PPPR: Electron spin changes during general anesthesia in Drosophila

I’m going to try something I’ve never done on this blog before. I’m posting a paper that has already been published. I made some negative comments about this work on Twitter and the first author Luca Turin (@lucaturin) invited me to comment formally in a letter to PNAS. I think it would be more interesting to get a discussion going that involves other people. Maybe I’m being unreasonable? As far as I know, PNAS has no facility for comments on its website, so let’s comment on it here. I for one would find it easier to elaborate on my viewpoint outside of 140 characters. Anyone who is interested should read the paper at the link provided below and add a comment to this post.


Luca Turin, Efthimios M. C. Skoulakis, and Andrew P. Horsfield
We show that the general anesthetics xenon, sulfur hexafluoride,
nitrous oxide, and chloroform cause rapid increases of different
magnitude and time course in the electron spin content of
Drosophila. With the exception of CHCl3, these changes are reversible.
Anesthetic-resistant mutant strains of Drosophila exhibit a different
pattern of spin responses to anesthetic. In two such mutants,
the spin response to CHCl3 is absent. We propose that these spin
changes are caused by perturbation of the electronic structure of
proteins by general anesthetics. Using density functional theory,
we show that general anesthetics perturb and extend the highest
occupied molecular orbital of a nine-residue α -helix. The calculated
perturbations are qualitatively in accord with the Meyer–Overton
relationship and some of its exceptions. We conclude that there
may be a connection between spin, electron currents in cells, and
the functioning of the nervous system

19 thoughts on “PPPR: Electron spin changes during general anesthesia in Drosophila

  1. So are you going to include your own lengthy comments here? It’s easier to comment if someone else does so first, and it sounds like you already have something to say.

  2. Ok, browsed the paper. Even though I intend to read it more carefully, for what is worth, here are some preliminary thoughts:

    **Interesting concept and paper, no question about it.
    **I am a little worried about the “nonphysiological” nature of the experiments. I know, I know… I did my PhD with a hard-core physical chemist and I was the “resident biologist” in his lab. ‘Nough said…
    **I do not quite understand how **calculations** can be **qualitatively** (my emphasis) in accord with the MO rule.
    **Suggestion for future experiments: Use n-alkanols! They display anesthetic potencies directly proportional to their length until they reach their “cuttoff” point at about 12-13 carbons in the chain. Maybe a dose-response relationship will appear and it will certainly be interesting to see how a non-anesthetic alkanol acts on electron spins…

    • Hi Oné, thank you for your positive comments and your questions.

      **Unphysiological** I agree. This paper fits in the tradition of unphysiological-but-useful methods in neurophysiology, like axons measured in 1/4 seawater at 4C and perfused with KF, heart voltage clamp in isotonic sucrose, hippocampal slices showing LTP at or below room temperature, etc. We’re pretty sure we’ll find a way, with paralysed mutants or otherwise, to do the same experiments at room temperature and with more graded gas mixtures, but for the moment that’s the best we could do.

      **qualitative vs quantitative** Perhaps that statement was not ideally worded. What we meant was that the pattern of MO perturbation was in rough proportion to anesthetic potency. Numbers can be qualitatively in agreement with data if, say, they show the same ranking order or fall into separate groups, etc. Since we do not know the exact site of anesthetic action, and despite the fact that DFT can calculate MO energies pretty accurately, it seemed pointless to calculate a rather artificial system —an alpha helix made of glycines— to higher precision. Transport calculations are the answer, and we’re on it.

      **Alkanols** Very good suggestion, but remember alkanol vapour pressures go down roughly a factor of 2 for every carbon added. Drosophila are an absolute bitch of a prep if you’re trying to administer liquid or solid drugs in known amounts, because you can’t inject it into a vein, etc. You have to feed them the stuff which takes hours and they take up uneven, hard to measure amounts. Maybe planarians? I’ve always wanted to work with those amazing critters.

    • Raised that point in comments here: http://phys.org/news/2014-08-electron-mechanism-anesthesia.html

      “Increasing the chain length in a homologous series of straight-chain alcohols or alkanes increases their lipid solubility, but their anesthetic potency stops increasing beyond a certain cutoff length”

      and got this response from @Toeia:

      It’s difficult to say without knowledge of conditions of particular experiment. The general solubility and ability of anesthetics to penetrate the tissue decreases with increasing of molecular weight as well. This is the reason, why the eating of polyethylene foil doesn’t act as an instant hypnotic killer for us, despite its chains have very high length. The schematic thinking doesn’t help here very much.

  3. I confess to not having read the paper deeply, but I didn’t see any indication that the flies were unconscious (viz. anaesthetized!) by the various treatments. Were they at least rendered immobile, as by the carbon dioxide?

    It seems as though the basic observation is what it is — the spin changes — and that’s interesting. I just don’t know how to differentiate between anaesthesia and some other effect on the flies.

