Microstructural and microglial changes after repetitive mild traumatic brain injury in mice.

Traumatic brain injury (TBI) is a major public health issue, with recently increased awareness of the potential long-term sequelae of repetitive injury. Although TBI is common, objective diagnostic tools with sound neurobiological predictors of outcome are lacking. Indeed, such tools could help to identify those at risk for more severe outcomes after repetitive injury and improve understanding of biological underpinnings to provide important mechanistic insights. We tested the hypothesis that acute and subacute pathological injury, including the microgliosis that results from repeated mild closed head injury (rmCHI), is reflected in susceptibility-weighted magnetic resonance imaging and diffusion-tensor imaging microstructural abnormalities. Using a combination of high-resolution magnetic resonance imaging, stereology, and quantitative PCR, we studied the pathophysiology of male mice that sustained seven consecutive mild traumatic brain injuries over 9 days in acute (24 hr) and subacute (1 week) time periods. rmCHI induced focal cortical microhemorrhages and impaired axial diffusivity at 1 week postinjury. These microstructural abnormalities were associated with a significant increase in microglia. Notably, microgliosis was accompanied by a change in inflammatory microenvironment defined by robust spatiotemporal alterations in tumor necrosis factor-α receptor mRNA. Together these data contribute novel insight into the fundamental biological processes associated with repeated mild brain injury concomitant with subacute imaging abnormalities in a clinically relevant animal model of repeated mild TBI. These findings suggest new diagnostic techniques that can be used as biomarkers to guide the use of future protective or reparative interventions. © 2016 Wiley Periodicals, Inc.

MRI and clinical manifestations of delayed encephalopathy after carbon monoxide poisoning.

To explore the relationship between the clinical manifestations and functional magnetic resonance images of delayed encephalopathy after carbon monoxide intoxication. Six patients received the MRI were diagnosed with delayed encephalopathy after carbon monoxide (CO) poisoning. Clinical manifestations were observed in each patient. MRI revealed multiple lesions. The majority of the lesions were located in the globus pallidus, sub cortical white matter, and basal ganglia. The cognitive injury, akinetic mutism, fecal and uroclepsia, forced crying, forced laughing and extra pyramidal syndromes such as chorea and parkinsonism were manifested in clinic. Cognitive impairment improved greatly while involuntary movements only improved slightly after several months. Meanwhile brain MRI suggested remarkable improvement. Neuroimaging directly correlated with the clinical manifestations.

Complex pattern of interaction between in utero hypoxia-ischemia and intra-amniotic inflammation disrupts brain development and motor function.

BACKGROUND: Infants born preterm commonly suffer from a combination of hypoxia-ischemia (HI) and infectious perinatal inflammatory insults that lead to cerebral palsy, cognitive delay, behavioral issues and epilepsy. Using a novel rat model of combined late gestation HI and lipopolysaccharide (LPS)-induced inflammation, we tested our hypothesis that inflammation from HI and LPS differentially affects gliosis, white matter development and motor impairment during the first postnatal month. METHODS: Pregnant rats underwent laparotomy on embryonic day 18 and transient systemic HI (TSHI) and/or intra-amniotic LPS injection. Shams received laparotomy and anesthesia only. Pups were born at term. Immunohistochemistry with stereological estimates was performed to assess regional glial loads, and western blots were performed for protein expression. Erythropoietin ligand and receptor levels were quantified using quantitative PCR. Digigait analysis detected gait deficits. Statistical analysis was performed with one-way analysis of variance and post-hoc Bonferonni correction. RESULTS: Microglial and astroglial immunolabeling are elevated in TSHI + LPS fimbria at postnatal day 2 compared to sham (both P < 0.03). At postnatal day 15, myelin basic protein expression is reduced by 31% in TSHI + LPS pups compared to shams (P < 0.05). By postnatal day 28, white matter injury shifts from the acute injury pattern to a chronic injury pattern in TSHI pups only. Both myelin basic protein expression (P < 0.01) and the phosphoneurofilament/neurofilament ratio, a marker of axonal dysfunction, are reduced in postnatal day 28 TSHI pups (P < 0.001). Erythropoietin ligand to receptor ratios differ between brains exposed to TSHI and LPS. Gait analyses reveal that all groups (TSHI, LPS and TSHI + LPS) are ataxic with deficits in stride, paw placement, gait consistency and coordination (all P < 0.001). CONCLUSIONS: Prenatal TSHI and TSHI + LPS lead to different patterns of injury with respect to myelination, axon integrity and gait deficits. Dual injury leads to acute alterations in glial response and cellular inflammation, while TSHI alone causes more prominent chronic white matter and axonal injury. Both injuries cause significant gait deficits. Further study will contribute to stratification of injury mechanisms in preterm infants, and guide the use of promising therapeutic interventions.

Clinical correlates in an experimental model of repetitive mild brain injury.

