compared to surrounding tissues (Figure S7D). Using immunohistochemistry, we confirmed that MOR was expressed in the RXFP1-positive islands (Figure 7C). Based on their distribution and the upregulation of μ-opioid receptor – upregulation that was not present in the ICjs (Figures 7D-7F) – we concluded that these RXFP1-positive interface islands corresponded with Neurochemically Unique Domains in the Accumbens and Putamen (NUDAPs).10,11 Therefore, we denoted the DRD1- and RXFP1-positive cells as D1-NUDAP neurons. Gene enrichment analysis revealed that D1-NUDAP neurons express genes that have been implicated in drug addiction and many other functions (Data S4). These data show a novel cell type that is associated with interface islands and could be critical for the hedonic aspects of reward. Altogether, these results demonstrate that the ventral striatum is characterized by the presence of discrete MSN subtypes that correspond to functionally relevant subdivisions including NAc shell, OT, and distinct types of interface islands.
