The development of lasting impairments: a mild pediatric brain injury alters gene expression, dendritic morphology, and synaptic connectivity in the prefrontal cortex of rats

Developmental functions of microglia: Impact of psychosocial and physiological early life stress

Microglia play numerous important roles in brain development. From early embryonic stages through adolescence, these immune cells influence neuronal genesis and maturation, guide connectivity, and shape brain circuits. They also interact with other glial cells and structures, influencing the brain's supportive microenvironment. While this central role makes microglia essential, it means that early life perturbations to microglia can have widespread effects on brain development, potentially resulting in long-lasting behavioral impairments. Here, we will focus on the effects of early life psychosocial versus physiological stressors in rodent models. Psychosocial stress refers to perceived threats that lead to stress axes activation, including prenatal stress, or chronic postnatal stress, including maternal separation and resource scarcity. Physiological stress refers to physical threats, including maternal immune activation, postnatal infection, and traumatic brain injury. Differing sources of early life stress have varied impacts on microglia, and these effects are moderated by factors such as developmental age, brain region, and sex. Overall, these stressors appear to either 1) upregulate basal microglia numbers and activity throughout the lifespan, while possibly blunting their responsivity to subsequent stressors, or 2) shift the developmental curve of microglia, resulting in differential timing and function, impacting the critical periods they govern. Either could contribute to behavioral dysfunctions that occur after the resolution of early life stress. Exploring how different stressors impact microglia, as well as how multiple stressors interact to alter microglia's developmental functions, could deepen our understanding of how early life stress changes the brain's developmental trajectory. This article is part of the Special Issue on "Microglia".

Temporal expression of brainstem neurotrophic proteins following mild traumatic brain injury

BDNF, a neurotrophic factor, and its receptors have been implicated in the pathophysiology of mild traumatic brain injury (mTBI). The brainstem houses many vital functions, that are also associated with signs and symptoms of mTBI, but has been understudied in mTBI animal models. We determined the extent to which neurotrophic protein and associated receptor expression is affected within the brainstem of adult rats following mTBI. Their behavioral function was assessed and temporal expression of the 'negative' regulators of neuronal function (p75, t-TrkB, and pro-BDNF) and 'positive' neuroprotective (FL-TrkB and m-BDNF) protein isoforms were determined via western blot and immunohistochemistry at 1, 3, 7, and 14 post-injury days (PID) following mTBI or sham (control) procedure. Within the brainstem, p75 expression increased at PID 1 vs. sham animals. t-TrkB and pro-BDNF expression increased at PID 7 and 14. The 'positive' protein isoforms of FL-TrkB and m-BDNF expression were increased only at PID 7. The ratio of t-TrkB:FL-TrkB (negative:positive) was substantial across groups and time points, suggesting a negative impact of neurotrophic signaling on neuronal function. Additional NeuN experiments revealed cell death occurring within a subset of neurons within the medulla. While behavioral measures improved by PID 7-14, negative neurotrophic biochemical responses persisted. Despite the assertion that mTBI produces "mild" injury, evidence of cell death was observed in the medulla. Ratios of TrkB and BDNF isoforms with conflicting functions suggest that future work should specifically measure each subtype since they induce opposing downstream effects on neuronal function.

A strike to the head: Parallels between the pediatric and adult human and the rodent in traumatic brain injury

Traumatic brain injury (TBI) is a condition that occurs commonly in children from infancy through adolescence and is a global health concern. Pediatric TBI presents with a bimodal age distribution, with very young children (0-4 years) and adolescents (15-19 years) more commonly injured. Because children's brains are still developing, there is increased vulnerability to the effects of head trauma, which results in entirely different patterns of injury than in adults. Pediatric TBI has a profound and lasting impact on a child's development and quality of life, resulting in long-lasting consequences to physical, cognitive, and emotional development. Chronic issues like learning disabilities, behavioral problems, and emotional disturbances can develop. Early intervention and ongoing support are critical for minimizing these long-term deficits. Many animal models of TBI exist, and each varies significantly, displaying different characteristics of clinical TBI. The neurodevelopment differs in the rodent from the human in timing and effect, so TBI outcomes in the juvenile rodent can thus vary from the human child. The current review compares findings from preclinical TBI work in juvenile and adult rodents to clinical TBI research in pediatric and adult humans. We focus on the four brain regions most affected by TBI: the prefrontal cortex, corpus callosum, hippocampus, and hypothalamus. Each has its unique developmental projections and thus is impacted by TBI differently. This review aims to compare the healthy neurodevelopment of these four brain regions in humans to the developmental processes in rodents.

