Genetic Differences Modify Anesthetic Preconditioning of Traumatic Brain Injury in Drosophila

Pre-clinical vertebrate models of traumatic brain injury (TBI) routinely use anesthetics for animal welfare; however, humans experience TBI without anesthetics. Therefore, translation of findings from vertebrate models to humans hinges on understanding how anesthetics influence cellular and molecular events that lead to secondary injuries following TBI. To investigate the effects of anesthetics on TBI outcomes, we used an invertebrate Drosophila melanogaster model to compare outcomes between animals exposed or not exposed to anesthetics prior to the same primary injury. Using a common laboratory fly line, w1118, we found that exposure to the volatile anesthetics isoflurane or sevoflurane, but not ether, prior to TBI produced a dose-dependent reduction in mortality within 24 h following TBI. Thus, isoflurane and sevoflurane precondition w1118 flies to deleterious effects of TBI. To examine the effects of genetic differences on anesthetic preconditioning of TBI, we repeated the experiment with the Drosophila Genetic Reference Panel (DGRP) collection of genetically diverse, inbred fly lines. Pre-exposure to either isoflurane or sevoflurane revealed a wide range of preconditioning levels among 171 and 144 DGRP lines, respectively, suggesting a genetic component for variation in anesthetic preconditioning of mortality following TBI. Finally, genome-wide association study analyses identified single-nucleotide polymorphisms in genes associated with isoflurane or sevoflurane preconditioning of TBI. Several of the genes, including the fly ortholog of mammalian Calcium Voltage-Gated Subunit Alpha1 D (CACNA1D), are highly expressed in neurons and are functionally linked to both anesthetics and TBI. These data indicate that anesthetic dose and genetic background should be considered when investigating effects of anesthetics in vertebrate TBI models, and they support use of the fly model for elucidating the mechanisms underlying anesthetic preconditioning of TBI.