the DRD1 and DRD2 grains using the “Find Maxima” function in ImageJ and then obtained binary images with a single pixel for each local maxima by choosing output type of “Single points”. We measured the integrated intensity of DRD1 and DRD2 above each nucleus using the “Measure” function within the “ROI Manager”. The number of grains in each nucleus is equal to the integrated intensity divided by 255. We considered cells containing three or more grains above the nucleus as positive for that gene. We chose this threshold because it provides clear separation from the background. We quantified the total number of DRD1-positive and DRD2-positive cells for each striatal region of interest (ROI) in each section and counted positive cells on three rostro-caudal sections. We calculated cell density as the number of positive cells divided by total number of nuclei in the area. We used a similar method to quantify the cell density in CPNE4 and RXFP1 clusters (Figure S6E) except that we drew ROIs for the whole CPNE4 and RXFP1 clusters after separating overlapping nuclei with the “Watershed” function. As control, we drew ROIs of roughly similar size to the RXFP1 or CPNE4 clusters in nearby regions and quantified
