Abstract
Nitrous Oxide (N(2)O), an N-methyl-D-aspartate (NMDA) receptor antagonist, and isoflurane (ISO), which acts on multiple receptors including postsynaptic gamma-aminobutyric acid (GABA) receptors, are frequently used inhalation anesthetics, alone or as a part of a balanced anesthetic regimen administered to pregnant women and to human neonates and infants requiring surgery. The current study investigated histological features and gene expression profiles in response to prolonged exposure to N(2)O or ISO alone, and their combination in developing rat brains. Postnatal day 7 rats were exposed to clinically-relevant concentrations of N(2)O (70%), ISO (1.0%) or N(2)O plus ISO (N(2)O + ISO) for 6 hours. The neurotoxic effects were evaluated and the brain tissues were harvested for RNA extraction 6 hours after anesthetic administration. The prolonged exposure to N(2)O + ISO produced elevated neuronal cell death as indicated by an increased number of TUNEL-positive cells in frontal cortical levels compared with control. No significant neurotoxic effects were observed in animals exposed to N(2)O or ISO alone. DNA microarray analysis revealed gene expression changes after N(2)O, ISO or N(2)O + ISO exposure. Differentially expressed genes (DEGs) from the N(2)O + ISO group were significantly associated with 45 pathways directly related to brain functions. Although the gene expression profiles from animals exposed to N(2)O or ISO alone were remarkably different from those of the control group, the pathways of these genes involved were not closely associated with neurons. These findings provide novel insights into the mechanisms by which N(2)O + ISO cause neurotoxicity in the developing brain, suggesting multiple factors are involved in the neuronal cell death-inducing effects (cascades) of N(2)O + ISO.