A further characterization of alpha-2 adrenoceptor involvement in the rough-and-tumble play of juvenile rats.

In order to further understand the extent to which alpha-2 adrenoceptors are involved in play behavior, a more detailed behavioral assessment was made of the effects of the alpha-2 agonist clonidine and the alpha-2 antagonist RX821002 on the rough-and-tumble play of juvenile rats. Clonidine reduced overall levels of playfulness, as indicated by fewer attacks directed to the nape, a lower probability of rotating completely to supine in response to nape attacks and fewer pins. In contrast, RX821002 increased playfulness, as indicated by more attacks directed to the nape, a higher probability of rotating completely to supine in response to nape attacks and more pins. Testing rats in an unfamiliar environment did not affect the ability of RX821002 to increase play. Abruptly turning on a bright light during an ongoing play session also did not affect the ability of RX821002 to increase play or the ability of clonidine to reduce play. These data suggest that alpha-2 noradrenergic compounds do not affect play by altering levels of distractibility. However, the extent to which RX821002 and clonidine influenced overall activity during a play bout was compromised by turning on a bright light. While this pattern of results is consistent with a presynaptic site of action for alpha-2 involvement in modulating overall activity during a play bout, the same cannot be concluded about any putative explanatory mechanism for alpha-2 involvement in play behavior

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.