Bifurcated projections from the trigeminal ganglion cells to the transverse sinus and infraorbital nerve in the rat: correlation with the oxytocin receptor and CGRP.

BACKGROUND: The ophthalmic branch (V1) of the trigeminal nerve innervating the meningeal and periorbital structures is implicated in the pathophysiology of headaches (e.g. migraine). In this regard, a recent report suggested the existence of bifurcated trigeminal ganglion (TG) cells concurrently projecting to the periphery via the V1 and V2 branches. To reinforce these findings, immunofluorescence experiments were designed to identify TG cells that simultaneously projected to the peripheral region through the V1 and V2 branches. Moreover, since the hypothalamic oxytocinergic system, through oxytocin receptor (OTR) activation, seems to block peripheral trigeminal nociception, a correlation between OTRs and CGRPergic fibres in the meningeal vasculature was explored. FINDINGS: In male Wistar rats, retrograde neural tracers injected into the V1 meningeal (True-blue, TB) and V2 infraorbital nerves (IoN; Fluoro-Gold, FG) showed that some TG cells were concomitantly labelled with FG and TB. Furthermore, immunofluorescence assays showed that some TG cells were triple-labelled with CGRP/FG/TB and OTR/FG/TB. In addition, at the meningeal level, OTR seems to be expressed perivascularly and in CGRPergic fibres. CONCLUSIONS: To the best of our knowledge, these data support the contention that some TG cells send bifurcated neuronal projections through the V1 and V2 branches. Furthermore, these data reinforce previous suggestions regarding the relevance of OTR in the trigeminovascular system.