Social memory in the rat: circadian variation and effect of circadian rhythm disruption

Disruption of circadian rhythm can impair long-term passive avoidance memor y of rats and mice. The present study investigated whether disruption of ci rcadian rhythm can also impair social memory of male rats. Social memory wa s assessed using the social discrimination test, in which a short-term olfa ctory memory is formed by social interaction with a juvenile rat during a l earning trial. After an intertrial interval, a retrieval trial is performed , in which social memory is expressed as a decreased attention paid to the same juvenile as compared to a new juvenile. First, the social memory at fo ur different time points across the light-dark cycle was measured with an i ntertrial interval of 10 or 25 min. There was no significant circadian vari ation of social memory across the light-dark cycle. Subsequently, the effec t of a - 6 or 12-h phase shift on social memory was studied. These phase sh ifts were previously found to impair long-term passive avoidance memory. Ho wever, no effect of either phase shift was observed in the social discrimin ation test. It is concluded that the disruption of circadian rhythm had no effect on the social memory of rats. Differences between short-term social memory and long-term passive avoidance memory are discussed in relation to their apparent differential susceptibility to the effects of circadian rhyt hm disruption. (C) 2001 Elsevier Science Inc. All rights reserved.