Microbiome depletion prior to repeat mild TBI differentially alters social deficits and prefrontal cortex plasticity in adolescent and adult rats

Although aging, repeat mild traumatic brain injury (RmTBI), and microbiome modifications independently change social behavior, there has been no investigation into their cumulative effects on social behavior and neuroplasticity within the prefrontal cortex. Therefore, we examined how microbiome depletion prior to RmTBI affected social behavior and neuroplasticity in adolescent and adult rats. Play, temperament analysis, elevated plus maze, and the hot/cold plate assessed socio-emotional function. Analyses of perineuronal nets (PNNs) and parvalbumin (PV) interneurons was completed. Social-emotional deficits were more pronounced in adults, with microbiome depletion attenuating social behavior deficits associated with RmTBI in both age groups. Microbiome depletion increased branch length and PNN arborization within the PFC but decreased the overall number of PNNs. Adults and males were more vulnerable to RmTBI. Interestingly, microbiome depletion may have attenuated the changes to neuroplasticity and subsequent social deficits, suggesting that the microbiome is a viable, but age-specific, target for RmTBI therapeutics.

Sex and Age-at-Injury as Determinants of Social Behavior Outcomes After TBI

While our understanding of long-term disability after traumatic brain injury (TBI) has habitually focused on cognitive and sensorimotor functioning, it is increasingly appreciated that changes in social function for survivors of a brain injury are common and have a profound impact on one's quality of life. In this chapter, we highlight the consequences of TBI on social behavior, taking into account evidence from studies of patient populations as well as from preclinical animal models. After first considering the protracted nature of the development of social behavior across the lifespan, including the neurobiological networks that underlie social functioning, we discuss how TBI results in social behavior impairments and how these manifest. We focus particularly on how age-at-injury influences TBI-induced social impairments, with most of the evidence suggesting age-dependent vulnerability after injury at a younger age. In addition, we explore how biological sex is a key determinant of social behavior impairments after TBI, while gender in humans may also influence the nature and extent of social outcomes. Finally, we identify key knowledge gaps and emphasize the need for further research in the field.

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.

Tactile stimulation improves cognition, motor, and anxiety-like behaviors and attenuates the Alzheimer's disease pathology in adult APPNL-G-F/NL-G-F mice

Alzheimer's disease (AD) is one of the largest health crises in the world. There are limited pharmaceutical interventions to treat AD, however, and most of the treatment options are not for cure or prevention, but rather to slow down the progression of the disease. The aim of this study was to examine the effect of tactile stimulation (TS) on AD-like symptoms and pathology in APP^{NL-G-F/NL-G-F} mice, a mouse model of AD. The results show that TS reduces the AD-like symptoms on tests of cognition, motor, and anxiety-like behaviors and these improvements in behavior are associated with reduced AD pathology in APP mice. Thus, TS appears to be a promising noninvasive strategy for slowing the onset of dementia in aging animals.

Repeated mild traumatic brain injuries in mice cause age- and sex-specific alterations in dendritic spine density

Mild traumatic brain injuries (mTBI) plague the human population and their prevalence is increasing annually. More so, repeated mTBIs (RmTBI) are known to manifest and compound neurological deficits in vulnerable populations. Age at injury and sex are two important factors influencing RmTBI pathophysiology, but we continue to know little about the specific effects of RmTBI in youth and females. In this study, we directly quantified the effects of RmTBI on adolescent and adult, male and female mice, with a closed-head lateral impact model. We report age- and sex-specific neurobehavioural deficits in motor function and working memory, microglia responses to injury, and the subsequent changes in dendritic spine density in select brain regions. Specifically, RmTBI caused increased footslips in adult male mice as assessed in a beam walk assay and significantly reduced the time spent with a novel object in adolescent male and female mice. RmTBIs caused a significant reduction in microglia density in male mice in the motor cortex, but not female mice. Finally, RmTBI significantly reduced dendritic spine density in the agranular insular cortex (a region of the prefrontal cortex in mice) and increased dendritic spine density in the adolescent male motor cortex. Together, the data provided in this study sheds new light on the heterogeneity in RmTBI-induced behavioural, glial, and neuronal architecture changes dependent on age and sex.

The Effect of Mild Hypothermia on Nogo-A and Neurological Function in the Brain after Cardiopulmonary Resuscitation in Rats

ObjectiveWe investigated the dynamic changes of Nogo-A protein in brain and the effects of mild therapeutic hypothermia (MTH) on its expression after cardiopulmonary resuscitation (CPR). Methods: Western-blotting and neurological scoring of 45 rats subjected to cardiac arrest and CPR with and without MTR were performed to investigate the changes in the expression of Nogo-A protein in the hippocampus and cortex over a period of time ranging from 6 h to 72 h after restoration of spontaneous circulation (ROSC). Results: Nogo-A expression levels were increased at 6 h after CPR in the hippocampus and cortex, peaked at 24 h in the cortex, and at 48 h in the hippocampus. The expression of Nogo-A in the MTR group was significantly lower at 12 h (p < 0.05) compared to those with no MTR after ROSC. Conclusions: MTR blunts the expression of Nogo-A protein in the hippocampus and cortex after cardiac arrest and resuscitation, and MTR may provide cerebral protection after ischemia.

