Decapitation in rats: latency to unconsciousness and the 'wave of death'

Abstract

The question whether decapitation is a humane method of euthanasia in awake animals is being debated. To gather arguments in this debate, obsolete rats were decapitated while recording the EEG, both of awake rats and of anesthetized rats. Following decapitation a fast and global loss of power of the EEG was observed; the power in the 13-100 Hz frequency band, expressing cognitive activity, decreased according to an exponential decay function to half the initial value within 4 seconds. Whereas the pre-decapitation EEG of the anesthetized animals showed a burst suppression pattern quite different from the awake animals, the power in the postdecapitation EEG did not differ between the two groups. This might indicate that either the power of the EEG does not correlate well with consciousness or that consciousness is briefly regained in the anesthetized group after decapitation. 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. Two conclusions were drawn from this experiment. It is likely that consciousness vanishes within seconds after decapitation, implying that decapitation is a quick and not an inhumane method of euthanasia. It seems that the massive wave which can be recorded approximately one minute after decapitation reflects the ultimate border between life and death. This observation might have implications in the discussions on the appropriate time for organ donation.

Figure 1. EEGs of rats after decapitation.

Examples of EEG of rats recorded from 10 seconds before until 30 seconds after decapitation. Band pass 0.1–100 Hz. Lower trace of an awake rat, upper trace of an anesthetized rat. Note the large artifact of the guillotine and the artifacts coinciding with chewing movements of the mouth.

Figure 2. Spectrograms of the EEG after decapitation.

Mean spectrograms of the EEGs for the baseline period, i.e. the 10 seconds before decapitation, and for 5 time points post decapitation. Data are in Volt, group means are given. On the raw mean spectrum 2nd order smoothing with 4 neighbors was applied. On the abscissa the data around 50 Hz are deleted due to the notch filter. Please note the log scale of the ordinate. In anesthesia, before decapitation the EEG has high power content, reflecting the bursts in the burst suppression pattern. Following decapitation in both groups, a fast and global decay of the power is observed. The quantification of this decay is shown in fig. 3.

Figure 3. Time dependency of the power of the EEG after decapitation.

Time dependency of the mean power of the EEG between 1 and 100 Hz (al) and between 13–100 Hz (b). Blue open symbols for the awake group, red symbols for the anesthetized group. In the pre-decapitation EEG of the awake animals the power increases with 30% during the last 10 seconds. The power of the pre-decapitation period for the anesthetized group is given for the burst (red closed symbols, high power) as well as for the suppression parts (red open symbols, low power). The power of all rats sharply decreases after decapitation. An exponential decay function described this time dependent decrease. For both groups the half time was 5.5 seconds for the 1–100 Hz band and 3.7 seconds for the 13–100 Hz band.

Figure 4. All EEGs until 120 seconds after decapitation.

All EEGs recorded from 10 seconds before until 120 seconds after decapitation. Band pass 0.1–100 Hz. Lower panel awake animals, upper panel anesthetized group. Note the large slow wave around 50 seconds after decapitation for the awake animals and around 80 seconds fir the anesthetized group.

Figure 5. EEGs around the wave.

Examples of EEG of rats recorded from 30 seconds before the wave until 30 seconds after the wave. Band pass 0.1–100 Hz. Lower trace of an awake rat, upper trace of an anesthetized rat. Note the scale of the ordinate. This EEG is assumed to be iso-electric, but the power after the wave is lower then that before the wave.

Figure 6. Power of the EEGs around the wave.

The mean power of the EEG between 1 and 100 Hz around the wave. Blue open symbols for the awake group, red closed symbols for the anesthetized group. In the post-wave EEG the power is lower then that in the pre-wave EEG.

Figure 7. EEG of two animals euthanatized with an overdose of pentobarbital.

EEG of two animals euthanatized with an overdose of pentobarbital. The time after injection of 120 mg/kg is indicated. The EEG before the break of the abscissa is a typical burst suppression pattern A considerable time after the last burst, a large wave is observed. Note the large difference in the time-delay after injection and after the last burst.