Characteristic Upregulation of Dopamine D1-Receptor in Rat Striatum after 6-Hydroxydopamine Treatment

We measured the number of D1-receptors (Bmax) in the striatum whose dopaminergic terminals were destroyed to various degrees by 6-hydroxydopamine (6-OHDA) to clarify the relationship between the degree of denervation and the change in Bmax for D1-receptor. Rats were sacrificed 28 days after 6-OHDA treatment, and [3H]SCH23390 (R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine) binding capacity and monoamine content were measured in striatal homogenate. Bmax was significantly upregulated when dopamine content was reduced to less than 5% of that in the vehicle-treated striatum. In contrast, it was significantly decreased when dopamine content was 5-25% of that in the vehicle-treated striatum. The D1-receptors showed either upregulation or downregulation depending on the degree of denervation.