On the process of inhibition in the superficial neuropil of the cerebral cortex.

Experiments were carried out on cats under Nembutal anaesthesia. The electrodes were placed on the gyrus suprasylvius. The recording macroelectrode and the K+--sensitive microelectrode were placed between two stimulating electrodes (S1 and S2). A strong stimulus applied through S1 elicited a slow surface negative potential (SNP) and an increase in [K/]0. The change of K+ potential correlated in time with SNP but the decay of K+ potential lasted longer. At this time depression of the dendritic potential (DP)--EPSP of apcial dendrites--evoked by stimulation through S2 took place. The greater the negative shift and the [K/]0 increase the greater was the depression. Tetraethylammonium increased SNP and this correlated with a strong depression of DP. Application of KCl or acetylcholine solutions resulted in DP depression. It may be supposed that the depression of dendritic potentials expresses presynaptic inhibition in the cortical neuropile based on the action of K+ ions.