Impact of Lighting Condition and Social Isolation on Rats' Playfighting Behaviour

Abstract

Playfighting in rats is a well-documented phenomenon, however, studies frequently differ in terms of the conditions under which play behaviour is assessed. This study examined the impact of lighting condition and social isolation on play, two conditions which vary in literature. The goal was to quantify and advance the understanding of optimal conditions for promoting playfighting behaviour in rats. Twenty-four male Long-Evans rats were randomly assigned a lighting condition (complete darkness vs. low mixed red-white light) and social isolation condition (0 hours vs. 5 hours vs. 24 hours). Rats were habituated in cagemate pairs to a plexiglass test chamber (60 x 60 x 40 cm) under their respective lighting conditions for three days prior to testing. Prior to the test day, cagemate pairs were randomly selected to be isolated from their play partners for different durations. After their respective isolation periods, cage-mate pairs of adolescent rats (PD30-37) were video-taped freely interacting in the test chamber for 10-minutes and their play behaviour was scored in NOLDUS by a trained coder. Data were analyzed in SPSS using a 2x3 ANOVA. Rats tested in complete darkness displayed higher rates of nape attacks (p = 0.008) and pinning (p = 0.002), two measures used to quantify playfighting. Post-hoc testing revealed that rats isolated for 24-hours prior to testing displayed higher rates of nape attacks (p = 0.028) and pins (p = 0.005) compared to non-isolated rats, but there were no other differences between other isolation conditions. These findings suggest that the conditions under which rats are tested can impact their play behaviour, driving differences in rates of commonly scored play behaviours. The data suggest it is ideal to assess rats’ play behaviour in complete darkness after at least 24-hours of social isolation to optimize baseline levels of playfighting.