Clinical Relevance of Behavior Testing in Animal Models of Traumatic Brain Injury

The horizontal ladder test (HLT) protocol: a novel, optimized, and reliable means of assessing motor coordination in Sus scrofa domesticus

Pigs can be an important model for preclinical biological research, including neurological diseases such as Alcohol Use Disorder. Such research often involves longitudinal assessment of changes in motor coordination as the disease or disorder progresses. Current motor coordination tests in pigs are derived from behavioral assessments in rodents and lack critical aspects of face and construct validity. While such tests may permit for the comparison of experimental results to rodents, a lack of validation studies of such tests in the pig itself may preclude the drawing of meaningful conclusions. To address this knowledge gap, an apparatus modeled after a horizontally placed ladder and where the height of the rungs could be adjusted was developed. The protocol that was employed within the apparatus mimicked the walk and turn test of the human standardized field sobriety test. Here, five Sinclair miniature pigs were trained to cross the horizontally placed ladder, starting at a rung height of six inches and decreasing to three inches in one-inch increments. It was demonstrated that pigs can reliably learn to cross the ladder, with few errors, under baseline/unimpaired conditions. These animals were then involved in a voluntary consumption of ethanol study where animals were longitudinally evaluated for motor coordination changes at baseline, 2.5, 5, 7.5, and 10% ethanol concentrations subsequently to consuming ethanol. Consistent with our predictions, relative to baseline performance, motor incoordination increased as voluntary consumption of escalating concentrations of ethanol increased. Together these data highlight that the horizontal ladder test (HLT) test protocol is a novel, optimized and reliable test for evaluating motor coordination as well as changes in motor coordination in pigs.

Functional recovery following traumatic brain injury in rats is enhanced by oral supplementation with bovine thymus extract

Traumatic brain injury (TBI) is one of the leading causes of death worldwide. There are currently no effective treatments for TBI, and trauma survivors suffer from a variety of long-lasting health consequences. With nutritional support recently emerging as a vital step in improving TBI patients' outcomes, we sought to evaluate the potential therapeutic benefits of nutritional supplements derived from bovine thymus gland, which can deliver a variety of nutrients and bioactive molecules. In a rat model of controlled cortical impact (CCI), we determined that animals supplemented with a nuclear fraction of bovine thymus (TNF) display greatly improved performance on beam balance and spatial memory tests following CCI. Using RNA-Seq, we identified an array of signaling pathways that are modulated by TNF supplementation in rat hippocampus, including those involved in the process of autophagy. We further show that bovine thymus-derived extracts contain antigens found in neural tissues and that supplementation of rats with thymus extracts induces production of serum IgG antibodies against neuronal and glial antigens, which may explain the enhanced animal recovery following CCI through possible oral tolerance mechanism. Collectively, our data demonstrate, for the first time, the potency of a nutritional supplement containing nuclear fraction of bovine thymus in enhancing the functional recovery from TBI.

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.

Behavioral deficits after mild traumatic brain injury by fluid percussion in rats

Mild traumatic brain injury (TBI) can lead to various disorders, encompassing cognitive and psychiatric complications. While pre-clinical studies have long investigated behavioral alterations, the fluid percussion injury (FPI) model still lacks a comprehensive behavioral battery that includes psychiatric-like disorders. To address this gap, we conducted multiple behavioral tasks over two months in adult male Wistar rats, focusing on mild FPI. Statistical analyses revealed that both naive and sham animals exhibited an increase in sweet liquid consumption over time. In contrast, the TBI group did not show any temporal changes, although mild FPI did induce a statistically significant decrease in sucrose consumption compared to control groups during the chronic phase. Additionally, social interaction tasks indicated reduced contact time in TBI animals. The elevated plus maze task demonstrated an increase in open-arm exploration following fluid percussion. Nonetheless, no significant differences were observed in the acute and chronic phases for the forced swim and light-dark box tasks. Evaluation of three distinct memory tasks in the chronic phase revealed that mild FPI led to long-term memory deficits, as assessed by the object recognition task, while the surgical procedure itself resulted in short-term spatial memory deficits, as evaluated by the Y-maze task. Conversely, working memory remained unaffected in the water maze task. Collectively, these findings provide a nuanced characterization of behavioral deficits induced by mild FPI.

