Diffuse neuronal perikaryon amyloid precursor protein immunoreactivity in a focal head impact model.

Amyloid precursor protein (APP) has been shown to accumulate in traumatically injured axons as early as 1 hour after injury. This accumulation may be due to interruption of fast axoplasmic transport and/or upregulation of APP synthesis. The aim of this study was to examine the neuronal cell body response to head impact using APP immunostaining in a focal non-missile head impact model. Ten anaesthetised and ventilated 2 year old Merino ewes were subjected to graded impact in the left temporal region by captive bolt. 2 hours after impact the brain was perfused fixed with formaldehyde. The tissue was mounted in paraffin, sectioned and stained with a monoclonal antibody to APP and standard H&E stain. APP positivity was semi-quantitated using a modification of our previously described sector scoring system [1]. Widespread neuronal APP positivity was found in the cerebral hemispheres and brain stem distant from the site of focal injury in all 10 animals. The most prominent APP positivity was found in the nerve cell bodies of the impacted left cerebral hemisphere. APP positive neurons were also found within regions which were structurally normal when stained with H&E. These results demonstrate diffuse neuronal perikaryon APP immunoreactivity following a focal head impact injury. The expression of APP within the neuronal cell body may be due to upregulation of APP synthesis or alterations in the availability of epitopes of APP. Further studies are in progress to address these hypotheses.