Calcitonin gene-related peptide and substance P immunoreactivity in rat trigeminal ganglia and brainstem following adjuvant-induced inflammation of the temporomandibular joint

The immunoreactivity of two inflammatory mediators, calcitonin gene-related peptide (CGRP) and substance P, was measured in the trigeminal ganglia and brainstem to characterize an adjuvant-induced inflammation within the rat temporomandibular joint at various acute (6, 24 and 48 h) and intermediate (10 day) time intervals. Concentrations of adjuvant-related neuropeptides were compared to those in both contralateral vehicle-related tissues and non-injected controls. By 6 h, CGRP immunoreactivity in the trigeminal ganglia was significantly above that in contralateral vehicle-injected tissue. The CGRP had decreased at each of the following time-points, but remained significantly elevated at 10 days. Substance P in the ganglion on the injected side was significantly increased for all four time periods. In brainstem subnucleus caudalis, CGRP was significantly increased for all four time periods. Substance P immunoreactivity in the subnucleus caudalis was significantly increased for the initial three time periods, but by day 10 had been reduced to that of the control. These data show that the pattern of changes in neuropeptides following the induction of inflammation is different between substance P and CGRP. Moreover, the pattern of change varies between the brainstem and the trigeminal ganglion. This suggests that the two neuropeptides may have different roles in the inflammatory process, and that this process may be modulated by different mechanisms at the brainstem and ganglion.