Newly Published
Perioperative Medicine  |   July 2018
Breakdown of Neural Function under Isoflurane Anesthesia: In Vivo, Multineuronal Imaging in Caenorhabditis elegans
Author Notes
  • From the Department of Physiology and Biophysics (M.R.A., D.A., C.V.G., C.W.C.) and Department of Pharmacology and Experimental Therapeutics, Photonics Center (C.V.G.), Boston University School of Medicine, Boston, Massachusetts; Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts (J.F., M.A.); and Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Boston, Massachusetts (C.W.C.).
  • Part of the work presented in this article has been presented as a poster for the session “Experimental Neurosciences: Exploring Novel Techniques and Molecules” at the 2017 Annual Meeting of the American Society of Anesthesiologists, October 21, 2017, Boston, Massachusetts, and at the 21st International C. elegans Conference, June 21 to 25, 2017, University of California Los Angeles, Los Angeles, California.
    Part of the work presented in this article has been presented as a poster for the session “Experimental Neurosciences: Exploring Novel Techniques and Molecules” at the 2017 Annual Meeting of the American Society of Anesthesiologists, October 21, 2017, Boston, Massachusetts, and at the 21st International C. elegans Conference, June 21 to 25, 2017, University of California Los Angeles, Los Angeles, California.×
  • C.V.G. and C.W.C. contributed equally to this article.
    C.V.G. and C.W.C. contributed equally to this article.×
  • Submitted for publication December 19, 2017. Accepted for publication June 5, 2018.
    Submitted for publication December 19, 2017. Accepted for publication June 5, 2018.×
  • Acknowledgments: C. elegans strains were obtained from Caenorhabditis Genetics Center (University of Minnesota, Minneapolis, Minnesota). Fluorescence imaging was performed within the Boston University School of Medicine Confocal Microscope Facility, directed by Vickery Trinkaus-Randall, Ph.D., (Boston University School of Medicine, Boston, Massachusetts).
    Acknowledgments: C. elegans strains were obtained from Caenorhabditis Genetics Center (University of Minnesota, Minneapolis, Minnesota). Fluorescence imaging was performed within the Boston University School of Medicine Confocal Microscope Facility, directed by Vickery Trinkaus-Randall, Ph.D., (Boston University School of Medicine, Boston, Massachusetts).×
  • Research Support: Supported by grant Nos. R01 GM121457, R01 GM084491, and UL1 TR001430 from the National Institutes of Health (Bethesda, Maryland) and by departmental support.
    Research Support: Supported by grant Nos. R01 GM121457, R01 GM084491, and UL1 TR001430 from the National Institutes of Health (Bethesda, Maryland) and by departmental support.×
  • Competing Interests: The authors declare no competing interests.
    Competing Interests: The authors declare no competing interests.×
  • Correspondence: Address correspondence to Dr. Connor: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, 75 Francis Street, CWN L1, Boston, Massachusetts 02115. cconnor@bwh.harvard.edu. 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 / Central and Peripheral Nervous Systems / Pharmacology / Radiological and Other Imaging
Perioperative Medicine   |   July 2018
Breakdown of Neural Function under Isoflurane Anesthesia: In Vivo, Multineuronal Imaging in Caenorhabditis elegans
Anesthesiology Newly Published on July 12, 2018. doi:10.1097/ALN.0000000000002342
Anesthesiology Newly Published on July 12, 2018. doi:10.1097/ALN.0000000000002342
Abstract

What We Already Know about This Topic:

  • Current approaches to the study of anesthetic effects are focused on specific molecular targets, such as the γ-aminobutyric acid type A receptor, or on measurements of neuronal activity across regions of the brain. A bridge between these cellular and systems approaches is lacking.

  • In Caenorhabditis elegans, the individual neurons and their interconnections that comprise the circuitry for commanding forward and reverse movement have been well characterized. Using this model, the impact of isoflurane on these individual neurons and how they function within this neuronal circuit were evaluated.

What This Article Tells Us That Is New:

  • Even though exposure to 4% isoflurane prevented movement, neurons in the movement circuitry remained highly active. However, the coordination among the neurons of the command circuitry was lost in comparison to the awake state.

  • The data suggest that the primary cause of the lack of motion in worms is not the suppression of neuronal activity per se but rather the loss of coordination between neurons in the command circuit.

Background: Previous work on the action of volatile anesthetics has focused at either the molecular level or bulk neuronal measurement such as electroencephalography or functional magnetic resonance imaging. There is a distinct gulf in resolution at the level of cellular signaling within neuronal systems. We hypothesize that anesthesia is caused by induced dyssynchrony in cellular signaling rather than suppression of individual neuron activity.

Methods: Employing confocal microscopy and Caenorhabditis elegans expressing the calcium-sensitive fluorophore GCaMP6s in specific command neurons, we measure neuronal activity noninvasively and in parallel within the behavioral circuit controlling forward and reverse crawling. We compare neuronal dynamics and coordination in a total of 31 animals under atmospheres of 0, 4, and 8% isoflurane.

Results: When not anesthetized, the interneurons controlling forward or reverse crawling occupy two possible states, with the activity of the “reversal” neurons AVA, AVD, AVE, and RIM strongly intercorrelated, and the “forward” neuron AVB anticorrelated. With exposure to 4% isoflurane and onset of physical quiescence, neuron activity wanders rapidly and erratically through indeterminate states. Neuron dynamics shift toward higher frequencies, and neuron pair correlations within the system are reduced. At 8% isoflurane, physical quiescence continues as neuronal signals show diminished amplitude with little correlation between neurons. Neuronal activity was further studied using statistical tools from information theory to quantify the type of disruption caused by isoflurane. Neuronal signals become noisier and more disordered, as measured by an increase in the randomness of their activity (Shannon entropy). The coordination of the system, measured by whether information exhibited in one neuron is also exhibited in other neurons (multiinformation), decreases significantly at 4% isoflurane (P = 0.00015) and 8% isoflurane (P = 0.0028).

Conclusions: The onset of anesthesia corresponds with high-frequency randomization of individual neuron activity coupled with induced dyssynchrony and loss of coordination between neurons that disrupts functional signaling.