The cholinergic hypothesis revisited--an unfinished story.

Though exogenously delivered acetylcholine excites the carotid body, past evidence has been considered as unsupportive in assigning acetylcholine an excitatory role during hypoxia or hypercapnia. With ganglionic transmission used as the model, data is presented which aims at blocking the postsynaptic cholinergic receptors, at preventing the presynaptic release of acetylcholine, and at quantitating its release under stimulating conditions. The data support an excitatory role for acetylcholine during hypoxia.