Morphologic changes after prolonged electrical stimulation of the cat's cortex at defined charge densities.

Experiments were conducted correlating neuronal activity, changes in ionic concentrations in the cerebral extracellular compartment, and neural damage during 4-h continuous electrical stimulations of the cat's sensorimotor cortex. Here we describe histological evaluations with the light and electron microscope of cortical tissue subjected to charge-balanced, biphasic, constant-current pulses delivered through subdurally implanted electrodes. Three combinations of charge density and pulse repetition rate were used. The results indicated a positive correlation of neural damage with both charge density and total charge. With electrical stimulation of low charge density [20 microC/cm2 . ph, 50 pulses per second (pps)] a transient increase in [K+]0 was observed with no histologically demonstrable neural damage. The most intense electrical stimulation studied (100 microC/cm2 . ph, 50 pps) resulted in a tonic increase and episodic fluctuations of [K+]0 and a marked decrease in [Ca2+]0 accompanied by moderate neural damage in the form of shrunken neurons, widespread extracellular edema, and swollen axons and dendrites.