NASAL MECHANORECEPTORS IN GUINEA-PIGS

The characteristics of nasal mechanoreceptors in the ethmoidal nerve ( EN) of guinea pigs were clarified by electrophysiological identificati on of their responsiveness to transmural pressure, i.e., the inspirato ry effort induced by tracheal occlusion and probing of the nasal cavit y, vestibule or alae nasi of the nose. A total of 73 mechanoreceptors were recorded from 18 guinea pigs breathing through the nose or a trac heostomy with an isolated nasal airway. Six receptors (6/22) in nasal- breathing animals were stimulated by upper airway occlusion, and 18 re ceptors (18/22) in tracheostomy-breathing animals were stimulated by m aintained negative pressure in the nose. Mechanoreceptors responding t o probing to the nose were found in both experimental set-ups. The mea n threshold of 'pressure'-responsive receptors to negative pressure wa s very high (-3.87 +/- 0.95 kPa). Most of the receptors were also exam ined for response to ammonia vapour or instillation of distilled water ; only three 'touch'-responsive receptors could be stimulated by ammon ia and/or distilled water. These results suggest low sensitivity to pr essure changes and noxious chemical stimuli of mechanoreceptors in the EN of guinea pigs.