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

From: An overview of the sensory receptors regulating cough

  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 cmH 2 O) 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. 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.