Assessment of Potential Neuronal Toxicity of Inhaled Anesthetics in the Developing Nonhuman Primate

Anesthetics have been used for years in pediatric patients without clinical evidence of adverse central nervous system (CNS) sequelae. In the current study, postnatal day (PND) 5-6 rhesus monkeys were exposed to nitrous oxide (N2O; 70%) alone, isoflurane (ISO; 1.0%) alone, or N2O plus ISO for 8 h. Six hours after completion of anesthetic administration, neuronal toxicity was examined using histochemical and molecular imaging approaches. Histochemical data demonstrated that exposure of the developing monkey to the inhaled anesthetic combination for 8 h results in significantly enhanced neuronal cell death in frontal cortex, temporal gyrus, and hippocampus. Imaging techniques also demonstrated that such anesthetic exposure causes significant neuronal damage in cortical brain regions as indicated by an elevated binding of the specific peripheral benzodiazepine receptor radiotracer ( 18 F)-N- (2-(2-fluoroethoxy)benzyl)-N-(4-phenoxypyridin-3-yl) ac- etamide (( 18 F)-FEPPA), a marker of activated microglia or inflammatory responses. No significant neurotoxic effects were observed in monkeys treated with N2O alone, ISO alone, or in monkeys treated with the anesthetic combination for only 3 h. These data suggest that prolonged exposures to inhaled anesthetics in the developing rhesus monkey can result in significant neuronal damage.