The development of juvenile-typical patterns of play fighting in juvenile rats does not depend on peer-peer play experience in the peri-weaning period

Open access article. Creative Commons Attribution 4.0 International License (CC BY 4.0) appliesPlay fighting in rats involves attack and defense of the nape. To protect the nape, rats use a variety of defensive tactics, with different strains having specific preferences. Targeting of the nape is established before weaning and defense matures over the course of the week preceding and the week proceeding weaning. Thus, it is possible that experience from engaging in immature forms of play is needed to consolidate the nape as the playful target and for the development of the juvenile-typical pattern of defense. Two experiments were conducted to evaluate this possibility. For the first experiment, male rats were reared over the week post-weaning in either pairs or alone, and their play tested with unfamiliar partners when juveniles (31-34 days). For the second experiment, during the week preceding weaning, male and female rats were placed into one of three conditions: (1) with the mother and no peers, (2) with same-sex siblings but no mother, or (3) with both the mother and same-sex siblings. The subjects were tested in same-sex, samecondition pairs when juveniles (31-34 days). Rats from all conditions, in both experiments, attacked the nape during play fighting and developed the same juvenile-typical patterns of playful defense. This suggests that the experience of peer-peer play in the peri-weaning period is not necessary for the development of the attack and defense components of juvenile-typical play.Ye

Pinning in the play fighting of rats: a comparative perspective with methodological recommendations

Open access article. Creative Commons Attribution 4.0 International LIcense (CC BY 4.0) appliesDuring play fighting, rats attack and defend the nape of the neck and during the course of this competitive interaction, they may adopt a configuration in which one animal stands over its supine partner (i.e., pin). Because the pin configuration is typically frequent and relatively easy to identify, it has been widely used as a marker to detect the effects of experimental treatments. In the present study, the frequency of pinning during standardized, 10-min trials in three strains of rats, Long Evans hooded (LE), Sprague-Dawley (SD) and wild (WWCPS), was compared. LE and SD had higher rates than WWCPS rats (#/min: 6.5, 5.5, 1.5, respectively). When adjusted for strain differences in the frequency of attacks, SD as well as WWCPS rats had lower rates of pinning compared to LE rats. Both SD and WWCPS rats were less likely to use tactics of defense that promote pinning. Moreover, while the majority of the pins achieved in LE rats arose from the defender actively rolling over onto its back, the majority of pins in WWCPS rats arose because one partner pushed the other onto its back. SD rats were intermediate in this regard. Finally, once they do adopt the pin configuration, SD rats are less likely to remain supine than LE and WWCPS rats. That is, both SD and WWCPS rats have significantly fewer pins than LE rats, but a different combination of factors account for this. These data highlight the need to use a battery of measures for ascertaining the effects of experimental manipulations on play. Some suggested guidelines are provided.Ye

The effect of playful experiences on the plasticity and metaplasticity of the brain

ix, 67 leaves ; 29 cmThe influence of play behavior on the brain was investigated through plasticity and metaplasticity methodology. Regions in both cortical and sub-cortical areas were investigated. Animals in both studies either experienced play with juvenile partners or did not experience play by being paired with an adult. Play experience alone was shown to affect the plasticity in the prefrontal cortex, although it did not show structural changes to sub-cortical regions. If animals were given nicotine after play experiences, the affects of play in the prefrontal cortex were abolished. In addition, playful behaviors appear to prime some sub-cortical regions of the brain for expression of later plasticity. Thus, play appears to alter the structure of multiple brain areas, but do so in different ways

Exploring the brain-behaviour interface : the role of juvenile play experiences

In laboratory rats, juvenile play behavior has been shown to influence the development of the medial prefrontal cortex (mPFC) and the experience of interacting with multiple partners has been shown to influence the orbital frontal cortex (OFC). Several studies in this thesis further explored these relationships. Two main findings arose. 1).The play-induced changes to the mPFC and the partner-induced changes to the OFC differ in their longevity. The neural remodeling of the mPFC remains relatively unchanged into adulthood, whereas that of the OFC decreases over time, suggesting that these two areas of the prefrontal cortex serve different roles in social behavior. 2) Though wild rats play in a similar manner to domesticated rats, the play-induced changes to the mPFC are not present, suggesting that complex patterns of play fighting have evolved independently of their role in the development of the mPFC. These findings shed new light on play.Funding Agencies: Natural Science and Engineering Research Council of Canada, Alberta Innovates-Health Solution

The Development of Juvenile-Typical Patterns of Play Fighting in Juvenile Rats does not Depend on Peer-Peer Play Experience in the Peri-Weaning Period

Play fighting in rats involves attack and defense of the nape. To protect the nape, rats use a variety of defensive tactics, with different strains having specific preferences. Targeting of the nape is established before weaning and defense matures over the course of the week preceding and the week proceeding weaning. Thus, it is possible that experience from engaging in immature forms of play is needed to consolidate the nape as the playful target and for the development of the juvenile-typical pattern of defense. Two experiments were conducted to evaluate this possibility. For the first experiment, male rats were reared over the week post-weaning in either pairs or alone, and their play tested with unfamiliar partners when juveniles (31-34 days). For the second experiment, during the week preceding weaning, male and female rats were placed into one of three conditions: (1) with the mother and no peers, (2) with same-sex siblings but no mother or (3) with both the mother and same-sex siblings. The subjects were tested in same-sex, same-condition pairs when juveniles (31-34 days). Rats from all conditions, in both experiments, attacked the nape during play fighting and developed the same juvenile-typical patterns of playful defense. This suggests that the experience of peer-peer play in the peri-weaning period is not necessary for the development of the attack and defense components of juvenile-typical play

Domestication and the role of social play on the development of socio-cognitive skills in rats

Several studies on rats and hamsters, across multiple laboratories, have shown that limiting play in the juvenile period leads to adults that have physiological and anatomical changes in the medial prefrontal cortex (mPFC) and reduced socio-cognitive skills. Peers raised with playful peers have better socio-cognitive skills than animals raised with adult partners. Using Long Evans hooded rats - a commonly used domesticated strain - this relationship has been replicated multiple times. However, when the same paradigm was used with laboratory-reared wild rats, no differences were found between rats reared with peers and ones reared with adults. It has been shown that the key play-generated experiences involved are those related to actively wrestling with a partner and turn taking (as measured by role reversals), which give both partners opportunity to gain the advantage during play fighting. In the present study, we tested the hypothesis that wild rat adults provide juveniles more such experiences than do adult Long Evans rats. The asymmetry in the play interactions in adult-juveniles pairs was compared between the two strains. As predicted, wild rat adults initiated more play with the juveniles, wrestled more and provided more opportunities for role reversals. The findings thus support the hypotheses for the observed strain differences in the effects of rearing condition on the mPFC