INTERACTIONS OF EXCITATORY POSTSYNAPTIC POTENTIALS GENERATED AT DIFFERENT SITES ON THE FROG MOTONEURON

Abstract

When axosomatic synapses on frog motor neurons were excited repetitively, the mean level of depolarization recorded intracellularly exhibited a progressive rise even though the individual EPSP''s became smaller. Using two shocks the testing EPSP was facilitated slightly. When axodendritic synapses were excited repetitively, the mean level of depolarization reached an early peak and then declined during the remainder of the period of excitation. Using two shocks, the testing EPSP exhibited a delayed recovery. EPSP''s initiated at the two sites showed only simple additive interaction. The findings could not be explained on the basis of alterations in the presynaptic volleys. It was suggested that repetitive excitation was accompanied by a progressive diminution in the amount of transmitter released by each impulse. The results were discussed in relation to the functional role of dendrites.