Abstract
Drugs affecting a cholinergic system (i.e. acetylcholine, nicotine, paraoxon, eserine, atropine, succinylcholine) and drugs having no cholinergic effects (i.e. norepinephrine, harmine, gamma-aminobutyric acid) were perfused into the metathoracic leg of the cockroach Periplaneta americana , and the physiological results were observed. Nicotine produced a reversible tetanic response, and succinylcholine decreased the amplitude of the contraction. All the other drugs had no effect. Electron micrographs of the peripheral neuromuscular system revealed a typical insect junction: no junctional folds, synaptic vesicles, and a synaptic cleft of 200 Å. The sarcoplasmic reticulum of the cockroach muscle is extensive and consists of a series of tubules and cisternae often seen as a three-dimensional collar around the myofibrils. Sarcolemmal invaginations formed dyads with the sarcoplasmic reticulum supposedly providing the pathway for rapid transmission of excitation to the interior of the muscle fibre. The morphological evidence indicates that the junction is chemically mediated, but the physiological data demonstrate that the mediator is not acetylcholine.
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