Archetypal analysis revealed a TAC3-positive archetype within the D1-Shell/OT subtype (Figures 5C and S5D-S5F; Table S3). In order to locate this MSN archetype and to distinguish it from TAC3-positive interneuons (Figure S2),18 we triple labelled coronal sections with probes against DRD1, DRD2, and TAC3 (Figures 5D and 5E). This labeling revealed the previously described TAC3 interneuons unifomly distributed throughout the striatum (Figure 5F); these cells did not show co-localization with DRD1 or DRD2. However, there was a cluster of TAC3-positive neurons located in the medial shell region of the NAc that co-localized with DRD1, and far fewer than that co-localized with DRD2 (Figures 5G and 5H). We observed the same DRD1- and TAC3-positive cluster in the medial shell region of a second monkey (Figure 5I). These results reveal a novel TAC3-positive MSN archetype in the primate NAc.
