Harleen Hehar

A mild traumatic brain injury (mTBI) induces secondary attention-deficit hyperactivity disorder-like symptomology in young rats.

Although attention-deficit hyperactivity disorder (ADHD) is commonly reported after moderate and severe traumatic brain injury (TBI), research is struggling to find a strong link between mild TBI or concussion and ADHD. Epidemiological studies often generate conflicting results which may be related to the difficulty identifying the lingering symptoms of mTBI, the lack of baseline knowledge and the possible exacerbation of pre-existing ADHD symptomology, and/or differential diagnostic criteria for secondary ADHD. The purpose of this study was to determine if a mild TBI/concussion in the juvenile period (postnatal day 30) could induce ADHD-like symptoms in young rodents. Using the Go/No-Go paradigm of the 5-choice serial reaction task, sustained attention, impulsivity, and response inhibition was measured. The open field was also used to measure activity levels at two time points. Animals that experienced an mTBI in the juvenile period exhibited ADHD symptomology, with sex-differences present on one of the tasks. Significant deficits were identified in sustained attention, response inhibition, and impulsivity. Immediately after the mTBI, all rats were hypoactive in the open field, and while male animals exhibited a trend toward hyperactivity in the long-term, females continued to trend toward hypoactivity for the duration of the experiment. These findings provide a unique platform upon which preventative and therapeutic strategies can be implemented and tested in an effort to improve ADHD-like symptoms following mTBI.

Mean girls: Sex differences in the effects of mild traumatic brain injury on the social dynamics of juvenile rat play behaviour

Clinical studies indicate that children who experience a traumatic brain injury (TBI) are often the victim of peer rejection, have very few mutual friends, and are at risk for long-term behavioural and social impairments. Owing to the fact that peer play is critical for healthy development, it is possible that the long-term impairments are associated not only with the TBI, but also altered play during this critical period of brain development. This study was designed to determine if social dynamics and juvenile play are altered in rats that experience a mild TBI (mTBI) early in life. Play-fighting behaviours were recorded and analyzed for young male and female Sprague Dawley rats that were given either an mTBI or a sham injury. The study found that the presence of an mTBI altered the play fighting relationship, and the nature of the alterations were dependent upon the sex of the pairing and the injury status of their peers. Sham rats were significantly less likely to initiate play with an mTBI rat, and were more likely to respond to a play initiation from an mTBI rat with an avoidant strategy. This effect was significantly more pronounced in female rats, whereby it appeared that female rats with an mTBI were particularly rejected and most often excluded from play experiences. Male rats with an mTBI learned normal play strategies from their sham peers (when housed in mixed cages), whereas female rats with an mTBI show heightened impairment in these conditions. Play therapy may need to be incorporated into treatment strategies for children with TBI.

The direction of the acceleration and rotational forces associated with mild traumatic brain injury in rodents effect behavioural and molecular outcomes

BACKGROUND The translation of research to clinical application is only as good as the modelling platforms employed. This study sought to improve understanding of mild traumatic brain injury (mTBI), by examining the importance of acceleration and rotational force directions on behavioural and molecular outcomes. It is believed that many symptoms associated with concussive forms of mTBI are related to white matter and fibre tract damage. Given that rodents have significantly less white matter, could changes in acceleration/rotational force directionality alter outcomes? NEW METHOD/COMPARISON WITH EXISTING METHODS Comparison of mTBIs with two distinct injury platforms, the lateral impact (LI) device, which produces horizontal acceleration/rotation; or the modified weight drop (WD) device, which produces sagittal or vertical acceleration/rotation. Male and female rats underwent a behavioural test battery followed by analysis of 5 TBI-associated biomarkers (BDNF, Eno2, GFAP, MAPT, TERT) from the prefrontal cortex and hippocampus. RESULTS Acute behavioural impairments were similar for both injury models; animals exhibited increased time-to-wake, and deficits of balance and motor control. However, as the post-injury interval increased LI animals displayed deficits on tasks related to emotional functioning, whereas WD animals showed impairment in cognitive measures. Biomarker expression varied as a function of injury platform, sex, and brain region. CONCLUSION Just as with humans, the direction of the acceleration and rotational forces produced injuries in different networks and connections, resulting in altered functional deficits for rodents as well. These findings suggest that rodents are a valuable resource for the study of mTBI, when appropriately modelled.

