Differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studies
Repetitive transcranial magnetic stimulation (rTMS) is primarily used in humans to change the state of corticospinal excitability. To assess the efficacy of different rTMS stimulation protocols, motor evoked potentials (MEPs) are used as a readout due to their non-invasive nature. Stimulation of the...
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doaj-0c3585f3c7894dbb964a65cfd360fd062020-11-24T23:53:28ZengFrontiers Media S.A.Frontiers in Neural Circuits1662-51102016-10-011010.3389/fncir.2016.00080215265Differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studiesMatthew Sykes0Matthew Sykes1Natalie Matheson2Natalie Matheson3Philip Brownjohn4Philip Brownjohn5Alexander Tang6Jennifer Rodger7Jonathan Shemmell8Jonathan Shemmell9John Reynolds10John Reynolds11University of OtagoBrain Research New ZealandUniversity of OtagoBrain Research New ZealandUniversity of OtagoBrain Research New ZealandUniversity of Western AustraliaUniversity of Western AustraliaBrain Research New ZealandUniversity of OtagoUniversity of OtagoBrain Research New ZealandRepetitive transcranial magnetic stimulation (rTMS) is primarily used in humans to change the state of corticospinal excitability. To assess the efficacy of different rTMS stimulation protocols, motor evoked potentials (MEPs) are used as a readout due to their non-invasive nature. Stimulation of the motor cortex produces a response in a targeted muscle, and the amplitude of this twitch provides an indirect measure of the current state of the cortex. When applied to the motor cortex, rTMS can alter MEP amplitude, however results are variable between participants and across studies. In addition, the mechanisms underlying any change and its locus are poorly understood. In order to better understand these effects, MEPs have been investigated in vivo in animal models, primarily in rats. One major difference in protocols between rats and humans is the use of general anesthesia in animal experiments. Anesthetics are known to affect plasticity-like mechanisms and so may contaminate the effects of an rTMS protocol. In the present study, we explored the effect of anesthetic on MEP amplitude, recorded before and after intermittent theta burst stimulation (iTBS), a patterned rTMS protocol with reported facilitatory effects. MEPs were assessed in the brachioradialis muscle of the upper forelimb under two anesthetics: a xylazine/zoletil combination and urethane. We found MEPs could be induced under both anesthetics, with no differences in the resting motor threshold or the average baseline amplitudes. However, MEPs were highly variable between animals under both anesthetics, with the xylazine/zoletil combination showing higher variability and most prominently a rise in amplitude across the baseline recording period. Interestingly, application of iTBS did not facilitate MEP amplitude under either anesthetic condition. Although it is important to underpin human application of TMS with mechanistic examination of effects in animals, caution must be taken when selecting an anaesthetic and in interpreting results during prolonged TMS recording.http://journal.frontiersin.org/Journal/10.3389/fncir.2016.00080/fullAnesthesiaTranscranial Magnetic Stimulationexcitabilityplasticityratmotor evoked potential |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Matthew Sykes Matthew Sykes Natalie Matheson Natalie Matheson Philip Brownjohn Philip Brownjohn Alexander Tang Jennifer Rodger Jonathan Shemmell Jonathan Shemmell John Reynolds John Reynolds |
spellingShingle |
Matthew Sykes Matthew Sykes Natalie Matheson Natalie Matheson Philip Brownjohn Philip Brownjohn Alexander Tang Jennifer Rodger Jonathan Shemmell Jonathan Shemmell John Reynolds John Reynolds Differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studies Frontiers in Neural Circuits Anesthesia Transcranial Magnetic Stimulation excitability plasticity rat motor evoked potential |
author_facet |
Matthew Sykes Matthew Sykes Natalie Matheson Natalie Matheson Philip Brownjohn Philip Brownjohn Alexander Tang Jennifer Rodger Jonathan Shemmell Jonathan Shemmell John Reynolds John Reynolds |
author_sort |
Matthew Sykes |
title |
Differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studies |
title_short |
Differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studies |
title_full |
Differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studies |
title_fullStr |
Differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studies |
title_full_unstemmed |
Differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studies |
title_sort |
differences in motor evoked potentials induced in rats by transcranial magnetic stimulation under two separate anesthetics: implications for plasticity studies |
publisher |
Frontiers Media S.A. |
series |
Frontiers in Neural Circuits |
issn |
1662-5110 |
publishDate |
2016-10-01 |
description |
Repetitive transcranial magnetic stimulation (rTMS) is primarily used in humans to change the state of corticospinal excitability. To assess the efficacy of different rTMS stimulation protocols, motor evoked potentials (MEPs) are used as a readout due to their non-invasive nature. Stimulation of the motor cortex produces a response in a targeted muscle, and the amplitude of this twitch provides an indirect measure of the current state of the cortex. When applied to the motor cortex, rTMS can alter MEP amplitude, however results are variable between participants and across studies. In addition, the mechanisms underlying any change and its locus are poorly understood. In order to better understand these effects, MEPs have been investigated in vivo in animal models, primarily in rats. One major difference in protocols between rats and humans is the use of general anesthesia in animal experiments. Anesthetics are known to affect plasticity-like mechanisms and so may contaminate the effects of an rTMS protocol. In the present study, we explored the effect of anesthetic on MEP amplitude, recorded before and after intermittent theta burst stimulation (iTBS), a patterned rTMS protocol with reported facilitatory effects. MEPs were assessed in the brachioradialis muscle of the upper forelimb under two anesthetics: a xylazine/zoletil combination and urethane. We found MEPs could be induced under both anesthetics, with no differences in the resting motor threshold or the average baseline amplitudes. However, MEPs were highly variable between animals under both anesthetics, with the xylazine/zoletil combination showing higher variability and most prominently a rise in amplitude across the baseline recording period. Interestingly, application of iTBS did not facilitate MEP amplitude under either anesthetic condition. Although it is important to underpin human application of TMS with mechanistic examination of effects in animals, caution must be taken when selecting an anaesthetic and in interpreting results during prolonged TMS recording. |
topic |
Anesthesia Transcranial Magnetic Stimulation excitability plasticity rat motor evoked potential |
url |
http://journal.frontiersin.org/Journal/10.3389/fncir.2016.00080/full |
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