Neonatal Sevoflurane Exposure Induces Adulthood Fear-induced Learning Disability and Decreases Glutamatergic Neurons in the Basolateral Amygdala.

Background: Neonatal mice exposed to sevoflurane show certain cognitive and behavioral impairments in adulthood. However, the mechanisms underlying long-term cognitive deficits induced by sevoflurane exposure remain unknown. The present study was performed to investigate whether there is differential neuronal activation between naive mice and sevoflurane-exposed neonates in fear-conditioning tests based on immediate early gene (c-Fos) expression. Methods: Male mice were exposed to 3% sevoflurane (SEVO group) or carrier gas alone (no anesthesia, NA group) for 6 hours on postnatal day 6. The mice were allowed to mature before performing the contextual fear-conditioning test. A reduced freezing response was confirmed in the SEVO group. Neural activation in the regions of the medial prefrontal cortex, hippocampus, and amygdala was investigated using c-Fos immunostaining 2 hours after the test. The types of neurons activated were also identified. Results: The number of c-Fos-positive cells decreased by 27% in the basolateral amygdala in the SEVO group, while no significant changes were observed in other regions. Furthermore, glutamatergic, but not [gamma]-aminobutyric acid (GABA)ergic, neurons expressed c-Fos after the contextual fear-conditioning test in both groups. The number of glutamatergic neurons in the basolateral amygdala in the SEVO group was reduced by 27%. Conclusions: Decreased neural activation in the basolateral amygdala may be associated with reduced freezing time in neonatal sevoflurane-exposed mice. Fewer glutamatergic neurons responding to fear stimuli in the basolateral amygdala may contribute to decreased neural activation and learning deficits in mice exposed to sevoflurane as neonates. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved

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