the Acb. The density of the D1/D2 MSNs is overall significantly higher in the Acb compared to the striatum. This difference becomes statistically significant in the shell compartment of the Acb with 45.0 ± 10.9 × 103 cells/mm3 compared to 3.8 ± 0.3 × 103 cells/mm3 in the dorsal striatum (P = 0.0098, Fig. 3c). Our stereological estimations indicate that the D1/D2 MSNs represent 14.6 ± 3.0% of the MSN population in the shell and 7.3 ± 2.2% in the core compartment of the Acb, percentages that are significantly higher than what was noted in the dorsal striatum (1.9 ± 0.2%, P = 0.0098). Interestingly, the density of the D1 MSNs is also higher in the shell of the Acb when compared to the dorsal striatum (180.0 ± 13.6 vs. 108.2 ± 5.4 × 103 cells/mm3, P = 0.0244, Fig. 3a) whereas no difference is noted regarding the density of the D2 MSNs between the dorsal striatum and the Acb. A higher density of the D1 and the D1/D2 MSNs in the Acb is congruent with an overall higher density of all MSNs in the shell (298.6 ± 15.0) and the core (267.9 ± 24.5 cells/mm3) compartments of the Acb