Sex and estrous-phase dependent alterations in depression-like behavior following mild traumatic brain injury in adolescent rats

Following mild traumatic brain injury (TBI), high school and collegiate-aged females tend to report more emotional symptoms than males. Adolescent male and female rats (35 days old) were subjected to mild TBI and evaluated for anxiety- and depression-like behaviors using the elevated plus maze and forced swim test (FST), respectively, and cellular alterations. Injured brains did not exhibit an overt lesion, atrophy of tissue or astrocytic reactivity underneath the impact site at 6-week post-injury, suggestive of the mild nature of trauma. Neither male nor female brain-injured rats exhibited anxiety-like behavior at 2 or 6 weeks, regardless of estrous phase at the time of behavior testing. Brain-injured male rats did not exhibit any alterations in immobility, swimming and climbing times in the FST compared to sham-injured rats at either 2- or 6-week post-injury. Brain-injured female rats did, however, exhibit an increase in immobility (in the absence of changes in swimming and climbing times) in the FST at 6 weeks post-injury only during the estrus phase of the estrous cycle, suggestive of a depression-like phenotype. Combined administration of the estrogen receptor antagonist, tamoxifen, and the progesterone receptor antagonist, mifepristone, during proestrus was able to prevent the depression-like phenotype observed during estrus. Taken together, these data suggest that female rats may be more vulnerable to exhibiting behavioral deficits following mild TBI and that estrous phase may play a role in depression-like behavior.

Subconcussive Head Impacts and Neurocognitive Function Over 3 Seasons of Youth Football

OBJECTIVE

To determine the association between repetitive subconcussive head impacts and neurobehavioral outcomes in youth tackle football players.

METHODS

Using helmet-based sensors, we measured head impacts for 3 consecutive seasons of play in 29 male players age 9-11. Cumulative impact g's were calculated. Players completed a battery of outcome measures before and after each season, including neuropsychological testing, vestibular-ocular sensitivity, and self- and parent-reported measures of symptoms and attention-deficit hyperactivity disorder (ADHD).

RESULTS

Average cumulative impact over 3 seasons was 13 900g. High-intensity hits predicted worse change for self-reported social adjustment (P = .001). Cumulative impact did not predict change in any of the outcome measures. History of ADHD, anxiety, and depression predicted worse change for self-reported symptoms and social adjustment, independent of head impacts. When players were stratified into 3 groups based on cumulative impact across all 3 seasons, differences in outcome measures existed prior to the start of the first season. These differences did not further increase over the course of the 3 seasons.

CONCLUSION

Over 3 consecutive seasons of youth tackle football, we found no association between cumulative head impacts and neurobehavioral outcomes. Larger sample sizes and longer follow-up times would further assist in characterizing this relationship.

Pathophysiology of Pediatric Traumatic Brain Injury

The national incidence of traumatic brain injury (TBI) exceeds that of any other disease in the pediatric population. In the United States the Centers for Disease Control and Prevention (CDC) reports 697,347 annual TBIs in children ages 0–19 that result in emergency room visits, hospitalization or deaths. There is a bimodal distribution within the pediatric TBI population, with peaks in both toddlers and adolescents. Preclinical TBI research provides evidence for age differences in acute pathophysiology that likely contribute to long-term outcome differences between age groups. This review will examine the timecourse of acute pathophysiological processes during cerebral maturation, including calcium accumulation, glucose metabolism and cerebral blood flow. Consequences of pediatric TBI are complicated by the ongoing maturational changes allowing for substantial plasticity and windows of vulnerabilities. This review will also examine the timecourse of later outcomes after mild, repeat mild and more severe TBI to establish developmental windows of susceptibility and altered maturational trajectories. Research progress for pediatric TBI is critically important to reveal age-associated mechanisms and to determine knowledge gaps for future studies.

