Molecular architecture of the neuromuscular junction

Abstract

The neuromuscular junction (NMJ) is a complex structure that serves to efficiently communicate the electrical impulse from the motor neuron to the skeletal muscle to signal contraction. Over the last 200 years, technological advances in microscopy allowed visualization of the existence of a gap between the motor neuron and skeletal muscle that necessitated the existence of a messenger, which proved to be acetylcholine. Ultrastructural analysis identified vesicles in the presynaptic nerve terminal, which provided a beautiful structural correlate for the quantal nature of neuromuscular transmission, and the imaging of synaptic folds on the muscle surface demonstrated that specializations of the underlying protein scaffold were required. Molecular analysis in the last 20 years has confirmed the preferential expression of synaptic proteins, which is guided by a precise developmental program and maintained by signals from nerve. Although often overlooked, the Schwann cell that caps the NMJ and the basal lamina is proving to be critical in maintenance of the junction. Genetic and autoimmune disorders are known that compromise neuromuscular transmission and provide further insights into the complexities of NMJ function as well as the subtle differences that exist among NMJ that may underlie the differential susceptibility of muscle groups to neuromuscular transmission diseases. In this review we summarize the synaptic physiology, architecture, and variations in synaptic structure among muscle types. The important roles of specific signaling pathways involved in NMJ development and acetylcholine receptor (AChR) clustering are reviewed. Finally, genetic and autoimmune disorders and their effects on NMJ architecture and neuromuscular transmission are examined.

Identity, developmental restriction and reactivity of extralaminar cells capping mammalian neuromuscular junctions

“…Nevertheless, the parallels are striking: like 'perisynaptic fibroblasts' the capping cells proliferate in response to denervation; they are fibroblast-like; and they appear to change their gene expression in response to nerve injury. It is therefore rather surprising that reviewers have been reluctant to depict these cell types as essential components of the NMJ (Sanes and Lichtman, 1999;Hughes et al, 2006).…”

“…that constitute the vertebrate neuromuscular junction (Sanes and Lichtman, 1999;Hughes et al, 2006).…”

Genetic heterogeneity and pathophysiological mechanisms in congenital myasthenic syndromes

“…The postsynaptic muscle membrane, also called endplate has a multitude of folds, which contains several acetylcholine receptor clusters on its surface. 1 Depolarisation at the nerve terminal opens the presynaptic voltage-gated calcium (Ca ++ ) channels allowing influx of Ca ++ into the presynaptic nerve bud, which triggers release of multiple vesicles (quanta) of acetylcholine by exocytosis. Acetylcholine diffuses across the synaptic space and binds to the acetylcholine receptors.…”

Antibothropic Action of Camellia sinensis Extract Against the Neuromuscular Blockade by Bothrops jararacussu Snake Venom and Its Main Toxin, Bothropstoxin-I

“…Besides, the use of snake venom and toxins as tools to study neuromuscular blockade in vitro (Gallacci & Cavalcante, 2010) is very useful given the excitation-contraction coupling process starts with transmission of electrical impulses from nerves towards muscle fibers via release of acetylcholine (ACh) (Hughes et al, 2006).…”