  4. 1) I don’t think I’ve ever read a paper that so thoroughly fails to cite its entire field. I don’t mean the authors didn’t cite specific people that I think they should have. I mean there is almost a total lack of acknowledgment of the past 15 to 20 years of work on the mechanism of general anesthesia. All that is stated about this veritable mountain of work essentially boils down to:

    “Indeed, GAs are now believed to act on proteins (40–42) and have now been seen in just such sites in protein structures, where they exert small but definite effects on protein (43) and ion channel (44) conformation.”

    I find it remarkable that the paper contains no mention of GABA receptors, their demonstrated binding sites for various anesthetics, the extensively characterized effects of those drugs on neuronal excitability, or (almost no mention of) structural biology of GABA receptors. There is no discussion of how their data squares with these decades of work.

    2) the reason I said I didn’t understand why the authors thought their results were related to anesthesia is as follows. They put a bunch of immobilized flies in a machine that measures electron spin and flowed several anesthetics over the flies. While doing this, they measured currents that reflect changes in spin associated with the presence of the anesthetic. Some of the anesthetics (I guess really two) led to a step-like change in electron spin. I suppose this says something about the way these compounds interact with the physicochemical properties of a fly, but from this experiment alone there is no reason to conclude that it has to do with anesthesia, especially since there was no signal from the half of the anesthetics.

    To address this point, the authors perform several additional experiments. First, they freeze and then thaw the flies and see that the spin signal is attenuated. Indeed, this does suggest that whatever they are measuring, it is larger in amplitude for an intact organism. Second, they tested a number of anesthesia-resistant strains with their four anesthetics. The authors emphasize a few differences in the overall pattern across flies, but if I may summarize my read of the results: given the larger variability in their signal shown by the standard deviations, to my eye it appears that one of the four anesthetics produces a substantially different signal for certainly two and maybe three of the six anesthesia resistant strains. Also, two of the anesthesia resistant strains give a signal to N2O that was not seen in either of the wild type strains. To me, this is not a compelling correlation between a compound’s capacity to anesthetize and whether it produces a change in electron spin. Therefore, I see no reason to conclude that the spin signal is related to anesthesia.

    3) At this point in the manuscript, in figure 8 and 9 the authors report another experiment. These figures show that there is a large signal similar in shape to that seen with their most often used anesthetic when the flies perfused with air.

    It was at that point that I stopped reading the manuscript.

  5. A note to the literal minded:

    I of course read the entire paper as promised. I hoped it would be obvious that my claim otherwise was a facetious rhetorical device. The point is this: I got all the way to Figure 8 before I was told by the authors that they see the same kind of signal with both anesthetics and air. I of course soldiered on through the section in which they argue that this observation is not a problem. I also continued to read through their modeling experiments, which they perform as if no one has any idea what proteins or sites any of these compounds act on. But Figure 8 marked the point at which I said to myself “We’re done here”.

  6. So to recap: in response to the following tweet:

    you called me sweetheart, rudely demanded that I read your paper, and suggested that science is a foreign language to me. Although I declined your suggestion to write a letter to PNAS, which seems rather extreme, I offered to make a space where you and I and anyone else who cared to could lay out their feelings about your paper. This was at the end of the day on Friday. I awoke Saturday morning to the first suggestion that my response was not swift enough and I must be full of hot air. In the middle of that afternoon, after having emerged from a movie with my family, you tweeted that if I wasn’t going to respond now, I needed to apologize. I awoke Sunday morning to your proclamation that you were done “hanging around my blog” and refused to interact on it further. Also, you announced that I “chickened out” and questioned what organ I lacked that prevented me from responding in accordance with your prescribed timetable.

    Despite my subjection to this infuriating nonsense, in good faith I spent a few hours on Sunday, hours that I could have spent doing almost anything else, reading and thinking about your paper and composing a serious albeit not comprehensive set of comments. Now I’m not demanding a response in any time frame, or even ever, but I just would like to point out that the substantive scientific content of your interaction with me is nil. I don’t know how to quantify the content of whining and insults, but it is quite high. While I suppose you can answer my review at any time, you made it clear above that you will only respond to a formal letter to the journal. Forgive me when I say that I will write no such letter, nor will I devote any more time to scientific dialogue with you.

    Like many scientists, I am a believer in mechanisms to enhance and accelerate scientific communication through e.g. preprint servers and post-publication peer review mechanisms. It is truly disappointing to me that critics of these mechanisms always point to behavior like yours as justification for why they will never work.

  7. I agree with you that his is a black eye for post publication peer review. But it’s also a black eye for the PNAS direct submission route.

  8. Note: I deleted a comment that used to be here (not written by me) that I felt was likely to be confusing. In what I interpret as satire, the commenter attributed the following paper to Luca Turin. The actual authors of the paper are Andreas Keller and Leslie Vosshall, and the paper in fact describes their failure to substantiate Turin’s qualitative odor judgments with double-blind human psychophysics. Sorry for the confusion this may have caused, and let’s not move the conversation to Turin’s level.


  9. Pingback: Neuromanti, cont. – Ocasapiens - Blog - Repubblica.it

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