Steady potential and extracellular potassium shifts in the rat neocortex during sustained low-frequency electrical stimulation of the cortical surface

Cyclic excitation arising in the rat neocortex under the influence of low-frequency electrical stimulation was studied. The duration of the excitation cycles and intervals between them depended on the stimulation parameters. In the period of excitation the negative shift of steady potential reached 4–5 mV, and the extracellular potassium ion concentration, measured with the aid of potassium-selective microelectrodes, rose to 8–10 mM. The process of periodic excitation was not self-maintained and it ceased after the current was stopped. As a result of small doses of pentobarbital (10–20 mg/kg) the response thresholds rose, and intervals between excitation phases were increased by several times. Pentobarbital in a dose of 30–40 mg/kg completely abolished cyclic excitation for 2–3 h. Correlation between shifts of steady potential and extracellular potassium concentration differed in anesthetized and unanesthetized animals.