The localization of calcitonin gene-related peptide in the human trigeminal ganglion and masseter muscle.

The localization of calcitonin gene-related peptide (CGRP) is similar to that of a neurotransmitter which indicates masticatory muscle pain in the area of the masseter fascia. CGRP is released from the trigeminal ganglion (TG). The aim of this study was to analyze the distribution of CGRP in the fascia of the masseter muscle (FMM) and TG in a morphometric manner, with respect to the location and density of CGRP-immunopositive reaction fiber (CGRP-IRF). A higher number of the CGRP-IRF were mainly found located around elongated blood vessels and small nerves on the origin side of the middle zone FMM in the O group (presented with occlusion). In the sectional histochemical analysis of the O group, the CGRP-IRF were clearly detected in oval vessels, large elongated vessels and large nerves in contrast with that of the Non-O group (presented with no occlusion) samples. The number of CGRP-immunopositive ganglion cells (CGRP-IPGCs) in the O group mandibular nerve division was higher than that of other divisions. A reduction of the CGRP-IRF numbers were found in the no-loading groups. The characterization of these locations of CGRP-IPGCs can also provide useful data for the understanding of myofascial pain syndrome of the masseter muscle (MM).