Mesenchymal stem cell-derived extracellular vesicles as a cell-free therapy for traumatic brain injury via neuroprotection and neurorestoration

Traumatic brain injury is a serious and complex neurological condition that affects millions of people worldwide. Despite significant advancements in the field of medicine, effective treatments for traumatic brain injury remain limited. Recently, extracellular vesicles released from mesenchymal stem/stromal cells have emerged as a promising novel therapy for traumatic brain injury. Extracellular vesicles are small membrane-bound vesicles that are naturally released by cells, including those in the brain, and can be engineered to contain therapeutic cargo, such as anti-inflammatory molecules, growth factors, and microRNAs. When administered intravenously, extracellular vesicles can cross the blood-brain barrier and deliver their cargos to the site of injury, where they can be taken up by recipient cells and modulate the inflammatory response, promote neuroregeneration, and improve functional outcomes. In preclinical studies, extracellular vesicle-based therapies have shown promising results in promoting recovery after traumatic brain injury, including reducing neuronal damage, improving cognitive function, and enhancing motor recovery. While further research is needed to establish the safety and efficacy of extracellular vesicle-based therapies in humans, extracellular vesicles represent a promising novel approach for the treatment of traumatic brain injury. In this review, we summarize mesenchymal stem/stromal cell-derived extracellular vesicles as a cell-free therapy for traumatic brain injury via neuroprotection and neurorestoration and brain-derived extracellular vesicles as potential biofluid biomarkers in small and large animal models of traumatic brain injury.

Polypathologies and Animal Models of Traumatic Brain Injury

Traumatic brain injury (TBI) is an important health issue for the worldwide population, as it causes long-term pathological consequences for a diverse group of individuals. We are yet to fully elucidate the significance of TBI polypathologies, such as neuroinflammation and tau hyperphosphorylation, and their contribution to the development of chronic traumatic encephalopathy (CTE) and other neurological conditions. To advance our understanding of TBI, it is necessary to replicate TBI in preclinical models. Commonly used animal models include the weight drop model; these methods model human TBI in various ways and in different animal species. However, animal models have not demonstrated their clinical utility for identifying therapeutic interventions. Many interventions that were successful in improving outcomes for animal models did not translate into clinical benefit for patients. It is important to review current animal models and discuss their strengths and limitations within a TBI context. Modelling human TBI in animals encounters numerous challenges, yet despite these barriers, the TBI research community is working to overcome these difficulties. Developments include advances in biomarkers, standardising, and refining existing models. This progress will improve our ability to model TBI in animals and, therefore, enhance our understanding of TBI and, potentially, how to treat it.

Spautin-1 Protects Against Mild TBI-Induced Anxiety-Like Behavior in Mice via Immunologically Silent Apoptosis

Anxiety is reportedly one of the most common mental changes after traumatic brain injury (TBI). Perineuronal nets (PNNs) produced by astrocytes in the lateral hypothalamus (LHA) that surround gamma-aminobutyric acid-ergic (GABAergic) neurons have been associated with anxiety. The potent anti-tumor effects of Spautin-1, a novel autophagy inhibitor, have been documented in malignant melanoma; moreover, the inhibition of autophagy is reported to mitigate anxiety disorders. However, little is known about the ability of spautin-1 to alleviate anxiety. In this study, we sought to investigate whether spautin-1 could alleviate anxiety-like behaviors post-TBI by reducing the loss of PNNs in the LHA. A mild TBI was established in mice through Feeney's weight-drop model. Then, Spautin-1 (20 mmol/2 μl) was immediately administered into the left lateral ventricle. Behavioral and pathological changes were assessed at 24 h, 7 days, 30 days, 31 days and 32 days after TBI by the neurological severity scores (NSS), open field test (OFT), elevated plus-maze (EPM) test, western blot, immunofluorescence assays and electron microscopy. Spautin-1 significantly reversed TBI-induced decreased time in the central zone during OFT and in the open-arm during the EPM test. Spautin-1 also increased PNNs around GABAergic neurons indicated by WFA- plus GAD2- positive A2-type astrocytes and attenuated M1-type microglia in the LHA 32 days after TBI compared to TBI alone. Moreover, compared to mice that only underwent TBI, spautin-1 downregulated autophagic vacuoles, abnormal organelles, the expression of Beclin 1, USP13, phospho-TBK1, and phospho-IRF3 and upregulated the levels of cleaved caspase-3, -7 and -9, but failed to increase TUNEL-positive cells in the LHA at 24 h. Spautin-1 alleviated anxiety-like behavior in mice exposed to mild TBI; this protective mechanism may be associated with decreased PNNs loss around GABAergic neurons via immunologically silent apoptosis induced by the caspase cascade.

