Dual afferent pathways of vasodilator reflex induced by lingual stimulation in the cat

Abstract

We investigated whether two groups of afferent fibers in the combined chorda tympani (CT) and lingual (LN) nerve that emanate from the facial and trigeminal nerves function in the vasodilator reflex in the cat lip. Experiments were conducted on 18 cats weighing 1–3 kg which were anesthetized with pentobarbital sodium (30 mg/kg, i.v.) and artificially ventilated (pancuronium bromide 0.2 mg/kg/h, i.v.). Blood flow changes in the lower lip adjacent to the canine tooth on both sides of the mouth were monitored with a laser Doppler flowmeter. Electrical (0–50 V, 2 ms, 40 Hz, 10 s) and capsaicin (1%) stimulation of the tongue or chorda-lingual nerve after cutting the chorda tympani evoked an increase in blood flow in the ipsilateral lower lip (LN-response). Electrical stimulation of the central cut ends of the chorda tympani nerve also caused an increase in blood flow in the ipsilateral lip (CT-response). Capsaicin application to the CT, however, did not elicit a blood flow increase. Both the LN- and CT-responses of the different afferent fibers were reduced by prior treatment with the autonomic ganglion blocking agent hexamethonium (1 mg/kg, i.v.). Results suggest that capsaicin-insensitive fibers in the chorda tympani branch of the facial nerve, as well as capsaicin-sensitive ones in the lingual branch of the trigeminal nerve, participate as afferents of the parasympa-thetic vasodilator reflex in cat lip.