On the mechanism of the cortical depression induced by afferent stimulation.

The cortical depression induced by the stimulation of some afferent fibers affects strychnine spikes elicited in two different ways: by direct electrical stimulation, and through the evoked potentials induced at the somatosensory area by single shocks to the radial nerve. The effects on these two types of responses were found to be very similar, which was taken to indicate that the site of action of the mechanism involved is the same, that is, the non-synaptic membranes of the dendrites of pyramidal neurons. It is suggested that the depressant action is mediated through the serotonergic neurons, since the previous administration of 5,6-Dihydroxytryptamine (5,6-DHT) blocked the changes. The 5-Hydroxytryptamine (5-HT) liberated would act as a neurohumoral agent, since the synaptic mechanisms do not seem to be involved and the effects are manifested in a diffuse manner.