Oxytocin Induces a Conditioned Social Preference in Female Mice

Friendships and other rewarding affilliative bonds are associated with the actions of the nonapeptide hormone oxytocin (OT) in humans and many social mammals. We determined if 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 non-social tests (conditioned place preference, CPP). Ovariectomised females received oestradiol implants and intracerebroventricular cannulas. During a pre-test, they were introduced to a 3-chamber apparatus for 10 minutes. 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 100ng) and were paired for 30 minutes with one stimulus female. On alternating days, they received saline vehicle and were paired with the opposite female, for a total of 4 pairings each. The final conditioned preference test was identical to the pre-test. OT induced CSP. Test mice that received 100ng OT increased their preference score from −67.4±22.1 seconds in pre-test to +55.7±35.1 seconds during the conditioned preference test (p<0.05). 200ng OT induced an increase in preference score from −162.7±47.3 to +74.3±23.7 seconds (p <0.001). There was no effect of 0 or 1000ng OT on CSP. An additional group of mice was tested for CPP at 200ng 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 seconds (p<0.05). OT had no effect on anxiety or odor recognition as assessed by elevated plus maze and olfactory habituation/dishabituation tests, respectively. In conclusion, OT like other motivating stimuli (drugs, food) is rewarding when tested under solitary conditions, but is also reinforcing in a social setting.