Characteristic upregulation of dopamine D-1-receptor in rat striatum after 6-hydroxydopamine treatment

We measured the number of D-1-receptors (B-max) 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 B-max for D-1-receptor. Rats were sacrificed 28 days after 6-OHDA treatment, and [H-3]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. B-max 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 D-1-receptors showed either upregulation or downregulation depending on the degree of denervation.