Dexmedetomidine Attenuates Isoflurane-induced Neurocognitive Impairment in Neonatal Rats

Background: Neuroapoptosis is induced by the administration of anesthetic agents to the young. As α 2 adrenoceptor signaling plays a trophic role during development and is neuroprotective in several settings of neuronal injury, the authors investigated whether dexmedetomidine could provide functional protection against isoflurane-induced injury. Methods: Isoflurane-induced injury was provoked in organotypic hippocampal slice cultures in vitro or in vivo in postnatal day 7 rats by a 6-h exposure to 0.75% isoflurane with or without dexmedetomidine. In vivo, the α 2 adrenoceptor antagonist atipamezole was used to identify if dexmedetomidine neuroprotection involved α 2 adrenoceptor activation. The γ-amino-butyric-acid type A antagonist, gabazine, was also added to the organotypic hippocampal slice cultures in the presence of isoflurane. Apoptosis was assessed using cleaved caspase-3 immunohistochemistry. Cognitive function was assessed in vivo on postnatal day 40 using fear conditioning. Results: In vivo dexmedetomidine dose-dependently prevented isoflurane-induced injury in the hippocampus, thalamus, and cortex; this neuroprotection was attenuated by treatment with atipamezole. Although anesthetic treatment did not affect the acquisition of short-term memory, isoflurane did induce long-term memory impairment. This neurocognitive deficit was prevented by administration of dexmedetomidine, which also inhibited isoflurane-induced caspase-3 expression in organotypic hippocampal slice cultures in vitro; however, gabazine did not modify this neuroapoptosis. Conclusion: Dexmedetomidine attenuates isoflurane-induced injury in the developing brain, providing neurocognitive protection. Isoflurane-induced injury in vitro appears to be independent of activation of the γ-amino-butyric-acid type A receptor. If isoflurane-induced neuroapoptosis proves to be a clinical problem, administration of dexmedetomidine may be an important adjunct to prevent isoflurane-induced neurotoxicity.