Montage images of CARTp-IR cell clusters and fibers in detrusor smooth muscle superimposed on schematic representations of urinary bladder at P1 (A) and P7 (B). At birth, CARTp-IR cells and fibers were observed throughout the detrusor. At P1, the size of CARTp-IR cells clusters was large (A, arrows) and clusters consisted of 50–100 cells/cluster. At P7, the size of the CARTp-IR cells clusters was decreased (B, arrows) and clusters were more distributed throughout the bladder. Prominent CARTp-immunoreactivity was associated with ureters at all rat ages examined.