title: Early developmental exposure to volatile anesthetics causes behavioral defects in Caenorhabditis elegans.
abstract: BACKGROUND
  Mounting evidence from animal studies shows that anesthetic exposure in early life leads to apoptosis in the developing nervous system. This loss of neurons has functional consequences in adulthood. Clinical retrospective reviews have suggested that multiple anesthetic exposures in early childhood are associated with learning disabilities later in life as well. Despite much concern about this phenomenon, little is known about the mechanism by which anesthetics initiate neuronal cell death. Caenorhabditis elegans, a powerful genetic animal model, with precisely characterized neural development and cell death pathways, affords an excellent opportunity to study anesthetic-induced neurotoxicity. We hypothesized that exposing the nematode to volatile anesthetics early in life would induce neuron cell death, producing a behavioral defect that would be manifested in adulthood.
  
  
  METHODS
  After synchronization and hatching, larval worms were exposed to volatile anesthetics at their 95% effective concentration for 4 hours. On day 4 of life, exposed and control worms were tested for their ability to sense and move to an attractant (i.e., to chemotax). We determined the rate of successful chemotaxis using a standardized chemotaxis index.
  
  
  RESULTS
  Wild-type nematodes demonstrated striking deficits in chemotaxis indices after exposure to isoflurane (ISO) or sevoflurane (SEVO) in the first larval stage (chemotaxis index: untreated, 85 ± 2; ISO, 52 ± 2; SEVO, 47 ± 2; P < 0.05 for both exposures). The mitochondrial mutant gas-1 had a heightened effect from the anesthetic exposure (chemotaxis index: untreated, 71 ± 2; ISO, 29 ± 12; SEVO, 24 ± 13; P < 0.05 for both exposures). In contrast, animals unable to undergo apoptosis because of a mutation in the pathway that mediates programmed cell death (ced-3) retained their ability to sense and move toward an attractant (chemotaxis index: untreated, 76 ± 10; ISO, 73 ± 9; SEVO, 76 ± 10). Furthermore, we discovered that the window of greatest susceptibility to anesthetic neurotoxicity in nematodes occurs in the first larval stage after hatching (L1). This coincides with a period of neurogenesis in this model. All values are means ± SD.
  
  
  CONCLUSIONS
  These data indicate that anesthetics affect neurobehavior in nematodes, extending the range of phyla in which early exposure to volatile anesthetics has been shown to cause functional neurological deficits. This implies that anesthetic-induced neurotoxicity occurs via an ancient underlying mechanism. C elegans is a tractable model organism with which to survey an entire genome for molecules that mediate the toxic effects of volatile anesthetics on the developing nervous system.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Seattle Children's Hospital, M/S W 9824, PO Box 5371, Seattle, WA 98105, USA. katherine.gentry@seattlechildrens.org
authors.forename: Katherine R
authors.initials: KR
authors.lastname: Gentry
authors.forename: Louise M
authors.initials: LM
authors.lastname: Steele
authors.forename: Margaret M
authors.initials: MM
authors.lastname: Sedensky
authors.forename: Philip G
authors.initials: PG
authors.lastname: Morgan
mesh_terms: D000704:Analysis of Variance; D018685:Anesthetics, Inhalation / Q000633:toxicity*; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000502:physiology; D001522:Behavior, Animal / Q000187:drug effects*; D017173:Caenorhabditis elegans / Q000502:physiology*; D016923:Cell Death / Q000187:drug effects; D002633:Chemotaxis / Q000187:drug effects; D007530:Isoflurane / Q000633:toxicity; D007814:Larva; D008738:Methyl Ethers / Q000633:toxicity; D055495:Neurogenesis / Q000187:drug effects; D009474:Neurons / Q000187:drug effects; D020258:Neurotoxicity Syndromes / Q000523:psychology*; D000077149:Sevoflurane
chemical_list: D018685:Anesthetics, Inhalation; D051017:Apoptosis Regulatory Proteins; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane