Lateralization of forelimb motor evoked potentials by transcranial magnetic stimulation in rats

Abstract

Objectives-To approximate methods for human transcranial magnetic stimulation (TMS) in rats, we tested whether lateralized cortical stimulation resulting in selective activation of one forelimb contralateral to the site of stimulation could be achieved by TMS in the rat.Methods-Motor evoked potentials (MEP) were recorded from the brachioradialis muscle bilaterally in adult male anesthetized rats (n=13). A figure-of-eight TMS coil was positioned lateral to midline. TMS intensity was increased stepwise from subthreshold intensities to maximal machine output in order to generate input-output curves and to determine the motor threshold (MT) for brachioradialis activation.Results-In 100% of the animals, selective activation of the contralateral brachiradialis, in the absence of ipsilateral brachiradialis activation was achieved, and the ipsilateral brachioradialis was activated only at TMS intensities exceeding contralateral forelimb MT. With increasing TMS intensity, the amplitudes of both the ipsilateral and contrlateral signals increased in proportion to TMS strength. However the input-output curves for the contralateral and ipsilateral brachioradialis were significantly different (p<0.001) such that amplitude of the ipsilateral MEP was reliably lower than the contralateral signal.Conclusions-We demonstrate that lateralized TMS leading to asymmetric brachioradialis activation is feasible with conventional TMS equipment in anesthetized rats.Significance-These data show that TMS can be used to assess the unilateral excitability of the forelimb descending motor pathway in the rat, and suggest that rat TMS protocols analogous to human TMS may be applied in future translational research.

A new measure of cortical inhibition by mechanomyography and paired-pulse transcranial magnetic stimulation in unanesthetized rats

“…The obtained input-output curve (averaged from 27 rats; Fig. 2B) shows a consistent slope and progressive increase in evoked MMG amplitude as TMS intensity is increased from 60 to 100% MO, similar to our previously published evoked brachioradialis MEP recruitment curve (Rotenberg et al 2010). We note that the MMG summed voltage is equal in the left and right hindlimb, confirming symmetric activation with a midline TMS coil position.…”

“…Additionally, the MEP latency suggests that the signal is of cortical origin. By extension, we assume the evoked MMG that follows the MEP is also of cortical origin, although we recognize that further studies in rodent will be necessary to clarify the origin of any TMS signal (Luft et al 2001;Rotenberg et al 2010). Thus, taken together, these data imply the potential utility of TMS-MMG in future studies aimed to measure the inhibition-to-excitation ratio either in rodent disease models or in animals exposed to a specific pharmacological or electrophysiological manipulation.…”

“…We note that without anesthesia, the TMS-MMG protocol in ways more closely approximates human experimental TMS than prior rat TMS methods (Luft et al 2001;Rotenberg et al 2010;Vahabzadeh-Hagh et al 2011). For instance, the noninvasive nature of the MMG in rodents approximates noninvasive surface EMG in humans and should enable longitudinal followup of an experimental manipulation by repeated studies in individual rodent subjects.…”

“…The MEP and evoked MMG were simultaneously recorded by tibialis anterior needle EMG and footpad accelerometry. The EMG signal sampled at 10 kHz was band-pass filtered at cutoff frequencies of 100 -1,000 Hz and amplified by 1,000 times (A-M Systems Model 1700; Sequim, WA; Rotenberg et al 2010;Vahabzadeh-Hagh et al 2011). We then measured the onset latency of both the mechanical and electrical signals, determined as the signal amplitude Ͼ3 SD above the average baseline signal noise collected 1 s before the TMS artifact.…”

Cognitive Impairment After Sleep Deprivation Rescued by Transcranial Magnetic Stimulation Application in Octodon degus

“…Furthermore, the practicability and reproducibility of TMS in the rat have been valued (Luft et al, 2001). The lateralized TMS advancing to asymmetric brachioradialis activation is achievable according to a study with traditional TMS equipment in rats (Rotenberg et al, 2010). In addition, it has been demonstrated the use of TMS as an electroconvulsive therapy in rats with anti-depressive activity and without side effects (Zyss et al, 2000).…”