Optimizing GABAA receptor antagonism for the induction of long-term potentiation in the mouse and rat dentate gyrus in vitro.

The reliable induction of long-term potentiation (LTP) in the dentate gyrus (DG) in vitro requires the blockade of the γ-aminobutyric acid A (GABAA) receptor. In these studies we examined the effectiveness of the specific GABAA receptor antagonist bicuculline methiodide (BMI) in facilitating LTP in the DG from hippocampal slices obtained from either C57Bl/6 mice or Sprague-Dawley rats, two commonly used species for electrophysiology. In the C57Bl/6 mice, maximal short-term potentiation and LTP in the DG were produced with a concentration of 5 mM BMI. In contrast, a concentration of 10 µM BMI was required to produce maximal short-term potentiation and LTP in the DG of Sprague-Dawley rats. These results reveal that there are species differences in the optimal amount of BMI required to produce robust and reliable long-term potentiation in the rodent DG in vitro and highlight the need to take consideration of the species being sued when choosing concentrations of pharmacological agents to employ for electrophysiological use.

Repeated mild traumatic brain injury causes sex-specific increases in cell proliferation and inflammation in juvenile rats.

Childhood represents a period of significant growth and maturation for the brain, and is also associated with a heightened risk for mild traumatic brain injuries (mTBI). There is also concern that repeated-mTBI (r-mTBI) may have a long-term impact on developmental trajectories. Using an awake closed head injury (ACHI) model, that uses rapid head acceleration to induce a mTBI, we investigated the acute effects of repeated-mTBI (r-mTBI) on neurological function and cellular proliferation in juvenile male and female Long-Evans rats. We found that r-mTBI did not lead to cumulative neurological deficits with the model. R-mTBI animals exhibited an increase in BrdU + (bromodeoxyuridine positive) cells in the dentate gyrus (DG), and that this increase was more robust in male animals. This increase was not sustained, and cell proliferation returning to normal by PID3. A greater increase in BrdU + cells was observed in the dorsal DG in both male and female r-mTBI animals at PID1. Using Ki-67 expression as an endogenous marker of cellular proliferation, a robust proliferative response following r-mTBI was observed in male animals at PID1 that persisted until PID3, and was not constrained to the DG alone. Triple labeling experiments (Iba1+, GFAP+, Brdu+) revealed that a high proportion of these proliferating cells were microglia/macrophages, indicating there was a heightened inflammatory response. Overall, these findings suggest that rapid head acceleration with the ACHI model produces an mTBI, but that the acute neurological deficits do not increase in severity with repeated administration. R-mTBI transiently increases cellular proliferation in the hippocampus, particularly in male animals, and the pattern of cell proliferation suggests that this represents a neuroinflammatory response that is focused around the mid-brain rather than peripheral cortical regions. These results add to growing literature indicating sex differences in proliferative and inflammatory responses between females and males. Targeting proliferation as a therapeutic avenue may help reduce the short term impact of r-mTBI, but there may be sex-specific considerations.

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.

Assessing Changes in Synaptic Plasticity Using an Awake Closed-Head Injury Model of Mild Traumatic Brain Injury.

Mild traumatic brain injuries (mTBIs) are a prevalent health issue in North America. There is increasing pressure to utilize ecologically valid models of closed-head mTBI in the preclinical setting to increase translatability to the clinical population. The awake closed-headed injury (ACHI) model uses a modified controlled cortical impactor to deliver closed-headed injury, inducing clinically relevant behavioral deficits without the need for a craniotomy or the use of an anesthetic. This technique does not normally induce fatalities, skull fractures, or brain bleeds, and is more consistent with being a mild injury. Indeed, the mild nature of the ACHI procedure makes it ideal for studies investigating repetitive mTBI (r-mTBI). Growing evidence indicates that r-mTBI can result in a cumulative injury that produces behavioral symptoms, neuropathological changes, and neurodegeneration. r-mTBI is common in youths playing sports, and these injuries occur during a period of robust synaptic reorganization and myelination, making the younger population particularly vulnerable to the long-term influences of r-mTBI. Further, r-mTBI occurs in cases of intimate partner violence, a condition for which there are few objective screening measures. In these experiments, synaptic function was assessed in the hippocampus in juvenile rats that had experienced r-mTBI using the ACHI model. Following the injuries, a tissue slicer was utilized to make hippocampal slices to evaluate bidirectional synaptic plasticity in the hippocampus at either 1 or 7 days following the r-mTBI. Overall, the ACHI model provides researchers with an ecologically valid model to study changes in synaptic plasticity following mTBI and r-mTBI.

