Differentiation of activated satellite cells in denervated muscle following single fusions in situ and in cell culture

Satellite cells represent a cellular source of regeneration in adult skeletal muscle. It remains unclear why a large pool of stem myoblasts in denervated muscle does not compensate for the loss of muscle mass during post-denervation atrophy. In this study, we present evidence that satellite cells in long-term denervated rat muscle are able to activate synthesis of contractile proteins after single fusions in situ. This process of early differentiation leads to formation of abnormally diminutive myotubes. The localization of such dwarf myotubes beneath the intact basal lamina on the surface of differentiated muscle fibers shows that they form by fusion of neighboring satellites or by the progeny of a single satellite cell following one or two mitotic divisions. We demonstrated single fusions of myoblasts using electron microscopy, immunocytochemical labeling and high resolution confocal digital imaging. Sequestration of nascent myotubes by the rapidly forming basal laminae creates a barrier that limits further fusions. The recruitment of satellite cells in the formation of new muscle fibers results in a progressive decrease in their local densities, spatial separation and ultimate exhaustion of the myogenic cell pool. To determine whether the accumulation of aberrant dwarf myotubes is explained by the intrinsic decline of myogenic properties of satellite cells, or depends on their spatial separation and the environment in the tissue, we studied the fusion of myoblasts isolated from normal and denervated muscle in cell culture. The experiments with a culture system demonstrated that the capacity of myoblasts to synthesize contractile proteins without serial fusions depended on cell density and the availability of partners for fusion. Satellite cells isolated from denervated muscle and plated at fusion-permissive densities progressed through the myogenic program and actively formed myotubes, which shows that their myogenic potential is not considerably impaired. The results of this study suggest that under conditions of denervation, progressive spatial separation and confinement of many satellite cells within the endomysial tubes of atrophic muscle fibers and progressive interstitial fibrosis are the important factors that prevent their normal differentiation. Our findings also provide an explanation of why denervated muscle partially and temporarily is able to restore its functional capacity following injury and regeneration: the release of satellite cells from their sublaminal location provides the necessary space for a more active regenerative process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47397/1/418_2005_Article_12.pd

The relationship of the lingual nerve to the third molar region using radiographic imaging

Objective Lingual nerve damage is a common complication during oral and maxillofacial surgery procedures to the third molar region. The anatomy of the lingual nerve is variable, therefore the precise knowledge of anatomy of this nerve is important for decreasing the damage risk. The purpose of this study was to determine the position and the shape of the lingual nerve in the third molar region using radiographic imaging. Setting The Anatomy Department of Cologne University in Germany. Materials and Methods Firstly, an anatomic dissection of the lingual nerve in the third molar region was done on 10 whole heads and one sagittal hemisection head specimen of adult cadavers. After marking the nerve, x-ray films were taken. Vertical and horizontal measurements were made from the radiographs with an electronic digital caliper. Results The mean vertical and horizontal distances of the nerve to the lingual crista and lingual plate of the mandible were found to be 9.5 +/- 5.2 mm and 4.1 +/- 1.9 mm respectively. Additionally, of the 21 lingual nerves examined, 17 (81%) were round and 4 (19%) were flat. Conclusions The results reflect the relationship of the nerve to this area and may help the clinician to avoid the damage risk