ADJUVANT-INDUCED INFLAMMATION OF RAT PAW IS ASSOCIATED WITH ALTERED CALCITONIN-GENE-RELATED PEPTIDE IMMUNOREACTIVITY WITHIN CELL-BODIES ANDPERIPHERAL ENDINGS OF PRIMARY AFFERENT NEURONS

Local inflammation is associated with profound changes in the biochemi stry and physiology of primary afferent nerve fibers and the central n eurons responding to their signals. In some tissues, the neural change s accompanying inflammation include sprouting and cytochemical changes that are delayed several days after the initial injury. In the presen t study, we have analyzed the effect of complete Freund's adjuvant (CF A)-induced inflammation in the rat paw on calcitonin gene-related pept ide (CGRP) immunoreactivity (IR) in dorsal root ganglia and within tis sue of the inflamed paw. We quantified the CGRP-IR within the L(1), L( 4), and L(6) ganglia, and in ankle, midpaw, joint and toe tissues. Ana lysis of the processed tissue revealed a significant increase in the p ercentage of CGRP-positive cells within Lq dorsal root ganglia ipsilat eral to an inflamed hindpaw six days after administration of CFA. Ther e was a parallel increase in the number and staining density of detect able CGRP-immunoreactive fibers in periarticular and perivascular tiss ues of the inflamed digits and inflamed ankle. The other tissues of th e paw, including epidermis and the regions surrounding the abcesses, d id not have detectable changes in CGRP-immunoreactive fibers, despite tissue swelling and dystrophic changes in the foot that included loss of mast cell staining. These data demonstrate that local inflammation of the rat paw has delayed influences on the peripheral nervous system , in addition to a number of previously characterized acute effects. T he alterations of CGRP-IR were focused around specific tissue types, s uch as joints and subdermal blood vessels, and absent from others, suc h as epidermis or in the areas surrounding abscesses. This suggests pr oduction of local factors within reactive tissues that selectively int eract with nerve fibers to induce changes in CGRP-IR within the fibers . (C) 1994 Wiley-Liss, Inc.