内喉頭筋運動ニューロンの再支配について

Abstract

Reinnervation and subsequent paradoxical movements of the motor nerve after injury is well known in the facial nerve, ocular nerve, peroneal nerve, etc. as well as the recurrent laryngeal nerve (RLN). Way of the experimental injury to the RLN at a level below 15 mm from the lower margin of the cricoid cartilage was accomplished two different methods : one to be neurorrhaphy under microscope after transection of the nerve and the other to be freezing by ophthalmological forceps at a temperature below 80 degrees for five minutes. This latter procedure allows the Schwann sheathe and perineurium to remain intact but damages the endoneurium. Movements of the pathological vocal fold were observed macroscopically and monitored regularly by electromyogram (EMG) from one week to nine months. Redistribution of the motoneuron originating from regrowth of the nerve fiber around the injured RLN was histologically verified by horseradish peroxidase (HRP) at the time of the EMG monitorings. The target muscles for observatory analyses were determined to be the posterior cricoarytenoid muscle (PCA) and thyroarytenoid muscle (TA). Monitoring of these muscles between the adductor and abductor is essential in order to assess the paradoxical movement after regrowth of nerve fibers. It was suggested that following transection of the nerve sprouting began three months later than it did in the group that underwent freezing injury two weeks after trial when the distribution rate was calculated in the nucleus ambiguus of the medulla oblongata. Furthermore, the numbers of sprouting fibers increased at one point beyond the normal level (in our study) of 90 six months after injury and gradually normalized in both groups at the 9 months. The rate of excessive growth in the first transected group was superior to the second freezing group. This result suggests that the rate of paradoxical movement following misdirected reinnervation is greater in the transected group than in the freezing group. This was verified by monitoring of the EMG. In both groups, HRP stained target neuron cells affecting the PCA muscle were observed in the localized control dorsoventral area at the more cephalad site. However, aberrant motoneurons also appeared out of the normal area and in the caudal and ventral regions (TA motoneuron). This also suggests paradoxical movement after reinnervation of nontarget organs.