The effect of electrical stimulation and drugs on the release of acetylcholine from the frog spinal cord

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Abstract
The isolated frog spinal cord preparation, hemisected longitudinally, has been used to study concurrently the release of endogenous acetylcholine (ACh) and the electrical responses to stimulation of the ventral or dorsal roots. In unstimulated cords, ACh release was high initially and then fell to a plateau level. ACh release was reduced by tetrodotoxin and increased by high K+. Stimulation of the ventral roots enhanced the ACh release. The magnitude of this effect was dependent on the frequency of stimulation and was antagonized by tetrodotoxin or Ca2+-free Ringer. During prolonged ventral root stimulation (50 min), the evoked ACh release became progressively smaller but was restored to the original high levels by the addition of choline to the bath fluid. Stimulation of the dorsal roots failed to augment the ACh output. The application of hyoscine was followed by a large rise in the unstimulated ACh output. However no increase in the antidromically-evoked release, when compared with control stimulations, was seen. The application on α-bungarotoxin was followed by a short-lasting decline in the unstimulated ACh output, whereas the electrically-evoked output was unaffected. In the frog spinal cord the determination of ACh release, together with the recording of the root potentials, offers the possibility of studying the output of a central transmitter in relation to the electrical activity of an in vitro central nervous system preparation.