Journal of Applied Physiology, Vol 56, Issue 2 447-453, Copyright © 1984 by American Physiological Society
Presynaptic neurotransmitter and chemosensory responses to natural stimuli
M. Pokorski and S. Lahiri
We investigated the hypothesis that release of acetylcholine from
presynaptic nerve terminals in the carotid body may be responsible for the
excitation of carotid body chemoreceptors by hypoxia and hypercapnia and
central ventilatory stimulation by hypercapnia. 4-Aminopyridine, an agent
known to release presynaptic transmitters including acetylcholine, was
administered intravenously (1 mg X kg-1) or by close intra-arterial
injection to the carotid body (200 micrograms) in anesthetized cats.
4-Aminopyridine did not change the carotid chemosensory responses to any
arterial PO2 or PCO2 levels studied, whereas it stimulated ventilation at
all arterial PO2 and PCO2 levels. Atropine blocked the ventilatory effects
of 4-aminopyridine but not the responses to hypoxia and hypercapnia. The
results add to the evidence, which shows that the presynaptic cholinergic
mechanism is not germane to carotid body chemoreception. Also,
acetylcholine does not seem to mediate the central hypercapnic stimulation
of ventilation.
