Distribution of calcitonin gene-related peptide-containing fibers in the urinary bladder of the rat and their origin.

By use of indirect immunofluorescence, this study demonstrated the presence of calcitonin gene-related peptide-like immunoreactive (CGRPI) fibers in the bladder of the rat. These fibers were abundant in the muscle layer, in which they ran parallel to the muscles, submucosa, and epithelium. No immunoreactive cells were detected. We also examined the origins of these fibers, using a method that combined biotinized retrograde tracer (biotin-wheat germ agglutinin) (B-WGA) and immunocytochemistry. Injection of the tracer into the bladder resulted in the demonstration of small to medium-sized labeled cells that contain CGRPI structures in single dorsal root ganglion cells mostly at the level of L6 and S1, but also a few at L2. Double-staining for CGRPI and immunoreactive P-like substance (SPI) indicated that there are cells in the dorsal root ganglia at the level of L6 and S1 that react to both, but that there are many CGRPI-positive cells that contain no demonstrable SPI; most of the latter are large.