Substance P-like immunoreactivity in the intramural nerve plexuses of the guinea-pig ureter: a light and electron microscopical study.

Immunofluorescence and immunoperoxidase techniques were used to study the distribution of substance P-like immunoreactivity in the intramural nerve plexuses of the guinea-pig ureter. In light microscopical preparations, immunoreactivity was observed in plexuses related to the muscle coat as well as in plexuses in the submucosa and beneath the epithelium. Ultrastructural examination showed that the immunoreactivity was located primarily in axons in the nerves. In perfusion-fixed specimens, there was evidence of its presence both in axons with terminals containing mainly large dense-cored vesicles and in axons with terminals containing mainly small vesicles. The presence of substance P-like immunoreactivity in axons with terminals containing mainly large dense-cored vesicles was supported by examination of specimens treated in vitro with capsaicin. In these specimens, the axons were dilated and showed a number of other changes in fine structure. There was also a substantial reduction in the amount of immunoreactivity in the nerve plexuses and the dilated axons contained little if any reaction product. The possibility that axons which contained large amounts of reaction product after treatment with capsaicin represented axons with terminals containing mainly small vesicles was discussed. Comparison of the distribution of the different types of small vesicle-containing terminal identified in glutaraldehyde-fixed material with that of axons containing reaction product suggested that the immunoreactivity present in such axons was located in those in which the small vesicles in the terminals were clear rather than those in which the vesicles contained dense material.