Dietary intake alters behavioral recovery and gene expression profiles in the brain of juvenile rats that have experienced a concussion

Concussion and mild traumatic brain injury (mTBI) research has made minimal progress diagnosing who will suffer from lingering symptomology or generating effective treatment strategies. Research demonstrates that dietary intake affects many biological systems including brain and neurological health. This study determined if exposure to a high fat diet (HFD) or caloric restriction (CR) altered post-concussion susceptibility or resiliency using a rodent model of pediatric concussion. Rats were maintained on HFD, CR, or standard diet (STD) throughout life (including the prenatal period and weaning). At postnatal day 30, male and female rats experienced a concussion or a sham injury which was followed by 17 days of testing. Prefrontal cortex and hippocampus tissue was collected for molecular profiling. Gene expression changes in BDNF, CREB, DNMT1, FGF-2, IGF1, LEP, PGC-1α, SIRT1, Tau, and TERT were analyzed with respect to injury and diet. Analysis of telomere length (TL) using peripheral skin cells and brain tissue found that TL in skin significantly correlated with TL in brain tissue and TL was affected by dietary intake and injury status. With respect to mTBI outcomes, diet was correlated with recovery as animals on the HFD often displayed poorer performance than animals on the CR diet. Molecular analysis demonstrated that diet induced epigenetic changes that can be associated with differences in individual predisposition and resiliency to post-concussion syndrome.

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

Apart from therapeutic discovery, the study of mild traumatic brain injury (mTBI) has been focused on two challenges: why do a majority of individuals recover with little concern, while a considerable proportion suffer with persistent and often debilitating symptomology; and, how do mild injuries significantly increase risk for an early-onset neurodegeneration? Owing to a lack of observable damage following mTBI, this study was designed to determine if there were changes in neuronal morphology, synaptic connectivity, and epigenetic patterning that could contribute to the manifestation of persistent neurological dysfunction. Prefrontal cortex tissue from male and female rats was used for Golgi-Cox analysis along with the profiling of changes in gene expression (BDNF, DNMT1, FGF2, IGF1, Nogo-A, OXYR, and TERT) and telomere length (TL), following a single mTBI or sham injury in the juvenile period. Golgi-Cox analysis of dendritic branch order, dendritic length, and spine density demonstrate that an early mTBI increases complexity of pyramidal neurons in the mPFC. Furthermore, there are also substantial changes in the expression levels of the seven genes of interest and TL following a single mild injury in this brain region. The results from the neuroanatomical measures and changes in gene expression indicate that the mTBI disrupts normal pruning processes that are typically underway at this point in development. In addition, there are significant interactions between the social environment and epigenetic processes that work in concert to perpetuate neurological dysfunction.

Diet, age, and prior injury status differentially alter behavioral outcomes following concussion in rats

Mild traumatic brain injury (mTBI) or concussion affects a large portion of the population and although many of these individuals recover completely, a small subset of people experience lingering symptomology and poor outcomes. Little is known about the factors that affect individual susceptibility or resilience to poor outcomes after mTBI and there are currently no biomarkers to delineate mTBI diagnosis or prognosis. Based upon the growing literature associated with caloric intake and altered neurological aging and the ambiguous link between repetitive mTBI and progressive neurodegeneration, the current study was designed to examine the effect of a high fat diet (HFD), developmental age, and repetitive mTBI on behavioral outcomes following a mTBI. In addition, telomere length was examined before and after experimental mTBI. Sprague Dawley rats were maintained on a HFD or standard rat chow throughout life (including the prenatal period) and then experienced an mTBI/concussion at P30, P30 and P60, or only at P60. Behavioral outcomes were examined using a test battery that was administered between P61-P80 and included; beam-walking, open field, elevated plus maze, novel context mismatch, Morris water task, and forced swim task. Animals with a P30 mTBI often demonstrated lingering symptomology that was still present during testing at P80. Injuries at P30 and P60 rarely produced cumulative effects, and in some tests (i.e., beam walking), the first injury may have protected the brain from the second injury. Exposure to the high fat diet exacerbated many of the behavioral deficits associated with concussion. Finally, telomere length was shortened following mTBI and was influenced by the animals dietary intake. Diet, age at the time of injury, and the number of prior concussion incidents differentially contribute to behavioral deficits and may help explain individual variations in susceptibility and resilience to poor outcomes following an mTBI.

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.

