ROLE of exercise in maintaining the integrity of the neuromuscular junction

Physical activity plays an important role in preventing chronic disease in adults and the elderly. Exercise has beneficial effects on the nervous system, including at the neuromuscular junction (NMJ). Exercise causes hypertrophy of NMJs and improves recovery from peripheral nerve injuries, whereas decreased physical activity causes degenerative changes in NMJs. Recent studies have begun to elucidate molecular mechanisms underlying the beneficial effects of exercise. These mechanisms involve Bassoon, neuregulin‐1, peroxisome proliferator–activated receptor gamma coactivator 1α, insulin‐like growth factor‐1, glial cell line–derived neurotrophic factor, neurotrophin 4, Homer, and nuclear factor of activated T cells c1. For example, NMJ denervation and active zone decreases have been observed in aged NMJs, but these age‐dependent degenerative changes can be ameliorated by exercise. In this review we assess the effects of exercise on the maintenance and regeneration of NMJs and highlight recent insights into the molecular mechanisms underlying these exercise effects. Muscle Nerve 49 :315–324, 2014     

Morphological variability is greater at developing than mature mouse neuromuscular junctions

The neuromuscular junction (NMJ) is the highly specialised peripheral synapse formed between lower motor neuron terminals and muscle fibres. Post-synaptic acetylcholine receptors (AChRs), which are found in high density in the muscle membrane, bind to acetylcholine released into the synaptic cleft of the NMJ, thereby enabling the conversion of motor action potentials to muscle contractions. NMJs have been studied for many years as a general model for synapse formation, development and function, and are known to be early sites of pathological changes in many neuromuscular diseases. However, information is limited on the diversity of NMJs in different muscles, how synaptic morphology changes during development, and the relevance of these parameters to neuropathology. Here, this crucial gap was addressed using a robust and standardised semi-automated workflow called NMJ-morph to quantify features of pre- and post-synaptic NMJ architecture in an unbiased manner. Five wholemount muscles from wild-type mice were dissected and compared at immature (post-natal day, P7) and early adult (P31−32) timepoints. The inter-muscular variability was greater in mature post-synaptic AChR morphology than that of the pre-synaptic motor neuron terminal. Moreover, the developing NMJ showed greater differences across muscles than the mature synapse, perhaps due to the observed distinctions in synaptic growth between muscles. Nevertheless, the amount of nerve to muscle contact was consistent, suggesting that pathological denervation can be reliably compared across different muscles in mouse models of neurodegeneration. Additionally, mature post-synaptic endplate diameters correlated with fibre type, independently of muscle fibre diameter. Altogether, this work provides detailed information on healthy pre- and post-synaptic NMJ morphology from five anatomically and functionally distinct mouse muscles, delivering useful reference data for future comparison with neuromuscular disease models.     

The Unc13A isoform is important for phasic release and olfactory memory formation at mushroom body synapses

Abstract

The cellular analysis of mushroom body (MB)-dependent memory forming processes is far advanced, whereas, the molecular and physiological understanding of their synaptic basis lags behind. Recent analysis of the Drosophila olfactory system showed that Unc13A, a member of the M(Unc13) release factor family, promotes a phasic, high release probability component, while Unc13B supports a slower tonic release component, reflecting their different nanoscopic positioning within individual active zones. We here use STED super-resolution microscopy of MB lobe synapses to show that Unc13A clusters closer to the active zone centre than Unc13B. Unc13A specifically supported phasic transmission and short-term plasticity of Kenyon cell:output neuron synapses, measured by combining electrophysiological recordings of output neurons with optogenetic stimulation. Knockdown of unc13A within Kenyon cells provoked drastic deficits of olfactory aversive short-term and anaesthesia-sensitive middle-term memory. Knockdown of unc13B provoked milder memory deficits. Thus, a low frequency domain transmission component is probably crucial for the proper representation of memory-associated activity patterns, consistent with sparse Kenyon cell activation during memory acquisition and retrieval. Notably, Unc13A/B ratios appeared highly diversified across MB lobes, leaving room for an interplay of activity components in memory encoding and retrieval.     

The irre Cell Recognition Module (IRM) Protein Kirre Is Required to Form the Reciprocal Synaptic Network of L4 Neurons in the Drosophila Lamina

Each neuropil module, or cartridge, in the fly's lamina has a fixed complement of cells. Of five types of monopolar cell interneurons, only L4 has collaterals that invade neighboring cartridges. In the proximal lamina, these collaterals form reciprocal synapses with both the L2 of their own cartridge and the L4 collateral branches from two other neighboring cartridges. During synaptogenesis, L4 collaterals strongly express the cell adhesion protein Kirre, a member of the irre cell recognition module (IRM) group of proteins (, J Neurogenet, 23, 48–67). The authors show by mutant analysis and gene knockdown techniques that L4 neurons develop their lamina collaterals in the absence of this cell adhesion protein. Using electron microscopy (EM), the authors demonstrate, however, that without Kirre protein these L4 collaterals selectively form fewer synapses. The collaterals of L4 neurons of various genotypes reconstructed from serial-section EM revealed that the number of postsynaptic sites was dramatically reduced in the absence of Kirre, almost eliminating any synaptic input to L4 neurons. A significant reduction of presynaptic sites was also detected in kirre⁰ mutants and gene knockdown flies using RNA interference. L4 neuron reciprocal synapses are thus almost eliminated. A presynaptic marker, Brp-short^GFP confirmed these data using confocal microscopy. This study reveals that removing Kirre protein specifically disrupts the functional L4 synaptic network in the Drosophila lamina.     

