This first detailed report on the morphological organization of D1/D2 MSNs reveals that these neurons have a smaller cell body and a shorter dendritic tree than their D1 or D2 counterparts. Our data also underline the less profuse dendritic aborization of the D2 compared to the D1 MSNs, a morphological feature that might explain, at least in part, why the D2 MSNs are more excitable than D1 MSNs55. Based on the morphology of their somatodendritic domains, it is tempting to speculate that the excitability and input resistance of the D1/D2 MSNs would be higher than the D1 or even the D2 MSNs, but such a view needs to be confirmed by detailed investigations of electrophysiological properties of the D1/D2 MSNs.
