Isolation changes the incentive value of sucrose and social behaviour in juvenile and adult rats

The present study was undertaken to assess the motivational aspects of social behaviour in juvenile and adult rats using the conditioned place preference (CPP) test and anticipatory behaviour for social contact. In addition, the consequences of social isolation during different periods of age on the motivational properties of sucrose-drinking and adult social behaviour were studied. Social play and adult social contact could be used as incentives for place preference conditioning and for inducing conditioned hyperactivity (anticipation) in rats. Both social activities have motivational properties for individually housed rats, whereas group-housing dramatically reduced the motivational aspects of adult social contact. In contrast, sucrose-drinking appears to have motivational aspects independent of the housing condition. Adult social behaviour could not induce a CPP in juvenile isolated rats, suggesting that juvenile isolation during 4 5 weeks reduced the motivational aspects of adult social contact. It seems likely that no CPP was established as a result of the reduced level of social behaviour during the conditioning sessions. Additionally, juvenile isolation during 4-5 weeks appeared to also decrease the motivational properties of sucrose-drinking in maturity, because the intensity of anticipation in response to sucrose was significantly suppressed. Thus, the data suggest that juvenile isolation during 4-5 weeks decreases the motivational properties of both social contact and sucrose-drinking in later life.