Cortical Slow Potentials, Depolarization of Glial Cells, and Extracellular Potassium Concentration

Abstract

It is known that in response to a stimulus applied to the surface of the cortex after dendritic potential-20 to 30 msec negative potential reflecting EPSPs of apical dendrites—slow negativity (SN) arises (Chang, 1951). SN has been investigated in detail (Goldring and O’Leary, 1960; Roitbak, 1963, 1965; Roitbak et al., 1974). SN arises at a greater intensity of stimulation than dendritic potential; its amplitude increases with increases in the intensity of the stimulus; it can be recorded at a distance of 3 mm; and latency of SN is about 15 msec. SN increases during 50–80 msec, reaches 2 mV or more, and lasts 300–3000 msec. At the stimulation frequency 5–100 Hz SN summates and a negative shift of potential (NSP) occurs. SN is recorded in a volume of the cortex having the shape of a spherical segment. If double stimuli are used with deep anesthesia, the response to the second stimulus remains attenuated for up to 1 min. Based on the evidence obtained in a number of laboratories (Ransom et al., 1977; Roitbak et al., 1984, 1987; Somjen and Trachtenberg, 1979) it has been established beyond any doubt that K⁺ and glial cells contribute to the genesis of prolonged negative potentials at the cortical surface. However, some interesting points still remain to be clarified.