Influences of dopamine receptors on chewing behaviour in rats.

1. Intraperitoneal (i.p.) injection of different doses of pilocarpine induced purposeless chewing in rats. Physostigmine (i.p.), but not neostigmine (i.p.) also induced chewing behaviour. 2. Subcutaneous (s.c.) pretreatment of animals with the D-1 receptor blocker SCH 23390 decreased the number of chews induced by pilocarpine. 3. The D-2 dopamine antagonist sulpiride (i.p.) and anticholinergic atropine (i.p.) pretreatment also decreased the frequency of chews induced by the drug. 4. The response induced by pilocarpine (1 mg/kg i.p.) also was dose-dependently decreased in animals pretreated with apomorphine (0.25-1 mg/kg s.c.). 5. Administration of low doses of apomorphine (s.c.) also induced chewing, which was decreased with increasing the doses of the drug. 6. Chewing-induced by apomorphine was decreased by sulpiride or atropine and increased by SCH 23390 pretreatment. 7. Single administration of D-2 dopamine agonist bromocriptine also showed a slight but significant purposeless chewing, which was decreased by sulpiride pretreatment. 8. Single administration of D-2 agonist quinpirole, D-1 agonist SKF 38393 or D-1 antagonist SCH 23390, but not sulpiride caused a slight chewing. 9. It may be concluded that D-1 or D-2 activation exert opposite influences on chewing behaviour in rats, although to prove this effect more elucidation is needed.