OBSERVATIONS ON THE ISOLATED PHRENIC NERVE DIAPHRAGM PREPARATION OF THE RAT

摘要

1. A strip of the rat's diaphragm with the phrenic nerve can be used as an isolated mammalian nerve muscle preparation. 2. If single submaximal shocks are applied to the phrenic nerve the contractions of the diaphragm muscle are increased by the addition of adrenaline to the bath. This effect is observed whether the adrenaline reaches the site of nerve stimulation or not. Unless the muscle is fatigued, adrenaline has no effect on the muscle response to maximal nerve stimuli. 3. The muscle contractions elicited by maximal nerve stimuli are increased by small doses of eserine or prostigmine at slow rates of stimulation. A depression is produced by prolonged action or by an overdose of the anticholinesterase or by increasing the stimulation rate in the presence of the anticholinesterase. 4. Adrenaline augments the action of eserine and prostigmine. This may be observed as an increase or as a decrease in the size of muscle contractions according to various conditions. Muscle contractions are increased when the amount of the anticholinesterase is small and when the rate of stimulation is slow. The size of contractions is depressed by adrenaline after an overdose of the anticholinesterase or with faster rates of stimulation. 5. The depressant effect of eserine or prostigmine and of subsequent adrenaline is more readily observed in a fresh preparation than in one which has been stimulated for several hours. The possibility that acetylcholine may accumulate during the initial stages of motor nerve stimulation in this isolated preparation is discussed. 6. Atropine increases slightly the size of muscle contractions elicited by maximal nerve stimuli in a fresh preparation. 7. If muscle contractions are increased by eserine or prostigmine, atropine reduces them to their normal size. If muscle contractions are depressed by an overdose of an anticholinesterase or by a faster rate of stimulation then atropine counteracts the depression. 8. In the presence of an anticholinesterase curarine abolishes the depressant effects of excess acetylcholine, whether this be produced by rapid nerve stimulation or by adding acetylcholine to the bath. Atropine differs from curarine. It abolishes the depressant effect of rapid motor nerve stimulation but it does not abolish the depression caused by the addition of acetylcholine to the bath. 9. The action of atropine was found to be very similar to that of procaine. The conclusion was therefore drawn that atropine acts not only by raising the threshold of the muscle, as curarine does, but also by interfering with nervous activity.