Substance P- and calcitonin gene-related peptide-like immunoreactive neurons in the rat trigeminal ganglion--with special reference to meningeal and pineal innervation.

The distribution of perikarya showing substance P- (SP) or calcitonin gene-related peptide-like immunoreactivity (CGRP-LI) in the rat trigeminal ganglion (TG) were investigated by means of immunohistochemical methods. Approximately 50% of the perikarya contain CGRP while SP-LI was observed in 1/3 of the cells. IR fibres were seen to leave the ganglion via the ophthalmic, maxillary, and mandibular nerves. The combination of peptide histochemistry and retrograde labelling of cells in the ganglion following injection of a fluorescent tracer into the pineal gland reveals that few SP- or CGRP-LI trigeminal neurons innervate the pineal gland. In contrast, the vast majority of perikarya in the TG were labelled upon application of the tracer to the meningeal surface supporting the view that meninges and meningeal arteries in rodents are heavily innervated by SP- and CGRP-LI trigeminal neurons.