Mechanisms of Developmental Anesthesia Toxicity

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PROJECT SUMMARY Epidemiologic studies of human patients have shown a correlation between childhood exposure to general anesthetic agents and subsequent cognitive deficits. This association is supported by data from animal models, which shows that developmental exposure to anesthetics causes lasting impairments in learning. The mechanism by which anesthetic exposure during childhood could impair subsequent brain function is unknown and no strategies currently exist in clinical practice to protect patients from the putative risk of anesthetic neurotoxicity. We hypothesize that developmental exposure to general anesthetics causes a disruption in brain circuit formation by interfering with dendrite growth and synapse formation, and further that this form of toxicity is caused by activation of the mTOR pathway, a signaling system associated with neurodevelopmental disorders. To test this hypothesis we will employ in vivo structural and functional analysis of mouse and human neurons in the dentate gyrus of the hippocampus. To address this hypothesis, we will determine the conditions in which commonly used anesthetics cause pathologic overgrowth of developing dendrites (Aim I); we will determine whether anesthetics alter the structure and function of synapses on the dendrites of exposed neurons in vivo (Aim II); finally, we will determine whether anesthetic induced activation of the mTOR pathway causes a disruption of neuronal circuits and deficits in learning that can be reversed with a pharmacologic mTOR inhibitor. (Aim III). The proposed studies will not only link pediatric anesthetic neurotoxicity to a well characterized mechanism of injury that is common to neurodevelopmental disorders, but it will also explore both a treatment modality, in the form of the mTOR inhibitor rapamycin, and a prevention strategy, in the form of differential effects anesthetic choice and dose. The findings will be established in vivo at the single cell level, both in terms of structure and function, in a well-defined brain circuit in the intact mouse and via the use using behavioral learning assays that are highly specific for the circuit under study. Key findings will be verified in human neurons in an in vivo setting, thus establishing relevance to human biology that is critical for translation. This proposal will explore the broader hypothesis that pediatric anesthetic neurotoxicity arises from disruptions of brain circuit formation, and more generally it will contribute to our understanding of neurodevelopmental disorders.