Phagocytic and metabolic reactions to intracerebral electrical stimulation of rat brain

Electrical stimulation of the brain has been used with a variety of different electrode types and different stimulating intensities. Few studies have explored neural damage resulting from electrical stimulation that may render the experiment unreliable. The present study used conventional intracerebral bipolar metal stimulating electrodes, delivered a range of defined charge levels, and systematically measured "acute" metabolic effects on glucose (2-deoxy[14C]glucose) metabolism as well as "chronic" (96 h poststimulation) neuronal death and phagocytosis at the electrode surfaces. Neither charge density per phase (QD) nor total charge density per phase (TQD) were independent predictors of "safe" or damaging stimulation; however, together they provided ranges of clearly safe or damaging stimulating conditions that lasted 1 to 2 h. The lowest QD (11.11 microC/cm2/ph) was safe even at 9.1 TQD but not when the pulses totaled 9.6 TQD in 4 h. The middle QD (22.22) was safe even at 9.3 TQD but not when the 2-h pulsing totaled 11.0 TQD. The highest QD (44.44) was safe at 0.4 and 0.8 TQD but irreversibly damaging at 1.6 and 9.6 TQD. These comparisons demonstrated conditions suitable for 1 to 2 h of safe stimulation, but did not provide evidence on the cumulative effects of longer periods or higher frequencies.