Traumatic brain injury with particular reference to diffuse traumatic axonal injury subpopulations
Al-Hasani, Omer Hussain
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Traumatic brain injury (TBI) remains an important cause of morbidity and mortality within society. TBI may result in both focal and diffuse brain injury. Diffuse traumatic axonal injury (TAI) is an important pathological substrate of TBI, and can be associated with a range of clinical states, ranging from concussion through to death, the clinical severity being associated with a number of factors related to the injury. A retrospective study was conducted using 406 cases with TBI, from the archive of the Academic Department of Pathology (Neuropathology) University of Edinburgh, during the period from1982 and 2005. This cohort was sequential and provided a unique description of the range of pathologies associated with fatal TBI within the Edinburgh catchment area. All the data was collected on a proforma and analysed to provide a description of the incidence in the injury patterns among the Edinburgh cohort. This cohort was then used to provide cases to try and critically assess the mechanisms of axonal injury in TBI. A study was undertaken to investigate TAI in an experimental model of non-impact head injury in a gyrencephalic mammalian model (piglet model) and in human autopsy materials using immunohistochemical analysis of a range of antibodies, and to define the distribution of axonal injury with flow and neurofilament markers in TAI. A further objective was to examine the expression of β-APP as an indicator of impaired axonal transport, three neurofilament markers targeting NF-160, NF-200, and the phosphorylated form of the neurofilament heavy chain (NFH), in different anatomical regions of piglet and human brains. The double immunofluorescence labelling method was then employed to investigate the hypothesis of co-localisation between β-APP and each one of the previous neurofilament markers. The animal studies showed significant differences in NF-160 between sham and injured 3-5 days old piglet cases (6 hour survival) and between 3-5 days sham and injured, when stained with SMI-34 antibody. In 4 weeks old piglet cases (6 hour survival), immunoreactivity of β-APP was significantly higher in injured than control. No other significant differences for any of the antibodies were noted, based on age, velocity, and survival time. Human results suggested that the brainstem had a higher level of β-APP and NF-160 than the corpus callosum and internal capsule. Co-localisation of β-APP with NFs was not a consistent feature of TAI in piglet and human brains, suggesting that markers of impaired axonal transport and neurofilament accumulation are sensitive to TAI, but may highlight different populations involved in the evolution of TAI.