Department and Graduate Institute of Pharmacology, College of Medicine, National Taiwan University, No. 1, Jen-Ai Rd., Section 1, Taipei, 10051, Taiwan.
Faculty of Pharmaceutical Sciences, UCSI University, Kuala Lumpur, 56000, Malaysia.
Neurotherapeutics. 2023 Mar;20(2):399-418. doi: 10.1007/s13311-023-01342-y. Epub 2023 Jan 25.
Ethanol has been shown to suppress essential tremor (ET) in patients at low-to-moderate doses, but its mechanism(s) of action remain unknown. One of the ET hypotheses attributes the ET tremorgenesis to the over-activated firing of inferior olivary neurons, causing synchronic rhythmic firings of cerebellar Purkinje cells. Purkinje cells, however, also receive excitatory inputs from granule cells where the α6 subunit-containing GABA receptors (α6GABARs) are abundantly expressed. Since ethanol is a positive allosteric modulator (PAM) of α6GABARs, such action may mediate its anti-tremor effect. Employing the harmaline-induced ET model in male ICR mice, we evaluated the possible anti-tremor effects of ethanol and α6GABAR-selective pyrazoloquinolinone PAMs. The burrowing activity, an indicator of well-being in rodents, was measured concurrently. Ethanol significantly and dose-dependently attenuated action tremor at non-sedative doses (0.4-2.4 g/kg, i.p.). Propranolol and α6GABAR-selective pyrazoloquinolinones also significantly suppressed tremor activity. Neither ethanol nor propranolol, but only pyrazoloquinolinones, restored burrowing activity in harmaline-treated mice. Importantly, intra-cerebellar micro-injection of furosemide (an α6GABAR antagonist) had a trend of blocking the effect of pyrazoloquinolinone Compound 6 or ethanol on harmaline-induced tremor. In addition, the anti-tremor effects of Compound 6 and ethanol were synergistic. These results suggest that low doses of ethanol and α6GABAR-selective PAMs can attenuate action tremor, at least partially by modulating cerebellar α6GABARs. Thus, α6GABARs are potential therapeutic targets for ET, and α6GABAR-selective PAMs may be a potential mono- or add-on therapy.
乙醇已被证明在低至中等剂量下可抑制特发性震颤(ET),但其作用机制仍不清楚。ET 的一个假说认为 ET 的震颤是由于下橄榄核神经元过度激活引起的,导致小脑浦肯野细胞同步节律性放电。然而,浦肯野细胞也接收来自颗粒细胞的兴奋性输入,其中富含α6 亚单位 GABA 受体(α6GABARs)。由于乙醇是 α6GABARs 的正变构调节剂(PAM),因此这种作用可能介导其抗震颤作用。我们在雄性 ICR 小鼠中采用哈马灵诱导的 ET 模型,评估了乙醇和 α6GABAR 选择性吡唑并喹啉酮 PAMs 的可能抗震颤作用。同时测量了啮齿动物幸福感的指标——挖洞活动。在非镇静剂量(0.4-2.4 g/kg,ip)下,乙醇显著且剂量依赖性地减轻了动作性震颤。普萘洛尔和 α6GABAR 选择性吡唑并喹啉酮也显著抑制了震颤活动。只有吡唑并喹啉酮而不是乙醇或普萘洛尔恢复了哈马灵处理的小鼠的挖洞活动。重要的是,小脑内注射呋塞米(α6GABAR 拮抗剂)有趋势阻断吡唑并喹啉酮化合物 6 或乙醇对哈马灵诱导的震颤的作用。此外,化合物 6 和乙醇的抗震颤作用具有协同作用。这些结果表明,低剂量的乙醇和 α6GABAR 选择性 PAMs 可以减轻动作性震颤,至少部分是通过调节小脑 α6GABARs。因此,α6GABARs 是 ET 的潜在治疗靶点,α6GABAR 选择性 PAMs 可能是潜在的单药或附加治疗药物。