Play Fighting Research Articles

Cholinergic agonists suppress play fighting in juvenile rats

Previous research has suggested that acetylcholine might activate play fighting in juvenile rats through its actions on central muscarinic receptors. To test this hypothesis we evaluated the effects on play fighting by the muscarinic agonists pilocarpine and arecoline given alone or in combination with the muscarinic antagonists scopolamine or methylscopolamine. Scopolamine, but not methylscopolamine which penetrates the brain poorly, suppressed play as indexed by frequency of pinning. Pilocarpine and arecoline also suppressed pinning at higher doses. Concurrent treatment with various agonist-antagonist dose combinations produced additive rather than counteractive effects. These data do not support the supposition that central muscarinic circuits are involved in the activation of play fighting.

Blindness and play fighting in juvenile rats

Play behavior of blinded and sighted juvenile rats was measured using the brief paired-encounter procedure. Dyads of sighted-sighted, blind-blind, or sighted-blind rats were observed in a large or small chamber on alternate days for ages 28 through 43 days. Blinded rats played as frequently as sighted rats regardless of pair composition or chamber size. Vision is not essential for initiating or maintaining play fighting.

A guide to the literature on aggressive behavior

A guide to the literature on aggressive behavior

Compensation of a vestibular deficit in kittens: Is there a critical period?

Childhood bullying or social stress in adolescent humans is generally considered to increase the risk of developing behavioral disorders like depression in adulthood. Juveniles are hypothesized to be particularly sensitive to stressors in their environment due to the relatively late maturation of brain areas that are targeted by stress such as the prefrontal cortex and hippocampus. In our study male adolescent rats were subjected to repeated social defeat on postnatal day (PND) 28, 31 and 34 (experiment 1) or to daily social defeats between PND 35 and 42 (experiment 2). Adolescent rats in experiment 1 were socially housed in pairs with a male of similar age during and after the social defeat. In experiment 2 adolescents were housed either alone or with an age-mate for 7 days (PND 35–42) next to either a highly aggressive or a non-aggressive adult male neighbor with whom a repeated physical interaction was allowed. In experiment 1 the adolescent defeats affected subsequent play behavior with the cage mate. Socially stressed rats more frequently initiated play behavior but also adopted more frequently submissive postures during the play fights. As adults, they seemed to cope behaviorally and physiologically better with a similar exposure to a residential aggressive male rat than unstressed controls. In experiment 2 acute effects of adolescent social stress were studied on neuroplasticity markers like hippocampal cell proliferation and neurogenesis as well as hippocampal brain-derived neurotrophic factor (BDNF) levels. The 2nd experiment also studied long-term effects of the adolescent stress in the response to an adult social defeat. A few acute but minor changes in brain plasticity markers and behavior were observed but these were transient and no behavioral or physiological effects persisted into adulthood. The results from both experiments support the theory developed in the so-called “match–mismatch hypothesis” which claims that the final consequence of childhood adversity depends on how well the early life environment matches the challenges in later life. Socially stressed adolescents are rather resilient to the lasting behavioral and physiological effects of the stress exposure if they are socially housed afterward and have the ability to recover.

Interactive Effects of Caffeine, 2-chloroadenosine and haloperidol on activity, social investigation and play fighting of juvenile rats

The effects of caffeine, 2-chloroadenosine and haloperidol and their interaction on activity, social investigation, and two measures of play fighting (crossover and pinning), were investigated in juvenile male rats. Caffeine (20 mg/kg) increased activity, decreased crossover and pinning, but had no effect on social investigation. Both 2-chloroadenosine (0–10 mg/kg) and haloperidol (0–10 mg/kg) depressed activity, social investigation, crossover and pinning. When given together in varying dosages, caffeine and 2-chloroadenosine had behavioral effects suggestive of a competitive interaction between the two drugs. In contrast, the effects of haloperidol were not appreciably altered by simultaneous caffeine treatment. These results suggest that the influence of caffeine and 2-chloroadenosine on activity, social investigation and play fighting involve interaction with adenosine receptors.

Suppression of play fighting by amphetamine: Effects of catecholamine antagonists, agonists and synthesis inhibitors

Moderate doses of amphetamine and methylphenidate profoundly depress play fighting in juvenile rats. To test the idea that this behavioral effect was dependent on the release of catecholamines (CAs) we administered haloperidol (0.05–0.8 mg/kg), chlorpromazine (0.5–5 mg/kg), phenoxybenzamine (0.5–20 mg/kg) or propranolol (0.5–20 mg/kg) alone or in combination with 0.5 ro 1 mg/kg d-amphetamine sulfate. None of these CA antagonists reversed the suppression of play fighting (indexed by pinning) caused by amphetamine, but at higher doses haloperidol, chlorpromazine and phenoxybenzamine depressed both pinning and rearing. The presynaptic NE agonist clonidine (0.05–0.2 mg/kg) also failed to block the effects of amphetamine on play; instead it too depressed both pinning and rearing. Finally the CA synthesis inhibitor, α-methyltyrosine (total dose: 100 mg/kg) did not attenuate the suppression of play by amphetamine. Ephedrine (10–80 mg/kg) mimicked the effects of amphetamine on pinning, but apomorphine did not. At doses from 0.125–0.5 mg/kg apomorphine stimulated pinning while 1 mg/kg had no effect. The present findings confirm earlier reports that amphetamine suppresses play fighting but the mechanism of action remains obscure.