Stem Cell Therapy for Pediatric Traumatic Brain Injury

There has been a growing interest in the potential of stem cell transplantation as therapy for pediatric brain injuries. Studies in pre-clinical models of pediatric brain injury such as Traumatic Brain Injury (TBI) and neonatal hypoxia-ischemia (HI) have contributed to our understanding of the roles of endogenous stem cells in repair processes and functional recovery following brain injury, and the effects of exogenous stem cell transplantation on recovery from brain injury. Although only a handful of studies have evaluated these effects in models of pediatric TBI, many studies have evaluated stem cell transplantation therapy in models of neonatal HI which has a considerable overlap of injury pathology with pediatric TBI. In this review, we have summarized data on the effects of stem cell treatments on histopathological and functional outcomes in models of pediatric brain injury. Importantly, we have outlined evidence supporting the potential for stem cell transplantation to mitigate pathology of pediatric TBI including neuroinflammation and white matter injury, and challenges that will need to be addressed to incorporate these therapies to improve functional outcomes following pediatric TBI.

Microglia dynamics in adolescent traumatic brain injury

Repetitive, mild traumatic brain injuries (RmTBIs) are increasingly common in adolescents and encompass one of the largest neurological health concerns in the world. Adolescence is a critical period for brain development where RmTBIs can substantially impact neurodevelopmental trajectories and life-long neurological health. Our current understanding of RmTBI pathophysiology suggests key roles for neuroinflammation in negatively regulating neural health and function. Microglia, the brain’s resident immune population, play important roles in brain development by regulating neuronal number, and synapse formation and elimination. In response to injury, microglia activate to inflammatory phenotypes that may detract from these normal homeostatic, physiological, and developmental roles. To date, however, little is known regarding the impact of RmTBIs on microglia function during adolescent brain development. This review details key concepts surrounding RmTBI pathophysiology, adolescent brain development, and microglia dynamics in the developing brain and in response to injury, in an effort to formulate a hypothesis on how the intersection of these processes may modify long-term trajectories.

DNA damage and repair following traumatic brain injury

Traumatic brain injury (TBI) is known to promote significant DNA damage irrespective of age, sex, and species. Chemical as well as structural DNA modification start within minutes and persist for days after TBI. Although several DNA repair pathways are induced following TBI, the simultaneous downregulation of some of the genes and proteins of these pathways leads to an aberrant overall DNA repair process. In many instances, DNA damages escape even the most robust repair mechanisms, especially when the repair process becomes overwhelmed or becomes inefficient by severe or repeated injuries. The persisting DNA damage and/or lack of DNA repair contributes to long-term functional deficits. In this review, we discuss the mechanisms of TBI-induced DNA damage and repair. We further discussed the putative experimental therapies that target the members of the DNA repair process for improved outcome following TBI.

Caffeine consumption during development alters spine density and recovery from repetitive mild traumatic brain injury in young adult rats

Caffeine is the most commonly used psychostimulant throughout the world, with its consumption being especially prevalent among adolescents and young adults, as over 75% of this group consumes caffeine daily. Similarly, the adolescent and young adult age group exhibit the highest incidence of traumatic brain injury (TBI). Given that both caffeine consumption and mild TBI (mTBI) are more prevalent among the late adolescent/young adult age group and that changes in dendritic spine morphology during this developmental period are poorly understood, this study sought to examine the effects of caffeine consumption during late adolescence/early adulthood on recovery from repetitive mTBI (RmTBI). The study specifically focused on changes to neuronal dendritic morphology as synaptic changes likely underlie long-term behavioral outcomes. The results demonstrate that during young adulthood caffeine consumption differentially affects the RmTBI outcomes of males and females, where the effects of caffeine and RmTBI were often additive in males while being equally detrimental, but rarely additive, in females. In general, caffeine and RmTBI induced the greatest impairments in males on cognitive and motor tasks whereas in females the most significant detriments were on pain-related tasks. Both caffeine and RmTBI increased spine density in the Cg3 (medial prefrontal cortex [mPFC]), AID (orbitofrontal cortex [OFC]), and nucleus accumbens (NAc), which is proposed to reflect an impairment in the normal pruning processes. Overall, despite caffeine's neuroprotective abilities among other age groups, this study offers concerning results regarding the detrimental effects of caffeine and RmTBI, in isolation, and especially in combination, in this susceptible population.

Epigenetics of the Synapse in Neurodegeneration

PURPOSE OF REVIEW

In the quest for understanding the pathophysiological processes underlying degeneration of nervous systems, synapses are emerging as sites of great interest as synaptic dysfunction is thought to play a role in the initiation and progression of neuronal loss. In particular, the synapse is an interesting target for the effects of epigenetic mechanisms in neurodegeneration. Here, we review the recent advances on epigenetic mechanisms driving synaptic compromise in major neurodegenerative disorders.

RECENT FINDINGS

Major developments in sequencing technologies enabled the mapping of transcriptomic patterns in human postmortem brain tissues in various neurodegenerative diseases, and also in cell and animal models. These studies helped identify changes in classical neurodegeneration pathways and discover novel targets related to synaptic degeneration. Identifying epigenetic patterns indicative of synaptic defects prior to neuronal degeneration may provide the basis for future breakthroughs in the field of neurodegeneration.

