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

Area of Science:

• Neuroscience
• Neurophysiology
• Histopathology

Background:

• Electrical stimulation is used in treating neurological disorders.
• Understanding the relationship between stimulation parameters and neural damage is crucial for safety.
• Cerebral extracellular ion concentration changes are indicators of neural activity and potential damage.

Purpose of the Study:

• To correlate neuronal activity, ionic concentration changes, and neural damage during electrical stimulation.
• To evaluate histological damage in feline sensorimotor cortex following controlled electrical stimulation.

Main Methods:

• Histological evaluation (light and electron microscopy) of feline cortical tissue.
• Delivery of charge-balanced, biphasic, constant-current pulses via subdural electrodes.
• Testing three combinations of charge density and pulse repetition rate over 4-hour continuous stimulation.

Main Results:

• Neural damage showed a positive correlation with charge density and total charge.
• Low charge density (20 microC/cm2 . ph, 50 pps) caused transient increases in extracellular potassium ([K+]0) without damage.
• High charge density (100 microC/cm2 . ph, 50 pps) led to sustained [K+]0 changes, decreased extracellular calcium ([Ca2+]0), and moderate neural damage (shrunken neurons, edema, axonal/dendritic swelling).

Conclusions:

• Electrical stimulation parameters, specifically charge density, directly influence the extent of neural damage.
• Significant changes in extracellular potassium and calcium concentrations are associated with observable neural damage.
• These findings provide critical insights into the safety limits of electrical stimulation for neural tissue.