Satellite Cells and Neuromuscular Spindles in Long Term Denervated Skeletal Muscles

Satellite cells (SC) are quiescent cell located between the sarcolemma and basal lamina of the skeletal muscle fibers. The SC can get activated contributing to regeneration and/or growth of muscle. The neuromuscular spindles are mechanoreceptors located within the skeletal muscle and are considered as contractile regulatory unit. It is composed of intrafusal muscle fibers (IF), surrounded by a sheath and is parallel to extrafusal fibers. Denervation cause changes in skeletal muscles both in the SC and neuromuscular spindles. This study analyzed quantitatively the IF and SC in Wistar rats denervated for long period. The animals were divided into normal and denervated groups. The soleus and extensor longus digitorum longus were denervated experimentally during periods of 0, 12, 16, 19, 30 and 38 weeks. The percentage of SC immediately after denervation increases when compared to normal group and later decreases in both the groups. During the process of denervation, there was an increase in IF when compared with normal group. The percentage of SC reduces significantly between the periods of denervation in both the groups. The smaller percentage of SC corresponds to higher number of IF. Besides that the number of SC decreases after denervation. As for IF, with the increase in time in normal group, the number of fibers was unaltered. However, in the experimental group, with increase in the time of denervation, the percentage of SC decreases while there is increase in the number of IF significantly. In denervated muscles for long period, there is decrease in the percentage of SC and increase in IF. Our results suggest that the period between 16th and 19th week post denervation is the best time for reinnervation of denervated muscle.

Pax7 is expressed in the capsules surrounding adult mouse neuromuscular spindles

The multigene Pax family of transcription factors plays an important role in the development of the central nervous system as well as in organ morphogenesis. Expression of one of the members of the family, Pax7, has been described in embryonic muscle and in both embryonic and adult brain. We recently detected Pax7 transcripts in RNA isolated from adult mouse skeletal muscle and brain and here use in situ hybridisation to localise the expression within these tissues. Pax7 expression was observed in neural cells of the brain and in cells of neural crest origin in the inner and outer capsules of neuromuscular spindles. The results suggest that Pax7 may be implicated in the formation and maintenance of neuromuscular contacts within the muscle spindle throughout life.Key words: Pax7 expression, skeletal muscle, neuromuscular spindle, basal lamina, Schwann cells.