In vivo occupancy of the striatal dopamine uptake complex by various inhibitors does not predict their effects on locomotion

We compared the ability of various dopamine (DA) uptake inhibitors to displace the in vivo striatal [ 3 H]GBR 12783 (1-[2(diphenylmethoxy) ethyl)-4-(3-phenyl-1[ 3 H]-2-propenyl)-piperazine) binding with their stimulant effect on locomotor activity on mice. GBR 12783 (8 mg/kg), GBR 13069 (10 mg/kg), cocaine (20 mg/kg), mazindol (3 mg/kg) or pyrovalerone (2 mg/kg) stimulated locomotion as long as they occupied the DA uptake complex. In contrast, nomifensine (3 mg/kg) did not stimulate locomotion although it completed with [ 3 ]GBR 12783 for the occupancy of the DA uptake complex at a significant level (> 50%). Administered at their ED 50 doses, GBR 12783, BTCP (N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine, GBR 13069, amineptine and dexamphetamine significantly increased locomotor activity whereas the other inhibitors tested did not. The locomotor response elicited by GBR 12783 (10 mg/kg) was not decreased by desipramine (20 mg/kg) nor by oxaprotiline (10 mg/kg). The increase in locomotion elicited by GBR 12783 was positively correlated with the basal locomotor activity of the mice. The stimulant effect of GBR 12783 was potentiated by SKF 525A and by budipine. Additional pharmacological properties might conceal the relationship between the effects of some DA uptake inhibitors on locomotion, and on in vivo occupancy of DA uptake sites.