Modelling lung infection with Klebsiella pneumoniae after murine traumatic brain injury

Pneumonia is a common comorbidity in patients with severe traumatic brain injury (TBI), and is associated with increased morbidity and mortality. In this study, we established a model of intratracheal Klebsiella pneumoniae administration in young adult male and female mice, at 4 days following an experimental TBI, to investigate how K. pneumoniae infection influences acute post-TBI outcomes. A dose-response curve determined the optimal dose of K. pneumoniae for inoculation (1 x 10^6 colony forming units), and administration at 4 days post-TBI resulted in transient body weight loss and sickness behaviors (hypoactivity and acute dyspnea). K. pneumoniae infection led to an increase in pro-inflammatory cytokines in serum and bronchoalveolar lavage fluid at 24 h post-infection, in both TBI and sham (uninjured) mice. By 7 days, when myeloperoxidase + neutrophil numbers had returned to baseline in all groups, lung histopathology was observed with an increase in airspace size in TBI + K. pneumoniae mice compared to TBI + vehicle mice. In the brain, increased neuroinflammatory gene expression was observed acutely in response to TBI, with an exacerbated increase in Ccl2 and Hmox1 in TBI + K. pneumoniae mice compared to either TBI or K. pneumoniae alone. However, the presence of neuroinflammatory immune cells in the injured brain, and the extent of damage to cortical and hippocampal brain tissue, was comparable between K. pneumoniae and vehicle-treated mice by 7 days. Examination of the fecal microbiome across a time course did not reveal any pronounced effects of either injury or K. pneumoniae on bacterial diversity or abundance. Together, these findings demonstrate that K. pneumoniae lung infection after TBI induces an acute and transient inflammatory response, primarily localized to the lungs with some systemic effects. However, this infection had minimal impact on secondary injury processes in the brain following TBI. Future studies are needed to evaluate the potential longer-term consequences of this dual-hit insult.

Shaking Up Our Approach: The Need for Characterization and Optimization of Pre-clinical Models of Infant Abusive Head Trauma

Traumatic brain injuries (TBIs) are a large societal and individual burden. In the first year of life, the vast majority of these injuries are the result of inflicted abusive events by a trusted caregiver. Abusive head trauma (AHT) in infants, formerly known as shaken baby syndrome, is the leading cause of inflicted mortality and morbidity in this population. In this review we address clinical diagnosis, symptoms, prognosis, and neuropathology of AHT, emphasizing the burden of repetitive AHT. Next, we consider existing animal models of AHT, and we evaluate key features of an ideal model, highlighting important developmental milestones in children most vulnerable to AHT. We draw on insights from other injury models, such as repetitive, mild TBIs (RmTBIs), post-traumatic epilepsy (PTE), hypoxic-ischemic injuries, and maternal neglect, to speculate on key knowledge gaps and underline important new opportunities in pre-clinical AHT research. Finally, potential treatment options to facilitate healthy development in children following an AHT are considered. Together, this review aims to drive the field toward optimized, well-characterized animal models of AHT, which will allow for greater insight into the underlying neuropathological and neurobehavioral consequences of AHT.

Experimental Models of Hospital-Acquired Infections After Traumatic Brain Injury: Challenges and Opportunities

Patients hospitalized after a moderate or severe traumatic brain injury (TBI) are at increased risk of nosocomial infections, including bacterial pneumonia and other upper respiratory tract infections. Infections represent a secondary immune challenge for vulnerable TBI patients that can lead to increased morbidity and poorer long-term prognosis. This review first describes the clinical significance of infections after TBI, delving into the known mechanisms by which a TBI can alter systemic immunological responses towards an immunosuppressive state, leading to promotion of increased vulnerability to infections. Pulmonary dysfunction resulting from respiratory tract infections is considered in the context of neurotrauma, including the bidirectional relationship between the brain and lungs. Turning to pre-clinical modeling, current laboratory approaches to study experimental TBI and lung infections are reviewed, to highlight findings from the limited key studies to date that have incorporated both insults. Then, practical decisions for the experimental design of animal studies of post-injury infections are discussed. Variables associated with the host animal, the infectious agent (e.g., species, strain, dose, and administration route), as well as the timing of the infection relative to the injury model are important considerations for model development. Together, the purpose of this review is to highlight the significant clinical need for increased pre-clinical research into the two-hit insult of a hospital-acquired infection after TBI to encourage further scientific enquiry in the field.

The Australian Traumatic Brain Injury Initiative: Systematic Review and Consensus Process to Determine the Predictive Value of Demographic, Injury Event, and Social Characteristics on Outcomes for People With Moderate-Severe Traumatic Brain Injury

The objective of the Australian Traumatic Brain Injury (AUS-TBI) Initiative is to develop a data dictionary to inform data collection and facilitate prediction of outcomes of people who experience moderate-severe TBI in Australia. The aim of this systematic review was to summarize the evidence of the association between demographic, injury event, and social characteristics with outcomes, in people with moderate-severe TBI, to identify potentially predictive indicators. Standardized searches were implemented across bibliographic databases to March 31, 2022. English-language reports, excluding case series, which evaluated the association between demographic, injury event, and social characteristics, and any clinical outcome in at least 10 patients with moderate-severe TBI were included. Abstracts and full text records were independently screened by at least two reviewers in Covidence. A pre-defined algorithm was used to assign a judgement of predictive value to each observed association. The review findings were discussed with an expert panel to determine the feasibility of incorporation of routine measurement into standard care. The search strategy retrieved 16,685 records; 867 full-length records were screened, and 111 studies included. Twenty-two predictors of 32 different outcomes were identified; 7 were classified as high-level (age, sex, ethnicity, employment, insurance, education, and living situation at the time of injury). After discussion with an expert consensus group, 15 were recommended for inclusion in the data dictionary. This review identified numerous predictors capable of enabling early identification of those at risk for poor outcomes and improved personalization of care through inclusion in routine data collection.

A pre-existing Toxoplasma gondii infection exacerbates the pathophysiological response and extent of brain damage after traumatic brain injury in mice

Traumatic brain injury (TBI) is a key contributor to global morbidity that lacks effective treatments. Microbial infections are common in TBI patients, and their presence could modify the physiological response to TBI. It is estimated that one-third of the human population is incurably infected with the feline-borne parasite, Toxoplasma gondii, which can invade the central nervous system and result in chronic low-grade neuroinflammation, oxidative stress, and excitotoxicity-all of which are also important pathophysiological processes in TBI. Considering the large number of TBI patients that have a pre-existing T. gondii infection prior to injury, and the potential mechanistic synergies between the conditions, this study investigated how a pre-existing T. gondii infection modified TBI outcomes across acute, sub-acute and chronic recovery in male and female mice. Gene expression analysis of brain tissue found that neuroinflammation and immune cell markers were amplified in the combined T. gondii + TBI setting in both males and females as early as 2-h post-injury. Glutamatergic, neurotoxic, and oxidative stress markers were altered in a sex-specific manner in T. gondii + TBI mice. Structural MRI found that male, but not female, T. gondii + TBI mice had a significantly larger lesion size compared to their uninfected counterparts at 18-weeks post-injury. Similarly, diffusion MRI revealed that T. gondii + TBI mice had exacerbated white matter tract abnormalities, particularly in male mice. These novel findings indicate that a pre-existing T. gondii infection affects the pathophysiological aftermath of TBI in a sex-dependent manner, and may be an important modifier to consider in the care and prognostication of TBI patients.

Regulation of microglial responses after pediatric traumatic brain injury: exploring the role of SHIP-1

Introduction

Severe traumatic brain injury (TBI) is the world's leading cause of permanent neurological disability in children. TBI-induced neurological deficits may be driven by neuroinflammation post-injury. Abnormal activity of SH2 domain-containing inositol 5' phosphatase-1 (SHIP-1) has been associated with dysregulated immunological responses, but the role of SHIP-1 in the brain remains unclear. The current study investigated the immunoregulatory role of SHIP-1 in a mouse model of moderate-severe pediatric TBI.

