Influence of environmental factors on social play behavior of juvenile rats.

The effects of light level and familiarity to the testing environment on social behaviors related and unrelated to play were investigated in juvenile rats accustomed to dim light conditions. Pinning, a measure characteristic for social play in rats, was completely suppressed under intense light conditions. Following/chasing and boxing/wrestling, social behaviors related to play, were also decreased under intense light. Of the measures of social behavior not related to play, contact behavior was decreased under intense light whereas social exploration was hardly affected. Levels of social exploration and following/chasing gradually declined during the 15-min test period. Frequency of contact behavior decreased, whereas duration increased with time. Under dim light conditions, unfamiliarity to the test cage suppressed pinning and boxing/wrestling but not the other social behaviors in the first part of the test period. These findings show that social behavior in juvenile rats, as in adult rats, can be influenced by light level and familiarity to the test cage. Social behaviors related and unrelated to play seem to be differentially influenced by environmental stimuli.