Thursday, 28 July 2011

Rats and the "Wave of Death"

Bit of a morbid topic for this post, but an article examining what happens in the brains of decapitated rats recently came to my attention. To be fair to the scientists involved, they're investigating whether euthanasia by decapitation is humane, but the idea still seems somewhat... grim.

Issues of personal queasiness aside, the paper did find something interesting;

Remarkably, after 50 seconds (awake group) or 80 seconds (anesthetized group) following decapitation, a high amplitude slow wave was observed. The EEG before this wave had more power than the signal after the wave. This wave might be due to a simultaneous massive loss of membrane potentials of the neurons. Still functioning ion channels, which keep the membrane potential intact before the wave, might explain the observed power difference.

This "wave of death" is suggested by the authors to reflect "the ultimate border between life and death". The question arises as to whether this wave is irreparably damaging to the cells involved, something which the authors apparently intend upon researching in future.

On a somewhat related note, the authors also argue that conscious brain activity probably vanishes a scant few seconds after decapitation, making the process a reasonably humane method of disposing of unwanted rodents.

A related study, published more recently, develops a computational model to attempt to account for this "wave of death" phenomenon. Of particular note is the end of the paper, where they argue against the wave as a biomarker of clinical death;

Irreversible functional damage due to oxygen and
glucose deprivation most likely occurs from damage to synapses,
rather than from cell death itself. In line with this perhaps
surprising result, cells from neocortical slices from adult human
brain obtained several hours postmortem, can survive for weeks in
vitro. We therefore reject the claim in the paper by van Rijn
et al. that this particular phenomenon can be used clinically to
determine brain death. In fact, this wave does not imply death,
neither of neurons nor of individuals.
In summary, our simulations and the data presented from
experimental physiology show that the ‘‘Wave of Death’’ reflects
the sudden change in membrane potential due to anoxic
depolarization, that is a direct result of the Hodgkin-Huxley
dynamics and ion concentrations. Although the wave is indeed a
typical signature of the final membrane voltage changes of neurons
suffering from severe oxygen and glucose deprivation, it is not a
biomarker for irreversibility.

A pair of pretty interesting papers, all round. Hopefully they'll inspire some fascinating follow-up research.

Rijn CMv, Krijnen H, Menting-Hermeling S, Coenen AML (2011) Decapitation in Rats: Latency to Unconsciousness and the ‘Wave of Death’. PLoS ONE 6(1): e16514. doi:10.1371/journal.pone.0016514

Zandt B-J, ten Haken B, van Dijk JG, van Putten MJAM (2011) Neural Dynamics during Anoxia and the “Wave of Death”. PLoS ONE 6(7): e22127. doi:10.1371/journal.pone.0022127

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