Department of Neurology, Children’s Hospital, Harvard Medical School, Boston, Massachusetts, USA.
J Neurophysiol. 2012 Feb;107(3):966-72. doi: 10.1152/jn.00690.2011. Epub 2011 Oct 19.
Paired-pulse transcranial magnetic stimulation (ppTMS) is a safe and noninvasive tool for measuring cortical inhibition in humans, particularly in patients with disorders of cortical inhibition such as epilepsy. However, ppTMS protocols in rodent disease models, where mechanistic insight into the ppTMS physiology and into disease processes may be obtained, have been limited due to the requirement for anesthesia and needle electromyography. To eliminate the confounding factor of anesthesia and to approximate human ppTMS protocols in awake rats, we adapted the mechanomyogram (MMG) method to investigate the ppTMS inhibitory phenomenon in awake rats and then applied differential pharmacology to test the hypothesis that long-interval cortical inhibition is mediated by the GABA(A) receptor. Bilateral hindlimb-evoked MMGs were elicited in awake rats by long-interval ppTMS protocols with 50-, 100-, and 200-ms interstimulus intervals. Acute changes in ppTMS-MMG were measured before and after intraperitoneal injections of saline, the GABA(A) agonist pentobarbital (PB), and GABA(A) antagonist pentylenetetrazole (PTZ). An evoked MMG was obtained in 100% of animals by single-pulse stimulation, and ppTMS resulted in predictable inhibition of the test-evoked MMG. With increasing TMS intensity, MMG amplitudes increased in proportion to machine output to produce reliable input-output curves. Simultaneous recordings of electromyography and MMG showed a predictable latency discrepancy between the motor-evoked potential and the evoked MMG (7.55 ± 0.08 and 9.16 ± 0.14 ms, respectively). With pharmacological testing, time course observations showed that ppTMS-MMG inhibition was acutely reduced following PTZ (P < 0.05), acutely enhanced after PB (P < 0.01) injection, and then recovered to pretreatment baseline after 1 h. Our data support the application of the ppTMS-MMG technique for measuring the cortical excitability in awake rats and provide the evidence that GABA(A) receptor contributes to long-interval paired-pulse cortical inhibition. Thus ppTMS-MMG appears a well-tolerated biomarker for measuring GABA(A)-mediated cortical inhibition in rats.
成对脉冲经颅磁刺激（ppTMS）是一种安全、非侵入性的测量人类皮质抑制的工具，尤其适用于皮质抑制障碍患者，如癫痫患者。然而，在啮齿动物疾病模型中，由于需要麻醉和针式肌电图，ppTMS 方案受到限制，因此无法获得关于 ppTMS 生理学和疾病过程的机制见解。为了消除麻醉的混杂因素，并在清醒大鼠中近似人类 ppTMS 方案，我们采用肌动描记图（MMG）方法来研究清醒大鼠中的 ppTMS 抑制现象，然后应用差异药理学来检验长时程皮质抑制是由 GABA(A) 受体介导的假设。通过长时程 ppTMS 方案，用 50、100 和 200ms 刺激间隔在清醒大鼠中诱发双侧后肢诱发 MMG。在腹腔注射生理盐水、GABA(A)激动剂戊巴比妥（PB）和 GABA(A)拮抗剂戊四氮（PTZ）前后，测量 ppTMS-MM 变化。单次刺激可使 100%的动物获得诱发 MMG，ppTMS 可预测抑制测试诱发的 MMG。随着 TMS 强度的增加，MMG 幅度与机器输出成比例增加，从而产生可靠的输入-输出曲线。肌电图和 MMG 的同步记录显示，运动诱发电位和诱发 MMG 之间存在可预测的潜伏期差异（分别为 7.55±0.08ms 和 9.16±0.14ms）。通过药物测试，时间过程观察显示，PTZ 后 ppTMS-MM 抑制急性减少（P<0.05），PB 后急性增强（P<0.01），1 小时后恢复到预处理基线。我们的数据支持使用 ppTMS-MM 技术测量清醒大鼠的皮质兴奋性，并提供证据表明 GABA(A)受体参与长时程成对脉冲皮质抑制。因此，ppTMS-MM 似乎是一种耐受良好的生物标志物，可用于测量大鼠的 GABA(A)介导的皮质抑制。
