[³H](+)-7-OH-DPAT and [³H]pramipexole binding in the striatum and nucleus accumbens of Sprague-Dawley and Fischer-344 rats

The binding of the D2-like agonists, (+)-7-hydroxy-N,N-di-n- [³H]propyl-2-aminotetralin (7-OH-DPAT) and [³H]pramipexole (2-amino-4,5,6- tetrahydro-6-propylamino-benzthiazole; MIRAPEX®) were determined in membranes from adult male Sprague-Dawley and Fischer-344 rats. Saturation analysis, which optimized binding to D3 receptors, revealed 3-6 fold differences in Bmax values between the two radioligands with no change in affinity. [³H](+)7-OH-DPAT labeled 41.4±4.1 to 61.8±3.0 fmol/mg protein in nucleus accumbens and striatal homogenates, yet [³H]pramipexole labeled only 7.0±1.2 to 18.9±5.3 fmol/mg protein. Regional differences with both radioligands were observed in Fischer-344 rats; the striatum exhibited a 52%- 69% greater density of sites in comparison to the nucleus accumbens. These data suggest that D3 receptor density can vary significantly between animal strains depending on the radioligand used, and [³H]pramipexole identifies a different ratio of sites in the striatum and nucleus accumbens compared to [³H](+)7-OH-DPAT.