Reducing the Time Interval Between Concussion and Voluntary Exercise Restores Motor Impairment, Short‐term Memory, and Alterations to Gene Expression

Despite the most common form of brain injury, there has been little progress in the prognosis and treatment of concussion/mild traumatic brain injury (mTBI). Current ‘return‐to‐play’ guidelines are conservative, deterring the initiation of physical and social activity until patients are asymptomatic; but the effects of post‐injury exercise have not been adequately investigated. Therefore, this study examined the effects of voluntary exercise on concussion recovery. Using a translational rodent model of concussion, we examined the influence of exercise on injury‐associated behaviours that comprise post‐concussive syndrome (PCS) and gene expression changes (bdnf, dnmt1, Igf‐1, pgc1‐a, Tert) in prefrontal cortex and hippocampus. In addition, as we have previously demonstrated telomere length (TL) to be a reliable predictor of mTBI prognosis, TL was also examined. The results suggest that exercise initiated within 1–3 days post‐concussion significantly improved motor and cognitive functioning, but had limited efficacy treating emotional impairments. What is more, when deprived of social interaction and exercise, a combination similar to clinical recommendations for rest until symptom resolution, animals did not recover and exhibited impairments similar to typical mTBI animals. Exercise aided in restoration of mTBI‐induced modifications to gene expression in both brain regions. An inverse relationship between the exercise return interval and TL was identified, indicating greater recovery with acute exercise reinstatement. Although additional strategies may need to be employed for emotional functioning, these findings support re‐evaluation of ‘return‐to‐play’ guidelines, suggesting that exercise is valuable for the treatment of concussion.

The use of telomere length as a predictive biomarker for injury prognosis in juvenile rats following a concussion/mild traumatic brain injury.

Telomeres were originally believed to be passive players in cellular replication, but recent research has highlighted their more active role in epigenetic patterning and promotion of cellular growth and survival. Furthermore, literature demonstrates that telomere length (TL) is responsive to environmental manipulations such as prenatal stress and dietary programming. As the search for a prognostic biomarker of concussion has had limited success, this study sought to examine whether or not telomere length (TL) could be an efficacious predictor of symptom severity in juvenile rats following concussion. Rats from four distinct experimental groups (caloric restriction (CR), high fat diet (HFD), exercise (EX), and standard controls (STD)) received a mild traumatic brain injury (mTBI)/concussion and were then subjected to a behavioural test battery. The test battery was scored and the animals were categorized as poor, average, or good, based on their performance on the 6 tests examined. Skin cells (from ear notch samples) were taken 17days post-injury and DNA was extracted for telomere length analysis. Ear notch skin cell TL was highly correlated with brain tissue TL for a given individual. Animals in the CR and EX cohorts had significantly longer telomeres, while animals in the HFD cohort had significantly shorter telomeres, when compared to controls. The mTBI/concussion reduced TL in all cohorts except the EX group. A significant linear relationship was found between TL and performance on the behavioural test battery, whereby shorter telomeres were associated with poorer performance and longer telomeres with better performance. As performance on the test battery is linked to symptom severity, this study found TL to be a reasonable tool for concussion prognosis. Future studies with human populations should examine the validity of TL in peripheral cells, as a predictor of concussion pathology.

Effects of Metabolic Programming on Juvenile Play Behavior and Gene Expression in the Prefrontal Cortex of Rats.

Early developmental processes, such as metabolic programming, can provide cues to an organism, which allow it to make modifications that are predicted to be beneficial for survival. Similarly, social play has a multifaceted role in promoting survival and fitness of animals. Play is a complex behavior that is greatly influenced by motivational and reward circuits, as well as the energy reserves and metabolism of an organism. This study examined the association between metabolic programming and juvenile play behavior in an effort to further elucidate insight into the consequences that early adaptions have on developmental trajectories. The study also examined changes in expression of four genes (Drd2, IGF1, Opa1, and OxyR) in the prefrontal cortex known to play significant roles in reward, bioenergetics, and social-emotional functioning. Using four distinct variations in developmental programming (high-fat diet, caloric restriction, exercise, or high-fat diet combined with exercise), we found that dietary programming (high-fat diet vs. caloric restriction) had the greatest impact on play behavior and gene expression. However, exercise also induced changes in both measures. This study demonstrates that metabolic programming can alter neural circuits and bioenergetics involved in play behavior, thus providing new insights into mechanisms that allow programming to influence the evolutionary success of an organism.