8 
Rats make abundant 50 kHz ultrasonic vocalizations (USVs) when they play and exhibit other positive social interactions. This response can be dramatically increased by tickling animals, especially when directed toward bodily areas toward which animals direct their own play solicitations (e.g., nape of the neck). The analysis of this system indicates that the response largely […]
5 
The social play of pairs of juvenile rats can be brought under tight experimental control using social deprivation, and it can be objectively quantified by measurement of pinning behavior. Research and conceptual issues concerning this paired-encounter procedure are summarized, including issues related to (1) measurement, (2) gender differences (and the absence thereof), (3) relations between […]
5 
The social play of juvenile rats was observed following administration of either the ?-2-adrenergic agonist clonidine (0.1, 0.5, 1, 5, 10, and 50 ?g/kg) or antagonist yohimbine (0.5, 1, 2, and 5 mg/kg). Using pins (one animal on its back with the other on top) as the dependent measure, we found that clonidine reliably reduced […]
7 
A composite index incorporating the frequency and structure (target, type of defence, etc.) of play fighting was used to compare the complexity of such play in 13 species of muroid rodents whose behaviour has been previously described. A phylogenetic comparison of the distribution of the complexity of play fighting revealed that relatedness did not predict […]
10
Play behavior is a fundamental and intrinsic neurobehavioral process in the mammalian brain. Using rough-and-tumble play in the juvenile rat as a model system to study mammalian playfulness, some of the relevant neurobiological substrates for this behavior have been identified, and in this review this progress. A primary-process executive circuit for play in the rat […]
6 
In rats (Rattus norvegicus), juvenile males engage in more play fighting (a male-typical behavior) than do juvenile females, and this difference is based on perinatal influences of androgens. We show that there are qualitative and quantitative differences between the sexes in the type of defensive responses and their manner of execution. In defensive responses rats […]
8 Play behavior, as indicated by frequency and duration of pinning behavior, was studied in young rats between 18 and 64 days of age. The incidence of play was markedly increased by social isolation. Play increased from 18-28 days of age, peaked between 32 and 40 days of age, and gradually declined thereafter. Animals developed stable […]
8 Social interaction (play fighting) was studied in socially housed and individually housed juvenile rat+D606). Pinning (an animal on its back, with the other on top) proved to be a simple measure of play which correlated highly with other measures of playful behavior (solicitive behaviors, following, rough-and-tumble play, and together-time measures). Play behaviors were markedly increased […]
7 
(3H)Diprenorphine binding was analyzed autoradiographically in the brains of 33 day old rat pups. A photographic atlas of diprenorphine binding in the coronal plane is provided to highlight the dispersion of opioid receptor systems through the brain. To determine whether brain opioid release may be induced by social interactions, half the animals were sacrificed following […]
2 play fighting in its most elaborate form involves nonagonistic wrestling between pairmates, where one partner grabs, holds, bites, or otherwise contacts the other. Such play occurs in the absence of the functional consequences associated with serious fighting (e.g., resource acquisition or protection). Typically, the biting, nosing, or grooming contact during play fighting is directed at […]
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Positive emotional states have been shown to confer resilience to depression and anxiety in humans, but the molecular mechanisms underlying these effects have not yet been elucidated. In laboratory rats, positive emotional states can be measured by 50-kHz ultrasonic vocalizations (hedonic USVs), which are maximally elicited by juvenile rough-and-tumble play behavior. Using a focused microarray […]
10
Negative social experiences during adolescence are central features for several stress-related mental illnesses. Social play fighting behavior in rats peaks during early adolescence and is essential for the final maturation of brain and behavior. Manipulation of the rat adolescent social experience alters many neurobehavioral measurements implicated in anxiety, depression, and substance abuse. In this review, […]
10 
Paul MacLean’s concept of epistemics – the neuroscientific study of subjective experience – requires animal brain research that can be related to predictions concerning the internal experiences of humans. Especially robust relationships come from studies of the emotional/affective processes that arise from subcortical brain systems shared by all mammals. Recent affective neuroscience research has yielded […]
7 
Juvenile play behavior in rats promotes later behavioral flexibility and appears to do so by modifying the neural systems that regulate the animal’s response to unexpected challenges. For example, the experience of play has been shown to prune the dendritic arbor of the cells in the medial prefrontal cortex (mPFC), part of the brain’s executive […]
6 
Due to the action of testicular hormones in the perinatal period, juvenile male rats engage in more play fighting than juvenile females. Also, following puberty, males, but not females, switch to using adultlike defensive tactics more frequently during play. This change in play is also due to the action of testicular hormones perinatally. In this […]
2 The effects of naloxone on social play and feeding behaviors of postweanling and adult Long-Evans hooded rats were studied. Administration of 1.0, 5.0, or 10.0 mg/kg naloxone reduced play in a dose-related fashion. The effects of a 5.0-mg/kg dose of naloxone could be detected at least 3 h after administration, in terms of both a […]
7 
As pairs of male juvenile sibling rats that are housed together become sexually mature, they develop a dominance-subordinance relationship. These dominance relationships appear to be reflected in the play fighting of the pairmates both as juveniles and as young adults, in that the seemingly subordinate partner initiates more playful attacks at both ages. However, as […]
4
During competitive interactions, such as fighting and predation, animals perform various actions, some of which are easy to characterize and label, some of which are reliably repeated. Such ‘behavior patterns’ are often the measures of choice when comparing across species and experimental contexts. However, as Bob Blanchard and others have pointed out, such measurements can […]
4
During postweaning development, rats exhibit several well documented trends in their play fighting: (1) It peaks between 30-40 days and then declines with the approach of sexual maturity; (2) males initiate more play fights than females; and (3) the overall complexity of play fights, as expressed by such measures as duration of bouts, also decreases […]
2
play fighting in deer mice, Peromyscus maniculatus bairdii, prairie voles, Microtus ochrogaster, and montane voles, M. Montanus, was compared to that of laboratory rats, Rattus norvegicus. Play in rats appears more complex for two reasons: 1) more of the playful contacts elicit defensive behaviors, and 2) more of these defenses lead to counterattacks, and hence, […]
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