Introducing a mammalian nerve-muscle preparation ideal for physiology and microscopy, the transverse auricular muscle in the ear of the mouse

Abstract

A new mammalian neuromuscular preparation is introduced for physiology and microscopy of all sorts: the intrinsic muscle of the mouse ear. The great utility of this preparation is demonstrated by illustrating how it has permitted us to develop a wholly new technique for staining muscle T-tubules, the critical conductive-elements in muscle. This involves sequential immersion in dilute solutions of osmium and ferrocyanide, then tannic acid, and then uranyl acetate, all of which totally blackens the T-tubules but leaves the muscle pale, thereby revealing that the T-tubules in mouse ear-muscles become severely distorted in several pathological conditions. These include certain mouse-models of muscular dystrophy (specifically, dysferlin-mutations), certain mutations of muscle cytoskeletal proteins (specifically, beta-tubulin mutations), and also in denervation-fibrillation, as observed in mouse ears maintained with in vitro tissue-culture conditions. These observations permit us to generate the hypothesis that T-tubules are the “Achilles' heel” in several adult-onset muscular dystrophies, due to their unique susceptibility to damage via muscle lattice-dislocations. These new observations strongly encourage further in-depth studies of ear-muscle architecture, in the many available mouse-models of various devastating human muscle-diseases. Finally, we demonstrate that the delicate and defined physical characteristics of this 'new' mammalian muscle are ideal for ultrastructural study, and thereby facilitate the imaging of synaptic vesicle membrane recycling in mammalian neuromuscular junctions, a topic that is critical to myasthenia gravis and related diseases, but which has, until now, completely eluded electron microscopic analysis. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.