Innervation of the lungs of the toad ( Bufo marinus)—I. Physiology and pharmacology

Abstract

1. 1. The toad lung is innervated by both excitatory and inhibitory fibres reaching it via the vagosympathetic nerve trunks. There is some crossing-over of both excitatory and inhibitory fibres to the contralateral lung. 2. 2. The excitatory nerves are probably cholinergic, since the contractile response is blocked by atropine and potentiated by neostigmine. Furthermore, acetylcholine mimics the nerve-mediated contraction. 3. 3. The inhibitory nerves are probably adrenergic since the inhibitory nerve-mediated responses are greatly reduced by DCI and bretylium, and because the response is mimicked by adrenaline and noradrenaline. 4. 4. Experiments with ganglion-blocking and stimulating agents suggest that the cholinergic excitatory fibres to the toad lung are postganglionic, while many of the inhibitory adrenergic fibres are preganglionic. 5. 5. Denervation experiments support these conclusions. When the vagus nerve is sectioned 30–40 days prior to the experiments, the response to stimulation of the vagal stump is purely excitatory, but transmural stimulation across the lung wall reveals intramural inhibitory fibres. 6. 6. “Sympathetic” nerves appear to synapse with cholinergic excitatory nerve cells in the upper vagal trunk.