DOPAMINE D-3 RECEPTORS IN THE BASAL GANGLIA OF THE COMMON MARMOSET AND FOLLOWING MPTP AND L-DOPA TREATMENT

The distribution of the dopamine D-3 receptor was studied by receptor autoradiography using [H-3]7-OH-DPAT in striatal and extrastriatal bra in regions of the common marmoset (Callithrix jacchus). Saturation stu dies demonstrated that [H-3]7-OH-DPAT bound with similar affinity to d ifferent regions of marmoset brain. In normal marmosets, specific [H-3 ]7-OH-DPAT binding was found in both striatal and extrastriatal region s. Very high levels of specific [H-3]7-OH-DPAT binding were detected i n the islands of Calleja and nucleus accumbens but in addition high le vels of binding were detected in rostral caudate nucleus and putamen. In common marmosets treated with the selective nigral neurotoxin 1-met hyl-4-phenyl-1,2,3,6-tetrakydropyrine (MPTP), the levels of specific [ 3H]7-OH-DPAT binding in striatal and extrastriatal regions were not di fferent to those in normal animals. Chronic treatment of MPTP-treated marmosets with L-DOPA/carbidopa did not alter the levels of specific [ H-3]7-OH-DPAT binding in any brain region. These results demonstrate t hat in common marmosets D-3 receptors are located in both striatal and limbic regions. The receptor density is not altered by dopaminergic d enervation or by chronic L-DOPA administration. The D-3 receptor may, therefore, be important in both the therapeutic and adverse effects of drugs used to treat Parkinson's disease.