that OT enhances reward valuation, and has broad effects on decision-making circuitry in the brain.
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