Brain interrupted: Early life traumatic brain injury and addiction vulnerability

Recent reports provide evidence for increased risk of substance use disorders (SUD) among patients with a history of early-life traumatic brain injury (TBI). Preclinical research utilizing animal models of TBI have identified injury-induced inflammation, blood-brain barrier permeability, and changes to synapses and neuronal networks within regions of the brain associated with the perception of reward. Importantly, these reward pathway networks are underdeveloped during childhood and adolescence, and early-life TBI pathology may interrupt ongoing maturation. As such, maladaptive changes induced by juvenile brain injury may underlie increased susceptibility to SUD. In this review, we describe the available clinical and preclinical evidence that identifies SUD as a persistent psychiatric consequence of pediatric neurotrauma by discussing (1) the incidence of early-life TBI, (2) how preclinical studies model TBI and SUD, (3) TBI-induced neuropathology and neuroinflammation in the corticostriatal regions of the brain, and (4) the link between childhood or adolescent TBI and addiction in adulthood. In summary, preclinical research utilizes an innovative combination of models of early-life TBI and SUD to recapitulate clinical features and to determine how TBI promotes a risk for the development of SUD. However, causal processes that link TBI and SUD remain unclear. Additional research to identify and therapeutically target underlying mechanisms of aberrant reward pathway development will provide a launching point for TBI and SUD treatment strategies.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

Modeling sports-related mild traumatic brain injury in animals-A systematic review

Sports-related head trauma has emerged as an important public health issue, as mild traumatic brain injuries (mTBIs) may result in neurodegenerative disorders such as chronic traumatic encephalopathy (CTE). Research into mTBI and CTE pathophysiology are difficult to undertake in athletes, with observational trials and post-mortem analysis the current mainstays. Thus, animal models play an important role in the study of mTBI, however, traditional animal models have focused on acute, severe injuries rather than the more typical mTBI's seen in sport injuries. Recently, a number of animal models have been developed that are both appropriately scaled and biomechanically relevant to the forces sustained by athletes. This review aimed to examine the literature for variables included in these animal models, and the resulting neurotrauma as evidenced by pathology and behavioral deficits. A systematic search of the literature was performed in multiple electronic databases. The inclusion criteria required mimicry of athlete mTBI conditions: freedom of head movement, lack of surgical alteration of the skull, and application of direct contact force. Studies were analyzed for variables including apparatus design features (impact force, change in animal head velocity, and kinetic energy transfer to the head), demonstrated pathology (phosphorylated tau, TDP-43 aggregation, diffuse axonal injury, gliosis, cytokine inflammation response, and genetic integrity), and behavioral changes. These studies suggested that appropriate animal models can assist in understanding the pathological and functional outcomes of athlete mTBI, and could be used as a platform for future studies of diagnostic/prognostic markers and in the development of treatment interventions.

Neuroendocrine Whiplash: Slamming the Breaks on Anabolic-Androgenic Steroids Following Repetitive Mild Traumatic Brain Injury in Rats May Worsen Outcomes

Sport-related concussion is an increasingly common injury among adolescents, with repetitive mild traumatic brain injuries (RmTBI) being a significant risk factor for long-term neurobiological and psychological consequences. It is not uncommon for younger professional athletes to consume anabolic-androgenic steroids (AAS) in an attempt to enhance their performance, subjecting their hormonally sensitive brains to potential impairment during neurodevelopment. Furthermore, RmTBI produces acute neuroendocrine dysfunction, specifically in the anterior pituitary, disrupting the hypothalamic-pituitary adrenal axis, lowering cortisol secretion that is needed to appropriately respond to injury. Some AAS users exhibit worse symptoms post-RmTBI if they quit their steroid regime. We sought to examine the pathophysiological outcomes associated with the abrupt cessation of the commonly abused AAS, Metandienone (Met) on RmTBI outcomes in rats. Prior to injury, adolescent male rats received either Met or placebo, and exercise. Rats were then administered RmTBIs or sham injuries, followed by steroid and exercise cessation (SEC) or continued treatment. A behavioral battery was conducted to measure outcomes consistent with clinical representations of post-concussion syndrome and chronic AAS exposure, followed by analysis of serum hormone levels, and qRT-PCR for mRNA expression and telomere length. RmTBI increased loss of consciousness and anxiety-like behavior, while also impairing balance and short-term working memory. SEC induced hyperactivity while Met treatment alone increased depressive-like behavior. There were cumulative effects whereby RmTBI and SEC exacerbated anxiety and short-term memory outcomes. mRNA expression in the prefrontal cortex, amygdala, hippocampus, and pituitary were modified in response to Met and SEC. Analysis of telomere length revealed the negative impact of SEC while Met and SEC produced changes in serum levels of testosterone and corticosterone. We identified robust changes in mRNA to serotonergic circuitry, neuroinflammation, and an enhanced stress response. Interestingly, Met treatment promoted glucocorticoid secretion after injury, suggesting that maintained AAS may be more beneficial than abstaining after mTBI.

