The low frequency depression of rat monosynaptic relfex.

The rat monosynaptic reflex shows marked depression in response to repetitive stimulation of low frequency, which is called 'low frequency depression'. The site and the mechanism of this depression was studied and discussed in relation to the characteristic features of the rat spinal cord. 1) The depressive effect of the repetitive stimulation is referable to the motoneurons invaded by the impulses, regardless of number of the mediating synapses, and not by some inhibitory agent on the outside of the impulse circuit. 2) Therefore, in the outlook a synchronous wave showed more marked depression than a dispersed wave, which explained the eminence of the depression of monosyn aptic reflex. 3) The depression was caused by two factors: cessation and delaying of a unit discharge in terms of unit activity. The delaying consists of two factors: gradual retreat of firing point owing to reduced EPSP and the skipping from insufficient EPSP to succeeding EPSP.