Sequential effect of nerve transection and regeneration on motoneuron (MN) and muscle fiber (MF) was examined in the present study, using an HRP method. The morphological changes of the hypoglossal MN and logitudinal tongue MF, after transection or excision of the right hypoglossal nerve in the Horse musk shrew (Suncus murinus) was observed. In the transection group, reinnervation to the muscle started about 1 week and finished about 10 weeks after surgery, and both MN and MF were considered to be regenerating since 4 weeks postoperatively. In the excision group, reinnervation hardly occurred and all of the experimental results showed degenerative tendencies. Though decrease of MN number in 2-4 weeks after excision indicated rapid deterioration of regenerative capacity of MN which lost its target, decrease of MF number appeared since 15 weeks post operatively. This matter suggested a possibility of muscle regeneration by the surgical technique (e. g. nerve anastomosis) even if muscle atrophy progresses after a long time of nerve injury.
