The regional distribution of D1, D2 and D1/D2 MSNs in the dorsal striatum of sham mice was estimated stereologically. The overall densities of D1 and D2 MSNs are 108 ± 5 and 95 ± 4 × 103 cells/mm3, representing respectively 52.2 ± 1.1% and 45.9 ± 1.1% of the total MSNs population of the striatum. In contrast, the D1/D2 MSNs have a much lower density with only 3.8 ± 0.3 × 103 cells/mm3 (P < 0.0001), representing 1.9 ± 0.2% of the striatal MSNs. Although not statistically significant (P = 0.2341), the density of the D1/D2 MSNs in the ventromedial sector of the striatum was lower in the post-commissural striatum (1.8 ± 0.4 × 103 cells/mm3) than in the pre-commissural striatum (4.3 ± 0.3 × 103 cells/mm3). Statistical evaluations (ANOVA) of neuronal densities in different striatal regions reveal no statistical differences (Fig. 3), supporting the homogeneous regional distribution of the D1, D2 and D1/D2 MSNs throughout the dorsal striatum. Occasionally, some D1/D2 MSNs can be seen to form small clusters of 2–3 cells at different striatal levels. Assessment of the
