It is now well established that co-expression of D1 and D2 receptors occurs in some striatal MSNs, but there is still some controversy regarding the relative importance of such a unique neuronal population. In the literature, the percentage of striatal MSNs that coexpress D1 and D2 ranges from low210112440, moderate121441 to nearly 100% 9. Such substantial differences may be explained, on one hand, by the various methods and species used and, on the other hand, by the specificity of the antibodies or the in situ hybridization probes employed to detect D1 and D2 receptors. In the present study, depending on striatal sectors that were examined, we estimate that the D1/D2 MSNs account for 0.8–2.4% of the total number of striatal MSNs, a proportion that agrees with figures reported in other studies conducted in BAC transgenic mice182042.
