Morphological and immunohistochemical modifications in progressive post-mortem changes and traumatic injury of the central nervous system

Veterinary forensic pathology, within the field of veterinary forensic sciences, is an emerging discipline with a visible growth of the published literature in the last few years. Animal models have been largely used to investigate on selected topics, but research on specific issues in veterinary forensic pathology is sparse. The bulk of knowledge on this discipline relies on extrapolation of data from the human forensic pathology literature and consequently there are several gaps and lack of detailed information on animal tissue reactions in forensic circumstances. Forensic neuropathology is considered an independent discipline within forensic science and has become an integral part of forensic human medicine and practice. The field of veterinary forensic neuropathology is nowadays largely unexplored and only a few studies have been performed up to date. Two studies have been carried out in this thesis in the field of veterinary forensic neuropathology. The first, based on an experimental mouse model of progressive post-mortem changes of the central nervous system (CNS), evaluated, both histologically and immunohistochemically, the temporal sequence of autolysis in selected anatomical areas of mouse brain kept at different temperatures (i.e. 4°C, 22°C, and 37°C) for up to 2 weeks, also investigating how post-mortem delay may affect the immunohistochemical identification of neuronal and glial cell epitopes (i.e. NeuN, SMI-32, 2F11, Olig2, GFAP). The second study was focused on traumatic CNS injury in canine and feline post-mortem cases to evaluate the immunohistochemical expression pattern of two anti-amyloid precursor protein antibodies (both C- and N-terminus) in order to validate a possible tool for identification and discrimination of traumatic brain injury (TBI) in domestic animals. Results of the first study showed a different tendency to autolysis of selected brain areas, with the cerebellum and hippocampus as the early affected areas. Moreover, antigens were found to be differently affected by autolytic processes resulting in different alteration of immunoreactivity during the post-mortem fixation delay. Based on these results, the use of morphological analysis (HE and LFB staining) joined with a panel of immunohistochemical markers, at least including NeuN, GFAP, and Olig2, was proposed for the evaluation of CNS in forensic cases, providing useful data for the estimation of post-mortem interval (PMI). In the second study, the N- and C-terminus β-amyloid precursor protein (β-APP) antibodies produced strong and specific signal within all tissue sections examined, being not affected by moderate tissue autolysis and freeze-thawing artefacts. β-APP immunoreactivity was detected as early as 3 to 4 hours after injury in acute head injury cases, increasing in intensity and distribution as the post-trauma interval progressed. A specific pattern of β-APP expression was recognized in all trauma cases, characterized by well-defined profiles of single cortical axons, as well as clustered or isolated axons, mostly recognized along white matter tracts and prevalently located in the internal capsule and fornix. Moreover, the differences between the patterns of axonal damage in traumatic and non-traumatic conditions have been discussed. The present studies could be helpful in elucidating forensic cases, where morphological analysis and specific immunohistochemical markers applied to the CNS could be used to evaluate the PMI and to identify TBI in domestic animals, as well as to assess a presumable time of death after brain trauma.