[Facial motoneurons death and caspase regulatory gene expression following facial nerve injury].

PURPOSE:To investigate the morphology of facial motoneurons and its death course as well as caspase 3, caspase 8, cyto-c death proteins' expression and their correlation following facial nerve distal transection or crush in rats. METHODS:The right facial nerve underwent distal transaction and crush as experimental group, while the left facial nerve acted as normal control. We observed the morphology and the death course of motoneurons by light microscope and transmission electron microscope. Expressions of caspase 3, 8, and cyto-c protein were studied by immunohistochemistry (S-P) and image analysis. SPSS 10.0 software package was used for statistical analysis. RESULTS:(1) Both axon distal transection and axon crush resulted in death of facial motoneurons. The motoneurons' loss reached peak 28 days after injuries and were mainly through apoptotic pathway. The number of motoneurons' loss in the distal transection group were more than that in the crush group. (2) Caspase 3, caspase 8 and cyto-c protein expressions were observed in wide spread areas of normal rat facial nucleus. In addition to neurons, glial cells were also stained. Cells of the distal transection group stained more strongly than that of crush group. Expressions of the proteins began to increase 3 days after the injuries. Caspase 3 and caspase 8 protein expression reached peak 14 days whereas cyto-c protein expression reached peak 7 days after the injuries. Expression of caspase 8 and cytoc protein were correlated with expression of caspase 3 protein. CONCLUSIONS:(1)Different facial nerve injuries result in death of facial motoneurons. The loss of motoneurons is related with the injuries' patterns. Clinical nerve reparation should be performed as early as possible within 4 weeks after the transection. (2)The expression of caspase 3, 8 and cyto-c protein were related with facial nerve injuries' patterns. Caspase 8 and cyto-c protein expressions were correlated with caspase 3 protein expression, indicating that caspase 8 and cyto-c may take part in activating caspase 3. Caspase cascade reaction may have an important role in the apoptosis of facial motoneurons.