Methods

SHIP-1+/- and SHIP-1-/- mice underwent experimental TBI or sham surgery at post-natal day 21. Brain gene expression was examined across a time course, and immunofluorescence staining was evaluated to determine cellular immune responses, alongside peripheral serum cytokine levels by immunoassays. Brain tissue volume loss was measured using volumetric analysis, and behavior changes both acutely and chronically post-injury.

Results

Acutely, inflammatory gene expression was elevated in the injured cortex alongside increased IBA-1 expression and altered microglial morphology; but to a similar extent in SHIP-1-/- mice and littermate SHIP-1+/- control mice. Similarly, the infiltration and activation of CD68-positive macrophages, and reactivity of GFAP-positive astrocytes, was increased after TBI but comparable between genotypes. TBI increased anxiety-like behavior acutely, whereas SHIP-1 deficiency alone reduced general locomotor activity. Chronically, at 12-weeks post-TBI, SHIP-1-/- mice exhibited reduced body weight and increased circulating cytokines. Pro-inflammatory gene expression in the injured hippocampus was also elevated in SHIP-1-/- mice; however, GFAP immunoreactivity at the injury site in TBI mice was lower. TBI induced a comparable loss of cortical and hippocampal tissue in both genotypes, while SHIP-1-/- mice showed reduced general activity and impaired working memory, independent of TBI.

Conclusion

Together, evidence does not support SHIP-1 as an essential regulator of brain microglial morphology, brain immune responses, or the extent of tissue damage after moderate-severe pediatric TBI in mice. However, our data suggest that reduced SHIP-1 activity induces a greater inflammatory response in the hippocampus chronically post-TBI, warranting further investigation.

Inherent Susceptibility to Acquired Epilepsy in Selectively Bred Rats Influences the Acute Response to Traumatic Brain Injury

Traumatic brain injury (TBI) often causes seizures associated with a neuroinflammatory response and neurodegeneration. TBI responses may be influenced by differences between individuals at a genetic level, yet this concept remains understudied. Here, we asked whether inherent differences in one's vulnerability to acquired epilepsy would determine acute physiological and neuroinflammatory responses acutely after experimental TBI, by comparing selectively bred "seizure-prone" (FAST) rats with "seizure-resistant" (SLOW) rats, as well as control parental strains (Long Evans and Wistar rats). Eleven-week-old male rats received a moderate-to-severe lateral fluid percussion injury (LFPI) or sham surgery. Rats were assessed for acute injury indicators and neuromotor performance, and blood was serially collected. At 7 days post-injury, brains were collected for quantification of tissue atrophy by cresyl violet (CV) histology, and immunofluorescent staining of activated inflammatory cells. FAST rats showed an exacerbated physiological response acutely post-injury, with a 100% seizure rate and mortality within 24 h. Conversely, SLOW rats showed no acute seizures and a more rapid neuromotor recovery compared with controls. Brains from SLOW rats also showed only modest immunoreactivity for microglia/macrophages and astrocytes in the injured hemisphere compared with controls. Further, group differences were apparent between the control strains, with greater neuromotor deficits observed in Long Evans rats compared with Wistars post-TBI. Brain-injured Long Evans rats also showed the most pronounced inflammatory response to TBI across multiple brain regions, whereas Wistar rats showed the greatest extent of regional brain atrophy. These findings indicate that differential genetic predisposition to develop acquired epilepsy (i.e., FAST vs. SLOW rat strains) determines acute responses after experimental TBI. Differences in the neuropathological response to TBI between commonly used control rat strains is also a novel finding, and an important consideration for future study design. Our results support further investigation into whether genetic predisposition to acute seizures predicts the chronic outcomes after TBI, including the development of post-traumatic epilepsy.

Regulation of Microglial Signaling by Lyn and SHIP-1 in the Steady-State Adult Mouse Brain

Chronic neuroinflammation and glial activation are associated with the development of many neurodegenerative diseases and neuropsychological disorders. Recent evidence suggests that the protein tyrosine kinase Lyn and the lipid phosphatase SH2 domain-containing inositol 5' phosphatase-1 (SHIP-1) regulate neuroimmunological responses, but their homeostatic roles remain unclear. The current study investigated the roles of Lyn and SHIP-1 in microglial responses in the steady-state adult mouse brain. Young adult Lyn-/- and SHIP-1-/- mice underwent a series of neurobehavior tests and postmortem brain analyses. The microglial phenotype and activation state were examined by immunofluorescence and flow cytometry, and neuroimmune responses were assessed using gene expression analysis. Lyn-/- mice had an unaltered behavioral phenotype, neuroimmune response, and microglial phenotype, while SHIP-1-/- mice demonstrated reduced explorative activity and exhibited microglia with elevated activation markers but reduced granularity. In addition, expression of several neuroinflammatory genes was increased in SHIP-1-/- mice. In response to LPS stimulation ex vivo, the microglia from both Lyn-/- and SHIP-1-/- showed evidence of hyper-activity with augmented TNF-α production. Together, these findings demonstrate that both Lyn and SHIP-1 have the propensity to control microglial responses, but only SHIP-1 regulates neuroinflammation and microglial activation in the steady-state adult brain, while Lyn activity appears dispensable for maintaining brain homeostasis.

Environmental modifications to rehabilitate social behavior deficits after acquired brain injury: What is the evidence?

Social behavior deficits are a common, debilitating consequence of traumatic brain injury and stroke, particularly when sustained during childhood. Numerous factors influence the manifestation of social problems after acquired brain injuries, raising the question of whether environmental manipulations can minimize or prevent such deficits. Here, we examine both clinical and preclinical evidence addressing this question, with a particular focus on environmental enrichment paradigms and differing housing conditions. We aimed to understand whether environmental manipulations can ameliorate injury-induced social behavior deficits. In summary, promising data from experimental models supports a beneficial role of environmental enrichment on social behavior. However, limited studies have considered social outcomes in the chronic setting, and few studies have addressed the social context specifically as an important component of the post-injury environment. Clinically, limited high-caliber evidence supports the use of specific interventions for social deficits after acquired brain injuries. An improved understanding of how the post-injury environment interacts with the injured brain, particularly during development, is needed to validate the implementation of rehabilitative interventions that involve manipulating an individuals' environment.

Cranial Bone Changes Induced by Mild Traumatic Brain Injuries: A Neglected Player in Concussion Outcomes?

Mild traumatic brain injuries (TBIs), particularly when repetitive in nature, are increasingly recognized to have a range of significant negative implications for brain health. Much of the ongoing research in the field is focused on the neurological consequences of these injuries and the relationship between TBIs and long-term neurodegenerative conditions such as chronic traumatic encephalopathy and Alzheimer's disease. However, our understanding of the complex relationship between applied mechanical force at impact, brain pathophysiology, and neurological function remains incomplete. Past research has shown that mild TBIs, even below the threshold that results in cranial fracture, induce changes in cranial bone structure and morphology. These structural and physiological changes likely have implications for the transmission of mechanical force into the underlying brain parenchyma. Here, we review this evidence in the context of the current understanding of bone mechanosensitivity and the consequences of TBIs or concussions. We postulate that heterogeneity of the calvarium, including differing bone thickness attributable to past impacts, age, or individual variability, may be a modulator of outcomes after subsequent TBIs. We advocate for greater consideration of cranial responses to TBI in both experimental and computer modeling of impact biomechanics, and raise the hypothesis that calvarial bone thickness represents a novel biomarker of brain injury vulnerability post-TBI.

