Epipharyngeal receptors responding to mechanical stimulation.

1. Action potentials were recorded from twenty-one afferent nerve fibres from receptors in the epipharynx in anaesthetized, paralysed cats. Sixteen of the fibres had no spontaneous discharge.2. Gentle mechanical stimulation of the epithelium of the epipharynx with a nylon fibre caused all twenty-one receptors to discharge with rapidly adapting bursts of impulses at a mean peak frequency of 197 impulses/sec.3. Stimulation with a stream of air through the epipharynx sufficient to distend the whole pharynx caused seven out of twelve receptors to discharge in rapidly adapting bursts. Stimulation with a jet of air directly on to the epithelium of the epipharynx caused seven out of nine receptors to discharge.4. Chemical stimulation of the epipharynx with ammonia vapour caused an increased discharge in only three out of twenty receptors, and intravenous histamine had no effect on the four units tested.5. It is concluded that the receptors mediate the ;aspiration reflex' elicited by mechanical stimulation of the epipharyngeal mucosa.