Selective blockade of apomorphine induced aggression and gnawing following fenfluramine or raphe lesions in the rat

The effects of drugs and electrolytic lesions on apomorphine induced fighting and stereotyped behavior were studied in Long Evans, male rats. Bilateral electrolytic lesions in a variety of dopamine rich nuclei failed to block either the apomorphine induced fighting or gnawing. However, lesions in the paraventricular gray matter, at the level of the dorsal raphe nucleus, prevented the induction of aggression with apomorphine. In addition, lesioned animals failed to perform the characteristic gnawing behavior following large doses of apomorphine, i.e. 15 mg/kg s.c., but instead, responded with stereotyped sniffing and licking characteristic of low doses of apomorphine. Haloperidol, 0.1 to 2.0 mg/kg i.p., blocked the apomorphine induced aggression, stereotyped gnawing and stereotyped sniffing and licking. In contrast to haloperidol, fenfluramine, 2 to 10 mg/kg i.p., blocked the aggressive response and the stereotyped gnawing but did not block the stereotyped sniffing and licking. These results suggest that central lesions or drugs suspected of influencing central serotonergic mechanisms block apomorphine induced aggression and stereotyped gnawing but not stereotyped sniffing and licking. An alternate interpretation, in the case of fenfluramine, may be that this agent selectively blocks dopamine receptors involved in the fighting and gnawing responses but not those receptors responsible for stereotyped sniffing and licking.