Modulating chronic outcomes after pediatric traumatic brain injury: Distinct effects of social and environmental enrichment

Impairments in social and cognitive function are a common consequence of pediatric traumatic brain injury (TBI). Rehabilitation has the potential to promote optimal behavioral recovery. Here, we evaluated whether an enhanced social and/or cognitive environment could improve long-term outcomes in a preclinical model of pediatric TBI. Male C57Bl/6 J mice received a moderately-severe TBI or sham procedure at postnatal day 21. After one week, mice were randomized to different social conditions (minimal socialization, n = 2/cage; or social grouping, n = 6/cage), and housing conditions (standard cage, or environmental enrichment (EE), incorporating sensory, motor, and cognitive stimuli). After 8 weeks, neurobehavioral outcomes were assessed, followed by post-mortem neuropathology. We found that TBI mice exhibited hyperactivity, spatial memory deficits, reduced anxiety-like behavior, and reduced sensorimotor performance compared to age-matched sham controls. Pro-social and sociosexual behaviors were also reduced in TBI mice. EE increased sensorimotor performance, and the duration of sociosexual interactions. Conversely, social housing reduced hyperactivity and altered anxiety-like behavior in TBI mice, and reduced same-sex social investigation. TBI mice showed impaired spatial memory retention, except for TBI mice exposed to both EE and group housing. In the brain, while TBI led to significant regional tissue atrophy, social housing had modest neuroprotective effects on hippocampal volumes, neurogenesis, and oligodendrocyte progenitor numbers. In conclusion, manipulation of the post-injury environment has benefit for chronic behavioral outcomes, but the benefits are specific to the type of enrichment available. This study improves understanding of modifiable factors that may be harnessed to optimize long-term outcomes for survivors of early-life TBI.

Ccr2 Gene Ablation Does Not Influence Seizure Susceptibility, Tissue Damage, or Cellular Inflammation after Murine Pediatric Traumatic Brain Injury

Pediatric traumatic brain injury (TBI) is a major public health issue, and a risk factor for the development of post-traumatic epilepsy that may profoundly impact the quality of life for survivors. As the majority of neurotrauma research is focused on injury to the adult brain, our understanding of the developing brain's response to TBI remains incomplete. Neuroinflammation is an influential pathophysiological mechanism in TBI, and is thought to increase neuronal hyperexcitability, rendering the brain more susceptible to the onset of seizures and/or epileptogenesis. We here hypothesized that peripheral blood-derived macrophages, recruited into the injured brain via C-C motif ligand 2 (CCL2) chemokine/C-C chemokine receptor type 2 (CCR2) signaling, contributes to neuroinflammation and thus seizure susceptibility after experimental pediatric TBI. Using Ccr2 gene-deficient mice in the controlled cortical impact (CCI) model of TBI, in 3-week-old male mice we found that TBI led to an increase in susceptibility to pentylenetetrazol (PTZ)-evoked seizures, associated with considerable cortical tissue loss, a robust cellular neuroinflammatory response, and oxidative stress. Intriguingly, although Ccr2-deficiency increased CCL2 levels in serum, it did not exacerbate seizure susceptibility or the neuroinflammatory cellular response after pediatric TBI. Similarly, acute post-injury treatment with a CCR2 antagonist did not influence seizure susceptibility or the extent of tissue damage in wild-type (WT) mice. Together, our findings suggest that CCR2 is not a crucial driver of epileptogenesis or neuroinflammation after TBI in the developing brain. We propose that age may be an important factor differentiating our findings from previous studies in which targeting CCL2/CCR2 has been reported to be anti-inflammatory, neuroprotective or anti-seizure.

Pre-existing Toxoplasma gondii infection increases susceptibility to pentylenetetrazol-induced seizures independent of traumatic brain injury in mice

Introduction

Post-traumatic epilepsy (PTE) is a debilitating chronic outcome of traumatic brain injury (TBI), and neuroinflammation is implicated in increased seizure susceptibility and epileptogenesis. However, how common clinical factors, such as infection, may modify neuroinflammation and PTE development has been understudied. The neurotropic parasite, Toxoplasma gondii (T. gondii) incurably infects one-third of the world's population. Thus, many TBI patients have a pre-existing T. gondii infection at the time of injury. T. gondii infection results in chronic low-grade inflammation and altered signaling pathways within the brain, and preliminary clinical evidence suggest that it may be a risk factor for epilepsy. Despite this, no studies have considered how a pre-existing T. gondii infection may alter the development of PTE.

Methods

This study aimed to provide insight into this knowledge gap by assessing how a pre-existing T. gondii infection alters susceptibility to, and severity of, pentylenetetrazol (PTZ)-induced seizures (i.e., a surrogate marker of epileptogenesis/PTE) at a chronic stage of TBI recovery. We hypothesized that T. gondii will increase the likelihood and severity of seizures following PTZ administration, and that this would occur in the presence of intensified neuroinflammation. To test this, 6-week old male and female C57BL/6 Jax mice were intraperitoneally injected with 50,000 T. gondii tachyzoites or with the PBS vehicle only. At 12-weeks old, mice either received a severe TBI via controlled cortical impact or sham injury. At 18-weeks post-injury, mice were administered 40 mg/kg PTZ and video-recorded for evaluation of seizure susceptibility. Fresh cortical tissue was then collected for gene expression analyses.

Results

Although no synergistic effects were evident between infection and TBI, chronic T. gondii infection alone had robust effects on the PTZ-seizure response and gene expression of markers related to inflammatory, oxidative stress, and glutamatergic pathways. In addition to this, females were more susceptible to PTZ-induced seizures than males. While TBI did not impact PTZ responses, injury effects were evident at the molecular level.

Discussion

Our data suggests that a pre-existing T. gondii infection is an important modifier of seizure susceptibility independent of brain injury, and considerable attention should be directed toward delineating the mechanisms underlying this pro-epileptogenic factor.

Temporal proteomics of human cerebrospinal fluid after severe traumatic brain injury

The pathophysiology of traumatic brain injury (TBI) requires further characterization to fully elucidate changes in molecular pathways. Cerebrospinal fluid (CSF) provides a rich repository of brain-associated proteins. In this retrospective observational study, we implemented high-resolution mass spectrometry to evaluate changes to the CSF proteome after severe TBI. 91 CSF samples were analyzed with mass spectrometry, collected from 16 patients with severe TBI (mean 32 yrs; 81% male) on day 0, 1, 2, 4, 7 and/or 10 post-injury (8-16 samples/timepoint) and compared to CSF obtained from 11 non-injured controls. We quantified 1152 proteins with mass spectrometry, of which approximately 80% were associated with CSF. 1083 proteins were differentially regulated after TBI compared to control samples. The most highly-upregulated proteins at each timepoint included neutrophil elastase, myeloperoxidase, cathepsin G, matrix metalloproteinase-8, and S100 calcium-binding proteins A8, A9 and A12-all proteins involved in neutrophil activation, recruitment, and degranulation. Pathway enrichment analysis confirmed the robust upregulation of proteins associated with innate immune responses. Conversely, downregulated pathways included those involved in nervous system development, and several proteins not previously identified after TBI such as testican-1 and latrophilin-1. We also identified 7 proteins (GM2A, Calsyntenin 1, FAT2, GANAB, Lumican, NPTX1, SFRP2) positively associated with an unfavorable outcome at 6 months post-injury. Together, these findings highlight the robust innate immune response that occurs after severe TBI, supporting future studies to target neutrophil-related processes. In addition, the novel proteins we identified to be differentially regulated by severe TBI warrant further investigation as potential biomarkers of brain damage or therapeutic targets.

Incidence and risk factors of posttraumatic epilepsy following pediatric traumatic brain injury: A systematic review and meta-analysis

Posttraumatic epilepsy (PTE) is a well-known chronic complication following traumatic brain injury (TBI). Despite some evidence that age at the time of injury may influence the likelihood of PTE, the incidence of PTE in pediatric populations remains unclear. We therefore conducted a systematic review to determine the overall reported incidence of PTE, and explore potential risk factors associated with PTE after pediatric TBI. A comprehensive literature search of the PubMed, Embase, and Web of Science databases was conducted, including randomized controlled trials and cohort studies assessing the incidence of PTE in TBI pediatric patients. We excluded studies with a sample size of <10 patients and those in which a pediatric cohort was not clearly discernable. The review was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We found that the overall incidence of PTE following pediatric TBI was 10% (95% confidence interval [CI] = 5.9%-15%). Subgroup analysis of a small number of studies demonstrated that the occurrence of early seizures (cumulative incidence ratio [CIR] = 7.28, 95% CI = 1.09-48.4, p = .040), severe TBI (CIR = 1.81, 95% CI = 1.23-2.67, p < .001), and intracranial hemorrhage (CIR = 1.60, 95% CI = 1.06-2.40, p = .024) increased the risk of PTE in this population. Other factors, including male sex and neurosurgical intervention, were nonsignificantly associated with a higher incidence of PTE. In conclusion, PTE is a significant chronic complication following childhood TBI, similar to in the adult population. Further standardized investigation into clinical risk factors and management guidelines is warranted. PROSPERO ID# CRD42021245802.