Optimizing Choice and Timing of Behavioral Outcome Tests After Repetitive Mild Traumatic Brain Injury: A Machine Learning-Based Approach on Multiple Pre-Clinical Experiments

Repetitive mild traumatic brain injury (rmTBI) is a potentially debilitating condition with long-term sequelae. Animal models are used to study rmTBI in a controlled environment, but there is currently no established standard battery of behavioral tests used. Primarily, we aimed to identify the best combination and timing of behavioral tests to distinguish injured from uninjured animals in rmTBI studies, and secondarily, to determine whether combinations of independent experiments have better behavioral outcome prediction accuracy than individual experiments. Data from 1203 mice from 58 rmTBI experiments, some of which have already been published, were used. In total, 11 types of behavioral tests were measured by 37 parameters at 13 time points during the first 6 months after injury. Univariate regression analyses were used to identify optimal combinations of behavioral tests and whether the inclusion of multiple heterogenous experiments improved accuracy. k-means clustering was used to determine whether a combination of multiple tests could distinguish mice with rmTBI from uninjured mice. We found that a combination of behavioral tests outperformed individual tests alone when distinguishing animals with rmTBI from uninjured animals. The best timing for most individual behavioral tests was 3-4 months after first injury. Overall, Morris water maze (MWM; hidden and probe frequency) was the behavioral test with the best capability of detecting injury effects (area under the curve [AUC] = 0.98). Combinations of open field tests and elevated plus mazes also performed well (AUC = 0.92), as did the forced swim test alone (AUC = 0.90). In summary, multiple heterogeneous experiments tended to predict outcome better than individual experiments, and MWM 3-4 months after injury was the optimal test, also several combinations also performed well. In order to design future pre-clinical rmTBI trials, we have included an interactive application available online utilizing the data from the study via the Supplementary URL.

Stress and traumatic brain injury: An inherent bi-directional relationship with temporal and synergistic complexities

Traumatic brain injury (TBI) and stress are prevalent worldwide and can both result in life-altering health problems. While stress often occurs in the absence of TBI, TBI inherently involves some element of stress. Furthermore, because there is pathophysiological overlap between stress and TBI, it is likely that stress influences TBI outcomes. However, there are temporal complexities in this relationship (e.g., when the stress occurs) that have been understudied despite their potential importance. This paper begins by introducing TBI and stress and highlighting some of their possible synergistic mechanisms including inflammation, excitotoxicity, oxidative stress, hypothalamic-pituitary-adrenal axis dysregulation, and autonomic nervous system dysfunction. We next describe different temporal scenarios involving TBI and stress and review the available literature on this topic. In doing so we find initial evidence that in some contexts stress is a highly influential factor in TBI pathophysiology and recovery, and vice versa. We also identify important knowledge gaps and suggest future research avenues that will increase our understanding of this inherent bidirectional relationship and could one day result in improved patient care.

An updated Barnes maze protocol for assessing the outcome of controlled cortical impact mouse models of traumatic brain injury

BACKGROUND

The Barnes Maze (BM) is a common method of testing cognitive deficits in rodents. Adapting BM protocols for specific neurological disorders could potentially aid in more effective testing, reduce research time, and help decrease variability between studies.

NEW METHOD

We tested differences an updated, shortened BM consisting of 6 days, 3 trials per day, only covering the equivalent of the spatial acquisition week BM protocol and a probe trial day consisting of one trial (7 total days).

RESULTS

Kaplan-Meier plots of escape percentage as a function of total latency showed a significant difference between control and CCI mice in the updated protocol on days 3 through 6. Additionally, probe trial data showed significant differences in primary latency, primary errors, and returns to goal.

COMPARISON WITH EXISTING METHODS

We tested differences between a traditional 5 days per week, 2 trials per day, spatial acquisition and reversal weeks BM protocol (12 total days with probe trials) with an updated 6-day BM protocol (7 total days with probe trial). In the probe trial, the updated protocol control mice showed an over 5-fold decrease in primary latency and primary errors and a 4.6-fold increase in returns to goal compared to the traditional protocol. Additionally, mice in both protocols performed similarly on a trial-by-trial basis suggesting that the changes made for the updated protocol increased learning and memory and was not simply an easier task.

CONCLUSION

The updated BM protocol showed an improved ability to distinguish between control and CCI mice and promoted improved and more consistent learning for both the control and CCI groups.

Chronic motor performance following different traumatic brain injury severity-A systematic review

Introduction

Traumatic brain injury (TBI) is now known to be a chronic disease, causing ongoing neurodegeneration and linked to increased risk of neurodegenerative motor diseases, such as Parkinson's disease and amyotrophic lateral sclerosis. While the presentation of motor deficits acutely following traumatic brain injury is well-documented, however, less is known about how these evolve in the long-term post-injury, or how the initial severity of injury affects these outcomes. The purpose of this review, therefore, was to examine objective assessment of chronic motor impairment across the spectrum of TBI in both preclinical and clinical models.

