Effects of acetylcholine on respiratory neurones in the nucleus ambiguus‐retroambigualis complex of the cat.

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Abstract
The effects of ionophoretic application of acetylcholine (ACh) and cholinergic antagonists to respiratory neurons of the nucleus ambiguus-retroambigualis complex were studied in cats. ACh was ineffective when applied to inspiratory neurons (27/31) but inhibited the spontaneous activity of a significant population of expiratory neurons (21/39). The expiratory neurons inhibited by ACh included neurons with axons projecting to the vagus or spinal cord, as well as neurons not antidromically activated from either of these sites. The cholinergic inhibition of expiratory neurons was blocked by atropine (6/9), but dihydro-.beta.-erythroidine was ineffective. In 7 expiratory neurons, ionophoresis of atropine alone evoked firing during the normal period of silence of the neuron (inspiration). A significant population of expiratory neurons receives an active inhibition during inspiration and this involves a cholinergic mechanism. The implications of these observations for the synaptology of central respiratory control and modifications of the vagal outflow to the heart are discussed.