Affiliations: Department of Anatomy, Chung-Shan Medical & Dental
College, Taichung, Taiwan | Department of Biology and Anatomy, National Defense
Medical Center, Taipei, Taiwan | Department of Anatomy, Faculty of Medicine, National
University of Singapore, Singapore
Note: [] Corresponding author: Dr. Chyn-Tair Lan, Department of Anatomy,
Chung-Shan Medical & Dental College, No. 110, Sec. 1, Chien Kuo North Road,
Taichung, Taiwan. Fax: +886 4 4739030.
Abstract: Purpose: To investigate the relationships between the axonal
sprouting and target neurotization by central neurons after nerve
heterocon-nection. Methods: Unilateral (right) vagal-hypoglossal nerve
anastomosis (VHA) was performed in adult cats. Following 3315 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 727 µm 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 (727 µm 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.