Methods

PubMed, Embase, Scopus, and PsycINFO databases were searched with a search strategy containing key search terms for TBI and motor function. Original research articles reporting chronic motor outcomes with a clearly defined TBI severity (mild, repeated mild, moderate, moderate-severe, and severe) in an adult population were included.

Results

A total of 97 studies met the inclusion criteria, incorporating 62 preclinical and 35 clinical studies. Motor domains examined included neuroscore, gait, fine-motor, balance, and locomotion for preclinical studies and neuroscore, fine-motor, posture, and gait for clinical studies. There was little consensus among the articles presented, with extensive differences both in assessment methodology of the tests and parameters reported. In general, an effect of severity was seen, with more severe injury leading to persistent motor deficits, although subtle fine motor deficits were also seen clinically following repeated injury. Only six clinical studies investigated motor outcomes beyond 10 years post-injury and two preclinical studies to 18-24 months post-injury, and, as such, the interaction between a previous TBI and aging on motor performance is yet to be comprehensively examined.

Conclusion

Further research is required to establish standardized motor assessment procedures to fully characterize chronic motor impairment across the spectrum of TBI with comprehensive outcomes and consistent protocols. Longitudinal studies investigating the same cohort over time are also a key for understanding the interaction between TBI and aging. This is particularly critical, given the risk of neurodegenerative motor disease development following TBI.

Inhibition of LRRK2 Attenuates Depression-Related Symptoms in Mice with Moderate Traumatic Brain Injury

Moderate traumatic brain injury (mTBI) has been associated with emotional dysregulation such as loss of consciousness, post-traumatic amnesia and major depressive disorder. The gene Leucine-rich repeat kinase 2 (LRRK2) is involved in protein synthesis and degradation, apoptosis, inflammation and oxidative stress, processes that trigger mTBI. The aim of this study was to investigate the role of LRRK2 in reducing depression-related symptoms after mTBI and to determine whether inhibition of LRRK2 mediated by PF-06447475 could have antidepressant effects. Moderate traumatic brain injury was induced by controlled cortical impact (CCI) and mice were treated with PF-06447475 at doses of 1, 2.5 and 5 mg/kg once daily for 14 days. We performed histological, immunohistochemical and molecular analyses of brain tissue 24 days after mTBI. Furthermore, the tissue changes found in the hippocampus and amygdala confirmed the depression-like behavior. PF-treatment with 06447475 significantly reduced the histological damage and behavioral disturbances. Thus, this study has shown that mTBI induction promotes the development of depression-like behavioral changes. LRRK2 inhibition showed an antidepressant effect and restored the changes in the copper/glutamate/N-methyl-D-aspartic acid receptor (Cu/NMDAR) system.

Repeat subconcussion in the adult rat gives rise to behavioral deficits similar to a single concussion but different depending upon sex

Although concussions are a popular focus of neurotrauma research, subconcussions occur with higher frequency but are less well-studied. A subconcussion is an impact to the head that does not result in immediately diagnosable concussion but can result in later neurological consequences. Repeat subconcussions can produce behavioral impairments and neuropathology that is similar to or worse than those seen following a single concussion. The current study modified a previously established closed head injury model of concussion to create a subconcussion model and examines sex differences in behavioral responses to repeated subconcussion in the adult rat. Rats received a single concussion, single or repeat subconcussions, or no impact and behavior was monitored from 2 h through 31 days post-injury. A single concussion or repeat subconcussion resulted in deficits in locomotion, righting reflexes, and recognition memory. The degree of deficit induced by repeat subconcussions were either similar (righting reflexes) or greater/more persistent (locomotor deficits and recognition memory) than that of a concussion. Single subconcussion resulted in acute deficits that were mild and limited to righting reflexes and locomotion. Sex differences were observed in responses to repeat subconcussion: females showed greater deficits in righting reflexes, locomotion, and vestibular function, while males showed greater alterations in anxiety and depressive-like behavior. This study established a model of subconcussive impact where a single subconcussive impact resulted in minimal behavioral deficits but repeat subconcussions resulted in deficits similar to or worse than a single concussion. Our data also suggest sex differences in behavioral responses to both concussive and subconcussive impacts.

