Reversible depression of hippocampus by local injections of anesthetics in monkeys

Abstract

In 5 unanesthetized monkeys equipped with intracerebral electrodes and chemitrodes, 2.5–10% dibucaine was continuously injected into the amygdala or hippocampus at a speed of 8–14 μl/h for 1–4 days with the following results: 1. 1. The local spontaneous electrical activity was depressed for 1–4 weeks in the injected region with minor or no modifications in other cerebral areas. 2. 2. Thresholds for after-discharge in the injected structure rose from a control value of 0.5–1.0 mA to above 6 mA and then slowly returned to normal in 2–4 weeks. Dibucaine modified the pattern and diminished the spread of electrically evoked after-discharges, but had only a minor effect, if any, on thresholds for motor manifestations. 3. 3. A few hours after the end of dibucaine injection, various types of epileptiform potentials appeared, localized within the injected area, and persisted for several days. 4. 4. Injection of 10% sodium phenobarbital or 4% xylocaine into the hippocampal region also depressed the local spontaneous activity and raised after-discharge thresholds without being followed by seizure activity. 5. 5. Injection of local anesthetics into the hippocampal region produced a transitory decrease in aggressiveness of the animals, without modifying alertness, or appetite, and without producing other behavioral manifestations.