Expression of the 5-HT1B receptor by subtypes of rat trigeminal ganglion cells

The type of trigeminal ganglion cells that express 5-HT1B receptors has not been well characterized, despite the fact that these receptors are importa nt targets for anti-migraine drugs. We have therefore used combined in situ hybridization and immunofluorescence to examine the expression of 5-HT1B r eceptor messenger RNA in identified subpopulations of rat trigeminal gangli on cells. 5-HT1B-expressing cells accounted for 15% of all trigeminal gangl ion cells, were medium sized, and showed immunoreactivity for either 200,00 0 mel. wt neurofilament, calcitonin gene-related peptide, or nerve growth f actor receptor (trkA). In contrast few 5-HT1B cells showed immunoreactivity for substance P or binding of the lectin Griffonia simplicifolia IB4. Our results are consistent with 5-HT1B receptors acting to control the rele ase of calcitonin gene-related peptide from trigeminal neurons with finely myelinated axons. 5-HT1B receptor agonists may reduce neurogenic vasodilati on by activating such receptors. However many nociceptive trigeminal neuron s, including the substance P and IB4-binding populations, do not express th e 5-HT1B receptor. (C) 1999 IBRO. Published by Elsevier Science Ltd.