Idazoxan increases rough-and-tumble play, activity and exploration in juvenile rats

Abstract

The effects of idazoxan, an alpha-2 noradrenergic antagonist, on play and open field behavior were assessed in juvenile rats. Play was assessed in two separate paradigms. Initially, juvenile rats were housed individually and given a daily 5 min opportunity to play with a responsive partner. Idazoxan (1-8 mg/kg) increased pinning, an indicator variable of play, but did not affect the frequency of dorsal contacts, an index of play solicitation. When rats were tested in a separate test for play solicitation using an unresponsive play partner, idazoxan increased all three measures of play solicitation. Idazoxan increased activity and exploration when rats were tested in an open field, suggesting that the effects of idazoxan on play may be due to an increase in behavioral arousal and/or attention. These data are consistent with a modulatory role for norepinephrine in the control of behavior.

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

“…Although nape attacks did not differ between the treated and untreated rats in Experiment 2, this could have been due to the increased likelihood of rotating by the treated rat, making it less likely to exhibit more nape attacks in the 5 minutes allowed for testing. This is supported by a previous ®nding that idazoxan increased several measures of play solicitation when tested with an unresponsive partner (Siviy et al, 1990). It is also possible that the increased playfulness of the RX821002-treated rats yielded higher levels of play in the untreated rats, due to the``contagious'' nature of play (e.g., Pellis, Pellis, & Kolb, 1992).…”

“…Previous studies that have looked at the effects of alpha-adrenoceptor agonists and antagonists on play have used pinning as the primary dependent measure of play (Normansell & Panksepp, 1985;Siviy et al, 1990Siviy et al, , 1994. Pinning refers to one animal being on its dorsal surface with the other on top in what appears to be a``dominant'' posture (Panksepp, Siviy, & Normansell, 1984).…”

“…While the frequency of pinning provides an overall index of playfulness, pinning is just one aspect of play which occurs during the course of a play bout. In our earlier work (Siviy et al, 1990), the alpha-2 antagonist idazoxan was also shown to increase several measures of play solicitation when the rats were tested with an unresponsive partner. While these data suggest that compounds selective for alpha-2 noradrenergic receptors may have a primary effect on play solicitation, they do not address the extent to which alpha-2 receptors might also be involved in responsiveness to playful overtures.…”

“…While these data support a role for noradrenergic involvement in both playful attack and defense, it is possible that changes in one of these aspects of play (i.e., attack or defense) could be producing parallel changes in the other. When rats were tested with a partner made nonresponsive to playful overtures by scopolamine, idazoxan was found to increase play soliciting behaviors (Siviy et al, 1990), demonstrating that this class of compound can still produce changes in playfulness in the absence of any defensive behaviors being exhibited by the animal's partner. This suggests that the ability of alpha-2 noradrenergic compounds to affect nape attacks in the present study are probably not incidental to changes in the relative likelihood of rotating to supine in response to a nape attack.…”

“…Since alpha-2 antagonists increase activity as well as play (Siviy et al, 1990), a simultaneous measurement of locomotor activity was also obtained in this experiment. For the purpose of measuring activity, the testing chamber was placed within the infrared ®eld of an Opto-Varimex-Minor Activity Monitor (Columbus Instruments, Columbus, OH).…”