Role of central alpha 2-adrenoceptors on the development of muricidal behavior in olfactory bulbectomized rats: effect of alpha 2-adrenoceptor antagonists.

Upon surgical removal of olfactory bulbs, by the 8th to 10th day after the surgery muricidal behavior has been demonstrated in 75.4% of rats. In the homogenates of forebrain obtained from rats demonstrating muricidal behavior, levels of noradrenaline, 5-hydroxytryptamine and their metabolites (i.e., 3-methoxy-4-hydroxyphenylglycol sulfate and 5-hydroxyindoleacetic acid) were not changed. However, the fractional turnover rate of noradrenaline in the forebrain of the olfactory bulbectomized rats was significantly decreased without alterations in the metabolism of 5-hydroxytryptamine when compared to that of the sham rats. The muricidal behavior and the aggressiveness were suppressed by antagonists of alpha 2-adrenoceptors (yohimbine, idazoxan and rauwolscine), but not by the alpha 1-adrenoceptor antagonist (corynanthine). Furthermore, upon administration of yohimbine or idazoxan to rats demonstrating the muricidal behavior, the level of noradrenaline in the homogenates of forebrain was decreased while that of 3-methoxy-4-hydroxyphenylglycol sulfate was increased. The maximum binding capacity (Bmax) of [3H]yohimbine to the forebrain membranes obtained from the olfactory bulbectomized rats was significantly higher than that from the sham rats without demonstrating any differences in dissociation constants (Kd) between the two brain membranes. Based on these results, it was suggested that olfactory bulbectomy has caused some functional changes in central alpha 2-adrenoceptors.