DCC/netrin-1 regulates cell death in oligodendrocytes after brain injury

Hallmark pathological features of brain trauma are axonal degeneration and demyelination because myelin-producing oligodendrocytes (OLs) are particularly vulnerable to injury-induced death signals. To reveal mechanisms responsible for this OL loss, we examined a novel class of "death receptors" called dependence receptors (DepRs). DepRs initiate pro-death signals in the absence of their respective ligand(s), yet little is known about their role after injury. Here, we investigated whether the deleted in colorectal cancer (DCC) DepR contributes to OL loss after brain injury. We found that administration of its netrin-1 ligand is sufficient to block OL cell death. We also show that upon acute injury, DCC is upregulated while netrin-1 is downregulated in perilesional tissues. Moreover, after genetically silencing pro-death activity using DCCD1290N mutant mice, we observed greater OL survival, greater myelin integrity, and improved motor function. Our findings uncover a novel role for the netrin-1/DCC pathway in regulating OL loss in the traumatically injured brain.

Serum neurofilament light as a biomarker of vulnerability to a second mild traumatic brain injury

A second mild traumatic brain injury (mTBI) sustained prior to neuropathological recovery can lead to exacerbated effects. Without objective indicators of this neuropathology, individuals may return to activities at risk of mTBI when their brain is still vulnerable. With axonal injury recognized as a neuropathological hallmark of mTBI, we hypothesized that serum levels of neurofilament light (NfL), a highly sensitive biomarker of axonal injury, may be predictive of vulnerability to worse outcomes in the event of a second mTBI. Given this hypothesis is difficult to test clinically, we used a two-hit model of mTBI in rats and staggered inter-injury intervals by 1-, 3-, 7-, or 14-days. Repeat-mTBI rats were dichotomized into NfL^high (NfL>median at the time of re-injury) and NfL^low (NfL<median) groups, with behavior and NfL levels analyzed throughout the 28-days, followed by ex vivo diffusion tensor imaging. NfL levels at the time of the second mTBI were found to be predictive of vulnerability to re-injury, with NfL^high rats displaying more neurological signs and a greater potentiation of NfL levels after the second mTBI. Importantly, this potentiation phenomenon remained even when limiting analyses to rats with longer inter-injury intervals, providing evidence that vulnerability to re-injury may not be exclusively dependent on inter-injury interval. Finally, NfL levels correlated with, and were predictive of, the severity of neurological signs following the second mTBI. These findings provide evidence that measurement of NfL during mTBI recovery may be reflective of the vulnerability to a second mTBI, and as such may have utility to assist return to sport, duty and work decisions.

beeRapp: an R shiny app for automated high-throughput explorative analysis of multivariate behavioral data

Summary

Animal behavioral studies typically generate high-dimensional datasets consisting of multiple correlated outcome measures across distinct or related behavioral domains. Here, we introduce the BEhavioral Explorative analysis R shiny APP (beeRapp) that facilitates explorative and inferential analysis of behavioral data in a high-throughput fashion. By employing an intuitive and user-friendly graphical user interface, beeRapp empowers behavioral scientists without programming and data science expertise to perform clustering, dimensionality reduction, correlational and inferential statistics and produce up to thousands of high-quality output plots visualizing results in a standardized and automated way.

Availability and implementation

The code and data underlying this article are available at https://github.com/anmabu/beeRapp.

A Focal Impact Model of Traumatic Brain Injury in Xenopus Tadpoles Reveals Behavioral Alterations, Neuroinflammation, and an Astroglial Response

Traumatic Brain Injury (TBI) is a global driver of disability, and we currently lack effective therapies to promote neural repair and recovery. TBI is characterized by an initial insult, followed by a secondary injury cascade, including inflammation, excitotoxicity, and glial cellular response. This cascade incorporates molecular mechanisms that represent potential targets of therapeutic intervention. In this study, we investigate the response to focal impact injury to the optic tectum of Xenopus laevis tadpoles. This injury disrupts the blood-brain barrier, causing edema, and produces deficits in visually-driven behaviors which are resolved within one week. Within 3 h, injured brains show a dramatic transcriptional activation of inflammatory cytokines, upregulation of genes associated with inflammation, and recruitment of microglia to the injury site and surrounding tissue. Shortly afterward, astrocytes undergo morphological alterations and accumulate near the injury site, and these changes persist for at least 48 h following injury. Genes associated with astrocyte reactivity and neuroprotective functions also show elevated levels of expression following injury. Since our results demonstrate that the response to focal impact injury in Xenopus resembles the cellular alterations observed in rodents and other mammalian models, the Xenopus tadpole offers a new, scalable vertebrate model for TBI.

