Noradrenergic and peptidergic innervation of the amphibian spleen: comparative studies

Spleens from representatives of the three amphibian orders were examined using sucrose-potassium phosphate-glyoxylic acid (SPG) histofluorescence to detect catecholamines and immunocytochemistry to detect several neural antigens. Nerve fibers are scattered throughout the spleens of adult salamanders (Taricha torosa, Notophthalmus viridescens, and Ambystoma mexicanum). A less abundant but similarly diffuse pattern of innervation characterizes the spleen of the caecilian, Typhlonectes sp. The spleen of the adult frog, Xenopus laevis, is separated into clearly defined compartments of red pulp and white pulp, much as is seen in the mammalian spleen. As in mammals, sympathetic innervation of the Xenopus spleen is noradrenergic (NA) and confined to the white pulp. The white pulp of Xenopus spleen also contains fibers which stain for neuropeptide Y and substance P. The spleen of the anuran, Rana pipiens, is also highly compartmentalized, with tyrosine hydroxylase positive fibers in proximity to blood vessels. These findings provide an anatomical substrate for neural-immune interactions in the Amphibia.