الفهرس 
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Abstract
Skeletal muscles are formed of differentiated myofibers that have irreversibly left the cell cycle. The neuromuscular junction (NMJ) is the key functional unit that controls muscle contraction and consists of a specialized region along a muscle fiber. Injured peripheral nerves and skeletal muscles have a remarkable ability for regeneration. Thymoquinone (TQ) was found to have a myogenic and neurogenic activity.
The aim: To investigate the effect of TQ on skeletal muscle regeneration and innervation in the 7,12-dimethylbenz[a]anthracene (DMBA) - induced degeneration of the hamster buccal pouch (HBP).
Material and methods: Ninety male golden Syrian hamsters were divided into 3 groups. group A: 5 animals served as negative control; they were euthanized at day zero. group B: 5 animals served as positive control. The left buccal pouches were painted with DMBA 3/week/6weeks. They were euthanized at next day of last painting. group C: 80 animals were painted with DMBA as in group B, then were subdivided into two sub-groups as follow: group CI: 40 hamsters were given one TQ i.p. injection (0.1 mg/kg body weight). group CII: 40 hamsters were given two TQ i.p. injections (0.1 mg/kg body weight) day after day. Both subgroups were euthanized at 1, 2, 4, 7, 14, 20, 30 and 37 days after the last TQ injection.
All HBPs were surgically excised, fixed and processed for H&E, Pax-7 and neurofilament heavy chain (NFH) using immunohistochemistry (IHC) stain. Fresh specimens were processed for quantitative real time polymerase chain reaction technique (RT-qPCR) to detect the muscle specific tyrosine kinase (MuSK) gene. Data were analyzed statistically.
Results:
Marked shortening of left pouches’ length to near 2 cm after 6 weeks of DMBA application (group B) while the negative control left and right pouches were about 5-6 cm. After two TQ injections, the left pouches’ length elongated to about 5.3 cm. The group B revealed marked reduction of muscle layer’ bulk in histopathological results. Whereas at four and seven days after one and two TQ injection(s), the muscle layer bulk was progressively forming. At about twenty days after one and two TQ injection(s), the muscle layer’ bulk was near normal thickness. The mononuclear cells (MNCs) were around BVs from second and first day(s) to twenty and seven days after one and two injection(s), respectively. These cells were Pax-7 positive, as well the peripheral nuclei of MFs from four and two days to about twenty and fourteen days after one and two TQ injection(s), respectively. The intensity of NFH IHC stain was progressively increasing after TQ injection(s) in all experimental groups as MFs membranes’ plaques. The RT-qPCR results of relative MuSK expression revealed downregulation in the DMBA-treated group, and after TQ injection(s) its expression slightly increased during MFs proliferation. Its expression was statistically elevated with the differentiation and fusion of MFs.
Conclusion: TQ is a strong anti-inflammatory phytochemical. In the present route of administration and very low concentration, had resulted in reduced inflammation as revealed from expulsion of the inflammatory cells from epithelium. Moreover, TQ could induce regeneration and reinnervation of skeletal muscles in the shortened pouches, as revealed from the elongation of their length, increased intensity of IHC stain of NFH and the increased expression of MuSK in all experimental groups. Its myogenic effect could be through
1. The mesenchymal stem cells that was differentiated to myogenic lineage, reflected by their Pax-7 positivity.
2. Fibroblasts of lamina propria and lipoblasts at distal end (FAPs) stimulation, could be differentiated to myogenic lineage. Both stem cells were Pax-7 positive.
Key words: Oral epithelial dysplasia (OED), 7,12-dimethylbenz[a]anthracene (DMBA), Syrian golden hamsters, Thymoquinone (TQ), Muscle regeneration, Neuromuscular junction (NMJ), Pax-7, Neurofilament heavy chain (NFH) and Muscle specific tyrosine kinase (MuSK).