Synaptic frequency response: the influence of sinusoidal changes in stimulation frequency on the amplitude of the end-plate potential.

1. The synaptic response to frequency modulated trains of stimuli was investigated at the neuromuscular junction of the frog. The frequency of stimulation was usually varied sinusoidally about a carrier frequency of ca. 25 impulses per sec (Hz).2. The post-synaptic response to sinusoidally modulated trains of nerve stimuli was found to grow almost linearly when the variations in input frequency were increased up to 60% of the carrier frequency.3. The synaptic frequency response (gain and phase) was reminiscent of that of a low-pass filter, best transmitting slow variations in input frequency.4. The synaptic filter characteristics could not be explained by the post-synaptic cable properties, but were attributed to presynaptic facilitation processes.