A companion to the preclinical common data elements for rodent models of pediatric acquired epilepsy: A report of the TASK3-WG1B, Pediatric and Genetic Models Working Group of the ILAE/AES Joint Translational Task Force

Epilepsy syndromes during the early years of life may be attributed to an acquired insult, such as hypoxic-ischemic injury, infection, status epilepticus, or brain trauma. These conditions are frequently modeled in experimental rodents to delineate mechanisms of epileptogenesis and investigate novel therapeutic strategies. However, heterogeneity and subsequent lack of reproducibility of such models across laboratories is an ongoing challenge to maintain scientific rigor and knowledge advancement. To address this, as part of the TASK3-WG1B Working Group of the International League Against Epilepsy/American Epilepsy Society Joint Translational Task Force, we have developed a series of case report forms (CRFs) to describe common data elements for pediatric acquired epilepsy models in rodents. The "Rodent Models of Pediatric Acquired Epilepsy" Core CRF was designed to capture cohort-general information; while two Specific CRFs encompass physical induction models and chemical induction models, respectively. This companion manuscript describes the key elements of these models and why they are important to be considered and reported consistently. Together, these CRFs provide investigators with the tools to systematically record critical information regarding their chosen model of acquired epilepsy during early life, for improved standardization and transparency across laboratories. These outcomes will support the ultimate goal of such research; that is, to understand the childhood onset-specific biology of epileptogenesis after acquired insults, and translate this knowledge into therapeutics to improve pediatric patient outcomes and minimize the lifetime burden of epilepsy.

Pediatric traumatic brain injury and a subsequent transient immune challenge independently influenced chronic outcomes in male mice

Traumatic brain injury (TBI) is a major contributor to death and disability worldwide. Children are at particularly high risk of both sustaining a TBI and experiencing serious long-term consequences, such as cognitive deficits, mental health problems and post-traumatic epilepsy. Severe TBI patients are highly susceptible to nosocomial infections, which are mostly acquired within the first week of hospitalization post-TBI. Yet the potential chronic impact of such acute infections following pediatric TBI remains unclear. In this study, we hypothesized that a peripheral immune challenge, such as lipopolysaccharide (LPS)-mimicking a hospital-acquired infection-would worsen inflammatory, neurobehavioral, and seizure outcomes after experimental pediatric TBI. To test this, three-week old male C57Bl/6J mice received a moderate controlled cortical impact or sham surgery, followed by 1 mg/kg i.p. LPS (or 0.9% saline vehicle) at 4 days TBI. Mice were randomized to four groups; sham-saline, sham-LPS, TBI-saline or TBI-LPS (n = 15/group). Reduced general activity and increased anxiety-like behavior were observed within 24 h in LPS-treated mice, indicating a transient sickness response. LPS-treated mice also exhibited a reduction in body weights, which persisted chronically. From 2 months post-injury, mice underwent a battery of tests for sensorimotor, cognitive, and psychosocial behaviors. TBI resulted in hyperactivity and spatial memory deficits, independent of LPS; whereas LPS resulted in subtle deficits in spatial memory retention. At 5 months post-injury, video-electroencephalographic recordings were obtained to evaluate both spontaneous seizure activity as well as the evoked seizure response to pentylenetetrazol (PTZ). TBI increased susceptibility to PTZ-evoked seizures; whereas LPS appeared to increase the incidence of spontaneous seizures. Post-mortem analyses found that TBI, but not LPS, resulted in robust glial reactivity and loss of cortical volume. A TBI × LPS interaction in hippocampal volume suggested that TBI-LPS mice had a subtle increase in ipsilateral hippocampus tissue loss; however, this was not reflected in neuronal cell counts. Both TBI and LPS independently had modest effects on chronic hippocampal gene expression. Together, contrary to our hypothesis, we observed minimal synergy between TBI and LPS. Instead, pediatric TBI and a subsequent transient immune challenge independently influenced chronic outcomes. These findings have implications for future preclinical modeling as well as acute post-injury patient management.

Dysregulated phosphoinositide 3-kinase signaling in microglia: shaping chronic neuroinflammation

Microglia are integral mediators of innate immunity within the mammalian central nervous system. Typical microglial responses are transient, intending to restore homeostasis by orchestrating the removal of pathogens and debris and the regeneration of damaged neurons. However, prolonged and persistent microglial activation can drive chronic neuroinflammation and is associated with neurodegenerative disease. Recent evidence has revealed that abnormalities in microglial signaling pathways involving phosphatidylinositol 3-kinase (PI3K) and protein kinase B (AKT) may contribute to altered microglial activity and exacerbated neuroimmune responses. In this scoping review, the known and suspected roles of PI3K-AKT signaling in microglia, both during health and pathological states, will be examined, and the key microglial receptors that induce PI3K-AKT signaling in microglia will be described. Since aberrant signaling is correlated with neurodegenerative disease onset, the relationship between maladapted PI3K-AKT signaling and the development of neurodegenerative disease will also be explored. Finally, studies in which microglial PI3K-AKT signaling has been modulated will be highlighted, as this may prove to be a promising therapeutic approach for the future treatment of a range of neuroinflammatory conditions.

Incidence of post-traumatic epilepsy following paediatric traumatic brain injury: protocol for systematic review and meta-analysis

INTRODUCTION

Post-traumatic epilepsy (PTE) is a recognised complication of traumatic brain injury (TBI), and is associated with higher rates of mortality and morbidity when compared with patients with TBI who do not develop PTE. The majority of the literature on PTE has focused on adult populations, and consequently there is a paucity of information regarding paediatric cohorts. Additionally, there is considerable heterogeneity surrounding the reported incidence of PTE following childhood TBI in the current literature. The primary aim of our study is to summarise reported PTE incidences in paediatric populations to derive an accurate estimate of the global incidence of PTE following childhood TBI. Our secondary aim is to explore risk factors that increase the likelihood of developing PTE.

METHODS AND ANALYSIS

A systematic literature search of Embase (1947-2021), PubMed (1996-2021) and Web of Science (1900-2021) will be conducted. Publications in English that report the incidence of PTE in populations under 18 years of age will be included. Publications that evaluate fewer than 10 patients, report an alternative cause of epilepsy, or in which a paediatric cohort is not discernable, will be excluded. Independent investigators will identify the relevant publications, and discrepancies will be adjudicated by a third independent investigator. Data extracted will include incidence of PTE, time intervals between TBI and PTE, seizure characteristics, injury characteristics, patient demographics and clinical data. Data extraction will be performed by two independent investigators and cross-checked by a third investigator. A descriptive analysis of PTE incidence will be conducted and a weighted mean will be calculated. If sufficient data are available, stratified meta-analysis of subgroups will also be conducted.

ETHICS AND DISSEMINATION

Ethics approval was not required for this study. We intend to publish our findings in a high-quality peer-reviewed journal on completion.

PROSPERO REGISTRATION NUMBER

CRD42021245802.

A Pro-social Pill? The Potential of Pharmacological Treatments to Improve Social Outcomes After Pediatric Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of injury-induced disability in young children worldwide, and social behavior impairments in this population are a significant challenge for affected patients and their families. The protracted trajectory of secondary injury processes triggered by a TBI during early life-alongside ongoing developmental maturation-offers an extended time window when therapeutic interventions may yield functional benefits. This mini-review explores the scarce but promising pre-clinical literature to date demonstrating that social behavior impairments after early life brain injuries can be modified by drug therapies. Compounds that provide broad neuroprotection, such as those targeting neuroinflammation, oxidative stress, axonal injury and/or myelination, may prevent social behavior impairments by reducing secondary neuropathology. Alternatively, targeted treatments that promote affiliative behaviors, exemplified by the neuropeptide oxytocin, may reduce the impact of social dysfunction after pediatric TBI. Complementary literature from other early life neurodevelopmental conditions such as hypoxic ischemic encephalopathy also provides avenues for future research in neurotrauma. Knowledge gaps in this emerging field are highlighted throughout, toward the goal of accelerating translational research to support optimal social functioning after a TBI during early childhood.