Repeated Mild TBI in Adolescent Rats Reveals Sex Differences in Acute and Chronic Behavioral Deficits

High school students who participate in contact sports are vulnerable to sustaining multiple concussions and exhibit deficits in cognitive function in both the acute and chronic phases and in emotional behavior in the chronic phase. Further, boys are more likely to suffer cognitive problems whereas girls tend to report depression and anxiety. The effects of repetitive mild TBI in adolescent (35-40-day old) male and female Sprague-Dawley rats on object location and spatial working memory (hippocampal-dependent) and object recognition memory (hippocampal-independent) at 1-and-4-weeks post-injury along with trait-dependent anxiety- and depressive-like behaviors at 5 weeks were examined. Compared to sham-injured rats, male brain-injured rats demonstrated significant impairment in both hippocampal-dependent and -independent memory tasks at both time points, whereas female brain-injured rats only exhibited impairment in these tests at the 4-week time point. In contrast, depressive-like behaviors were present in the forced swim test in only the female brain-injured animals at 5 weeks post-injury; anxiety-like behaviors were not evident in either male or female brain-injured animals. Histological analysis at 6 weeks after injury revealed that repeated mild TBI in male and female adolescent rats resulted in increased reactivity of astrocytes and microglia within the corpus callosum below the impact site and in the stratum oriens and stratum pyramidale of the CA2 region of the dorsal hippocampus. Together, these data are indicative of the differences in the temporal pattern of post-traumatic behavioral deficits between male and female animals and that female animals may be more likely to develop deficits in the chronic post-traumatic period.

Traumatic brain injury-induced submissive behavior in rats: link to depression and anxiety

Traumatic brain injury (TBI) affects millions of people worldwide, many of whom are affected with post-TBI mood disorders or behavioral changes, including aggression or social withdrawal. Diminished functionality can persist for decades after TBI and delay rehabilitation and resumption of employment. It has been established that there is a relationship between these mental disorders and brain injury. However, the etiology and causal relationships behind these conditions are poorly understood. Rodent models provide a helpful tool for researching mood disorders and social impairment due to their natural tendencies to form social hierarchies. Here, we present a rat model of mental complications after TBI using a suite of behavioral tests to examine the causal relationships between changes in social behavior, including aggressive, hierarchical, depressive, and anxious behavior. For this purpose, we used multivariate analysis to identify causal relationships between the above post-TBI psychiatric sequelae. We performed statistical analysis using principal component analysis, discriminant analysis, and correlation analysis, and built a model to predict dominant-submissive behavior based on the behavioral tests. This model displayed a predictive accuracy of 93.3% for determining dominant-submissive behavior in experimental groups. Machine learning algorithms determined that in rats, aggression is not a principal prognostic factor for dominant-submissive behavior. Alternatively, dominant-submissive behavior is determined solely by the rats' depressive-anxious state and exploratory activity. We expect the causal approach used in this study will guide future studies into mood conditions and behavioral changes following TBI.

2, 3, 5, 4'-tetrahydroxystilbene-2-O-beta-D-glucoside protects against neuronal cell death and traumatic brain injury-induced pathophysiology

Traumatic brain injury (TBI) is a global health issue that affects at least 10 million people per year. Neuronal cell death and brain injury after TBI, including apoptosis, inflammation, and excitotoxicity, have led to detrimental effects in TBI. 2, 3, 5, 4’-tetrahydroxystilbene-2-O-beta-D-glucoside (THSG), a water-soluble compound extracted from the Chinese herb Polygonum multiflorum, has been shown to exert various biological functions. However, the effects of THSG on TBI is still poorly understood. THSG reduced L-glutamate-induced DNA fragmentation and protected glial and neuronal cell death after L-glutamate stimulation. Our results also showed that TBI caused significant behavioral deficits in the performance of beam walking, mNSS, and Morris water maze tasks in a mouse model. Importantly, daily administration of THSG (60 mg/kg/day) after TBI for 21 days attenuated the injury severity score, promoted motor coordination, and improved cognitive performance post-TBI. Moreover, administration of THSG also dramatically decreased the brain lesion volume. THSG reduced TBI-induced neuronal apoptosis in the brain cortex 24 h after TBI. Furthermore, THSG increased the number of immature neurons in the subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus. Our results demonstrate that THSG exerts neuroprotective effects on glutamate-induced excitotoxicity and glial and neuronal cell death. The present study also demonstrated that THSG effectively protects against TBI-associated motor and cognitive impairment, at least in part, by inhibiting TBI-induced apoptosis and promoting neurogenesis.

