Calcitonin gene-related peptide-immunoreactive nerves in the rat kidney.

Cryostat- and vibratome-cut rat kidney secretions were singly or doubly labeled to visualize immunoreactive calcitonin-gene-related peptide (CGRPI) and substance P (SPI). Rats were perfused with 2-4% paraformaldehyde + 0.15% picric acid then rinsed with buffer. Horseradish peroxidase (HRP) was used to visualize CGRP in vibratome sections, and combined HRP and fluorophore were used to visualize the two peptides simultaneously in cryostat sections. There is a complex, multilayered plexus of CGRP nerves on the renal pelvis and a less dense, single-layered plexus on the major branches of the renal artery and on interlobar arteries and veins. A few axons innervate finer branches of the arterial tree and other intrarenal structures. Results of double immunolabeling suggest that SPI axons comprise a subpopulation of the CGRP axon population in the rat kidney. There was no evidence for a separate population of SPI axons.