Teo J T H, Terranova C, Swayne O, Greenwood R J, Rothwell J C
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, Queen Square, London WC1N 3BG, UK.
Exp Brain Res. 2009 Mar;193(4):555-63. doi: 10.1007/s00221-008-1658-4. Epub 2008 Dec 2.
Practice of a motor task leads to an increase in amplitude of motor-evoked potentials (MEP) in the exercised muscle. This is termed practice-dependent plasticity, and is abolished by the NMDA antagonist dextromethorphan and the GABA(A) agonist lorazepam. Here, we sought to determine whether specific subtypes of GABA(A) circuits are responsible for this effect by comparing the action of the non-selective agonist, lorazepam with that of the selective GABA(A)-alpha(1) receptor agonist, zolpidem. In seven healthy subjects, transcranial magnetic stimulation (TMS) was used to quantify changes in amplitude of MEP after practice of a ballistic motor task. In addition we measured how the same drugs affected MEP amplitudes and the excitability of a number of cortical inhibitory circuits [short-interval intracortical inhibition (SICI), short-interval afferent inhibition (SAI) and long-interval intracortical inhibition]. This allowed us to explore correlations between drugs effects in measures of cortical excitability and practice-dependent plasticity of MEP amplitudes. As previously reported, lorazepam increased SICI and decreased SAI, while zolpidem only decreased SAI. The new findings were that practice-dependent plasticity of MEPs was impaired by lorazepam but not zolpidem, and that this was negatively correlated with lorazepam-induced changes in SICI but not SAI. This suggests that the intracortical circuits involved in SICI (and not neurons expressing GABA(A)-alpha(1) receptor subunits that are implicated in SAI) may be involved in controlling the amount of practice-dependent MEP plasticity.
进行一项运动任务会导致所锻炼肌肉的运动诱发电位（MEP）幅度增加。这被称为练习依赖性可塑性，并且会被NMDA拮抗剂右美沙芬和GABA(A)激动剂劳拉西泮消除。在此，我们试图通过比较非选择性激动剂劳拉西泮与选择性GABA(A)-α(1)受体激动剂唑吡坦的作用，来确定GABA(A)回路的特定亚型是否对此效应负责。在7名健康受试者中，经颅磁刺激（TMS）被用于量化进行一项弹道式运动任务后的MEP幅度变化。此外，我们测量了相同药物如何影响MEP幅度以及一些皮质抑制回路的兴奋性[短间隔皮质内抑制（SICI）、短间隔传入抑制（SAI）和长间隔皮质内抑制]。这使我们能够探索药物在皮质兴奋性测量中的作用与MEP幅度的练习依赖性可塑性之间的相关性。如先前报道，劳拉西泮增加SICI并降低SAI，而唑吡坦仅降低SAI。新的发现是，劳拉西泮会损害MEP的练习依赖性可塑性，而唑吡坦则不会，并且这与劳拉西泮诱导的SICI变化呈负相关，而与SAI变化无关。这表明参与SICI的皮质内回路（而非参与SAI的表达GABA(A)-α(1)受体亚基的神经元）可能参与控制练习依赖性MEP可塑性的程度。
