在迷走－舌下神經雜接後，本研究以山葵過氧化氫脢之逆向標誌技術來追蹤此雜接神經的細胞源頭---疑核與迷走神經背側運動核的時序性神經元再生情形，並觀察其雜接神經近心端的超微構造變化以及軸突出芽現象。本研究的最重大發現是：神經元再生的時序性變化完全吻合軸突出芽與回縮的過程，而且因為改換了新目標器官---舌頭的緣故，雜接神經及其細胞源頭均顯現了高度重塑性。疑核神經元的樹突有顯著的出芽現象，而其發出的有髓鞘軸突也展現了最佳的神經再生，此應與新目標器官的合適性有關，因為疑核類似舌下神經核，兩者原先都是支配骨骼肌的。迷走神經背側運動核原先支配的是內臟平滑肌，因此與新目標器官較不相容，導致神經元以及無髓鞘軸突有神經再生不良現象。
Purpose: To investigate the relationships between the axonal sprouting and target neurotization by central neurons after nerve heteroconnection. Methods: Unilateral (right) vagal-hypoglossal nerve anastomosis (VHA) was performed in adult cats. Following 3-315 days postoperation (dpo), quantitative analyses and ultrastructural changes in the proximal portion of the vagal-hypoglossal heteroconnected nerve as well as the time course of neuronal regeneration were studied. Along with this, horseradish peroxidase (HRP) retrograde tracing technique was used to label the neurons of dorsal motor vagal nucleus (DMV) and nucleus ambiguus (NA) to ascertain if target neurotization was established. Results: The contralateral (left) intact vagus nerve proximal to the level of ansa cervicalis showed an average of 33±1 myelinated and 74±4 unmyelinated axons in 727μm/sup 2/ sectional area of the nerve. In the heteroconnected nerve at the corresponding level just proximal to the anastomosis site, there was a marked increase in the number of small axons sprouting from the unmyelinated nerve fibers between 18 and 25 dpo. The number of these axonal sprouts appeared to decline at 32 dpo but its increase of 131% was sustained until the late regeneration stage at 315 dpo when compared with the contralateral nerve serving as a control. The mean number of myelinated axons per area unit (727μm/sup 2/) was reduced to 18 at 3 dpo but was immediately restored to the normal range at 7 dpo. The retrograde labelling of neurons in both the DMV and NA was first detected at 22 dpo and was progressively increased peaking by about 67 dpo. Conclusions: We conclude that compared with the unmyelinated axons, the myelinated axons may acquire a superior interaction with the new target. Furthermore, the postoperative neurotization of tongue muscles may initiate and facilitate the retraction of the redundant axonal sprouts.
