DIFFERENTIAL ROLE OF NUCLEUS-ACCUMBENS AND CAUDATE-PUTAMEN IN MEDIATING THE EFFECT OF NOMIFENSINE AND METHAMPHETAMINE ON AMBULATION AND REARING OF RATS IN THE OPEN-FIELD TEST

The effects of nomifensine (NOM) and methamphetamine (MA) on ambulation and rearing of rats in the open-field test were investigated. NOM and MA were injected i.p. into intact rats and nucleus accumbens (ACC)- and caudate-putamen (CP)-lesioned rats and infused into the ACC and CP. NOM (1-10 mg/kg, i.p.) and MA (1-5 mg/kg, i.p.) produced hyperactivity. However, NOM at 20 mg/kg, i.p. decreased the activity and induced repetitive head bobbing and squatting. Lesions of the ACC and CP increased open-field activity. However, lesion of the CP increased rearing more than lesion of the ACC. The increase in ambulation induced by NOM was inhibited by lesion of the ACC, whereas that induced by MA was inhibited by lesion of the CP. Although NOM (1-10 mu g/2 mu l) and MA (0.5-10 mu g/2 mu l) injections into the ACC and CP induced hyperactivity, the effect of NOM was greater after injection into the ACC, whereas the effect of MA was greater following injection into the CP. These results suggest that the ACC has a greater role in ambulation, while CP has a greater one in rearing. The present results, while they verified the significance of the ACC and CP in NOM- and MA-hyperactivity, also revealed a differential role of the ACC in NOM-hyperactivity and the CP in MA-hyperactivity.