NASAL RECEPTORS RESPONDING TO COLD AND L-MENTHOL AIR-FLOW IN THE GUINEA-PIG

The aim of this study was to demonstrate the presence of nasal 'cold' receptors, through recordings of action potentials from the ethmoidal nerve (EN), in guinea pigs and to characterize their responsiveness to l-menthol and capsaicin. Constant flows (400 ml/min) of room air (20 degrees C), warm air (45 degrees C), room air containing l-menthol, an d cold air (-5 degrees C) were directed into the nasal cavity in the i nspiratory direction via a nasopharyngeal catheter in the anesthetized guinea pigs breathing spontaneously through a tracheostomy. The ethmo idal afferent activity was increased by cold air, and to a greater ext ent by l-menthol but hardly by warm air. After topical anesthesia of t he nasal cavity with 2% lidocaine, cold air and l-menthol no longer st imulated the EN. L-menthol noticeably stimulated the EN even after rep eated capsaicin instillation into the nose, but these values were lowe r than those following the l-menthol stimulus before the 1st capsaicin treatment. These results suggest that the ethmoidal nerve in guinea p igs has cold-sensitive receptors which consist of both small myelinate d fibers and C-fiber endings.