Vasoactive intestinal peptide-immunoreactive nerves in the rat kidney

An indirect immunohistochemical method in which an avidin-biotinylated horseradish peroxidase complex is bound to the secondary antibody was used to visualize vasoactive intestinal peptide-immunoreactive (VIPI) nerves in the rat kidney. Rats were perfused with 4% paraformaldehyde or 2% paraformaldehyde + 0.15% picric acid in 0.1 M phosphate buffer, then transferred to the buffer. After 24–48 hours, the kidneys were sectioned with a Vibratome at 200 or 300 μm and incubated in the primary antiserum for 18 hours at room temperature. A sparse plexus of VIPI nerves innervates the rat renal calyx. Some VIPI nerves innervate interlobar arteries and each succeeding segment of the arterial tree including afferent arterioles, but most innervate arcuate and interlobular arteries. VIPI axons do not innervate each arcuate artery or each interlobular branch of an arcuate artery with equal density. Although some axons follow each interlobular branch, most form a dense plexus on only one or two branches. Therefore, most VIPI nerves in the rat kidney innervate a restricted segment of the renal arterial tree. These nerves may be efferent and may selectively dilate arcuate and smaller arteries, or they may be afferent and may sense local changes in mechanical or chemical parameters.