Bridging the gap: Mechanisms of plasticity and repair after pediatric TBI

Traumatic brain injury is the leading cause of death and disability in the United States, and may be associated with long lasting impairments into adulthood. The multitude of ongoing neurobiological processes that occur during brain maturation confer both considerable vulnerability to TBI but may also provide adaptability and potential for recovery. This review will examine and synthesize our current understanding of developmental neurobiology in the context of pediatric TBI. Delineating this biology will facilitate more targeted initial care, mechanism-based therapeutic interventions and better long-term prognostication and follow-up.

Assessment of a nutritional supplement containing resveratrol, prebiotic fiber, and omega-3 fatty acids for the prevention and treatment of mild traumatic brain injury in rats

Children and adolescents have the highest rates of traumatic brain injury (TBI), with mild TBI (mTBI) accounting for most of these injuries. Adolescents are particularly vulnerable and often suffer from post-injury symptomologies that may persist for months. We hypothesized that the combination of resveratrol (RES), prebiotic fiber (PBF), and omega-3 fatty acids (docosahexaenoic acid (DHA)) would be an effective therapeutic supplement for the mitigation of mTBI outcomes in the developing brain. Adolescent male and female Sprague-Dawley rats were randomly assigned to the supplement (3S) or control condition, which was followed by a mTBI or sham insult. A behavioral test battery designed to examine symptomologies commonly associated with mTBI was administered. Following the test battery, tissue was collected from the prefrontal cortex (PFC) and primary auditory cortex for Golgi-Cox analysis of spine density, and for changes in expression of 6 genes (Aqp4, Gfap, Igf1, Nfl, Sirt1, and Tau). 3S treatment altered the behavioral performance of sham animals indicating that dietary manipulations modify premorbid characteristics. 3S treatment prevented injury-related deficits in the longer-term behavior measures, medial prefrontal cortex (mPFC) spine density, and levels of Aqp4, Gfap, Igf1, Nfl, and Sirt1 expression in the PFC. Although not fully protective, treatment with the supplement significantly improved post-mTBI function and warrants further investigation.

Staying in the game: a pilot study examining the efficacy of protective headgear in an animal model of mild traumatic brain injury (mTBI)

PRIMARY OBJECTIVE

Rugby is one of the few contact sports that do not mandate protective headgear, possibly because studies have shown poor efficacy for protection related to concussion pathology with existing headguards.

RESEARCH DESIGN

Following innovative material technology utilization to produce headgear believed to have protective capabilities, this study examined the effects of a soft-shell headgear constructed from a novel viscoelastic material, on both behaviour and serum biomarkers after high and average impact force mild traumatic brain injuries (mTBI).

METHODS AND PROCEDURES

Seventy-five male Sprague Dawley rats were divided into five groups: control, average - 37G impact, with and without headgear, and high - 106G impact, with and without headgear. Rats were sacrificed at 3 or 48 hours and serum samples were analyzed for levels of TNF-α, NEF-L, and GFAP. Animals sacrificed at 48 hours also underwent testing for balance and motor coordination, and exploratory/locomotor behaviour.

MAIN OUTCOMES AND RESULTS

The novel headgear offered significant protection against mTBI symptomology and biomarkers in the group that experienced an average impact force, but only moderated protection for the animals in the high impact group.

CONCLUSIONS

This innovative headgear may prevent some of the negative sequel associated with concussion pathology.

Brain volumetric correlates of inhibition and cognitive flexibility 16 years following childhood traumatic brain injury

Executive functions (EFs), such as inhibition and cognitive flexibility, are essential for everyday functioning, including regulation of socially appropriate emotional responses. These skills develop during childhood and continue maturing into early adulthood. The current study aimed to investigate the very long-term impact of childhood traumatic brain injury (TBI) on inhibition and cognitive flexibility, and to examine whether global white matter is associated with these abilities. Twenty-eight young adult survivors of childhood TBI (mean age at 16-year follow-up = 21.67 years, SD = 2.70) and 16 typically developing controls (TDCs), group-matched for age, sex, and socioeconomic status, completed tests of inhibition and cognitive flexibility and underwent structural MRI. Survivors of childhood TBI did not significantly differ from TDCs on EF or white matter volume. However, the relationship between EF and white matter volume differed between survivors of TBI and TDCs. Survivors of TBI did not mimic the brain behavior relationship that characterized EF in TDCs. The inverse brain behavior relationship, exhibited by childhood TBI survivors, suggests disruptions in the whole brain underpinning EF following childhood TBI.

