Deficient Play-Derived Experiences in Juvenile Long Evans Rats Reared with a Fischer 344 Partner: A Deficiency Shared by Both Sexes

Play fighting during the juvenile period has been shown to be an important experience for the development of sociocognitive skills and the underlying neural mechanisms that support them. Various paradigms have been used to deprive rats of play while still providing social contact. We used the paradigm of rearing a playful rat with a low-playing Fischer 344 (F344) partner to limit the play experienced by Long Evans (LE) rats during the juvenile period. This rearing paradigm has previously been shown to cause sociocognitive impairments in adulthood. In the present paper, we examined the play of same sex LE rats with LE or F344 partners at the peak juvenile period (around 35 days of age). F344 rats launched fewer playful attacks and when attacked, defended atypically compared to how LE do in LE-LE pairs. Playing with an F344 partner afforded LE rats fewer opportunities to engage in prolonged wrestling and fewer opportunities to ward off counterattacks (in which the defending rat becomes the attacker). In addition, there are fewer vocalizations emitted during the encounters in LE-F344 pairs and the types of calls most often emitted differed to those between LE-LE pairs. The altered play and communication experiences were equally present in male and female pairs. These findings are consistent with the hypothesis that, in such rearing paradigms, it is impoverished play experiences in the juvenile period that lead to impaired sociocognitive skills in adulthood.