Measuring Play Fighting in Rats: A Multilayered Approach

Abstract

Rough-and-tumble play or play fighting is an important experience in the juvenile period of many species of mammals, as it facilitates the development of social skills, and for some species, play fighting is retained into adulthood as a tool for assessing and managing social relationships. Laboratory rats have been a model species for studying the neurobiology of play fighting and its key developmental and social functions. However, play fighting interactions are complex, involving competition and cooperation; therefore, no single measure to quantify this behavior is able to capture all its facets. Therefore, in this paper, we present a multilayered framework for scoring all the relevant facets of play that can be affected by experimental manipulations and the logic of how to match what is measured with the question being asked.

The rough-and-tumble play of rats as a natural behavior suitable for studying the social brain

“…For instance, attack and defense during RTP tend to involve independent mechanisms (Himmler et al, 2016 ). Within a strain, high players not only initiate more nape attacks, but also preferentially use a different suite of the rat-typical defensive tactics than do low players (Pellis et al, 2022 ). As the use of ultrasonic vocalizations (USV) can be critical for communication during play, facilitating role reversals and avoiding escalation to aggression (Kisko et al, 2017 ; Burke et al, 2020 ), rats with different styles of RTP may need to modify their use of such calls (Pellis et al, 2022 ) to play together effectively, making RTP in rats a useful window into subtle social communication processes.…”

“…Consequently, a dyadic paradigm was developed—rats are tested in pairs in an enclosure to which they have been habituated following a period of social isolation to increase their motivation to engage in play (Panksepp and Beatty, 1980 ; Panksepp, 1981 ). This dyadic paradigm has now become the most widely used experimental paradigm for testing RTP in rats (Pellis et al, 2022 ). Variations on the theme include the length of pre-test social isolation and whether experimental rats are tested with a same condition partner, an untreated partner, or both.…”

“…When rats are tested in groups, in which multiple partners are available, play is not distributed evenly. Rather, some partners are favored over others, and this is not simply a by-product of which of the animals are in closest proximity—rats will leave the company of animals in one part of the enclosure and travel to the other side to initiate play with a particular animal (Pellis et al, 2022 ). That is, some potential play partners are preferred over others.…”

“…In a group setting, rats preferentially play with particular partners (Pellis et al, 2022 ), but what makes one partner more attractive than another? As indicated above, some rats are more playful than others and also have differing styles of play.…”

“…As shown in Figure 1 , RTP in rats involves competition to gain access to the partner's nape of the neck, which is nuzzled with the snout if contacted (Pellis and Pellis, 1987 ; Siviy and Panksepp, 2011 ). A variety of tactics are used to attack and defend the nape, including launching counterattacks following a successful defense (Himmler et al, 2013 ; Pellis et al, 2022 ). Rats are a particularly good model species for studying RTP, as this behavior not only differs from serious fighting in the ways described above, but also because serious fighting involves attacking other body targets, namely the flanks and rump, which are bitten if contacted (Blanchard et al, 1977 ; Pellis and Pellis, 1987 ).…”