DRD2 and Parkinson disease: Western blot analysis revealed a selective increase of dopamine D1 receptor density in the striatum (Figure 3A, p = 0.0159) with no alteration in the nigra (Figure 3B, p = 0.2119), whereas dopamine D2 receptor density decreased in the nigra (Figure 3D, p = 0.0085), but not in the striatum (Figure 3C, p = 0.9982) of LID rats (i.e., treated with 6-OHDA and then with L-DOPA) compared to PD rats (i.e., treated only with 6-OHDA).