Drug-induced purposeless chewing: animal model of dyskinesia or nausea?

Drug-induced purposeless chewing movements in rodents are often considered to represent movement disorders or dyskinesias. We have compared the ability of drugs to induce chewing and retching or emesis in squirrel monkeys; such studies are not possible in rodents, which do not vomit. Acute administration of oxotremorine (3.3-33 micrograms/kg IM), SKF38393 (1-30 mg/kg SC) or ipecacuanha (0.5-0.75 mg/kg PO) caused dose-related increases in purposeless chewing which was frequently associated with retching and emesis. Treatment with haloperidol (0.015-0.06 mg/kg IM) did not induce chewing. Rather, haloperidol decreased spontaneous chewing at doses of 0.03 and 0.06 mg/kg. Our findings indicate that at least some drug-induced oral behaviours in rodents may reflect nausea rather than dyskinesia.