Social play in juvenile rats during scopolamine withdrawal

Scopolamine induced blockade of play fighting in juvenile rats and the rapid induction of behavioral tolerance to an initially effective dosage suggested a rebound in social play following chronic scopolamine exposure. Juvenile rats received daily intraperitoneal scopolamine or saline injections for one week. Play soliciting and play fighting behavior were then measured at 24 and 168 hr after drug withdrawal. Scopolamine treated juveniles engaged in markedly greater play soliciting and play fighting behavior than did controls. Drug-induced increase in muscarinic receptors and supersensitivity to endogenous acetylcholine following scopolamine withdrawal is suggested as the basis for observed differences in social play.

Play soliciting in juvenile male rats: Effects of caffeine, amphetamine and methylphenidate

Three standard CNS stimulants were tested for effect on juvenile play soliciting in prepubertal male rats (n = 120). Three dosages of each stimulant were compared with a saline control. Soliciting behavior was isolated and magnified by a novel method incorporating pretest social deprivation and social response to a standard nonplayful social stimulus pretreated with scopolamine HBr. Caffeine significantly decreased frequency of play soliciting only at the high dose of 40 mg/kg. Methylphenidate and d-amphetamine significantly decreased play soliciting at all dosages tested. The method is proposed as a generally useful experimental paradigm in analyses of drug effect on play soliciting. Advantages include individual measures of soliciting behavior that correlate reliably with measures of rough-and-tumble play fighting.

Medial hypothalamic lesions and play fighting in juvenile rats

The effects of medial preoptic area (MPOA), anterior hypothalamic (AH) and ventromedial hypothalamic (VMH) lesions on play fighting were studied in juvenile rats that were housed and observed in heterosexual groups of 6–8 animals. Overall males engaged in play fighting more frequently than females and mone of the lesions reliably affected this measure. Males also initiated more play fights. AH and VMH lesions reduced the frequency of play initiation in both sexes, but MPOA lesions had no reliable effect in either sex.

Play-solicitation behavior in juvenile male and female rats

Play-solicitation and social investigatory behaviors were observed in male and female juvenile rats exposed to playful and nonplayful juvenile social stimuli. A nonplayful state was induced by treatment with scopolamine HBr. In Experiment 1, the play-solicitation behavior of males exposed to nonplayful stimuli was reliably greater than that of females; social investigation did not differ by gender. In Experiment 2, males and females were exposed to nonplayful male and female stimuli. Male subjects engaged in more soliciting than did female subjects, and male social stimuli were subjected to more soliciting than were female social stimuli. Experiment 3 compared the influence of varying social deprivation intervals on play soliciting by male juveniles. Although social investigation did not vary reliably with interval of social deprivation, play soliciting increased reliably with longer intervals of isolation. In Experiment 4, play-soliciting behavior of males exposed to nonplayful males correlated positively and reliably with play fighting behavior upon exposure to normally playful males. The results support the proposal that some specific behaviors functionally provoke interactive play fighting.

Suppression of play fighting by amphetamine does not depend upon peripheral catecholaminergic influences

As reported earlier, d-amphetamine (0.25–1.0 mg/kg) produced a dose-dependent depression of play fighting as indexed by the frequency of pins and the total duration of play fighting. Amphetamine reduced both the frequency of play bouts and the duration of those bouts that occurred. At the highest dose, play fighting was virtually eliminated. In contrast, 4-OH-amphetamine, which crosses the blood-brain barrier less readily than does d-amphetamine, did not depress play fighting at doses from 0.25 to 2 mg/kg. At 4 mg/kg, this drug reduced pinning, total play duration, and the frequency of play bouts, but did not affect bout duration. In a second experiment, the effects of d-amphetamine on play fighting were studied in animals that had been adrenal demedullated, subjected to chemical sympathectomy with 6-hydroxydopamine, or given a combination of both treatments. Amphetamine produced comparable suppression of play fighting regardless of the functional state of the sympathetic nervous system. Apparently, the effects of psychomotor stimulants on play fighting by juvenile rats are mediated by the central actions of these drugs.

Scopolamine blocks play fighting behavior in juvenile rats

Play fighting, social investigation, and locomotor activity of prepubescent male laboratory rats were observed 20 min following administration of scopolamine hydrobromide. Play fighting was inhibited by an intraperitoneal dosage of 0.3 mg/kg and was effectively blocked at all dosages greater than 0.5 mg/kg; activity and social investigatory behavior were increased by scopolamine. Play fighting inhibition following a threshold dosage of 0.3 mg/kg scopolamine was effective at 30 min; after 120 min, drug- and saline-treated groups failed to differ reliably. Behavioral tolerance to scopolamine was observed after five days of daily treatment with 0.5 mg/kg scopolamine; play fighting, following a 0.5 mg/kg dosage of scopolamine, did not differ from that of saline-treated controls. The results are discussed in terms of central and peripheral effects of scopolamine and the competing response hypothesis.

