Lack of dopamine receptor agonists effect on striatal dopamine transporter binding sites.

Depending on experimental conditions, chronic cocaine exposure can induce an increase in binding to the dopamine transporter (DAT). One possible mechanism for the cocaine-induced-upregulation in DAT binding sites is through stimulation of presynaptic D2 receptors by excess synaptic dopamine. To test this hypothesis, the present experiment examined in rats the effect of chronic quinpirole and apomorphine treatments on striatal DAT binding sites. Rats were chronically injected subcutaneously with either: quinpirole, 0.7 mg/kg body weight, apomorphine, 2.0 mg/kg body weight, or vehicle. Striatal DAT binding was then examined autoradiographically using the DAT-selective cocaine congeners [125I]RTI-121 and [3H]WIN 35428. Analysis of the results indicated that quinpirole and apomorphine administration did not alter DAT cocaine binding sites.