Stephen M. Siviy

Effects of neonatal decortication on the social play of juvenile rats

The effects of radical neonatal decortication on the social play of juvenile rats, as well as the effects of neonatal ablation of frontal or parietal cortex, were examined in this series of experiments. When total decorticates were tested in like-lesioned pairs, the frequency of pinning was reduced by about 50% and their average pin durations were shorter. Nevertheless, the play of decorticates appeared essentially normal in general appearance, and did not differ from controls in a measure of overall play vigor using an electronic activity platform. Further, there were no differences in pin frequencies when controls and decorticates were paired together in cross-lesion testing. Separate tests of play solicitation behaviors did not detect any differences between controls and decorticates suggesting that play motivation was essentially intact after decortication. No deficits in pinning resulted from frontal ablations; however, pin durations were shorter in like-lesion testing. In cross-lesion testing, there was an increase in dorsal contacts and a trend toward shortening of pin durations. Parietal aspirations resulted in a 65% reduction in pin frequency, without substantially altering dorsal contacts. Anesthetization of the anterior surface of the animals back with xylocaine reduced pinning in controls but eliminated pinning in parietals. Although the results generally indicate little participation of the neocortex in the instigation of rough-and-tumble play, the reliable numerical changes that were observed may be explained by apparent motor changes as well as reduced somatosensory sensitivity.

In search of the neurobiological substrates for social playfulness in mammalian brains

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 that includes thalamic intralaminar nuclei, frontal cortex and striatum can be gleaned from these data. Other neural areas that may interact with this putative circuit include amygdala, ventral hypothalamus, periaqueductal gray (PAG), and deep tectum, as well as ascending dopamine systems which participate in all types of seeking urges. At the neurochemical level, considerable evidence points to specific cholinergic and dopaminergic controls, but also endogenous opioids and cannabinoids as having a positive modulatory influence over playfulness, with all neuropeptides known to have aversive effects to reduce play. Monoamines such as norepinephrine and serotonin certainly modulate play, but they influence all psychobehavioral systems, suggesting non-specific effects. We proceed to discuss how increased insights into the neurobiological mechanisms of play can inform our understanding of normal and abnormal childhood development.

Endophinergic modulation of acceptability of putative reinforcers

A series of experiments was conducted in order to gain additional insight into how endogenous opioids may modulate taste reactivity and, thus, hedonic processes. Using a wide range of saccharin concentrations ranging from mildly preferred to aversive, it was demonstrated that naloxone reduced preference for saccharin over water. This reduction was not dependent upon concentration of saccharin and resulted in a downward displacement of the preference/aversion curve. Naltrexone was shown to result in a greater decrease in intake in animals drinking a mildly aversive quinine solution, as compared to animals drinking tap water. In conclusion, endogenous opioids may serve to broaden the range of food-related stimuli which are avidly accepted, perhaps by inhibiting any aversive component associated with ingestion.

Intracerebral administration of naloxone and drinking in water-deprived rats

In 24-hr water-deprived rats, naloxone, at various doses (0, 12.5, 25, 50 micrograms/rat), was administered prior to a 15-min drinking period. Infusions were made bilaterally into each lateral ventricle, frontal cortex, lateral preoptic area, lateral hypothalamus, and caudate nucleus. Naloxone reliably reduced water consumption at 50 micrograms/rat when infused into the lateral ventricles and lateral hypothalamic areas. When comparable doses of naloxone were given by peripheral injection, no effect on drinking was observed. There appeared to be a trend developing for greater sensitivity to naloxone when infusions were made into a particular part of the hypothalamus. These data support the idea that naloxone reduces drinking by acting at central opiate receptors.

Casomorphins reduce separation distress in chicks

Intraventricular administration of various chain length casomorphins (CM) reliably reduced separation induced distress vocalizations (DVs) in young domestic chicks. At a dose of 50 nanomoles, CM-5 was more potent than either CM-4 or CM-7, but for each the duration of action was approximately half an hour, with CM-7 having a somewhat longer effect. This suppression of DVs was partially antagonized by naloxone (1 mg/kg).

