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 animal's 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.

Effects of ACTH(1-24) and ACTH/MSH(4-10) on isolation-induced distress vocalization in domestic chicks.

The effects of centrally administered ACTH(1-24) and ACTH(4-10) on isolation-induced distress vocalizations (DVs) were assessed in the presence or absence of social cues (mirrored and plain environments). A dose-response analysis indicated that ACTH(1-24) at doses of 0.5 nM and above increased DVs relative to controls when the animals were tested in mirrored or social environments which reduce baseline levels of calling. This effect, however, was short-lived (approx. 15 min). When tested again 1 hr after injection, the treated animals did not differ from controls. ACTH/MSH(4-10) had no effect on vocalization when the animals were tested immediately after injection, but marginally increased calling when animals were tested an hour later. In addition to vocalization changes, ACTH(1-24) induced squatting when animals were isolated in the test boxes, and yawning, head shaking, wing flapping and preening when animals were reunited after testing. ACTH(1-24)-treated chicks also exhibited longer latencies to close their eyes when they were held in the cupped hands of the experimenter. Taken together, the results suggest that ACTH(1-24) induces a central state of arousal in chicks that resembles fear/anxiety.

Effects of morphine and naloxone on play-rewarded spatial discrimination in juvenile rats.

Juvenile rats were trained on a spatial discrimination task (T-maze) rewarded by the opportunity to play with a conspecific. Neither morphine (MS; 1 mg/kg) nor naloxone (NX; 1 mg/kg) administration affected choice or running time during the acquisition of the task, even though in the goal box, MS-treated animals played more than and NX-treated animals less than vehicle-treated controls. Thus, brain opioid systems seem to influence the expression of play without affecting the apparent appetitive strength of play motivation. When play reward was no longer available in the goal box, animals that continued to be treated with MS were more resistant to extinction than either vehicle- or NX-treated animals. They continued to complete the task more often and in less time than the controls. NX-treated rats, on the other hand, extinguished faster than controls. The evidence supports the conclusion that opioid systems are important in the maintenance of social habits.

Effects of clonidine and yohimbine on the social play of juvenile rats.

The social play of juvenile rats was observed following administration of either the alpha-2-adrenergic agonist clonidine (0.1, 0.5, 1, 5, 10, and 50 micrograms/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 the amount of play at all but the lowest dose tested, while yohimbine had no effect at any but the highest dose. In addition, we tested a clonidine-yohimbine interaction to assess neurospecificity of the results. While yohimbine alone (0.5 mg/kg) had no effect on play, it partially reversed the clonidine-induced suppression, indicating that the effect may be mediated to some degree through an alpha-2-adrenergic mechanism.

Effects of quipazine and methysergide on play in juvenile rats.

Social play of juvenile rats was analyzed following administration of either the serotonin receptor agonist quipazine (1, 2.5, 5 and 10 mg/kg) or the antagonist methysergide at the same doses. Quipazine reduced pinning at all doses, while methysergide did so at only the highest two. An interaction study using the lowest doses of the agents used above, indicated that methysergide could reverse quipazine induced reductions of play. Thus, the quipazine effect was probably mediated through a serotonin receptor; however, the role of serotonin in play appears to be a general modulatory one rather than a specific influence on play.

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 psychobiology of play: theoretical and methodological perspectives.

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 measurement, gender differences (and the absence thereof), relations between play and aggression, the regulatory processes interacting with and underlying play, the neurochemical and neuroanatomical substrates of play, the functions of play in dominance and other adult behaviors. Existing results suggest the operation of a harmoniously operating brain process which generates a unique emotive brain process that is appropriately referred to as social play. Although the concept of play remains to be adequately defined, the position is advocated that rigorous psychobiological analysis will ultimately provide an empirical definition based upon neural circuit characteristics. Analysis of the underlying circuits may help reveal the manner in which more complex levels of behavioral competence arise ontogenically, and work in the area may yield clues to the genesis of several psychopathologies.

Effects of beta-chlornaltrexamine on separation distress in chicks.

Intraventricular B-chlornaltrexamine (2 micrograms) increased distress vocalizations (DVs) in chicks, and reduced the ability of intraventricular morphine (.1-.5 micrograms), to inhibit DVs. Object imprinting was not blocked by central CNA, but systemic naloxone (10 mg/kg) did attenuate imprinting to a green but not a red object.