Lateral Fluid Percussion Injury Causes Sex-Specific Deficits in Anterograde but Not Retrograde Memory

Cognitive impairment is a common symptom after traumatic brain injury (TBI). Memory, in particular, is often disrupted during chronic post-injury recovery. To understand the sex-specific effects of brain injury on retrograde and anterograde memory, we examined paired associate learning (PAL), spatial learning and memory, and fear memory after lateral fluid percussion TBI. We hypothesized that male and female mice would display unique memory deficits after TBI. PAL task acquisition was initiated via touchscreen operant conditioning 22 weeks before sham injury or TBI. Post-injury PAL testing occurred 7 weeks post-injury. Barnes maze and fear conditioning were completed at 14- and 15-weeks post-injury, respectively. Contrary to our expectations, behavioral outcomes were not primarily influenced by TBI. Instead, sex-specific differences were observed in all tasks which exposed task-specific trends in male TBI mice. Male mice took longer to complete the PAL task, but this was not affected by TBI and did not compromise the ability to make a correct choice. Latency to reach the goal box decreased across testing days in Barnes maze, but male TBI mice lagged in improvement compared to all other groups. Use of two learning indices revealed that male TBI mice were deficient in transferring information from 1 day to the next. Finally, acquisition and contextual retention of fear memory were similar between all groups. Cued retention of the tone-shock pairing was influenced by both injury and sex. Male sham mice displayed the strongest cued retention of fear memory, evidenced by increased freezing behavior across the test trial. In contrast, male TBI mice displayed reduced freezing behavior with repetitive tone exposure. An inverse relationship in freezing behavior to tone exposure was detected between female sham and TBI mice, although the difference was not as striking. Together, these studies show that retrograde memory is intact after lateral TBI. However, male mice are more vulnerable to post-injury anterograde memory deficits. These behaviors were not associated with gross pathological change near the site injury or in subcortical brain regions associated with memory formation. Future studies that incorporate pre- and post-injury behavioral analysis will be integral in defining sex-specific memory impairment after TBI.

Perspectives on Primary Blast Injury of the Brain: Translational Insights Into Non-inertial Low-Intensity Blast Injury

Most traumatic brain injuries (TBIs) during military deployment or training are clinically "mild" and frequently caused by non-impact blast exposures. Experimental models were developed to reproduce the biological consequences of high-intensity blasts causing moderate to severe brain injuries. However, the pathophysiological mechanisms of low-intensity blast (LIB)-induced neurological deficits have been understudied. This review provides perspectives on primary blast-induced mild TBI models and discusses translational aspects of LIB exposures as defined by standardized physical parameters including overpressure, impulse, and shock wave velocity. Our mouse LIB-exposure model, which reproduces deployment-related scenarios of open-field blast (OFB), caused neurobehavioral changes, including reduced exploratory activities, elevated anxiety-like levels, impaired nesting behavior, and compromised spatial reference learning and memory. These functional impairments associate with subcellular and ultrastructural neuropathological changes, such as myelinated axonal damage, synaptic alterations, and mitochondrial abnormalities occurring in the absence of gross- or cellular damage. Biochemically, we observed dysfunctional mitochondrial pathways that led to elevated oxidative stress, impaired fission-fusion dynamics, diminished mitophagy, decreased oxidative phosphorylation, and compensated cell respiration-relevant enzyme activity. LIB also induced increased levels of total tau, phosphorylated tau, and amyloid β peptide, suggesting initiation of signaling cascades leading to neurodegeneration. We also compare translational aspects of OFB findings to alternative blast injury models. By scoping relevant recent research findings, we provide recommendations for future preclinical studies to better reflect military-operational and clinical realities. Overall, better alignment of preclinical models with clinical observations and experience related to military injuries will facilitate development of more precise diagnosis, clinical evaluation, treatment, and rehabilitation.

Repetitive Mild Traumatic Brain Injury in an Awake, Unanesthetized Mouse Model of Perinatal Nicotine Exposure Produces Transient Novelty-Seeking and Depression-Like Behaviors

Attention deficit hyperactivity disorder (ADHD) can be a risk factor for repetitive mild traumatic brain injury (mTBI) or concussions such as those that can occur in contact sports. Individuals with ADHD also appear to have a higher risk of poor neurocognitive outcomes after repetitive mTBI. Findings from clinical studies examining the interactions between ADHD and repetitive mTBI vary, likely because of variabilities in experimental design and outcome measures. We used a mouse model of perinatal nicotine exposure (PNE), which displays behavioral, neuroanatomical, and neurotransmitter features consistent with ADHD and subjected the mice to repetitive mTBI. We used a closed head model of mTBI in awake, unanesthetized mice to mimic concussions in humans. The mTBI was repeated three times daily for seven days. The mice in the PNE-mTBI group took longer to regain consciousness after the mTBI and showed transient novelty-seeking and depression-like behaviors. Before the repetitive mTBI, the mice in the PNE group showed attention deficit, which persisted after the mTBI. The mice in the control (non-PNE) group showed a transient attention deficit after the repetitive mTBI but not any of the other behavioral changes seen in the PNE-mTBI group. These findings from an unanesthetized mouse model with a pre-existing condition show that ADHD and repetitive mTBI together contribute to transient novelty-seeking and depression-like behavior supporting the notion that untreated ADHD may be a risk factor for poor neurocognitive outcomes after concussions.

