Figure 5. Microinjection of capsaicin or substance P into the cnTS sensitizes the cough reflex in anaesthetized guinea pigs.

Cough was evoked electrically from the trachea (16 Hz, 10 s train, 1–10 V). The effects of capsaicin (A) and substance P (B) microinjection on the voltage–coughing-response curve are depicted. The results are presented as the percentage of animals coughing in response to a given stimulation voltage. Microinjection of 0.5 nmol capsaicin or 5 nmol substance P into the cnTS increased the likelihood of coughing at lower stimulation intensities (2–6 V) relative to control (P < 0.001).