OBJECTIVE: Although there is growing awareness of the long-term cognitive effects of repetitive mild traumatic brain injury (rmTBI; eg, sports concussions), whether repeated concussions cause long-term cognitive deficits remains controversial. Moreover, whether cognitive deficits depend on increased amyloid ß deposition and tau phosphorylation or are worsened by the apolipoprotein E4 allele remains unknown. Here, we use an experimental model of rmTBI to address these clinical controversies. METHODS: A weight drop rmTBI model was used that results in cognitive deficits without loss of consciousness, seizures, or gross or microscopic evidence of brain damage. Cognitive function was assessed using a Morris water maze (MWM) paradigm. Immunostaining and enzyme-linked immunosorbent assay (ELISA) were used to assess amyloid ß deposition and tau hyperphosphorylation. Brain volume and white matter integrity were assessed by magnetic resonance imaging (MRI). RESULTS: Mice subjected to rmTBI daily or weekly but not biweekly or monthly had persistent cognitive deficits as long as 1 year after injuries. Long-term cognitive deficits were associated with increased astrocytosis but not tau phosphorylation or amyloid ß (by ELISA); plaques or tangles (by immunohistochemistry); or brain volume loss or changes in white matter integrity (by MRI). APOE4 was not associated with worse MWM performance after rmTBI. INTERPRETATION: Within the vulnerable time period between injuries, rmTBI produces long-term cognitive deficits independent of increased amyloid ß or tau phosphorylation. In this model, cognitive outcome is not influenced by APOE4 status. The data have implications for the long-term mental health of athletes who suffer multiple concussions.

Beneficial effect of amyloid beta after controlled cortical impact.

BACKGROUND: Worse functional outcomes after controlled cortical impact (CCI) in Bace1(-/-) mice have previously been demonstrated. This study investigated whether reconstitution of amyloid-beta (Aß) after CCI in Bace1(-/-) animals would reverse the detrimental effect of Bace1 deletion. METHODS: Bace1(-/-) and wild type Bace1(+/+) (C57Bl/6) mice were subjected to CCI (n = 14-23/group) or sham injury (n = 6/group). After injury, mice underwent intracerebroventricular injections of Aß40 (n = 23 Bace1(-/-) and 17 Bace1(+/+) per group) or vehicle (n = 14 Bace1(-/-) and 22 Bace1(+/+) per group). Functional outcomes were assessed with wire grip (motor) and Morris water maze (spatial memory). Soluble Aß levels were assessed at 24 hours and 21 days after CCI. Lesion volume was assessed 21 days after injury. RESULTS: At 24 hours after injury, Aß-treated Bace1(-/-) mice had Aß40 levels similar to vehicle-treated Bace1(+/+) mice, but by 21 days after injury there were no differences between Aß-treated versus vehicle-treated Bace1(-/-) mice. Reconstitution with Aß40 improved motor but not spatial memory or histopathological outcome in injured Bace1(-/-) mice. In contrast, treatment with Aß40 worsened motor performance in Bace1(+/+) mice. CONCLUSIONS: The data suggest Aß40 may have some beneficial effects after CCI in young adult mice and that therapies targeting BACE should be approached cautiously.

Sex differences in the effect of progesterone after controlled cortical impact in adolescent mice: a preliminary study.

OBJECT: While progesterone has been well studied in experimental models of adult traumatic brain injury (TBI), it has not been evaluated in pediatric models. The study of promising interventions in pediatric TBI is important because children have the highest public health burden of such injuries. Therapies that are beneficial in adults may not necessarily be effective in the pediatric population. The purpose of this study was to evaluate whether progesterone treatment improves outcomes in an experimental model of pediatric TBI. METHODS: The authors determined whether progesterone administered after controlled cortical impact (CCI) improves functional and histopathological outcomes in 4-week-old mice. Both male and female mice (58 mice total) were included in this study, as the majority of prior studies have used only male and/or reproductively senescent females. Mice were randomized to treatment with progesterone or vehicle and to CCI injury or sham injury. Motor (wire grip test) and memory (Morris water maze) testing were performed to determine the effect of progesterone on TBI. Lesion volume was also assessed. RESULTS: Compared with their vehicle-treated counterparts, the progesterone-treated CCI-injured male mice had improved motor performance (p < 0.001). In contrast, progesterone-treated CCI-injured female mice had a worse performance than their vehicle-treated counterparts (p = 0.001). Progesterone treatment had no effect on spatial memory performance or lesion volume in injured male or female mice. CONCLUSIONS: These data suggest a sex-specific effect of progesterone treatment after CCI in adolescent mice and could inform clinical trials in children.

Chronic gliosis and behavioral deficits in mice following repetitive mild traumatic brain injury.

OBJECT: With the recent increasing interest in outcomes after repetitive mild traumatic brain injury (rmTBI; e.g., sports concussions), several models of rmTBI have been established. Characterizing these models in terms of behavioral and histopathological outcomes is vital to assess their clinical translatability. The purpose of this study is to provide an in-depth behavioral and histopathological phenotype of a clinically relevant model of rmTBI. METHODS: The authors used a previously published weight-drop model of rmTBI (7 injuries in 9 days) in 2- to 3-month-old mice that produces cognitive deficits without persistent loss of consciousness, seizures, gross structural imaging findings, or microscopic evidence of structural brain damage. Injured and sham-injured (anesthesia only) mice were subjected to a battery of behavioral testing, including tests of balance (rotarod), spatial memory (Morris water maze), anxiety (open field plus maze), and exploratory behavior (hole-board test). After behavioral testing, brains were assessed for histopathological outcomes, including brain volume and microglial and astrocyte immunolabeling. RESULTS: Compared with sham-injured mice, mice subjected to rmTBI showed increased exploratory behavior and had impaired balance and worse spatial memory that persisted up to 3 months after injury. Long-term behavioral deficits were associated with chronic increased astrocytosis and microgliosis but no volume changes. CONCLUSIONS: The authors demonstrate that their rmTBI model results in a characteristic behavioral phenotype that correlates with the clinical syndrome of concussion and repetitive concussion. This model offers a platform from which to study therapeutic interventions for rmTBI.