Head injury in routine and forensic pathological practice

CXCR7 antagonism prevents axonal injury during experimental autoimmune encephalomyelitis as revealed by in vivo axial diffusivity

Background

Multiple Sclerosis (MS) is characterized by the pathological trafficking of leukocytes into the central nervous system (CNS). Using the murine MS model, experimental autoimmune encephalomyelitis (EAE), we previously demonstrated that antagonism of the chemokine receptor CXCR7 blocks endothelial cell sequestration of CXCL12, thereby enhancing the abluminal localization of CXCR4-expressing leukocytes. CXCR7 antagonism led to decreased parenchymal entry of leukocytes and amelioration of ongoing disease during EAE. Of note, animals that received high doses of CXCR7 antagonist recovered to baseline function, as assessed by standard clinical scoring. Because functional recovery reflects axonal integrity, we utilized diffusion tensor imaging (DTI) to evaluate axonal injury in CXCR7 antagonist- versus vehicle-treated mice after recovery from EAE.

Methods

C57BL6/J mice underwent adoptive transfer of MOG-reactive Th1 cells and were treated daily with either CXCR7 antagonist or vehicle for 28 days; and then evaluated by DTI to assess for axonal injury. After imaging, spinal cords underwent histological analysis of myelin and oligodendrocytes via staining with luxol fast blue (LFB), and immunofluorescence for myelin basic protein (MBP) and glutathione S-transferase-π (GST-π). Detection of non-phosphorylated neurofilament H (NH-F) was also performed to detect injured axons. Statistical analysis for EAE scores, DTI parameters and non-phosphorylated NH-F immunofluorescence were done by ANOVA followed by Bonferroni post-hoc test. For all statistical analysis a p < 0.05 was considered significant.

Results

In vivo DTI maps of spinal cord ventrolateral white matter (VLWM) axial diffusivities of naïve and CXCR7 antagonist-treated mice were indistinguishable, while vehicle-treated animals exhibited decreased axial diffusivities. Quantitative differences in injured axons, as assessed via detection of non-phosphorylated NH-F, were consistent with axial diffusivity measurements. Overall, qualitative myelin content and presence of oligodendrocytes were similar in all treatment groups, as expected by their radial diffusivity values. Quantitative assessment of persistent inflammatory infiltrates revealed significant decreases within the parenchyma of CXCR7 antagonist-treated mice versus controls.

Conclusions

These data suggest that CXCR7 antagonism not only prevents persistent inflammation but also preserves axonal integrity. Thus, targeting CXCR7 modifies both disease severity and recovery during EAE, suggesting a role for this molecule in both phases of disease.

Inflicted head injury in infants

There is scant neuropathological information in the child abuse literature; even the best reviews include assumptions based on the findings of a few inadequate early studies. Our recent series of 53 fatal cases (Brain 124 (2001) 1290, 1299 [1,2]) demonstrated age-related patterns of brain injury and showed the substrate of severe encephalopathy in the infants to be hypoxic brain damage, not diffuse traumatic axonal injury ('DAI'), as had previously been thought. About one-third had craniocervical injuries, particularly in the brain stem, suggestive of stretch injury to the neuraxis. Our interpretation was that this finding implied a mechanism of injury--brain stem damage from stretch injury to the neck with resultant apnoea--that could account for the clinical scenario in many cases, and for which violence would not necessarily be required. Since publishing this study we have turned our attention to the subgroup of infants who die without objective signs of injury, such as skull fracture or impact, whose carers are accused of abuse, usually, "violent shaking", on the pathologic findings alone. Given the striking discrepancy that there often is in such cases between the relatively trivial findings in the brain and the accusations of violence, we have been looking at the pathogenesis of the typical intracranial bleeding. A histologic study of dura from 50 paediatric autopsies, none of whom had suffered a head injury, has led us to propose that the subdural and retinal bleeding in such cases may well have a physiological aetiology, rather than being caused directly by trauma.