The role of clonidine in behavioral and corticosterone responses to social competition
It is postulated that the noradrenergic brain neuronal activity is closely related to the control of the hypothalamo-pituitary-adrenocortical (HPA) system. Our previous observations showed that the brain noradrenergic system is implicated in the control of social position studied in social competition tests. In order to obtain some further evidence speaking for a specifi c role of noradrenaline system activity in the control of social position we studied the effects of administration of the α2-adrenoceptor agonist clonidine on social behavior analyzed in the social competition test. Simultaneously, the concentration of corticosterone (RIA) was measured in the plasma of rats after social competition test and tested individually. We used an acute social competition situation that consisted of simultaneous placing of two experimental rats into the familiar cage supplied with feeder of glucose pellets. The obtained data revealed that social competitive behavior was affected by peripherally administered clonidine. The animals got better position for competition and received higher social rank in pairs after stimulation of α2-drenoceptor. Plasma corticosterone concentration was elevated in rats injected peripherally with clonidine in comparison with individually tested rats. The obtained results suggest that stimulation of α2-adrenoceptor affects HPA system activity and may facilitate appearance of tendency to social confrontations in rats.