Brudnick Neuropsychiatric Research Institute, Department of Psychiatry, University of Massachusetts Medical School, 303 Belmont Street, Worcester, MA 01604, USA.
Neuropharmacology. 2013 Oct;73:19-30. doi: 10.1016/j.neuropharm.2013.05.001. Epub 2013 May 17.
Nicotinic acetylcholine receptors (nAChRs) containing either the α4 and/or α6 subunit are robustly expressed in dopaminergic nerve terminals in dorsal striatum where they are hypothesized to modulate dopamine (DA) release via acetylcholine (ACh) stimulation from cholinergic interneurons. However, pharmacological blockade of nAChRs or genetic deletion of individual nAChR subunits, including α4 and α6, in mice, yields little effect on motor behavior. Based on the putative role of nAChRs containing the α4 subunit in modulation of DA in dorsal striatum, we hypothesized that mice expressing a single point mutation in the α4 nAChR subunit, Leu9'Ala, that renders nAChRs hypersensitive to agonist, would exhibit exaggerated differences in motor behavior compared to WT mice. To gain insight into these differences, we challenged WT and Leu9'Ala mice with the α4β2 nAChR antagonist dihydro-β-erythroidine (DHβE). Interestingly, in Leu9'Ala mice, DHβE elicited a robust, reversible motor impairment characterized by hypolocomotion, akinesia, catalepsy, clasping, and tremor; whereas the antagonist had little effect in WT mice at all doses tested. Pre-injection of nicotine (0.1 mg/kg) blocked DHβE-induced motor impairment in Leu9'Ala mice confirming that the phenotype was mediated by antagonism of nAChRs. In addition, SKF82958 (1 mg/kg) and amphetamine (5 mg/kg) prevented the motor phenotype. DHβE significantly activated more neurons within striatum and substantia nigra pars reticulata in Leu9'Ala mice compared to WT animals, suggesting activation of the indirect motor pathway as the circuit underlying motor dysfunction. ACh evoked DA release from Leu9'Ala striatal synaptosomes revealed agonist hypersensitivity only at α4(non-α6)* nAChRs. Similarly, α6 nAChR subunit deletion in an α4 hypersensitive nAChR (Leu9'Ala/α6 KO) background had little effect on the DHβE-induced phenotype, suggesting an α4(non-α6)* nAChR-dependent mechanism. Together, these data indicate that α4(non-α6)* nAChR have an impact on motor output and may be potential molecular targets for treatment of disorders associated with motor impairment.
烟碱型乙酰胆碱受体（nAChRs）包含α4 和/或α6 亚基，在背侧纹状体的多巴胺能神经末梢中大量表达，据推测它们通过胆碱能中间神经元的乙酰胆碱（ACh）刺激来调节多巴胺（DA）释放。然而，在小鼠中，nAChR 的药理学阻断或单个 nAChR 亚基（包括α4 和α6）的基因缺失对运动行为几乎没有影响。基于包含α4 亚基的 nAChR 在调节背侧纹状体中 DA 的假定作用，我们假设表达单个点突变的α4 nAChR 亚基 Leu9'Ala 的小鼠，该突变使 nAChR 对激动剂变得超敏，与 WT 小鼠相比，在运动行为上会表现出更明显的差异。为了深入了解这些差异，我们用α4β2 nAChR 拮抗剂二氢-β-erythroidine (DHβE) 挑战 WT 和 Leu9'Ala 小鼠。有趣的是，在 Leu9'Ala 小鼠中，DHβE 引起了强烈的、可逆的运动障碍，表现为运动减少、运动不能、僵住、握持和震颤；而在所有测试剂量下，拮抗剂对 WT 小鼠几乎没有影响。预先注射尼古丁（0.1 mg/kg）阻断了 Leu9'Ala 小鼠中 DHβE 诱导的运动障碍，证实表型是通过 nAChR 的拮抗作用介导的。此外，SKF82958（1 mg/kg）和安非他命（5 mg/kg）可预防运动表型。与 WT 动物相比，DHβE 在 Leu9'Ala 小鼠的纹状体和黑质网状部中激活了更多的神经元，表明作为运动功能障碍的潜在回路，间接运动通路被激活。从 Leu9'Ala 纹状体突触小体中诱发的 ACh 释放显示出激动剂超敏性，仅在α4（非-α6）*nAChR 上。同样，在α4 超敏 nAChR（Leu9'Ala/α6 KO）背景下缺失α6 nAChR 亚基对 DHβE 诱导的表型几乎没有影响，这表明存在一种α4（非-α6）*nAChR 依赖性机制。总之，这些数据表明α4（非-α6）*nAChR 对运动输出有影响，可能是治疗与运动障碍相关疾病的潜在分子靶点。
