Perioperative Medicine  |   September 2019
Syntaxin1A Neomorphic Mutations Promote Rapid Recovery from Isoflurane Anesthesia in Drosophila melanogaster
Author Notes
  • From the Queensland Brain Institute (M.T., O.H.Z., B.D.K., S.K., V.A., B.v.S.), School of Biomedical Sciences (O.H.Z.), and Clem Jones Centre for Ageing Dementia Research (V.A.), The University of Queensland, Brisbane, Queensland, Australia; School of Medical Science and Griffith Health Institute, Griffith University Gold Coast Campus, Queensland, Australia (S.K.).
  • Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are available in both the HTML and PDF versions of this article. Links to the digital files are provided in the HTML text of this article on the Journal’s Web site (www.anesthesiology.org).
    Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are available in both the HTML and PDF versions of this article. Links to the digital files are provided in the HTML text of this article on the Journal’s Web site (www.anesthesiology.org).×
  • For a downloadable PPT slide containing this article’s citation information, please visit https://anesthesiology.pubs.asahq.org/ss/downloadable_slide.aspx.
    For a downloadable PPT slide containing this article’s citation information, please visit https://anesthesiology.pubs.asahq.org/ss/downloadable_slide.aspx.×
  • M.T. and O.H.Z. contributed equally to this article.
    M.T. and O.H.Z. contributed equally to this article.×
  • Submitted for publication September 10, 2018. Accepted for publication May 16, 2019.
    Submitted for publication September 10, 2018. Accepted for publication May 16, 2019.×
  • Address correspondence to Dr. van Swinderen: Queensland Brain Institute, The University of Queensland, Brisbane QLD 4072 Australia. b.vanswinderen@uq.edu.au. Information on purchasing reprints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. Anesthesiology’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue.
Article Information
Perioperative Medicine / Basic Science / Pharmacology
Perioperative Medicine   |   September 2019
Syntaxin1A Neomorphic Mutations Promote Rapid Recovery from Isoflurane Anesthesia in Drosophila melanogaster
Anesthesiology 9 2019, Vol.131, 555-568. doi:10.1097/ALN.0000000000002850
Anesthesiology 9 2019, Vol.131, 555-568. doi:10.1097/ALN.0000000000002850
Abstract

Editor’s Perspective:

What We Already Know about This Topic:

  • Syntaxin1A is a presynaptic molecule that plays a key role in vesicular neurotransmitter release

  • Mutations of syntaxin1A result in resistance to both volatile and intravenous anesthetics

  • Truncated syntaxin1A isoforms confer drug resistance in cell culture and nematode models of anesthesia

What This Article Tells Us That Is New:

  • Resistance to isoflurane anesthesia can be produced by transiently expressing truncated syntaxin1A proteins in adult Drosophila flies

  • Electrophysiologic and behavioral studies in Drosophila show that mutations in syntaxin1A facilitate recovery from isoflurane anesthesia

  • These observations suggest that presynaptic mechanisms, via syntaxin1A-mediated regulation of neurotransmitter release, are involved in general anesthesia maintenance and recovery

Background: Mutations in the presynaptic protein syntaxin1A modulate general anesthetic effects in vitro and in vivo. Coexpression of a truncated syntaxin1A protein confers resistance to volatile and intravenous anesthetics, suggesting a target mechanism distinct from postsynaptic inhibitory receptor processes. Hypothesizing that recovery from anesthesia may involve a presynaptic component, the authors tested whether syntaxin1A mutations facilitated recovery from isoflurane anesthesia in Drosophila melanogaster.

Methods: A truncated syntaxin1A construct was expressed in Drosophila neurons. The authors compared effects on isoflurane induction versus recovery in syntaxin1A mutant animals by probing behavioral responses to mechanical stimuli. The authors also measured synaptic responses from the larval neuromuscular junction using sharp intracellular recordings, and performed Western blots to determine whether the truncated syntaxin1A is associated with presynaptic core complexes.

Results: Drosophila expressing a truncated syntaxin1A (syx227, n = 40) were resistant to isoflurane induction for a behavioral responsiveness endpoint (ED50 0.30 ± 0.01% isoflurane, P < 0.001) compared with control (0.240 ± 0.002% isoflurane, n = 40). Recovery from isoflurane anesthesia was also faster, with syx227-expressing flies showing greater levels of responsiveness earlier in recovery (reaction proportion 0.66 ± 0.48, P < 0.001, n = 68) than controls (0.22 ± 0.42, n = 68 and 0.33 ± 0.48, n = 66). Measuring excitatory junction potentials of larvae coexpressing the truncated syntaxin1A protein showed a greater recovery of synaptic function, compared with controls (17.39 ± 3.19 mV and 10.29 ± 4.88 mV, P = 0.014, n = 8 for both). The resistance-promoting truncated syntaxin1A was not associated with presynaptic core complexes, in the presence or absence of isoflurane anesthesia.

Conclusions: The same neomorphic syntaxin1A mutation that confers isoflurane resistance in cell culture and nematodes also produces isoflurane resistance in Drosophila. Resistance in Drosophila is, however, most evident at the level of recovery from anesthesia, suggesting that the syntaxin1A target affects anesthesia maintenance and recovery processes rather than induction. The absence of truncated syntaxin1A from the presynaptic complex suggests that the resistance-promoting effect of this molecule occurs before core complex formation.