Distribution and origin of TRPV1 receptor-containing nerve fibers in the dura mater of rat

We examined the distribution and origin of the nerve fibers innervating the dura mater of the rat that show immunoreactivity for the TRPV1 receptor (TRPV1-IR). Nearly 70% of the nerve fibers showing TRPV1-IR in the dura mater also exhibited CGRP-IR. Using a combination of immunohistochemistry and a retrograde tracer technique, we detected tracer accumulation in 0.6% of the neurons in the trigeminal ganglion and a few neurons in the dorsal root ganglion; half of the neurons in the trigeminal ganglion were small- and medium-sized (≤ 1000 μm2). Among the tracer-accumulated neurons in the trigeminal ganglion, approximately 25% exhibited TRPV1-IR. Furthermore, nearly 80% of the tracer-accumulated small- and medium-sized neurons in the trigeminal ganglion that exhibited TRPV1-IR also exhibited CGRP-IR. Our findings indicate that the TRPV1 receptor in the dura mater and sensory ganglia may contribute to the pathophysiology of migraine, providing an important clue for the development of therapeutic strategies for migraine.