Manipulating cognitive reserve: Pre-injury environmental conditions influence the severity of concussion symptomology, gene expression, and response to melatonin treatment in rats

In an effort to understand the factors that contribute to heterogeneity in outcomes often associated with mTBI in youth, this study examined the role of premorbid differences in cognitive reserve on post-concussive symptoms (PCS), molecular markers, and treatment response. Male and female rats matured in one of three environmental conditions (Stress, Enrichment, Control), received a mTBI in adolescence, and were randomized to melatonin or placebo treatment. All animals underwent a behavioural test battery designed to examine PCS. Using prefrontal cortex and hippocampus tissue, expression of 9 genes was assessed in an effort to determine how the brain's epigenome was influenced by cognitive reserve, mTBI, and melatonin. Enrichment increased cognitive reserve (CR) and prevented lingering symptoms. Conversely, stress was associated with progressive worsening and manifestation of PCS in the longer-term. Melatonin was able to restore baseline function for control and enriched animals, but was ineffective for the stress condition. Epigenetic change in the prefrontal cortex was largely driven by the injury, while gene expression changes in the hippocampus were dependent upon cognitive reserve. The occurrence and severity of PCS is dependent upon a complex and multifaceted array of factors that modify behavioural and epigenetic responses to mTBI and its treatment.

Sex-dependent changes in neuronal morphology and psychosocial behaviors after pediatric brain injury

Chronic social behavior problems after pediatric traumatic brain injury (TBI) significantly contribute to poor quality of life for survivors. Using a well-characterized mouse model of early childhood TBI, we have previously demonstrated that young brain-injured mice develop social deficits by adulthood. As biological sex may influence both normal and aberrant social development, we here evaluated potential sex differences in post-TBI psychosocial deficits by comparing the behavior of male and female mice at adulthood (8 weeks post-injury). Secondly, we hypothesized that pediatric TBI would influence neuronal morphology identified by Golgi-Cox staining in the hippocampus and prefrontal cortex, regions involved in social cognition and behavior, before the onset of social problems (3 weeks post-injury). Morphological analysis of pyramidal neurons in the ipsilateral prefrontal cortex and granule cells of the hippocampal dentate gyrus revealed a reduction in dendritic complexity after pediatric TBI. This was most apparent in TBI males, whereas neurons from females were less affected. At adulthood, consistent with previous studies, TBI males showed deficits in sociability and social recognition. TBI females also showed a reduction in sociability, but intact social recognition and increased sociosexual avoidance. Together, these findings indicate that sex is a determinant of regional neuroplasticity and social outcomes after pediatric TBI. Reduced neuronal complexity in the prefrontal cortex and hippocampus, several weeks after injury in male mice, appears to precede the subsequent emergence of social deficits. Sex-specific alterations in the social brain network are thus implicated as an underlying mechanism of social dysfunction after pediatric TBI.

Transcriptional and Epigenetic Regulation in Injury-Mediated Neuronal Dendritic Plasticity

Injury to the nervous system induces localized damage in neural structures and neuronal death through the primary insult, as well as delayed atrophy and impaired plasticity of the delicate dendritic fields necessary for interneuronal communication. Excitotoxicity and other secondary biochemical events contribute to morphological changes in neurons following injury. Evidence suggests that various transcription factors are involved in the dendritic response to injury and potential therapies. Transcription factors play critical roles in the intracellular regulation of neuronal morphological plasticity and dendritic growth and patterning. Mounting evidence supports a crucial role for epigenetic modifications via histone deacetylases, histone acetyltransferases, and DNA methyltransferases that modify gene expression in neuronal injury and repair processes. Gene regulation through epigenetic modification is of great interest in neurotrauma research, and an early picture is beginning to emerge concerning how injury triggers intracellular events that modulate such responses. This review provides an overview of injury-mediated influences on transcriptional regulation through epigenetic modification, the intracellular processes involved in the morphological consequences of such changes, and potential approaches to the therapeutic manipulation of neuronal epigenetics for regulating gene expression to facilitate growth and signaling through dendritic arborization following injury.