The Impact of Traumatic Injury to the Immature Human Brain: A Scoping Review with Insights from Advanced Structural Neuroimaging

Traumatic brain injury (TBI) during critical periods of early-life brain development can affect the normal formation of brain networks responsible for a range of complex social behaviors. Because of the protracted nature of brain and behavioral development, deficits in cognitive and socioaffective behaviors may not become evident until late adolescence and early adulthood, when such skills are expected to reach maturity. In addition, multiple pre- and post-injury factors can interact with the effects of early brain insult to influence long-term outcomes. In recent years, with advancements in magnetic-resonance-based neuroimaging techniques and analysis, studies of the pediatric population have revealed a link between neurobehavioral deficits, such as social dysfunction, with white matter damage. In this review, in which we focus on contributions from Australian researchers to the field, we have highlighted pioneering longitudinal studies in pediatric TBI, in relation to social deficits specifically. We also discuss the use of advanced neuroimaging and novel behavioral assays in animal models of TBI in the immature brain. Together, this research aims to understand the relationship between injury consequences and ongoing brain development after pediatric TBI, which promises to improve prediction of the behavioral deficits that emerge in the years subsequent to early-life injury.

A systemic immune challenge to model hospital-acquired infections independently regulates immune responses after pediatric traumatic brain injury

Background

Traumatic brain injury (TBI) is a major cause of disability in young children, yet the factors contributing to poor outcomes in this population are not well understood. TBI patients are highly susceptible to nosocomial infections, which are mostly acquired within the first week of hospitalization, and such infections may modify TBI pathobiology and recovery. In this study, we hypothesized that a peripheral immune challenge such as lipopolysaccharide (LPS)—mimicking a hospital-acquired infection—would worsen outcomes after experimental pediatric TBI, by perpetuating the inflammatory immune response.

Methods

Three-week-old male mice received either a moderate controlled cortical impact or sham surgery, followed by a single LPS dose (1 mg/kg i.p.) or vehicle (0.9% saline) at 4 days post-surgery, then analysis at 5 or 8 days post-injury (i.e., 1 or 4 days post-LPS).

Results

LPS-treated mice exhibited a time-dependent reduction in general activity and social investigation, and increased anxiety, alongside substantial body weight loss, indicating transient sickness behaviors. Spleen-to-body weight ratios were also increased in LPS-treated mice, indicative of persistent activation of adaptive immunity at 4 days post-LPS. TBI + LPS mice showed an impaired trajectory of weight gain post-LPS, reflecting a synergistic effect of TBI and the LPS-induced immune challenge. Flow cytometry analysis demonstrated innate immune cell activation in blood, brain, and spleen post-LPS; however, this was not potentiated by TBI. Cytokine protein levels in serum, and gene expression levels in the brain, were altered in response to LPS but not TBI across the time course. Immunofluorescence analysis of brain sections revealed increased glia reactivity due to injury, but no additive effect of LPS was observed.

Conclusions

Together, we found that a transient, infection-like systemic challenge had widespread effects on the brain and immune system, but these were not synergistic with prior TBI in pediatric mice. These findings provide novel insight into the potential influence of a secondary immune challenge to the injured pediatric brain, with future studies needed to elucidate the chronic effects of this two-hit insult.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02114-1.

Acute treatment with TrkB agonist LM22A-4 confers neuroprotection and preserves myelin integrity in a mouse model of pediatric traumatic brain injury

Young children have a high risk of sustaining a traumatic brain injury (TBI), which can have debilitating life-long consequences. Importantly, the young brain shows particular vulnerability to injury, likely attributed to ongoing maturation of the myelinating nervous system at the time of insult. Here, we examined the effect of acute treatment with the partial tropomyosin receptor kinase B (TrkB) agonist, LM22A-4, on pathological and neurobehavioral outcomes after pediatric TBI, with the hypothesis that targeting TrkB would minimize tissue damage and support functional recovery. We focused on myelinated tracts-the corpus callosum and external capsules-based on recent evidence that TrkB activation potentiates oligodendrocyte remyelination. Male mice at postnatal day 21 received an experimental TBI or sham surgery. Acutely post-injury, extensive cell death, a robust glial response and disruption of compact myelin were evident in the injured brain. TBI or sham mice then received intranasal saline vehicle or LM22A-4 for 14 days. Behavior testing was performed from 4 weeks post-injury, and brains were collected at 5 weeks for histology. TBI mice showed hyperactivity, reduced anxiety-like behavior, and social memory impairments. LM22A-4 ameliorated the abnormal anxiolytic phenotype but had no effect on social memory deficits. Use of spectral confocal reflectance microscopy detected persistent myelin fragmentation in the external capsule of TBI mice at 5 weeks post-injury, which was accompanied by regionally distinct deficits in oligodendrocyte progenitor cells and post-mitotic oligodendrocytes, as well as chronic reactive gliosis and atrophy of the corpus callosum and injured external capsule. LM22A-4 treatment ameliorated myelin deficits in the perilesional external capsule, as well as tissue volume loss and the extent of reactive gliosis. However, there was no effect of this TrkB agonist on oligodendroglial populations detected at 5 weeks post-injury. Collectively, our results demonstrate that targeting TrkB immediately after TBI during early life confers neuroprotection and preserves myelin integrity, and this was associated with some improved neurobehavioral outcomes as the pediatric injured brain matures.

Catastrophic consequences: can the feline parasite Toxoplasma gondii prompt the purrfect neuroinflammatory storm following traumatic brain injury?

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality worldwide; however, treatment development is hindered by the heterogenous nature of TBI presentation and pathophysiology. In particular, the degree of neuroinflammation after TBI varies between individuals and may be modified by other factors such as infection. Toxoplasma gondii, a parasite that infects approximately one-third of the world’s population, has a tropism for brain tissue and can persist as a life-long infection. Importantly, there is notable overlap in the pathophysiology between TBI and T. gondii infection, including neuroinflammation. This paper will review current understandings of the clinical problems, pathophysiological mechanisms, and functional outcomes of TBI and T. gondii, before considering the potential synergy between the two conditions. In particular, the discussion will focus on neuroinflammatory processes such as microglial activation, inflammatory cytokines, and peripheral immune cell recruitment that occur during T. gondii infection and after TBI. We will present the notion that these overlapping pathologies in TBI individuals with a chronic T. gondii infection have the strong potential to exacerbate neuroinflammation and related brain damage, leading to amplified functional deficits. The impact of chronic T. gondii infection on TBI should therefore be investigated in both preclinical and clinical studies as the possible interplay could influence treatment strategies.

Systemic treatment with human amnion epithelial cells after experimental traumatic brain injury

Systemic administration of human amnion epithelial cells (hAECs) was recently shown to reduce neuropathology and improve functional recovery following ischemic stroke in both mice and marmosets. Given the significant neuropathological overlap between ischemic stroke and traumatic brain injury (TBI), we hypothesized that a similar hAEC treatment regime would also improve TBI outcomes. Male mice (12 weeks old, n ​= ​40) were given a sham injury or moderate severity TBI by controlled cortical impact. At 60 ​min post-injury, mice were given a single tail vein injection of either saline (vehicle) or 1 ​× ​10⁶ hAECs suspended in saline. At 24 ​h post-injury, mice were assessed for locomotion and anxiety using an open field, and sensorimotor ability using a rotarod. At 48 ​h post-injury, brains were collected for analysis of immune cells via flow cytometry, or histological evaluation of lesion volume and hAEC penetration. To assess the impact of TBI and hAECs on lymphoid organs, spleen and thymus weights were determined. Treatment with hAECs did not prevent TBI-induced sensorimotor deficits at 24 ​h post-injury. hAECs were detected in the injured brain parenchyma; however, lesion volume was not altered by hAEC treatment. Robust increases in several leukocyte populations in the ipsilateral hemisphere of TBI mice were found when compared to sham mice at 48 ​h post-injury; however, hAEC treatment did not alter brain immune cell numbers. Both TBI and hAEC treatment were found to increase spleen weight. Taken together, these findings indicate that-unlike in ischemic stroke-treatment with hAEC was unable to prevent immune cell infiltration and sensorimotor deficits in the acute stages following controlled cortical impact in mice. Although further investigations are required, our data suggests that the lack of hAEC-induced neuroprotection in the current study may be explained by the differential splenic contributions to neuropathology between these brain injury models.

