The effect of dextromethorphan on apomorphine-induced pecking behavior in chick

Dextromethorphan is an NMDA receptor antagonist in the glutamatergic system. Currently, there are some reports showing that the glutamatergic NMDA receptor mechanism stimulates dopamine release from several brain regions. This effect may in part modulate the stereotyped behaviors of dopaminergic system. The purpose of the present study was to determine the interaction between the blockade of NMDA receptor and the stereotyped pecking behavior in chicks. Dextromethorphan was used for the blockade of NMDA receptors. In the present study, the effects of dextromethorphan and different dopamine receptor antagonists on apomorphine-induced pecking behavior were examined. For the induction of pecking, apomorphine (ED53) at a dose of 0.5 mg/kg (s.c.) was used. The results showed that dextromethorphan (5-15 mg/kg, s.c.) in a dose-dependent pattern reduced the pecking behavior. Subcutaneous injection of dextromethorphan (5 mg/kg, ED50) did not alter the suppressive action of the dopamine Dl receptor antagonist SCH 23390 (1-4 mg/kg, s.c.), but potentiated the suppressive action of the dopamine D2 receptor antagonist sulpiride (10-30 mg/kg, s.c.). The peripheral dopamine receptor antagonist domperidone (5 and 10 mg/kg, s.c.) elicited no significant effect. These results suggested that the central dopamine Dl receptor mechanism in part mediates the suppressive action of dextromethorphan on apomorphine-induced pecking behavior.