Quantification of cat's articular afferents containing calcitonin gene-related peptide or substance P innervating normal and acutely inflamed knee joints.

In cats with an acute (32 h) unilateral knee joint inflammation the proportion of calcitonin gene-related peptide-(CGRP) and substance P-(SP) immunoreactive articular afferents, retrogradely labelled by Fast Blue (FB), were determined using immunohistochemistry. The proportion of neurons containing CGRP was significantly higher on the inflamed side (52%) than on the contralateral side (39%) and in controls (42%). However, the proportion of SP-immunoreactive articular perikarya on the inflamed side (26%) did not differ from the contralateral side (24%) and the control cats (22%). These data indicate that acute inflammation induces the synthesis of CGRP but not of SP in joint afferents.