The Complete Regeneration Of Nerve And Muscle During Lower Jaw Regeneration In Adult Zebra Fish, Danio Rerio

The aim of the current study was to determine whether the nerves and muscles can completely regenerate after cutting the lower jaw in the adult zebra fish, Danio rerio. When the lower jaw was removed about distal one-third, we found the number of muscles in regenerated lower jaw and nerves supplying these regenerated muscles by HE staining, Sudan Black B nerve staining and anatomy technology. Five muscles are arranged from dorsal view to ventral view in the regenerated jaw: a paired symmetric PR-H-D, an INTM-A and a paired symmetric PR-H-V. INTM-A is innervated by distal branches of trigeminal nerves. PR-H-D and PR-H-V is innervated by distal branches of trigeminal nerves and the marginal mandible branch of facial nerves, respectively. Our results indicate that there are five muscles and two nerves in the regenerated lower jaw. In addition, acetylcholine receptors arrange in circles on the surface membrance of muscle fibers, and orientation of muscle fibers is parallel to the nerve fiber terminals innervating them.In order to investigate the nerves and muscles in regenerated lower jaw muscle of the adult zebra fish, Danio rerio, we analyzed the nerves and muscles during zebra fish lower jaw regeneration by immunohistochemistry. After the distal one-third of the lower jaw was amputated, both of the muscles and nerve fibres degenerated rapidly. The nerve fibres began to extend over the cut surface by 2 days-post-amputation(dpa), reaching the tissue degenerated prior to the blastema formation. And the nerve fibres increased significantly at 5 dpa when the blastema formed. The new muscle fibres without neuromuscular junctions arose at 9 dpa. The neuromuscular junctions began to form at approximately 14 dpa. By 30 dpa, the pattern of muscle fibres and neuromuscular junctions recovered to the control level. Our results show that nerve fibers occur earlier than blatema, which imply that nerves may play important roles on the formation of blastema. In addition, nerves always exist during the muscle precursor cells developing into mature muscle fibers, and it indicates that nerves maybe influence muscle regeneration. We observed the recovery of the regeneration muscles. The results showed that the arrangement direction of nerve fibers was parallel to lower jaw plane and perpendicular or parallel to the body axis, which was similar to normal lower jaw. Acetylcholine receptors arranged in circles on the surface membrance of muscle fibers, which was consistent to the normal lower jaw. The mass of neuromuscular junction also recoved. Five muscles were found from dorsal view to ventral view in the regenerated jaw: a paired symmetric PR-H-D, a INTM-A, a paired symmetric PR-H-V, and the orientation of muscle fibers was parallel to the nerve fiber terminals innervate them. We conclude that nerves and muscles can regenerate after the distal one-third of the lower jaw is amputated.To further demonstrate the condition of the complete regeneration of nerve and muscle, we investigated the regenerated process of nerves and muscles after the distal one-third and beyond the distal one-third of the lower jaw was removed, respectively. When beyond the distal one-third of the lower jaw was removed, the regenerated nerve fibers elongate and become diminution. The arrangement direction of regenerated nerve fibre is parallel to the lower jaw plane but neither perpendicular nor parallel to the body axis. Acetylcholine receptor becomes thinner and diminution, and their outline vague. The orientation of regenerated muscle fibers was parallel to the direction of regenerated nerve fibers. Thus, we conclude that the nerve fibers appear unable to restore normal direction, instead occur abnormal and inaccuracies positioning, when more than distal one-third of lower jaw is removed. Acetylcholine receptors and muscle fibers’ orientation also show abnormality. However, we found abnormal orientation of regenerated muscle fibers aligned parallel to the direction of the nerve fibers innervating them. We speculated that cutting more than one third of the lower jaw cause serious damage to the nerve fibers, resulting innerve fibers positioning in accurate, as a result, orientation of acetylcholine receptors and muscle fibers are abnormal. The results mostly imply that nerves may play important roles on rebuilding morphology and function of regenerated muscles.The relationship between nerves and muscles can reveal parts of the mechanism of muscle regeneration, providing a theoretical basis for the regenerative treatment of muscle diseases. Meanwhile, there are a large number of studies about limbs regeneration which can happen at any extent shear. But the regenerative capacity of the lower jaw,which differs from the limbs’ is limited. The lower jaw can regenerate only when less than one third of the lower jaw have been removed. The destination to learn the relationship between nerves and muscles in regenerated lower jaw muscle of the adult zebra fish is that it will help us to further uncover the mechanism why different organizations have different regenerative capacity. As a result, it can offer us more worth-while information on ascertaining the regeneration mystery and regeneration treatment of various diseases to promote the rapid development of regenerative medicine.