Immune Challenges and Seizures: How Do Early Life Insults Influence Epileptogenesis?

The development of epilepsy, a process known as epileptogenesis, often occurs later in life following a prenatal or early postnatal insult such as cerebral ischemia, stroke, brain trauma, or infection. These insults share common pathophysiological pathways involving innate immune activation including neuroinflammation, which is proposed to play a critical role in epileptogenesis. This review provides a comprehensive overview of the latest preclinical evidence demonstrating that early life immune challenges influence neuronal hyperexcitability and predispose an individual to later life epilepsy. Here, we consider the range of brain insults that may promote the onset of chronic recurrent spontaneous seizures at adulthood, spanning intrauterine insults (e.g. maternal immune activation), perinatal injuries (e.g. hypoxic–ischemic injury, perinatal stroke), and insults sustained during early postnatal life—such as fever-induced febrile seizures, traumatic brain injuries, infections, and environmental stressors. Importantly, all of these insults represent, to some extent, an immune challenge, triggering innate immune activation and implicating both central and systemic inflammation as drivers of epileptogenesis. Increasing evidence suggests that pro-inflammatory cytokines such as interleukin-1 and subsequent signaling pathways are important mediators of seizure onset and recurrence, as well as neuronal network plasticity changes in this context. Our current understanding of how early life immune challenges prime microglia and astrocytes will be explored, as well as how developmental age is a critical determinant of seizure susceptibility. Finally, we will consider the paradoxical phenomenon of preconditioning, whereby these same insults may conversely provide neuroprotection. Together, an improved appreciation of the neuroinflammatory mechanisms underlying the long-term epilepsy risk following early life insults may provide insight into opportunities to develop novel immunological anti-epileptogenic therapeutic strategies.

Validation of reference genes for gene expression analysis following experimental traumatic brain injury in a pediatric mouse model

Quantitative polymerase chain reaction (qPCR) is the gold standard method in targeted analysis of messenger RNA (mRNA) levels in a tissue. To minimize methodological errors, a reference gene (or a combination of reference genes) is routinely used for normalization to account for technical variables such as RNA quality and sample size. While presumed to have stable expression, reference genes in the brain can change during normal development, as well as in response to injury, such as traumatic brain injury (TBI). This study is the first to evaluate the stability of reference genes in a controlled cortical impact (CCI) model in the pediatric mouse brain, using two methods of qPCR normalization for optimal reference gene selection. Three week old mice were subjected to unilateral CCI at two severity of injuries (mild or severe), compared to sham controls. At 1 and 8 weeks post-injury, the ipsilateral hemisphere was analyzed to determine reference gene stability. Five commonly-used reference genes were compared: tyrosine 3 monooxygenase/tryptophan 5 monooxygenase activation protein zeta (Ywhaz), cyclophilin A (Ppia), hypoxanthine phosphoribosyl transferase (Hprt), glyceraldehyde-3-phosphate dehydrogenase (Gapdh) and β-actin (Actb). Ppia and Hprt were chosen as the most stable combination of genes using GeNORM software analysis. These results highlight the instability of several commonly used reference genes after TBI, and provide a selection of validated genes for future gene expression analyses in the injured pediatric mouse brain.

An animal model of genetic predisposition to develop acquired epileptogenesis: The FAST and SLOW rats

Epidemiological data and gene association studies suggest a genetic predisposition to developing epilepsy after an acquired brain insult, such as traumatic brain injury. An improved understanding of genetic determinants of vulnerability is imperative for early disease diagnosis and prognosis prediction, with flow-on benefits for the development of targeted antiepileptogenic treatments as well as optimal clinical trial design. In the laboratory, one approach to investigate why some individuals are more vulnerable to acquired epilepsy than others is to examine unique rodent models exhibiting either vulnerability or resistance to epileptogenesis. This review focuses on the most well-characterized of these models, the FAST (seizure-prone) and SLOW (seizure-resistant) rat strains, which were derived by selective breeding for differential amygdala electrical kindling rates. We describe how these strains differ in their seizure profiles, neuroanatomy, and neurobehavioral phenotypes, both at baseline and after a brain insult, with this knowledge proving fruitful to identify common pathological abnormalities associated with seizure susceptibility and psychiatric comorbidities. It is important to note that accruing data on strain differences in multiple biological processes provides insight into why some individuals may be more vulnerable to epileptogenesis, although future studies are evidently needed to identify the precise molecular and genetic risk factors. Together, the FAST and SLOW rat strains, and other similar experimental models, are invaluable neurobiological tools to investigate the effect of genetic background on acquired epilepsy risk, as well as the poorly understood relationship between epilepsy development and associated comorbidities.

Aged rats have an altered immune response and worse outcomes after traumatic brain injury

Initial studies suggest that increased age is associated with worse outcomes after traumatic brain injury (TBI), though the pathophysiological mechanisms responsible for this remain unclear. Immunosenescence (i.e., dysregulation of the immune system due to aging) may play a significant role in influencing TBI outcomes. This study therefore examined neurological outcomes and immune response in young-adult (i.e., 10 weeks old) compared to middle-aged (i.e., 1 year old) rats following a TBI (i.e., fluid percussion) or sham-injury. Rats were euthanized at either 24 h or one-week post-injury to analyze immune cell populations in the brain and periphery via flow cytometry, as well as telomere length (i.e., a biomarker of neurological health). Behavioral testing, as well as volumetric and diffusion-weighted MRI, were also performed in the one-week recovery rats to assess for functional deficits and brain damage. Middle-aged rats had worse sensorimotor deficits and shorter telomeres after TBI compared to young rats. Both aging and TBI independently worsened cognitive function and cortical volume. These changes occurred in the presence of fewer total leukocytes, fewer infiltrating myeloid cells, and fewer microglia in the brains of middle-aged TBI rats compared to young rats. These findings indicate that middle-aged rats have worse sensorimotor deficits and shorter telomeres after TBI than young rats, and this may be related to an altered neuroimmune response. Although further studies are required, these findings have important implications for understanding the pathophysiology and optimal treatment strategies in TBI patients across the life span.

Infections after a traumatic brain injury: The complex interplay between the immune and neurological systems

Traumatic brain injury (TBI) is a serious global health issue, being the leading cause of death and disability for individuals under the age of 45, and one of the largest causes of global neurological disability. In addition to the brain injury itself, it is increasingly appreciated that a TBI may also alter the systemic immune response in a way that renders TBI patients more vulnerable to infections in the acute post-injury period. Such infections pose an additional challenge to the patient, increasing rates of mortality and morbidity, and worsening neurological outcomes. Hospitalization, surgical interventions, and a state of immunosuppression induced by injury to the central nervous system (CNS), may all contribute to the high rate of infections seen in the population with TBI. Ongoing research to better understand the immunomodulators that underlie TBI-induced immunosuppression may aid in the development of effective therapeutic strategies to improve the recovery trajectory for patients. This review first describes the clinical scenario, posing the question of whether TBI patients are more susceptible to infections such as pneumonia, and if so, why? We then consider how cross-talk between the injured brain and the systemic immune system occurs, and further, how the additional immune challenge of an acquired infection can contribute to ongoing neuroinflammation and neurodegeneration after a TBI. Experimental models combining TBI with infection are discussed, as well as current treatment options available for this double-barreled insult. The aims of this review are to summarize current understanding of the bidirectional relationship between the CNS and the immune system when faced with a mechanical trauma combined with a concomitant infection, and to highlight key outstanding questions that remain in the field.

