Altered prosaposin expression in the rat facial nerve nucleus following facial nerve transection and repair

BACKGROUND: Studies have demonstrated that damaged facial nerves synthesize prosaposin to promote repair of facial neurons. OBJECTIVE: To observe time-course changes of prosaposin expression in the facial nerve nucleus of Sprague Dawley rats following facial nerve transection and repair. DESIGN, TIME AND SETTING: A randomized control neuropathological animal experiment was performed in Chongqing Medical University between March 2007 and September 2008. MATERIALS: A total of 48 adult, male, Sprague Dawley rats were selected and randomly divided into transection and transection + end-to-end anastomosis groups (n =24). Rabbit anti-rat prosaposin antibody, instant SABC immunohistochemical kit, and antibody dilution solution were purchased from Wuhan Uscn Science Co., Ltd., China. METHODS: In the transection group, the nerve trunk of the distal retroauricular branch of the left facial nerves was ligated in Sprague Dawley rats, and a 5-mm nerve trunk at the distal end of the ligation site was removed. In the transection + end-to-end anastomosis group, epineurial anastomosis was performed immediately following transection of the left facial nerves. The right facial nerves in the two groups served as the normal control group. MAIN OUTCOME MEASURES: The number of prosaposin-positive neurons, as well as intensity of immunostaining in facial nerve nucleus, following transection and end-to-end anastomosis were determined by immunohistochemistry at 1, 3, 7, 14, 21, and 35 days after injury. RESULTS: Transection group: transection of facial nerves resulted in increased number of prosaposin-positive neurons and immunoreactivity intensity in the facial nucleus on day 1. These values significantly increased by day 3. Expression was greater than in the control side. The peak of the reduction was reached at 7 days post-surgery. Transection + end-to-end anastomosis group: the number of prosaposin-positive neurons and immunoreactivity intensity was reduced in the facial nerve nucleus following immediate end-to-end anastomosis on day 7 post-surgery. These values began to gradually increase by day 14 post-anastomosis. By day 35 post-anastomosis, the number of prosaposin-positive neurons in the operated side recovered to normal levels. The number of prosaposin-positive neurons, as well as immunoreactivity intensity, was significantly greater in the facial nerve nucleus, compared with the transection group on days 14, 21, and 35 post-surgery (P < 0.05). The rhythmic whisking of vibrissa recovered, and recovery time was consistent with increased numbers of prosaposin-positive neurons. CONCLUSION: Within 7 days after injury, prosaposin expression in the facial nerve nucleus exhibited an initial increase, followed by a decrease, and was not affected by facial nerve repair. Following facial nerve damage, neural anastomosis was shown to increase prosaposin expression in the facial nerve nucleus after 14 days. Recovery of prosaposin occurred simultaneously with reinnervation.