The effect of local anaesthetic agents on afferent and motor nerve impulses in the frog.

In the frog nerve-muscle preparation an attempt was made to determine the sites of local anaesthetic activity. The drugs were applied not only to the nerve fiber, but also to other structures of the nerve. Different blocking concentrations proved that the drugs effected different sites. It was shown that small concentrations of the agents effected the sensory endings of afferent nerves and the muscle spindles. The muscle spindle needed the smallest minimal concentration (Cm) to be blocked. The sensory endings of the C fibers needed a higher one and the motor terminal a still higher one. However, all these concentrations belonged to a similar range (3 X, 4 X and 5 X 10(-5) g/ml bupivacaine or etidocaine). To block the nerve trunk a much higher Cm was mandatory (4 X 10(-4) for C fibers and greater than 5 X 10(-4) g/ml for A alpha fibers). This means that the effect of the local anaesthetic drugs on the nervous system is not single but multiple.