Oxytocin Induces a Conditioned Social Preference in Female Mice

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Friendships and other rewarding affilliative bonds are associated with the actions of the nonapeptide hormone oxytocin (OT) in humans and many social mammals. We investigated whether OT itself is rewarding, and if that reward is dependent upon the presence of conspecifics. We evaluated the reinforcing effects of OT infusion in female mice on social (conditioned social preference; CSP) and nonsocial tests (conditioned place preference; CPP). Ovariectomised females received oestradiol implants and i.c.v. cannulas. During a pre-test, they were introduced to a three-chamber apparatus for 10 min. Social and place apparatus were identical, except that each end-chamber contained a novel stimulus female for CSP, whereas they were distinguished by visual and tactile cues for CPP. For CSP, test females received OT (0, 100, 200 or 100 ng) and were paired for 30 min with one stimulus female. On alternating days, they received saline vehicle and were paired with the opposite female, for a total of four pairings each. The final conditioned preference test was identical to the pre-test. OT induced CSP. Test mice that received 100 ng of OT increased their preference score from −67.4 ± 22.1 s in pre-test to +55.7 ± 35.1 s during the conditioned preference test (P < 0.05). It was observed that 200 ng OT induced an increase in preference score from −162.7 ± 47.3 to +74.3 ± 23.7 s (P < 0.001). There was no effect of 0 or 1000 ng of OT on CSP. An additional group of mice was tested for CPP at 200 ng of OT. Testing and pairings were identical to CSP. OT induced a small but significant CPP. Mice increased their preference score from −222.4 ± 38.0 to −126.0 ± 58.7 s (P < 0.05). OT had no effect on anxiety or odour recognition, as assessed by elevated plus maze and olfactory habituation/dishabituation tests, respectively. In conclusion, OT, similar to other motivating stimuli (drugs, food), not only is rewarding when tested under solitary conditions, but also is reinforcing in a social setting.

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