Peripheral Targets of 5-HT1D Receptor Immunoreactive Trigeminal Ganglion Neurons

Objective: The aim of the current study was to determine the proportion of trigeminal primary afferent neurons that innervate the intracranial vasculature, and other craniofacial tissues, that are also 5 hydroxy triptamine (5-HT)1D receptor immunoreactive. Methods: Retrograde tracing and immunohistochemistry was used to identify 5-HT1D receptor labeled trigeminal primary afferent neurons that innervate the lacrimal gland (n = 3 animals), nasal mucosa (n = 3 animals), and the intracranial vasculature (middle meningeal artery in the dura [n = 3 animals] and middle cerebral artery [n = 3 animals]). Results: The percentage of neurons that were 5-HT1D receptor immunoreactive was greater for primary afferent neurons innervating the middle meningeal artery (41.8 ± 1%) than those innervating the middle cerebral artery (28.4 ± 0.8%), nasal mucosa (25.6 ± 1%), or lacrimal gland (23.5 ± 3%). For each retrograde labeled population, the 5-HT1D receptor immunoreactive cells were among the smallest of the retrograde labeled cells. Conclusions: These findings provide a basis for understanding the role of 5-HT1D receptor agonists (eg, triptans) in the treatment of primary vascular headaches and suggest that the selectivity of triptans in the treatment of these headaches does not appear to result from specific localization of the 5-HT1D receptor to trigeminovascular neurons alone.