The relative playfulness of juvenile Lewis and Fischer-344 rats.

The relative playfulness of inbred Lewis and Fischer-344 rats was characterized. Fischer rats were consistently less playful than Lewis rats, with rats of this strain less likely to initiate playful interactions with either responsive or unresponsive partners and also less likely to respond playfully when playful solicitations were directed to them. While less playful, Fischer rats were more socially inquisitive than Lewis rats when tested with an unresponsive partner, suggesting that Fischer rats are less likely to escalate a social encounter into a playful one. Strain differences in playful responsiveness were present with or without prior social isolation, suggesting that this aspect of play represents a relatively stable trait difference. Unlike play responsiveness, strain differences in play solicitation were only apparent after a period of social isolation. Low levels of play were still present in Fischer rats that had been reared by Lewis dams, suggesting a genetic source for the altered play in rats of this strain. Further studies of play behavior in Lewis and Fischer rats could illuminate relevant neural involvement in rough-and-tumble play and also help understand the genetic bases for this complex social behavior.

Fear, risk assessment, and playfulness in the juvenile rat.

The effects of predatory odors on play were assessed in juvenile rats. When rats were exposed directly to a collar previously worn by a cat, play was abolished and remained suppressed for up to 6 days. Providing rats with an opportunity to hide did not alter cat odors ability to reduce their play. Rat play was also suppressed shortly after they were exposed to cat odor in their home cage, and a substantial amount of risk assessment behavior was present up to 24 hr later. Trimethylthiazoline, a component found in fox feces, only reduced play during exposure. These data suggest that predatory odor-induced reductions in play may provide a useful model for gaining insight into the consequences of fear and anxiety in young animals.

A temporal analysis of naloxone's suppressant effect on drinking

Licking activity was monitored in water deprived rats following various doses of naloxone. It was found that naloxone, at doses ranging from 0.01 to 10.0 mg/kg, had very little effect on initial drinking. However, naloxone did slow sustained drinking after 2 to 6 min into the bout, dependent upon dose. We takes these results to mean that naloxone is interfering with those processes which serve to sustain continued drinking throughout a drinking bout.

Rough‐and‐tumble play as a window on animal communication

Rough‐and‐tumble play (RT) is a widespread phenomenon in mammals. Since it involves competition, whereby one animal attempts to gain advantage over another, RT runs the risk of escalation to serious fighting. Competition is typically curtailed by some degree of cooperation and different signals help negotiate potential mishaps during RT. This review provides a framework for such signals, showing that they range along two dimensions: one from signals borrowed from other functional contexts to those that are unique to play, and the other from purely emotional expressions to highly cognitive (intentional) constructions. Some animal taxa have exaggerated the emotional and cognitive interplay aspects of play signals, yielding admixtures of communication that have led to complex forms of RT. This complexity has been further exaggerated in some lineages by the development of specific novel gestures that can be used to negotiate playful mood and entice reluctant partners. Play‐derived gestures may provide new mechanisms by which more sophisticated communication forms can evolve. Therefore, RT and playful communication provide a window into the study of social cognition, emotional regulation and the evolution of communication systems.

Rough-and-tumble play behavior in Fischer-344 and Buffalo rats: Effects of social isolation

Play behavior was assessed in two inbred strains of rats. Rats of the Fischer-344 strain (F344) were found to be less playful than Buffalo rats after social isolation, as evident from fewer pins and fewer playful attacks to the nape. When tested in same-strain pairings, overall defense of the nape did not differ between strains, although there were strain differences in the specific pattern of defense. When tested in cross-strain pairings, F344 rats were less likely to direct nape attacks toward a Buffalo play partner, and were also less likely to defend their nape when attacked by Buffalo rats. Although different levels of pinning and nape attacks in the two strains were dependent on the amount of isolation prior to the play period, differences in nape defense were not dependent on prior isolation. This pattern of results suggests that the neural mechanisms for playful attack differ from those underlying playful defense. These data also suggest that the F344 strain could be useful in better understanding the neural and genetic bases of mammalian playfulness.