Olfactory bulbectomy and play fighting in juvenile rats

To determine the influence on play fighting of inputs to the brain that arise in or course through the olfactory bulbs juvenile male and female rats were bilaterally bulbectomized at 23 or 24 days of age. The frequency of play fighting and play initiation was observed in tests conducted in the home cage. Bulbectomy did not affect the frequency of play fighting or play initiation by males, but slightly increased the frequency of play fighting without altering play initiation in females. Since peripheral anosmia has only modest effects on play fighting, neither the chemosensory nor the modulatory influences of the olfactory bulbs on limbic system activity appear to be especially important in the control of play by juvenile rats.

Scopolamine depresses play fighting: A replication

The effects of scopolamine and methylscopolamine (0.125—1.0 mg/kg) on play fighting by juvenile rats were compared. At doses of 0.25 mg/kg or higher, the centrally active anticholinergic, scopolamine hydrobromide, depressed pinning and reduced the total duration of play fighting. In contrast, scopolamine methylbromide had no effect. Neither drug reliably affected social investigation or rearing.

Play fighting and the development of agonistic behavior in male and female rats

Two longitudinal studies were conducted to quantify the social behaviors exhibited by both male and female Long-Evans rats from the immediate postweaning period until young adulthood. In Experiment 1, male sibling pairs engaged in a high level of play fighting during the early juvenile period but such activity declined to a level significantly lower than that of female and mixed-sex pairs after 54 days of age. In Experiment 2, social exchanges during maturation were examined during the presence and absence of the piloerection response in an effort to distinguish play fighting from agonistic interactions. In male pairs, piloerection was rarely seen before 55–75 days of age but thereafter occurred with increasing frequency especially among dominant males. Furthermore, subordinate males retreated from their dominant partners and remained in an escape chamber for a significant amount of time only during encounters involving the exhibition of piloerection. This finding suggests that piloerection can be useful in identifying play and aggressive interactions. In female and heterosexual pairs, piloerection was observed infrequently during social encounters occurring throughout maturation. In addition, when given the opportunity to escape, females were less likely to retreat from play activity if their partner was another female than a male.

Naloxone and play fighting in juvenile rats

According to the opioid hypothesis of social attachment opiate receptor blockade should increase the need for social contact. Yet naloxone reduces play fighting [11], a major form of social interaction in young rats. This observation might be reconciled with the opioid attachment hypothesis if it could be shown that naloxone produced compensatory increases in other social activities or if naloxone shortened play fighting bouts without reducing their frequency. In the present experiment naloxone reduced play fighting in a dose-dependent fashion. However, the frequency of play bouts was reduced, their duration unchanged and no compensatory increase in social sniffing and grooming was observed. In addition, naloxone inhibited rearing almost as potently as it affected play fighting.

Anosmia and play fighting behavior in prepubescent male and female rats

Prepubescent male and female rats were paired after intranasal treatment with isotonic zinc sulfate or saline solutions to determine the influence of peripheral anosmia upon play fighting behavior. In Experiment 1, male isolate residents pinned intruders significantly more often than intruders pinned residents but anosmia treatment had no influence on pinning behavior. In Experiment 2, males and females differed significantly in all major categories of play fighting but anosmia treatment had no influence on play fighting of either males or females. In Experiment 3, male groups matched for play fighting behavior prior to intranasal zinc or saline treatment were paired with like-treated males. All males in all pairings engaged in play behavior but anosmic males played less than controls. Evidently, intranasal zinc treatment depresses play behavior only when both members of a pair are anosmic. Play behavior is more markedly affected by resident-intruder status and by gender than by peripheral anosmia.

Septal lesions increase play fighting in juvenile rats

Play fighting is a behavior exhibited by juveniles of many mammalian species, but the neurology of this behavior is poorly understood. In the present study lesions of the septal area or control operations were performed in rats at 23 days of age and social play was studied between the ages of 27–41 days of age. Septal lesions increased the frequency of play fighting and play initiation in both sexes; within the lesion and control groups males played more frequently and initiated more play bouts than females. Animals with septal lesions were somewhat lighter in body weight than controls, but since play frequency and body weight were not associated, it is unlikely that changes in body weight caused by the lesions are responsible for the effects of the lesions on play.

Psychomotor stimulants, social deprivation and play in juvenile rats

Treatment with d-amphetamine (0.125–1 mg/kg) or methylphenidate (0.5–4 mg/kg) caused dose-dependent decreases in play fighting in juvenile rats which were independent of sex and strain. Although brief social isolation profoundly increased play fighting, qualitatively similar drug effects on play were observed in socially housed and isolated animals. By contrast, at the highest doses tested both amphetamine and methylphenidate increased social investigation, but only if the rats were socially isolated. Stimulation of catecholamine systems is evidently incompatible with the expression of playful behavior.

Social deprivation and play in rats

Social interaction (play fighting) was studied in socially housed and individually housed juvenile rats (18–30 days of age). 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 by social deprivation and reduced by social satiation. The results suggest that social play is a regulated process which can be easily quantified by the simple and objective measure of pinning behavior.