ADRENERGIC INHIBITION AT SYMPATHETIC SYNAPSES

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Abstract
In cats, anesthetized with nembutal, changes in sympathetic transmission in the S.C.G. are studied by recording the postganglionic action potentials in response to fixed preganglionic stimuli. Synaptic inhibition is elicited by adrenaline liberated from the adrenal medulla (by splanchnic nerve stimulation), and by ephedrine injected intraven. Ephedrine produces the same effect in adrenalectomized cats, and is interpreted as causing an accumulation of adrenaline or an adrenaline-like substance about the synaptic ends of specific, inhibitory preganglionic nerves. Sensitization of ganglion cells to acetylcholine by adrenaline is shown not to be the cause of inhibition. On the basis of the ganglionic inhibition caused by adrenaline when it is injected or when it is liberated from the adrenals, and supported by the similar action of ephedrine as above interpreted, it seems justifiable in the case of the S.C.G. to elaborate the existing concept of transmission of "short duration," mediated by acetylcholine, to include a prolonged inhibition mediated by adrenaline or a closely allied substance. This would complete a ganglionic humoral system which could independently affect synaptic transmission as well as supplement the quick, precision mechanism of electrical excitation and inhibition.

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