The complexity of neuroinflammation consequent to traumatic brain injury: from research evidence to potential treatments

This review recounts the definitions and research evidence supporting the multifaceted roles of neuroinflammation in the injured brain following trauma. We summarise the literature fluctuating from the protective and detrimental properties that cytokines, leukocytes and glial cells play in the acute and chronic stages of TBI, including the intrinsic factors that influence cytokine responses and microglial functions relative to genetics, sex, and age. We elaborate on the pros and cons that cytokines, chemokines, and microglia play in brain repair, specifically neurogenesis, and how such conflicting roles may be harnessed therapeutically to sustain the survival of new neurons. With a brief review of the clinical and experimental findings demonstrating early and chronic inflammation impacts on outcomes, we focus on the clinical conditions that may be amplified by neuroinflammation, ranging from acute seizures to chronic epilepsy, neuroendocrine dysfunction, dementia, depression, post-traumatic stress disorder and chronic traumatic encephalopathy. Finally, we provide an overview of the therapeutic agents that have been tested to reduce inflammation-driven secondary pathological cascades and speculate the future promise of alternative drugs.

In search of antiepileptogenic treatments for post-traumatic epilepsy

Post-traumatic epilepsy (PTE) is diagnosed in 20% of individuals with acquired epilepsy, and can impact significantly the quality of life due to the seizures and other functional or cognitive and behavioral outcomes of the traumatic brain injury (TBI) and PTE. There is no available antiepileptogenic or disease modifying treatment for PTE. Animal models of TBI and PTE have been developed, offering useful insights on the value of inflammatory, neurodegenerative pathways, hemorrhages and iron accumulation, calcium channels and other target pathways that could be used for treatment development. Most of the existing preclinical studies test efficacy towards pathologies of functional recovery after TBI, while a few studies are emerging testing the effects towards induced or spontaneous seizures. Here we review the existing preclinical trials testing new candidate treatments for TBI sequelae and PTE, and discuss future directions for efforts aiming at developing antiepileptogenic and disease-modifying treatments.

Determinants of social behavior deficits and recovery after pediatric traumatic brain injury

Traumatic brain injury (TBI) during early childhood is associated with a particularly high risk of developing social behavior impairments, including deficits in social cognition that manifest as reduced social interactions, with profound consequences for the individuals' quality of life. A number of pre-injury, post-injury, and injury-related factors have been identified or hypothesized to determine the extent of social behavior problems after childhood TBI. These include variables associated with the individual themselves (e.g. age, genetics, the injury severity, and extent of white matter damage), proximal environmental factors (e.g. family functioning, parental mental health), and more distal environmental factors (e.g. socioeconomic status, access to resources). In this review, we synthesize the available evidence demonstrating which of these determinants influence risk versus resilience to social behavior deficits after pediatric TBI, drawing upon the available clinical and preclinical literature. Injury-related pathology in neuroanatomical regions associated with social cognition and behaviors will also be described, with a focus on findings from magnetic resonance imaging and diffusion tensor imaging. Finally, study limitations and suggested future directions are highlighted. In summary, while no single variable can alone accurately predict the manifestation of social behavior problems after TBI during early childhood, an increased understanding of how both injury and environmental factors can influence social outcomes provides a useful framework for the development of more effective rehabilitation strategies aiming to optimize recovery for young brain-injured patients.

A Concomitant Muscle Injury Does Not Worsen Traumatic Brain Injury Outcomes in Mice

Traumatic brain injury (TBI) often involves multitrauma in which concurrent extracranial injury occurs. We previously demonstrated that a long bone fracture exacerbates neuroinflammation and functional outcomes in mice given a TBI. Whether other forms of concomitant peripheral trauma that are common in the TBI setting, such as skeletal muscle injury, have similar effects is unknown. As such, here we developed a novel mouse multitrauma model by combining a closed-skull TBI with a cardiotoxin (CTX)-induced muscle injury to investigate whether muscle injury affects TBI outcomes. Adult male mice were assigned to four groups: sham-TBI + sham-muscle injury (SHAM); sham-TBI + CTX-muscle injury (CTX); TBI + sham-muscle injury (TBI); TBI + CTX-muscle injury (MULTI). Some mice were euthanized at 24 h post-injury to assess neuroinflammation and cerebral edema. The remaining mice underwent behavioral testing after a 30-day recovery period, and were euthanized at 35 days post-injury for post-mortem analysis. At 24 h post-injury, both TBI and MULTI mice had elevated edema, increased expression of GFAP (i.e., a marker for reactive astrocytes), and increased mRNA levels of inflammatory chemokines. There was also an effect of injury on cytokine levels at 35 days post-injury. However, the TBI and MULTI mice did not significantly differ on any of the measures assessed. These initial findings suggest that a concomitant muscle injury does not significantly affect preclinical TBI outcomes. Future studies should investigate the combination of different injury models, additional outcomes, and other post-injury time points.

Modelling traumatic brain injury and posttraumatic epilepsy in rodents

Posttraumatic epilepsy (PTE) is one of the most debilitating and understudied consequences of traumatic brain injury (TBI). It is challenging to study the effects, underlying pathophysiology, biomarkers, and treatment of TBI and PTE purely in human patients for a number of reasons. Rodent models can complement human PTE studies as they allow for the rigorous investigation into the causal relationship between TBI and PTE, the pathophysiological mechanisms of PTE, the validation and implementation of PTE biomarkers, and the assessment of PTE treatments, in a tightly controlled, time- and cost-efficient manner in experimental subjects known to be experiencing epileptogenic processes. This article will review several common rodent models of TBI and/or PTE, including their use in previous studies and discuss their relative strengths, limitations, and avenues for future research to advance our understanding and treatment of PTE.

Affective, neurocognitive and psychosocial disorders associated with traumatic brain injury and post-traumatic epilepsy

Survivors of traumatic brain injury (TBI) often develop chronic neurological, neurocognitive, psychological, and psychosocial deficits that can have a profound impact on an individual's wellbeing and quality of life. TBI is also a common cause of acquired epilepsy, which is itself associated with significant behavioral morbidity. This review considers the clinical and preclinical evidence that post-traumatic epilepsy (PTE) acts as a 'second-hit' insult to worsen chronic behavioral outcomes for brain-injured patients, across the domains of emotional, cognitive, and psychosocial functioning. Surprisingly, few well-designed studies have specifically examined the relationship between seizures and behavioral outcomes after TBI. The complex mechanisms underlying these comorbidities remain incompletely understood, although many of the biological processes that precipitate seizure occurrence and epileptogenesis may also contribute to the development of chronic behavioral deficits. Further, the relationship between PTE and behavioral dysfunction is increasingly recognized to be a bidirectional one, whereby premorbid conditions are a risk factor for PTE. Clinical studies in this arena are often challenged by the confounding effects of anti-seizure medications, while preclinical studies have rarely examined an adequately extended time course to fully capture the time course of epilepsy development after a TBI. To drive the field forward towards improved treatment strategies, it is imperative that both seizures and neurobehavioral outcomes are assessed in parallel after TBI, both in patient populations and preclinical models.

Mild Traumatic Brain Injury in Adolescent Mice Alters Skull Bone Properties to Influence a Subsequent Brain Impact at Adulthood: A Pilot Study

Mild traumatic brain injuries (mTBI) are common during adolescence, and limited clinical evidence suggests that a younger age at first exposure to a mTBI may lead to worse long-term outcomes. In this study, we hypothesized that a mTBI during adolescence would predispose toward poorer neurobehavioral and neuropathological outcomes after a subsequent injury at adulthood. Mice received a mild weight drop injury (mTBI) at adolescence (postnatal day 35; P35) and/or at adulthood (P70). Mice were randomized to 6 groups: 'sham' (sham-surgery at P35 only); 'P35' (mTBI at P35 only); 'P35 + sham' (mTBI at P35 + sham at P70); 'sham + P70' (sham at P35 + mTBI at P70); 'sham + sham' (sham at both P35 and P70); or 'P35 + P70' (mTBI at both P35 and P70). Acute apnea and an extended righting reflex time confirmed a mTBI injury at P35 and/or P70. Cognitive, psychosocial, and sensorimotor function was assessed over 1-week post-injury. Injured groups performed similarly to sham controls across all tasks. Immunofluorescence staining at 1 week detected an increase in glial activation markers in Sham + P70 brains only. Strikingly, 63% of Sham + P70 mice exhibited a skull fracture at impact, compared to 13% of P35 + P70 mice. Micro computed tomography of parietal skull bones found that a mTBI at P35 resulted in increased bone volume and strength, which may account for the difference in fracture incidence. In summary, a single mTBI to the adolescent mouse brain did not exacerbate the cerebral effects of a subsequent mTBI in adulthood. However, the head impact at P35 induced significant changes in skull bone structure and integrity. These novel findings support future investigation into the consequences of mTBI on skull bone.

