BACKGROUND: Previous studies have demonstrated that postsynaptic density protein-95 (PSD-95) is widely distributed in the central nervous system and is related to the development of the CNS and sensory signal transmission as well as acute or chronic nerve cell death following ischemic brain injury. OBJECTIVE: To semi-quantitatively determine the pathological changes of apoptotic facial neurons and the expression of PSD-95 in the facial nucleus following facial nerve injury of varying extents using immu- nohistochemical staining methods. DESIGN, TIME AND SETTING: Randomized, controlled animal experiments were performed in the Ul- trasonic Institute of the Second Affiliated Hospital of Chongqing University of Medical Sciences from Sep- tember to December 2007. MATERIALS: Sixty-five healthy, adult, Sprague-Dawley (SD) rats, both male and female, were used for this study. Rabbit anti-rat PSD-95 polyclonal antibody was purchased from Beijing Biosynthesis Biotech- nology Co., Ltd. METHODS: SD rats were randomly assigned into a control group with five rats and three injured groups with 20 rats per group. Exposure, clamp and cut for bilateral facial nerve trunks were performed in the rats of the injury groups, and no injury was inflicted on the rats of the control group. MAIN OUTCOME MEASURES: The brainstems of all the rats were excised on days 1, 3, 7, and 14 post injury, and then the facial nuclei were stained with hematoxylin-eosin to observe any pathological changes due to apoptosis in facial neurons. PSD-95 expression in facial nuclei was detected by immunohistochemistry and the number of PSD-95 positive cells was counted under a light microscope. RESULTS: The expression of PSD-95 in the facial nucleus and morphology of the facial neuron within the exposure group had no obvious changes at various points in time tested (P > 0.05). However, the expressions of PSD-95 in the facial nucleus of the clamp group and cut group increased on day 1 post injury (P < 0.05), and showed further increase on day 7 post injury (P < 0.01). This did not decrease until day 14 post injury. Facial neuron apoptosis was detected on day 3 post injury and this was even more obvious on day 7 and was maintained to day 14 post injury. The number of cells expressing PSD-95 and displaying severe degrees of facial neuron apoptosis were as follows: cut group > clamp group > exposure group. CONCLUSION: The apoptotic extent of facial neurons and the expression of PSD-95 in apoptotic facial neurons increased with the degree of aggravation of injured severity of facial nerve. BACKGROUND: Previous studies have demonstrated that postsynaptic density protein-95 (PSD-95) is widely distributed in the central nervous system and is related to the development of the CNS and sensory signal transmission as well as acute or chronic nerve cell death following ischemic brain injury. OBJECTIVE: To semi-quantitatively determine the pathological changes of apoptotic facial neurons and the expression of PSD-95 in the facial nucleus following facial nerve injury of varying extents using immu- nohistochemical staining methods. DESIGN, TIME AND SETTING: Randomized, controlled animal experiments were performed in the Ultrasonic Institute of the Second Affiliated Hospital of Chongqing University of Medical Sciences from Septem to December 2007. MATERIALS: Sixty-five healthy, adult, Sprague-Dawley (SD) rats, both male and female , used for this study. Rabbit anti-rat PSD-95 polyclonal antibody was purchased from Beijing Biosynthesis Biotechnology Co., Ltd. METHODS: S D rats were randomly assigned to a control group with five rats and three injured groups with 20 rats per group. Exposure, clamp and cut for bilateral facial nerve trunks were performed in the rats of the injury groups, and no injury was inflicted on the rats of the control group. The MAIN OUTCOME MEASURES: The brainstems of all the rats were excised on days 1, 3, 7, and 14 post injury, and then the facial nuclei were stained with hematoxylin-eosin to observe any pathological changes due to apoptosis in facial neurons. PSD-95 expression in facial nuclei was detected by immunohistochemistry and the number of PSD-95 positive cells was counted under a light microscope. Exposure groups had no obvious changes at various points in time tested (P> 0.05). However, the expressions of PSD-95 in the facial nucleus of the clamp group and cut group increased on day 1 post injury (P <0.05), and showThis further increase on day 7 post injury (P <0.01). This did not decrease until day 14 post injury. Facial neuron apoptosis was detected on day 3 post injury and this was even more obvious on day 7 and was maintained to day 14 post The number of cells expressing PSD-95 and displaying severe degrees of facial neuron apoptosis were as follows: cut group> clamp group> exposure group. CONCLUSION: The apoptotic extent of facial neurons and the expression of PSD-95 in apoptotic facial neurons increased with the degree of aggravation of injured severity of facial nerve.