An overview of the sensory receptors regulating cough

Cough

Table 2 Properties of chemosensor subtypes innervating the guinea pig airways.

	C-Fiber	C-Fiber	Aδ-Fiber
Anatomical Characteristics:
Ganglionic Origin	Nodose	Jugular	Jugular
Extrapulmonary Termination	No	Yes	Yes
Intrapulmonary Termination	Yes	Yes	Few
Substance P Expression (%) ¹	Yes (50)	Yes (90–100)	No (0)
TRPV1 Expression ²	Yes	Yes	Yes
*Functional Characteristics:*
Conduction Velocity (m/sec)	<1	<1	~6
Mechanical Threshold	High	High	High
Sensitive to:
Punctate Mechanical	Yes³	Yes³	Yes³
Capsaicin	Yes	Yes	Yes
Hypertonic Saline	Unknown	Yes	Yes
Bradykinin	Yes	Yes	Yes
Acid	Yes	Yes	Yes
Inflation (≤50 cmH₂O)	No	No	No
Deflation/Collapse	No	No	No
Stretch	No	No	No
Bronchoconstriction	No	No	No
ATP	Yes	No	No
Serotonin (5-HT)	Yes	No	Unknown
Reflex Effects on Respiration	Apnea⁴	Apnea⁴	Apnea⁴

¹ Percentage of soma expressing substance P shown in parentheses [taken from ref 36]. ² Functionally responsive to capsaicin and/or TRPV1 detected immunohistochemically. There is no data available indicating percentage of cells expressing TRPV1. ³ All airway afferents are responsive to punctate mechanical stimulation. However, the threshold for activation is approximately 100 fold higher for chemosensors compared to mechanosensors. ⁴ The basic respiratory reflex evoked by capsaicin is apnea or respiratory slowing, often proceeded by rapid shallow breathing. However, the precise reflex response evoked by each chemosensor subtype has not been described. See text for references.