Nasal 'flow' receptors of the rat.

This study was performed to identify trigeminal nasal 'flow' receptors and to investigate their firing characteristics. For this purpose, single unit afferent activity was recorded from the anterior ethmoidal nerve in anesthetized rats breathing through the nose or a tracheostomy. In fourteen rats breathing through the nose, 40 of 73 endings tested were identified as 'flow' receptors for the following characteristics: their spontaneous activity had an inspiratory modulation that disappeared during nasal occlusions, they were markedly stimulated by exposure to cold air and inhibited by warm air. In eleven rats breathing through a tracheostomy, 85 endings were identified as 'flow' receptors being stimulated by a constant nasal airflow (100-300 ml/min) with room air (22-26 degrees C) or cold air (0-15 degrees C), but inhibited with warm air (30-45 degrees C). Fifty-five 'flow' receptors (Type R1 and R2) exhibited a dynamic response to the constant airflow, while the other 30 receptors (Type S) showed a static response. A large proportion of 'flow' receptors (more than 52%) were responsive to tactile stimuli. For all the flow receptors, a decrease in intranasal temperature was the primary factor to excite them. These results suggest that the trigeminal nerve has a number of 'flow' receptors which operate as thermoreceptors.