The Nanotheranostic Researcher’s Guide for Use of Animal Models of Traumatic Brain Injury

Traumatic brain injury (TBI) is currently the leading cause of injury-related morbidity and mortality worldwide, with an estimated global cost of USD 400 billion annually. Both clinical and preclinical behavioral outcomes associated with TBI are heterogeneous in nature and influenced by the mechanism and frequency of injury. Previous literature has investigated this relationship through the development of animal models and behavioral tasks. However, recent advancements in these methods may provide insight into the translation of therapeutics into a clinical setting. In this review, we characterize various animal models and behavioral tasks to provide guidelines for evaluating the therapeutic efficacy of treatment options in TBI. We provide a brief review into the systems utilized in TBI classification and provide comparisons to the animal models that have been developed. In addition, we discuss the role of behavioral tasks in evaluating outcomes associated with TBI. Our goal is to provide those in the nanotheranostic field a guide for selecting an adequate TBI animal model and behavioral task for assessment of outcomes to increase research in this field.

The Neurobehavioral Effects of Buprenorphine and Meloxicam on a Blast-Induced Traumatic Brain Injury Model in the Rat

Previous findings have indicated that pain relieving medications such as opioids and non-steroidal anti-inflammatory drugs (NSAIDs) may be neuroprotective after traumatic brain injury in rodents, but only limited studies have been performed in a blast-induced traumatic brain injury (bTBI) model. In addition, many pre-clinical TBI studies performed in rodents did not use analgesics due to the possibility of neuroprotection or other changes in cognitive, behavioral, and pathology outcomes. To examine this in a pre-clinical setting, we examined the neurobehavioral changes in rats given a single pre-blast dose of meloxicam, buprenorphine, or no pain relieving medication and exposed to tightly-coupled repeated blasts in an advanced blast simulator and evaluated neurobehavioral functions up to 28 days post-blast. A 16.7% mortality rate was recorded in the rats treated with buprenorphine, which might be attributed to the physiologically depressive side effects of buprenorphine in combination with isoflurane anesthesia and acute brain injury. Rats given buprenorphine, but not meloxicam, took more time to recover from the isoflurane anesthesia given just before blast. We found that treatment with meloxicam protected repeated blast-exposed rats from vestibulomotor dysfunctions up to day 14, but by day 28 the protective effects had receded. Both pain relieving medications seemed to promote short-term memory deficits in blast-exposed animals, whereas vehicle-treated blast-exposed animals showed only a non-significant trend toward worsening short-term memory by day 27. Open field exploratory behavior results showed that blast exposed rats treated with meloxicam engaged in significantly more locomotor activities and possibly a lesser degree of responses thought to reflect anxiety and depressive-like behaviors than any of the other groups. Rats treated with analgesics to alleviate possible pain from the blast ate more than their counterparts that were not treated with analgesics, which supports that both analgesics were effective in alleviating some of the discomfort that these rats potentially experienced post-blast injury. These results suggest that meloxicam and, to a lesser extent buprenorphine alter a variety of neurobehavioral functions in a rat bTBI model and, because of their impact on these neurobehavioral changes, may be less than ideal analgesic agents for pre-clinical studies evaluating these neurobehavioral responses after TBI.

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.

Translational relevance of fear conditioning in rodent models of mild traumatic brain injury

Mild traumatic brain injury (mTBI) increases the risk of posttraumatic stress disorder (PTSD) in military populations. Utilizing translationally relevant animal models is imperative for establishing a platform to delineate neurobehavioral deficits common to clinical PTSD that emerge in the months to years following mTBI. Such platforms are required to facilitate preclinical development of novel therapeutics. First, this mini review provides an overview of the incidence of PTSD following mTBI in military service members. Secondly, the translational relevance of fear conditioning paradigms used in conjunction with mTBI in preclinical studies is evaluated. Next, this review addresses an important gap in the current preclinical literature; while incubation of fear has been studied in other areas of research, there are relatively few studies pertaining to the enhancement of cued and contextual fear memory over time following mTBI. Incubation of fear paradigms in conjunction with mTBI are proposed as a novel behavioral approach to advance this critical area of research. Lastly, this review discusses potential neurobiological substrates implicated in altered fear memory post mTBI.