Play in Rats: Association across Contexts and Types, and Analysis of Structure

Abstract

-Play has been proposed as a promising indicator of positive animal welfare. We aimed to study play in rats across contexts (conspecific/heterospecific) and types (social: pinning, being pinned; solitary: scampering), and we investigated its structure using behavioral sequence analysis. Group-housed (three per cage) adolescent male Lister Hooded rats (n = 21) were subjected to a Play-In-Pairs test: after a 3 hour isolation period, a pair of cagemates was returned to the home cage and both social and solitary play were scored for 20 min. This procedure was repeated for each pair combination across three consecutive days, and individual play scores were calculated. Heterospecific play was measured using a Tickling test: rats were individually tickled by the experimenter through bouts of gentle, rapid finger movements on their underside, and the number of positive 50 kHz frequency modulated vocalizations and experimenter-directed approach behaviors were recorded. Both of the above tests were compared with social play in the home cage. While conspecific play in both the Play-In-Pairs test and home cage were correlated, both seemed to be unrelated to heterospecific play in the Tickling test. During the Play-In-Pairs test, although both solitary and social play types occurred, they were unrelated, and solitary locomotor play of one rat did not predict the subsequent play behavior of its cage mate. Analysis of play structure revealed that social play occurred more often in bouts of repeated behaviors while solitary play sequences did not follow a specific pattern. If play is to be used as an indicator of positive welfare in rats, context, type and structure differences should be taken into account.

Context‐dependent individual differences in playfulness in male rats

“…Since, PN frequencies in the Play‐in‐Pairs test and HCP were unrelated, contrary to previous findings (Melotti et al, ), we further investigated the nature of this discrepancy by comparing their variances. At Age 1, the variance of PN in the Play‐in‐Pairs test (with isolation) was smaller than the variance in HCP (Play‐in‐Pairs test: SD 2 = 32.6; HCP: SD 2 = 119.0; Pitman‐Morgan test, t 22 = 3.28, p = .01).…”

“…Previous attempts to standardize the propensity to play of the play partner via scopolamine injection have only partially succeeded, as subject rats increased or decreased playful attacks over time depending on whether they were lower or higher players to begin with, respectively (Pellis & McKenna, ). By testing different pair combinations of familiar cage mates, the Play‐in‐Pairs test provides a measure of individual playfulness that is at least partly independent of the playfulness and body weight of the play partners (Melotti et al, ). The current study provides evidence on the capacity of this test to measure playfulness rather than transient play levels in rats.…”

“…Play behavior has been suggested to be crucial for development, as cognitive and social skills and kinematic control are rehearsed, when unexpected situations and sudden loss of control are experienced during play, with playing partners typically switching between controlled and self‐handicapping movements (Spinka et al, ). Types of play in animals include object, locomotor‐rotational, and social play (Held & Spinka, ), the latter being the most extensively studied (Burghardt, ), especially in rats (Douglas, Varlinskaya, & Spear, ; Knutson, Burgdorf, & Panksepp, ; Melotti, Bailoo, Murphy, Burman, & Würbel, ; Panksepp, ; Pellis & McKenna, ; Pellis & Pellis, , ; Pellis, Field, Smith, & Pellis, ; Vanderschuren, ).…”

“…Furthermore, few studies have touched on the relationship between conspecific social play and vocalizations during heterospecific tickling. While Melotti et al () found that social play levels (pinning) showed consistency across a Play‐in‐Pairs test, in which each possible pair combination in a cage was matched and scored for play behavior, and a Home Cage Play (HCP) context, conspecific play was unrelated to heterospecific play during tickling. In contrast, Panksepp and Burgdorf () found that initiations of conspecific social play correlated with vocalizations during tickling at 44 days of age, yet not at 58 days of age.…”

Facial Indicators of Positive Emotions in Rats

“…During the tickling procedure, rats emit positive vocalisations both while being tickled and during pauses between tickling bouts, and the number of positive USVs emitted in these two phases of the tickling procedure are positively correlated [56]. In this study, rats were photographed during pauses between tickling bouts and only while they were emitting positive USVs, to ensure that the hedonic effect of tickling could be captured in the photographs without any influence from the tickling manipulation by the experimenter.…”