DRUG-INDUCED MODULATION OF THE POSITIVE AFTERPOTENTIAL FOLLOWING THE PROPAGATED IMPULSE AND OF THE DISCHARGE PATTERN IN THE FROG MUSCLE SPINDLE

A previous work (1) has shown that an individual propagated impulse recorded at the sensory nerve terminal of the frog muscle spindle was always followed by a long-lasting positivity of up to 0.1 sec in duration and of 0.1-0.3 mV in the maximal amplitude, during which the appearance of propagated and abortive spikes was suppressed. Time course of the positive after-potential was similar to that of the after-hyperpolarization following spike discharge of amphibian motoneuron, during which excitatory processes were depressed (2). Matthews (3) has suggested that similarity in the electrical responses of the motoneuron and the sensory ending may result from similar properties of polarized surfaces. Objectives of the present experiments are to determine whether or not the positive afterpotential is selectively modulated by certain ions or drugs and to clarify the root of the selective modification from the effects of the drugs on the sensory terminal.