Activational Effects of Gonadal Hormones on Social Reward Motivation in Adolescence and Adulthood in Female and Male Long-Evans Rats.

There are age and sex differences in the processing of social reward, although the basis for these differences is not well established. We previously found greater social motivation at P50 (postpubertal adolescence) than at P70 (adulthood), and that female rats showed greater social motivation than male rats. Thus, we investigated whether gonadal hormones may contribute to age and sex differences in social reward motivation. Rats underwent either gonadectomy or sham surgery at P41 (adolescent group) or P69 (adult group) and began testing in the operant conditioning paradigm 5 days later. When trained on a fixed ratio of one, gonadectomized rats had a greater social preference relative to control rats, irrespective of sex and age. When tested on a progressive ratio (effort required to access social reward continually increased), adolescents were more motivated than were adults, irrespective of sex or gonadal status. However, resistance to extinction was evident in gonadectomized rats relative to control rats, irrespective of sex and age. Thus, the results provide evidence that gonadal hormones influence social preference, although not social motivation. Ongoing maturation, rather than puberty, is responsible for age-related changes in social reward motivation, and the presence of gonadal hormones independently influences the preference for a social partner.