Treatment with an interleukin-1 receptor antagonist mitigates neuroinflammation and brain damage after polytrauma

Traumatic brain injury (TBI) and long bone fracture are common in polytrauma. This injury combination in mice results in elevated levels of the pro-inflammatory cytokine interleukin-1β (IL-1β) and exacerbated neuropathology when compared to isolated-TBI. Here we examined the effect of treatment with an IL-1 receptor antagonist (IL-1ra) in mice given a TBI and a concomitant tibial fracture (i.e., polytrauma). Adult male C57BL/6 mice were given sham-injuries or polytrauma and treated with saline-vehicle or IL-1ra (100mg/kg). Treatments were subcutaneously injected at 1, 6, and 24h, and then once daily for one week post-injury. 7-8 mice/group were euthanized at 48h post-injury. 12-16 mice/group underwent behavioral testing at 12weeks post-injury and MRI at 14weeks post-injury before being euthanized at 16weeks post-injury. At 48h post-injury, markers for activated microglia and astrocytes, as well as neutrophils and edema, were decreased in polytrauma mice treated with IL-1ra compared to polytrauma mice treated with vehicle. At 14weeks post-injury, MRI analysis demonstrated that IL-1ra treatment after polytrauma reduced volumetric loss in the injured cortex and mitigated track-weighted MRI markers for axonal injury. As IL-1ra (Anakinra) is approved for human use, it may represent a promising therapy in polytrauma cases involving TBI and fracture.

Inflammation in epileptogenesis after traumatic brain injury

Background

Epilepsy is a common and debilitating consequence of traumatic brain injury (TBI). Seizures contribute to progressive neurodegeneration and poor functional and psychosocial outcomes for TBI survivors, and epilepsy after TBI is often resistant to existing anti-epileptic drugs. The development of post-traumatic epilepsy (PTE) occurs in a complex neurobiological environment characterized by ongoing TBI-induced secondary injury processes. Neuroinflammation is an important secondary injury process, though how it contributes to epileptogenesis, and the development of chronic, spontaneous seizure activity, remains poorly understood. A mechanistic understanding of how inflammation contributes to the development of epilepsy (epileptogenesis) after TBI is important to facilitate the identification of novel therapeutic strategies to reduce or prevent seizures.

Body

We reviewed previous clinical and pre-clinical data to evaluate the hypothesis that inflammation contributes to seizures and epilepsy after TBI. Increasing evidence indicates that neuroinflammation is a common consequence of epileptic seizure activity, and also contributes to epileptogenesis as well as seizure initiation (ictogenesis) and perpetuation. Three key signaling factors implicated in both seizure activity and TBI-induced secondary pathogenesis are highlighted in this review: high-mobility group box protein-1 interacting with toll-like receptors, interleukin-1β interacting with its receptors, and transforming growth factor-β signaling from extravascular albumin. Lastly, we consider age-dependent differences in seizure susceptibility and neuroinflammation as mechanisms which may contribute to a heightened vulnerability to epileptogenesis in young brain-injured patients.

Conclusion

Several inflammatory mediators exhibit epileptogenic and ictogenic properties, acting on glia and neurons both directly and indirectly influence neuronal excitability. Further research is required to establish causality between inflammatory signaling cascades and the development of epilepsy post-TBI, and to evaluate the therapeutic potential of pharmaceuticals targeting inflammatory pathways to prevent or mitigate the development of PTE.

Long-Term Anesthetic-Dependent Hypoactivity after Repetitive Mild Traumatic Brain Injuries in Adolescent Mice

Recent evidence supports the hypothesis that repetitive mild traumatic brain injuries (rmTBIs) culminate in neurological impairments and chronic neurodegeneration, which have wide-ranging implications for patient management and return-to-play decisions for athletes. Adolescents show a high prevalence of sports-related head injuries and may be particularly vulnerable to rmTBIs due to ongoing brain maturation. However, it remains unclear whether rmTBIs, below the threshold for acute neuronal injury or symptomology, influence long-term outcomes. To address this issue, we first defined a very mild injury in adolescent mice (postnatal day 35) as evidenced by an increase in Iba-1- labeled microglia in white matter in the acutely injured brain, in the absence of indices of cell death, axonal injury, and vasogenic edema. Using this level of injury severity and Avertin (2,2,2-tribromoethanol) as the anesthetic, we compared mice subjected to either a single mTBI or 2 rmTBIs, each separated by 48 h. Neurobehavioral assessments were conducted at 1 week and at 1 and 3 months postimpact. Mice subjected to rmTBIs showed transient anxiety and persistent and pronounced hypoactivity compared to sham control mice, alongside normal sensorimotor, cognitive, social, and emotional function. As isoflurane is more commonly used than Avertin in animal models of TBI, we next examined long-term outcomes after rmTBIs in mice that were anesthetized with this agent. However, there was no evidence of abnormal behaviors even with the addition of a third rmTBI. To determine whether isoflurane may be neuroprotective, we compared the acute pathology after a single mTBI in mice anesthetized with either Avertin or isoflurane. Pathological findings were more pronounced in the group exposed to Avertin compared to the isoflurane group. These collective findings reveal distinct behavioral phenotypes (transient anxiety and prolonged hypoactivity) that emerge in response to rmTBIs. Our findings further suggest that selected anesthetics may confer early neuroprotection after rmTBIs, and as such mask long-term abnormal phenotypes that may otherwise emerge as a consequence of acute pathogenesis.

Behavioral, blood, and magnetic resonance imaging biomarkers of experimental mild traumatic brain injury

Repeated mild traumatic brain injuries (mTBI) may lead to serious neurological consequences, especially if re-injury occurs within the period of increased cerebral vulnerability (ICV) triggered by the initial insult. MRI and blood proteomics might provide objective measures of pathophysiological changes in mTBI, and indicate when the brain is no longer in a state of ICV. This study assessed behavioral, MRI, and blood-based markers in a rat model of mTBI. Rats were given a sham or mild fluid percussion injury (mFPI), and behavioral testing, MRI, and blood collections were conducted up to 30 days post-injury. There were cognitive impairments for three days post-mFPI, before normalizing by day 5 post-injury. In contrast, advanced MRI (i.e., tractography) and blood proteomics (i.e., vascular endothelial growth factor) detected a number of abnormalities, some of which were still present 30 days post-mFPI. These findings suggest that MRI and blood proteomics are sensitive measures of the molecular and subtle structural changes following mTBI. Of particular significance, this study identified novel tractography measures that are able to detect mTBI and may be more sensitive than traditional diffusion-tensor measures. Furthermore, the blood and MRI findings may have important implications in understanding ICV and are translatable to the clinical setting.

Social dysfunction after pediatric traumatic brain injury: A translational perspective

Social dysfunction is common after traumatic brain injury (TBI), contributing to reduced quality of life for survivors. Factors which influence the development or persistence of social deficits after injury remain poorly understood, particularly in the context of ongoing brain maturation during childhood and adolescence. Aberrant social interactions have recently been modeled in adult and juvenile rodents after experimental TBI, providing an opportunity to gain new insights into the underlying neurobiology of these behaviors. Here, we review our current understanding of social dysfunction in both humans and rodent models of TBI, with a focus on brain injuries acquired during early development. Modulators of social outcomes are discussed, including injury-related and environmental risk and resilience factors. Disruption of social brain network connectivity and aberrant neuroendocrine function are identified as potential mechanisms of social impairments after pediatric TBI. Throughout, we highlight the overlap and disparities between outcome measures and findings from clinical and experimental approaches, and explore the translational potential of future research to prevent or ameliorate social dysfunction after childhood TBI.