FLAT AND STEEP TERMINAL NEGATIVITY IN THE DC-POTENTIAL AFTER DEPRIVATION OF OXYGEN AND GLUCOSE IN HUMAN NEOCORTICAL SLICES

The so-called terminal negativity (TN) of the DC-potential is a charac teristic reaction of neuronal tissue to hypoxia or ischemia, In a prev ious study on human neocortical slices, two types of TN with flat and steep slopes of rise (< or > 10 mV/min) were found with hypoxia, The a im of the present study was to further investigate causes underlying t he occurrence of flat and steep TN. Experiments were performed on 23 h uman neocortical slices (500 mu m) resected from 13 patients (epilepsy and tumour surgery). DC-potential and evoked potentials (white matter stimulation) were recorded in layer LII. The extracellular potassium concentration ([K+](0)) was measured by K+-sensitive microelectrodes. in an interface type chamber, ischemic episodes were induced by oxygen and glucose deprivation. They were terminated when TN had peaked. Bot h flat and steep TN also existed with ischemic conditions. There was a linear correlation between the slope of rise of TN and the associated slope of rise in [K+],, respectively, but none regarding latencies of TN or recovery of evoked potentials. Peak levels in [K+](0) were 13.9 +/- 0.9 mmol/l. Compared to control, the slope of rise and latency of TN were clearly increased by addition of dimethyl sulfoxide (DMSO, 0. 4%) to the bath solution, whereas nimodipine (40 mu mol/l) in 0.4% DMS O had neither an effect on slope of rise of TN nor on latency of TN. A s a whole, our observations suggest, that the actual metabolic state d etermines the occurrence of flat or steep TN. (C) 1998 Elsevier Scienc e B.V. All rights reserved.