Pathological striatopallidal neuronalensembles in learned motor impairment in PD

摘要 在帕金森病（PD）中，多巴胺能（DA）神经元的变性导致严重的运动障碍。 虽然运动症状最初可通过DA前体左旋多巴（L-DOPA）治疗，但患者会出现不良反应。 使运动波动，包括L-DOPA作用持续时间缩短，仅部分用 药理学手段和深部脑刺激。防止左旋多巴的效力下降将大大 提高患者生活质量，降低社会成本。出现失能性运动波动与 随着左旋多巴抗帕金森病反应的一个组成部分，即长持续反应的下降， （LDR）的最大值。LDR是一种持久的运动改善，在L-DOPA血浆水平恢复后持续很长时间。 在停用左旋多巴后数小时至数天内逐渐衰减。电机 波动可能是由LDR下降太快引起的，停止LDR衰减的治疗可能会阻止乳腺癌。 或波动。然而，LDR的潜在机制目前尚不清楚。使用两种不同的运动任务， 我们最近发现，LDR的诱导和衰减都是任务特异性的，需要任务暴露的配对， L-DOPA（用于LDR诱导）或L-DOPA停药（用于LDR衰减）。这些结果表明， 主动学习和神经可塑性作为潜在机制。此外，间接途径中等多刺 神经元（iMSN）被LDR衰减激活，并且D2受体（D2 R）敲除大大减缓了LDR衰减。 基于上述结果和以前的发现，i）iMSN激活抑制运动，可能也不- ii）iMSN经历异常的长时程增强（LTP），当 DA耗尽，我们将测试这一假设，即在LDR衰减过程中， 在正常运动期间被D2 R刺激抑制的iMSN特定集合中的LTP- 但在任务暴露过程中，如果DA耗尽，则会变得病理活跃。使用Drd 2-EGFP小鼠标记 iMSN，我们将首先检查L-DOPA拯救的运动性能与LDR衰减是否激活不同的 iMSN集成在同一个鼠标中：我们将在第一时间点使用 Fos启动子驱动，多西环素门控荧光团，然后在第二次标记任务激活的iMSN系综 点用内源性Fos标记，并比较它们的共定位。然后我们将研究这是否 在LDR衰减期间激活的“不正确的”iMSN系综（通过Fos驱动的荧光团可视化）具有突触突触 与LTP发生一致的输入变化。最后，我们将使用Fos驱动的视蛋白来双- 定向调节这种“不正确的”iMSN集合，以显示其因果、病理作用：其激活 导致任务特异性运动障碍，其抑制导致任务特异性运动障碍。通过示范- 研究帕金森病患者任务特异性运动障碍中病理性iMSN集合体的存在及其作用， 并通过识别导致运动过程中招募的异常神经可塑性的形式， 实验将为未来的研究奠定基础，以开发新的治疗方法来阻止或逆转LDR衰减， 运动波动

ABSTRACT In Parkinson's disease (PD), degeneration of dopaminergic (DA) neurons leads to profound motor impairment. Although motor symptom is initially treatable by the DA precursor levodopa (L-DOPA), patients experience dis- abling motor fluctuations, including a shortened duration of action for L-DOPA, only partially treated with pharmacological means and deep brain stimulation. Preventing L-DOPA's declining effectiveness will greatly improve patients' quality of life and reduce social cost. Emergence of disabling motor fluctuation is associated with the decline of a component of L-DOPA's antiparkinsonian response, known as the long duration response (LDR). The LDR is a long-lasting motor improvement that persists long after L-DOPA plasma level has re- turned to baseline, gradually decaying over many hours to days after discontinuation of L-DOPA. Motor fluctuation may be caused by LDR declining too rapidly, and treatments that halt LDR decay may prevent mo- tor fluctuations. However, the mechanism underlying LDR is currently unknown. Using two distinct motor tasks, we recently found that both induction and decay of LDR is task-specific, requiring the pairing of task exposure with L-DOPA (for LDR induction) or with L-DOPA withdrawal (for LDR decay). These results point to associa- tive learning and neuroplasticity as the underlying mechanism. Furthermore, indirect pathway medium spiny neurons (iMSNs) are activated by LDR decay, and D2 receptor (D2R) knockout greatly slowed LDR decay. Based on the above results and previous findings that i) iMSN activation suppresses movement and may nor- mally function to inhibit competing responses; ii) iMSNs undergo aberrant long-term potentiation (LTP) when DA depleted, we will test the hypothesis that gradual motor impairment during LDR decay results from aberrant LTP in specific ensembles of iMSNs that are normally suppressed during normal movement by D2R stimula- tion, but become pathologically active during task exposure if DA is depleted. Using Drd2-EGFP mice to label iMSNs, we will first examine whether L-DOPA-rescued motor performance vs. LDR decay activate different iMSN ensembles in the same mouse: we will tag task-activated iMSN ensemble at the 1st time point using a Fos-promoter driven, doxycycline-gated fluorophore, then tag task-activated iMSN ensemble at the 2nd time point using endogenous Fos labeling, and compare their co-localization. We will then examine whether this “incorrect” iMSN ensemble activated during LDR decay (visualized by a Fos-driven fluorophore) has synaptic input changes that are consistent with the occurrence of LTP. Finally, we will use Fos-driven opsins to bi- directionally modulate this “incorrect” iMSN ensemble to show its causal, pathological role: that its activation leads to task-specific motor impairment, and its inhibition recues impairment task-specifically. By demonstrat- ing the existence of, and the role of, pathological iMSN ensembles in task-specific motor impairment in PD, and by identifying the form of aberrant neuroplasticity that leads to their recruitment during movement, these experiments will form a basis for future studies to develop novel treatments to halt or reverse LDR decay and motor fluctuation.