This study was conducted in order to investigate the relationship between wound healing of skin and their surrounding nerves and how this relationship is reciprocal. Wounds were made on embryos at different stages of development and some embryos studied had no nerves in the area of the wound site. Other studies have suggested that the rate of wound healing is dependent on nerves and that the wound sites become hyperinnervated by sensory nerves during healing. On the other hand, the authors want to confirm that wound healing does not trigger hyperinnervation in the embryo as it does in adults. Fertilized White Leghorn chicken eggs were used and incubated until they reached the embryonic stage 4 (E 4) and / or E 7. Chick embryos are a good choice because wound healing can occur without scarring or inflammation, which could have an effect on the results.
The wing bud was chosen as the site of incision because it is easily accessible for microsurgery and because the nerve pattern in the wing bud is known. The wounds were created by dissecting the wings using an electrolytically sharpened tungsten needle. The surrounding nerves were stained at the incision sites in order to allow the nerve branch points to be seen and counted. Some embryos were made nerveless in order to study any effect this may have on the wound. The embryos chosen to be nerveless were exposed to UV radiation at the E 2 stage.
The amniotic membranes were torn to expose the somites and neural tube. Once exposed, they were irradiated for 10 minutes in order to damage their wing level neural tube resulting in the arrest of nerve formation in that area. The process of healing was documented by using a scanning electron microscope and also by a camera attached to a dissecting microscope. This equipment was both necessary and efficient for observation at such microscopic levels. There are 4 cutaneous nerve branches [Dorsal Cutaneous (DC Elbow), DC Alar, DC Interosseous and DC Ulnar] that innervate the limb bud and that subsequently branch to the wing. The authors made incisions at two important stages, E 4 and E 7, just before and just after the nerves have reached the skin.
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These stages were chosen for the following reasons: 1) No damage would occur to the nerves at the E 4 stage allowing investigators to observe whether the wound would have an effect on nerve formation and 2) The nerves at E 7 would be damaged and this would allow observation of the effect of nerves on the healing process. Both stages were observed at the E 10 stage. The results revealed that 65% of the chicks wounded at E 4 had normal innervation and 35% had 1 or 2 major branches missing. The most common missing nerve branch was DC Interosseous.
Although this nerve was missing, other branches from other nerves grew along the DC Interosseous pathway leading to normal innervation of the wound site. This suggests that although the nerve pathway was diverted, there was no effect on the healing process or the innervation of the wound site. The wounds made at E 7 were examined next and the authors found that 94% had normal branches with none missing in spite of the damage caused to them. However, 72% of these had some type of disruption to their pathway or pattern. With these findings, it was evident that fetal wound healing occurs with normal innervation and with no evidence of hyperinnervation. In order to confirm their findings, some of the embryos were left to develop to the E 14 stage.
As predicted, these wounds were also not hyperinnervated. Next, the chick embryos rendered nerveless were examined. These chicks had a defect at the level of the limb bud and cutaneous innervation was absent. Their wings, however, appeared to be normal in all other aspects. The wounds made to these nerveless wings at E 4 had healed regardless. This important finding suggests that wound healing can occur even in the absence of nerves.
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... is an often-overlooked requirement for normal wound healing. Vitamin and mineral deficiencies also require ... factors have a modestly beneficial effect in promoting wound healing. Other topical agents that have ... of maceration. It is at this stage that the characteristic signs of ... tissue surrounding muscles, blood vessels and nerves) regional lymphadenopathy Fever, chills, malaise, leukocytosis, ...
This confirmed that nerves do not have an effect on the healing process at this stage of development. Those wounded at E 7 resulted in slower healing. This suggests that the nerves serve as signal transmitters that signal for repair and that these signals have specific timing. In conclusion, these experiments helped to show that nerves have guidance cues / signals that function up to a certain time and cease by stage E 7.
This supports the authors’ belief that nerves are beneficial to wound healing and have a positive effect after the E 7 stage. Conversely, wounds are found to have an effect on the nerves by disrupting the signals that are responsible for normal pattern of nerve branching. This study is significant because it gives a better understanding of how wounds can heal through the help of the surrounding nerves and gives insight to the timing that is necessary for these nerves to function properly. This information is an important contribution to embryology because it is further proof that the developing embryo is a place for new discovery that can be very beneficial to the medical field. These experiments help to give and insight to the importance of the specific timing involved in the development of nerves and further studies can be conducted with this in mind. Researchers studying ways to speed up the rate of wound healing may benefit from this study and perhaps these results can help advance research for those who suffer from Diabetes and the effects of slow wound healing..
