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. 2013 May 10;13:10.
doi: 10.1186/1471-2253-13-10.

Comparing the Effects of Isoflurane and Pentobarbital on the Responses of Cutaneous Mechanoreceptive Afferents

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Free PMC article

Comparing the Effects of Isoflurane and Pentobarbital on the Responses of Cutaneous Mechanoreceptive Afferents

Ju-Wen Cheng et al. BMC Anesthesiol. .
Free PMC article

Abstract

Background: While pentobarbital has been used extensively in neurophysiological experiments investigating activity in peripheral nerves, it has fallen out of favor as an anesthetic because of safety concerns and is often replaced with isoflurane. However, the effects of isoflurane on the excitability of mechanoreceptive afferents have yet to be conclusively elucidated.

Methods: To fill this gap, we collected extracellular single-unit recordings of cutaneous mechanoreceptive afferents from the sciatic nerve of 21 rats during vibratory stimulation of the hindpaw. We then compared the strength and temporal structure of the afferent response measured under pentobarbital and isoflurane anesthesia.

Results: We found that the strength and temporal structure of afferent responses were statistically equivalent whether these were evoked under isoflurane or pentobarbital.

Conclusions: We conclude that, if these two anesthetics have any effect on the responses of mechanoreceptive afferents, their effects are indistinguishable.

Figures

Figure 1
Figure 1
Neurophysiological recordings. An illustration of 90 (2-ms-long) action potential traces from a single unit displayed using custom-made spike sorting software (range of full screen: ±1 V). The signal to noise ratio is very high for these recordings.
Figure 2
Figure 2
Typical responses of a single unit under anesthesia with isoflurane only. Top: Raster plots of the responses to 50-Hz stimulation in first (left) and second (right) blocks. Each row on the raster plots represents the spike train of the single unit corresponding to a given stimulus lasting for 2 seconds. Stimuli were presented ten times at each of five amplitudes (each indicated by a different color; at this frequency, the faintest stimulus did not elicit a response in this afferent). Bottom: Mean firing rates as a function of amplitude at the three frequencies tested. Each point indicates the average firing rate over 10 repetitions of each stimulus. Error bars denote the standard deviation. Note that we observed entrainment plateaus in a subset of fibers [14], but these were relatively uncommon given how sparsely amplitudes were sampled at each frequency.
Figure 3
Figure 3
Typical responses of a single unit under anesthesia with first isoflurane and then pentobarbital. Top: Raster plots of the responses to 50-Hz stimulation under isoflurane (left) and pentobarbital (right). Each row on the raster plots represents the spike train of the single unit corresponding to a given stimulus lasting for 2 seconds. Stimuli were presented ten times at each of five amplitudes. Bottom: Mean firing rates as a function of amplitude at the three frequencies tested. Error bars denote the standard deviation.
Figure 4
Figure 4
Effect of anesthesia on response strength over the population. Top: Normalized firing rates for the control group. Each point indicates the average normalized firing rate across single units of the same block under the same condition of stimulus. Error bars denote the standard error of the mean. Bottom: Normalized firing rates for the experimental group.
Figure 5
Figure 5
Entrainment of a single unit recorded in the experimental condition. Raster plots of the response evoked by 50-Hz, 500-μm sinusoidal vibration delivered for 0.5s.
Figure 6
Figure 6
Effect of anesthesia on the temporal structure of the response over the population. Top: Entrainment in the control condition. Each point indicates the mean vector strength across single units of the same block under the same condition of stimulus. Error bars denote the standard error of the mean. While the degree of entrainment is highly variable across afferents (as indicated by the large error bars), it is consistent across blocks. Bottom: Entrainment in the experimental group.

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