Neuronal pathways to the rat middle meningeal artery revealed by retrograde tracing and immunocytochemistry.

The origin of nerve fibers to the middle meningeal artery of rat was studied by retrograde tracing in combination with immunocytochemistry. Application of the retrograde tracer, True blue (TB), to the middle meningeal artery labeled nerve cell bodies in the ipsilateral superior cervical ganglion, the otic ganglion, the sphenopalatine ganglion, the jugular-nodose ganglionic complex, the trigeminal ganglion and the cervical dorsal root ganglion at level C2. A few nerve cell bodies were labeled in the contralaterally placed ganglia. Judging from the number of labeled nerve cell bodies, the ipsilateral superior cervical ganglion, the otic ganglion, the sphenopalatine and the trigeminal ganglia contribute most to its innervation. A moderate supply of labeled nerve cell bodies was seen in the cervical dorsal root ganglion at level C2 whereas there were only few in the jugular-nodose ganglionic complex. The TB-labeled nerve cell bodies were further examined for the presence of neuropeptides. For that purpose antibodies against neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP) and substance P (SP) were used. Most of the TB-labeled nerve cell bodies in the superior cervical ganglion exhibited NPY-immunoreactivity. In the sphenopalatine and otic ganglia the majority of the TB-labelled neurons were VIP-immunoreactive whereas in the trigeminal and dorsal root ganglion at level C2 the majority of labeled nerve cell bodies displayed CGRP-immunofluorescence and a minority of the labeled nerve cell bodies were substance P-immunoreactive. Together the findings indicate that several ganglia project to the middle meningeal artery of the rat and that many neuropeptides are involved in vasomotor control and in mediation of afferent information.