Fig. 3.

Diagram of respiratory assay (modified Alarie test). Following a tracheotomy, the anesthetized mouse was permitted to breathe freely through the lower end of the trachea; respiration was monitored by thermocouple. A constant flow of saline was injected into the upper end of the trachea and allowed to pass freely through the nasal passages exiting the nostril. Alterations in respiration reflected detection of irritants injected into the constant retronasal flow, as shown in the lower left. In TrpM5 (or α-gustducin)-KO mice, the irritant effect of the bitter-tasting substance denatonium was absent although other irritants, which directly activate nerve fibers, remain effective at altering the respiratory rate[78].