Cross-Phenotype Polygenic Risk Score Analysis of Persistent Post-Concussive Symptoms in U.S. Army Soldiers with Deployment-Acquired Traumatic Brain Injury

Traumatic brain injury (TBI) contributes to the increased rates of suicide and post-traumatic stress disorder in military personnel and veterans, and it is also associated with the risk for neurodegenerative and psychiatric disorders. A cross-phenotype high-resolution polygenic risk score (PRS) analysis of persistent post-concussive symptoms (PCS) was conducted in 845 U.S. Army soldiers who sustained TBI during their deployment. We used a prospective longitudinal survey of three brigade combat teams to assess deployment-acquired TBI and persistent physical, cognitive, and emotional PCS. PRS was derived from summary statistics of large genome-wide association studies of Alzheimer's disease, Parkinson's disease, schizophrenia, bipolar disorder, and major depressive disorder (MDD); and for years of schooling, college completion, childhood intelligence, infant head circumference (IHC), and adult intracranial volume. Although our study had more than 95% of statistical power to detect moderate-to-large effect sizes, no association was observed with neurodegenerative and psychiatric disorders, suggesting that persistent PCS does not share genetic components with these traits to a moderate-to-large degree. We observed a significant finding: subjects with high IHC PRS recovered better from cognitive/emotional persistent PCS than the other individuals (R² = 1.11%; p = 3.37 × 10^-3). Enrichment analysis identified two significant Gene Ontology (GO) terms related to this result: GO:0050839∼Cell adhesion molecule binding (p = 8.9 × 10^-6) and GO:0050905∼Neuromuscular process (p = 9.8 × 10^-5). In summary, our study indicated that the genetic predisposition to persistent PCS after TBI does not have substantial overlap with neurodegenerative and psychiatric diseases, but mechanisms related to early brain growth may be involved.

Pediatric Rodent Models of Traumatic Brain Injury

Due to a high incidence of traumatic brain injury (TBI) in children and adolescents, age-specific studies are necessary to fully understand the long-term consequences of injuries to the immature brain. Preclinical and translational research can help elucidate the vulnerabilities of the developing brain to insult, and provide model systems to formulate and evaluate potential treatments aimed at minimizing the adverse effects of TBI. Several experimental TBI models have therefore been scaled down from adult rodents for use in juvenile animals. The following chapter discusses these adapted models for pediatric TBI, and the importance of age equivalence across species during model development and interpretation. Many neurodevelopmental processes are ongoing throughout childhood and adolescence, such that neuropathological mechanisms secondary to a brain insult, including oxidative stress, metabolic dysfunction and inflammation, may be influenced by the age at the time of insult. The long-term evaluation of clinically relevant functional outcomes is imperative to better understand the persistence and evolution of behavioral deficits over time after injury to the developing brain. Strategies to modify or protect against the chronic consequences of pediatric TBI, by supporting the trajectory of normal brain development, have the potential to improve quality of life for brain-injured children.

Impulsivity and Concussion in Juvenile Rats: Examining Molecular and Structural Aspects of the Frontostriatal Pathway

Impulsivity and poor executive control have been implicated in the pathogenesis of many developmental and neuropsychiatric disorders. Similarly, concussions/mild traumatic brain injuries (mTBI) have been associated with increased risk for neuropsychiatric disorders and the development of impulsivity and inattention. Researchers and epidemiologists have therefore considered whether or not concussions induce symptoms of attention-deficit/hyperactivity disorder (ADHD), or merely unmask impulsive tendencies that were already present. The purpose of this study was to determine if a single concussion in adolescence could induce ADHD-like impulsivity and impaired response inhibition, and subsequently determine if inherent impulsivity prior to a pediatric mTBI would exacerbate post-concussion symptomology with a specific emphasis on impulsive and inattentive behaviours. As these behaviours are believed to be associated with the frontostriatal circuit involving the nucleus accumbens (NAc) and the prefrontal cortex (PFC), the expression patterns of 8 genes (Comt, Drd2, Drd3, Drd4, Maoa, Sert, Tph1, and Tph2) from these two regions were examined. In addition, Golgi-Cox staining of medium spiny neurons in the NAc provided a neuroanatomical examination of mTBI-induced structural changes. The study found that a single early brain injury could induce impulsivity and impairments in response inhibition that were more pronounced in males. Interestingly, when animals with inherent impulsivity experienced mTBI, injury-related deficits were exacerbated in female animals. The single concussion increased dendritic branching, but reduced synaptic density in the NAc, and these changes were likely associated with the increase in impulsivity. Finally, mTBI-induced impulsivity was associated with modifications to gene expression that differed dramatically from the gene expression pattern associated with inherent impulsivity, despite very similar behavioural phenotypes. Our findings suggest the need to tailor treatment strategies for mTBI in light of an individual's premorbid characteristics, given significant differences in molecular profiles of the frontostriatal circuits that depend upon sex and the etiology of the behavioural phenotype.