Naratriptan Has a Selective Inhibitory Effect on Trigeminovascular Neurones at Central 5-HT1A and 5-HT1B/1D Receptors in the Cat: Implications for Migraine Therapy

Abstract

The triptans are agonists at serotonin(5-HT) 1B/1D receptors; however, they are also active at 5-HT1A and 5-HT1F receptors. We conducted this series of experiments to further elucidate the site of action of naratriptan using a well-established animal model of trigeminovascular stimulation. Following electrical stimulation of the superior sagittal sinus of the cat, single cell responses ( n = 83) were recorded in the trigeminal nucleus caudalis. Most cells (91%) also responded to electrical and mechanical stimulation of cutaneous or mucosal facial receptive fields. The micro-iontophoretic application of naratriptan resulted in a significant suppression of the response to sagittal sinus stimulation (response suppressed by 47 ± 4%, P < 0.001). The effect of naratriptan was significantly attenuated by application of either the 5-HT1B/1D receptor antagonist GR-127935 ( P < 0.001) or the 5-HT1A antagonist WAY-100635 ( P < 0.05). The response of single cells to receptive field stimulation was also suppressed by microiontophoretic application of naratriptan, but by only 20 ± 3%. Intravenous administration of naratriptan resulted in a similar selective suppression of sagittal sinus vs. receptive field responses in trigeminal neurones. These results indicate that naratriptan has a central effect in the trigeminovascular system, selectively inhibiting afferent activity in craniovascular neurones, via both 5-HT1B/1D and 5-HT1A receptors.