牛膝活性提取物对大鼠海马神经元生长的促进作用

目的:研究牛膝活性提取物(ABPPk)对体外培养的大鼠海马神经元生长的促进作用.方法:以体外原代培养的胎鼠海马神经元为模型,通过微管蛋白(β-tubulinⅢ)免疫荧光染色,采用Leica Qwin软件测量不同浓度ABPPk处理24 h对海马神经元突起延伸和突起分支的影响;通过突触结合蛋白(SYN)和突触后致密蛋白(PSD95)双标免疫荧光染色,采用LeicaQwin软件测量ABPPk(250 ng/ml)处理7d对海马神经元突触形成的影响;通过免疫印迹定量分析不同浓度ABPPk作用24 h对海马神经元生长相关蛋白(GAP-43)表达水平的影响,作用7d对PSD-95表达水平的影响,以及ABPPk(250 ng/ml)作用不同时间对磷酸化胞外信号调节激酶(ERK1/2)水平的调节.分析ABPPk对海马神经元的作用与ERK通路的关系.结果:ABPPk可有效促进海马神经元的突起延伸和突触形成,免疫印迹结果显示,ABPPk能显著增加海马神经元GAP-43和PSD-95蛋白表达,作用5 min即能显著上调ERK磷酸化水平,作用15 min ERK磷酸化水平达到峰值,PD98059可抑制该过程.结论:ABPPk能促进体外培养的海马神经元突起生长和突触形成,上调GAP-43和PSD-95蛋白水平,其作用可能与ERK通路的激活有关.     

Functional and Structural Development of Mouse Cone Photoreceptor Ribbon Synapses

PurposeCone photoreceptors of the retina use a sophisticated ribbon-containing synapse to convert light-dependent changes in membrane potential into release of synaptic vesicles (SVs). We aimed to study the functional and structural maturation of mouse cone photoreceptor ribbon synapses during postnatal development and to investigate the role of the synaptic ribbon in SV release.MethodsWe performed patch-clamp recordings from cone photoreceptors and their postsynaptic partners, the horizontal cells during postnatal retinal development to reveal the functional parameters of the synapses. To investigate the occurring structural changes, we applied immunocytochemistry and electron microscopy.ResultsWe found that immature cone photoreceptor terminals were smaller, they had fewer active zones (AZs) and AZ-anchored synaptic ribbons, and they produced a smaller Ca²⁺ current than mature photoreceptors. The number of postsynaptic horizontal cell contacts to synaptic terminals increased with age. However, tonic and spontaneous SV release at synaptic terminals stayed similar during postnatal development. Multiquantal SV release was present in all age groups, but mature synapses produced larger multiquantal events than immature ones. Remarkably, at single AZs, tonic SV release was attenuated during maturation and showed an inverse relationship with the appearance of anchored synaptic ribbons.ConclusionsOur developmental study suggests that the presence of synaptic ribbons at the AZs attenuates tonic SV release and amplifies multiquantal SV release. However, spontaneous SV release may not depend on the presence of synaptic ribbons or voltage-sensitive Ca²⁺ channels at the AZs.     

老年小鼠海马CA1区轴棘突触微细结构的定量分析

目的观察老年小鼠海马CA1区轴棘突触相关结构的改变,为衰老引起的学习记忆减退提供神经解剖学依据。方法利用Golgi染色、超薄连续切片及NIH图像分析系统测量海马CA1区锥体细胞树突棘的密度、树突棘头及突触后致密斑的大小。结果海马CA1第2、3级顶树突的树突棘密度在3月龄组与22月龄组分别为(1.056±0.049)/μm和(0.868±0.038)/μm;穿孔型突触的比率3月龄与22月龄组分别为12.7%和19%。结论老年小鼠海马CA1区锥体细胞树突棘的减少、穿孔型突触比率的增加可能是衰老引起学习记忆减退的形态学基础。     

发育中突触可塑性相关分子的研究进展

突触传递效能的各种变化称为突触可塑性,它是脑内信息存储的基础,同时也使繁杂的信息储存及学习行为、意识、记忆等功能的获得成为可能。参与突触可塑性形成及调节的主要机制包括活动（activity）依赖的兴奋性谷氨酸受体转运（trafficking）、钙离子／钙调蛋白依赖性蛋白激酶Ⅱ（CaMKⅡ）介导的信号转导以及存在于突触前/后膜的细胞黏附分子（CAMs）等。