Changes in activity of vagal bronchopulmonary C fibres by chemical and physical stimuli in the cat.

Abstract

SUMMARY1. In eighteen anaesthetized cats, action potentials in non-myelinated vagal afferent neurones were recorded in the nodose ganglion by means of extracellular micro-electrodes.2. The pulmonary or bronchial origin of these C fibres was assessed in closed chest preparations by injecting phenyl diguanide into either the right atrium or the ascending aorta (bronchial circulation). This was confirmed in two animals by local mechanical stimulation.3. Eighty per cent of bronchopulmonary C fibres increased their discharge frequency when the end-tidal CO2 concentration (FA co2) increased from 002 to 0-1O.Most of these C endings showed a maximal response when FA co, reached 004. For the others a further increase in discharge occurred when CO2 concentration reached 008-010. Continuous measurement of C fibre discharge frequency indicated that they detected preferentially changes in the inspired CO2 content, but adapted when a high CO2 level was maintained. Their activation by hypercapnia was followed by an increase in lung resistance.4. Lowering the 02 content of the inspired gas had no effect on the spontaneous activity of bronchopulmonary C endings. 5. When the stroke volume of the pump was doubled, the spontaneous activity of bronchopulmonary C fibres decreased in intact chest preparations. Inflation of the lungs had the opposite effect after the chest was opened. In both cases hyperdeflation was a potent stimulus to these receptors.6. In tracheotomized cats, the tracheal temperature was 28-29 'C. When normal thermal conditions were restored in the tracheal lumen (33-34 'C) the spontaneous discharge frequency of some bronchial C fibres was greatly increased.7. It is concluded that the spontaneous activity of most of the bronchial or pulmonary C fibres was maximal when chemical and physical physiological conditions were restored in the lungs. It appears that changes in alveolar CO2 concentration constitute the usual stimulus for these fibres.

Stimulatory effect of CO2 on vagal bronchopulmonary C-fiber afferents during airway inflammation

“…On the basis of response latency, they further postulated that these "CO 2 sensors" are located between alveoli and capillaries. A paradoxical stimulatory effect of CO 2 on pulmonary C fibers was reported in cats by Delpierre et al (6), but the locations of most of the receptors were not identified in the lung in their study. In comparison, our study showed a much smaller percentage of pulmonary C fibers exhibiting CO 2 sensitivity in rats under normal conditions.…”

Capsaicin inhalation in man and the effects of sodium cromoglycate

“…Animal studies however have not revealed this response but this could be because in all instances the animals were anaesthetized and in some the animals were given morphine and/or intubated via the trachea. In animals C-fibre stimulation leads to bronchoconstriction (Russell & Lai-Fook, 1979;Delpierre et al, 1981;Coleridge et al, 1982). This does not appear to be the response in man.…”

“…It might be that to cause bronchoconstriction C-fibres sited lower in the airways need to be stimulated and that in the present study these were protected from exposure by the laryngeal 'guard'. The experimental design of the animal studies (Delpierre et al, 1981;Coleridge etal., 1982;1983) would have tended to direct the capsaicin to sites in the lower airways.…”

Control of ventilation during submaximal exercise: A brief review

“…Trenchard et al (1984) have recently suggested than nonmyelinated vagal lung receptors are sensitive to CO 2 and exhibit reflex effects on respiration in rabbits. Similar receptors have been identified in the cat (Delpierre et al, 1981) and the dog (Banzett et al, 1978; Downloaded by [University of Illinois at Urbana-Champaign] at 18:17 16 March 2015 Russell et al, 1984). Unequivocal establishment of this CO 2 sensitive receptor in mammalian lungs would provide the 'CO 2 flow hypothesis' with a solid foundation.…”