Immunohistochemical Detection of Axonal Injury in Chimpanzee (Pan troglodytes) with Traumatic and Fatal Brain Injury

Estimating the time of death after traumatic brain injury (TBI) in wildlife is a significant challenge in forensic veterinary medicine. The understanding of histopathological changes and predicting the survival time can prompt critical emergency measures and health management strategies for animals in managed care. Glial fibrillary acidic protein (GFAP) is a well-established astrocytic biomarker for diagnosing, monitoring, and predicting TBI outcomes. Moreover, the buildup of Beta-Amyloid Precursor Protein (βAPP) resulting from axonal damage is an energetic process intricately connected to the survival period following the injury. To date, no study has explored the accumulation of GFAP and βAPP in TBI chimpanzees. In human studies, the earliest reported time for detecting axonal injury postmortem in TBI using βAPP is approximately 30 minutes. This study aimed to investigate whether GFAP and βAPP staining can be used to detect postmortem axonal injury within 30 minutes in TBI chimpanzees. Cerebral and cerebellar tissues from a postmortem TBI chimpanzee and control samples were screened for immunopositivity for GFAP and βAPP in neurons using immunohistochemistry and immunofluorescence. The results suggested that neuronal immunopositivity for GFAP was likely a staining artifact, as negative controls also showed neuronal GFAP staining. However, it was not easy to assume the absence of post-traumatic neuronal GFAP. Conversely, the βAPP assay results indicated that axonal damage can be detected within 22 minutes after death, marking the fastest recorded time to date and aiding in diagnosing severe TBI with short survival times. In conclusion, we demonstrated that the axonal damage in captivated chimpanzee caused by severe and sudden concussion can be detected with βAPP staining within 22 minutes.