Evidence for central histaminergic mechanism in foot shock aggression

The role of central histaminergic system in foot shock induced aggression was studied in mice. Histamine administered by intracerebral (IC) injection (25-200 micrograms) produced a significant increase in fighting episodes in a dose dependent manner. It was observed that mepyramine (H1 blocker) given intraperitoneally (IP) significantly increased and metiamide (H2 blocker) given IC decreased significantly the fighting response. To determine the nature of receptors involved in histamine induced facilitation of aggressive behaviour, histamine was administered IC in mice pretreated with mepyramine or metiamide. Mepyramine pretreatment further increased the facilitatory effect of histamine while metiamide blocked the enhancement of aggressiveness by histamine. Combined pretreatment with metiamide and mepyramine decreased significantly the fighting counts which remained unaffected after histamine. Haloperidol did not block the enhancement of aggression by histamine or mepyramine. However, atropine pretreatment partially inhibited the histamine induced increase in the fighting counts. Results of pretreatment with metiamide and atropine were similar to those obtained with pretreatment of metiamide and mepyramine. Metiamide alone or in combination with atropine failed to affect the facilitatory effect of amphetamine on the foot-shock aggression. It is concluded that central histamine H2 receptors have a facilitatory role and H1 receptors an inhibitory role on aggressive behaviour in mice induced by foot-shock. Since histamine per se had a facilitatory effect on foot-shock induced aggression, the central H2 receptors seem to dominate over the H1 receptors.