Kreko-Pierce Tabita, Pugh Jason R
Department of Cellular and Integrative Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States.
Center for Biomedical Neuroscience, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States.
Front Cell Neurosci. 2022 Jul 5;16:926518. doi: 10.3389/fncel.2022.926518. eCollection 2022.
Duchenne muscular dystrophy (DMD) is generally regarded as a muscle-wasting disease. However, human patients and animal models of DMD also frequently display non-progressive cognitive deficits and high comorbidity with neurodevelopmental disorders, suggesting impaired central processing. Previous studies have identified the cerebellar circuit, and aberrant inhibitory transmission in Purkinje cells, in particular, as a potential site of dysfunction in the central nervous system (CNS). In this work, we investigate potential dysfunction in the output of the cerebellum, downstream of Purkinje cell (PC) activity. We examined synaptic transmission and firing behavior of excitatory projection neurons of the cerebellar nuclei, the primary output of the cerebellar circuit, in juvenile wild-type and mice, a common mouse model of DMD. Using immunolabeling and electrophysiology, we found a reduced number of PC synaptic contacts, but no change in postsynaptic GABA receptor expression or clustering in these cells. Furthermore, we found that the replenishment rate of synaptic vesicles in Purkinje terminals is reduced in neurons, suggesting that dysfunction at these synapses may be primarily presynaptic. We also found changes in the excitability of cerebellar nuclear neurons. Specifically, we found greater spontaneous firing but reduced evoked firing from a hyperpolarized baseline in neurons. Analysis of action potential waveforms revealed faster repolarization and greater after-hyperpolarization of evoked action potentials in neurons, suggesting an increased voltage- or calcium- gated potassium current. We did not find evidence of dystrophin protein or messenger RNA (mRNA) expression in wild-type nuclear neurons, suggesting that the changes observed in these cells are likely due to the loss of dystrophin in presynaptic PCs. Together, these data suggest that the loss of dystrophin reduces the dynamic range of synaptic transmission and firing in cerebellar nuclear neurons, potentially disrupting the output of the cerebellar circuit to other brain regions and contributing to cognitive and neurodevelopmental deficits associated with DMD.
杜氏肌营养不良症（DMD）通常被视为一种肌肉萎缩性疾病。然而，DMD的人类患者和动物模型也经常表现出非进行性认知缺陷以及与神经发育障碍的高共病率，这表明中枢处理功能受损。先前的研究已经确定小脑回路，尤其是浦肯野细胞中异常的抑制性传递，是中枢神经系统（CNS）功能障碍的一个潜在部位。在这项研究中，我们调查了小脑输出（浦肯野细胞（PC）活动下游）的潜在功能障碍。我们检测了小脑核兴奋性投射神经元的突触传递和放电行为，小脑核是小脑回路的主要输出部位，实验对象为幼年野生型小鼠和mdx小鼠（一种常见的DMD小鼠模型）。通过免疫标记和电生理学方法，我们发现PC突触接触数量减少，但这些细胞中突触后GABA受体的表达或聚集没有变化。此外，我们发现mdx神经元中浦肯野终末突触小泡的补充率降低，这表明这些突触的功能障碍可能主要是突触前的。我们还发现小脑核神经元的兴奋性发生了变化。具体而言，我们发现mdx神经元的自发放电增加，但从超极化基线诱发的放电减少。动作电位波形分析显示，mdx神经元诱发动作电位的复极化更快，超极化后电位更大，这表明电压门控或钙门控控控钾电流增加。我们在野生型核神经元中未发现肌营养不良蛋白或信使核糖核酸（mRNA）表达的证据，这表明在这些细胞中观察到的变化可能是由于突触前PC中肌营养不良蛋白的缺失所致。总之，这些数据表明肌营养不良蛋白的缺失降低了小脑核神经元突触传递和放电的动态范围，可能会破坏小脑回路向其他脑区的输出，并导致与DMD相关的认知和神经发育缺陷。
