Reflex vasodilatation in the cat lip evoked by stimulation of vagal afferents

In 36 cats under nembutal anaesthesia, stimulation of the central end of the cut vagus nerve caused blood flow to increase in only the ipsilateral side in six cats (17%) and in the bilateral sides in 30 cats (83%) in the lower lips. Pretreatment with hexamethonium to block nicotinic synapses in autonomic ganglia resulted in a time-dependent reduction of the reflex vasodilator response, while phentolamine, propranolol (alpha-, beta-adrenoreceptor antagonists) and tripelennamine (histamine receptor antagonist) had no effect. Pretreatment with atropine (muscarinic receptor antagonist) showed a slight, but not statistically insignificant attenuation of the reflex vasodilatation. Ipsilateral section of either the glossopharyngeal nerve root or the inferior alveolar nerve completely abolished the reflex vasodilator response elicited by central vagal stimulation. The reflex vasodilator response induced by stimulation of the central end of the cut vagus nerve was abolished by topical capsaicin application on the central cut ends of the vagus nerve but not by capsaicin on the inferior alveolar nerve. These results suggest that there is a cutaneous reflex vasodilator system that can be activated via capsaicin-sensitive afferent fibres in the vagus nerve. Parasympathetic vasodilator fibres of this system emerge from the brain stem with the glossopharyngeal nerve and reach the blood vessels in the cat mandibular lip via the inferior alveolar nerve.