Figure 1.

MTII facilitates immediate and long-term partner preference in prairie voles. (a) Female prairie voles given either a low or high dose of MTI failed to spend significantly more time with either stimulus animal and therefore did not form a ‘partner preference'. (b) Female prairie voles receiving a high dose (10 mg/kg) of MTII (partner vs stranger p<0.05) spent significantly more time with the partner male vs the stranger male, indicative of a partner preference. (c) MTII (10 mg/kg) also induced partner preference formation in male prairie voles (partner vs stranger p<0.05) under conditions in which vehicle-treated animals did not. (d) The effect of MTII (10 mg/kg) is maintained in the female prairie voles after a 7-day period of separation. Comparison of time spent with the partner vs the stranger indicates a partner preference in MTII-treated animals (partner vs stranger p<0.05), with an average of three times more time spent with the partner than the stranger. (e) The administration of MTII had no effect on partner preference formation in meadow voles. There was no significant difference in the amount of time spent huddling with the partner or the stranger after 24 h of cohabitation. (f) Administration of Pf-446687 resulted in significant partner preference. Female prairie voles receiving a low dose (1 mg/kg) of MTII (partner vs stranger p<0.05) spent significantly more time with the partner male vs the stranger male. The 10 mg/kg doses trended toward the formation of a preference but did not reach significance. *Indicates a statistically significant partner preference (p<0.05).