Brain changes: aerobic exercise for traumatic brain injury rehabilitation.

Introduction: Traumatic Brain Injury (TBI) accounts for millions of hospitalizations and deaths worldwide. Aerobic exercise is an easily implementable, non-pharmacological intervention to treat TBI, however, there are no clear guidelines for how to best implement aerobic exercise treatment for TBI survivors across age and injury severity. Methods: We conducted a PRISMA-ScR to examine research on exercise interventions following TBI in children, youth and adults, spanning mild to severe TBI. Three electronic databases (PubMed, PsycInfo, and Web of Science) were searched systematically by two authors, using keywords delineated from "Traumatic Brain Injury," "Aerobic Exercise," and "Intervention." Results: Of the 415 papers originally identified from the search terms, 54 papers met the inclusion criteria and were included in this review. The papers were first grouped by participants' injury severity, and subdivided based on age at intervention, and time since injury where appropriate. Discussion: Aerobic exercise is a promising intervention for adolescent and adult TBI survivors, regardless of injury severity. However, research examining the benefits of post-injury aerobic exercise for children and older adults is lacking.

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.

Paternal exposure to exercise and/or caffeine and alcohol modify offspring behavioral and pathophysiological recovery from repetitive mild traumatic brain injury in adolescence.

Only recently has the scope of parental research expanded to include the paternal sphere with epidemiological studies implicating stress, nutrition and alcohol consumption in the neurobiological and behavioral characteristics of offspring. This study was designed to determine if paternal exposure to caffeine, alcohol and exercise prior to conception would improve or exacerbate offspring recovery from adolescent repetitive mild traumatic brain injury (RmTBI). Sires received 7 weeks of standard drinking water, or caffeine and ethanol and were housed in regular cages or cages with running wheels, prior to being mated to control females. At postnatal day 40, offspring were administered RmTBI or sham injuries and were assessed for post concussive symptomology. Post-mortem quantitative real-time polymerase chain reaction (qRT-PCR) was used to assess gene expression in the prefrontal cortex (PFC), nucleus accumbens (NAc) and changes in telomere length. Additionally, enzyme-linked immunosorbent assay (ELISA's) were run on serum to detect levels of cytokines, chemokines and sex hormones. Paternal experience did not improve or exacerbate RmTBI behavioral outcomes. However, female and male offspring displayed unique responses to RmTBI and paternal experience, resulting in changes in physical, behavioral and molecular outcomes. Injury and paternal exercise modified changes in female offspring, whereas male offspring were affected by paternal exercise, caffeine and alcohol treatment. Additionally, paternal experience and RmTBI modified expression of many genes in the PFC, NAc, telomere length and levels of sex hormones. Although further exploration is required to understand the heterogeneity that exists in disease risk and resiliency, this study provides corroborating evidence that paternal experiences prior to conception influences offspring development.

Sexually Dimorphic Behavioral and Genetic Outcomes Associated With Administration of TA65 (A Telomerase Activator) Following Repetitive Traumatic Brain Injury: A Pilot Study.

Children and adolescents have the highest rates of traumatic brain injury (TBI), with mild TBI (mTBI) accounting for most of these injuries. This demographic also often suffers from post-injury symptomologies that may persist for months. Telomere length (TL) has previously been used as a marker for outcomes following repetitive mild TBI (RmTBI) and it may be possible that telomere elongation can reduce post-traumatic behavioral impairments. Telomerase activator-65 (TA-65) is a telomerase small-molecule activator purified from the root of Chinese herbs that has been anecdotally reported to have anti-aging and life-extending potential. We hypothesized that RmTBI would shorten TL but administration of TA-65 would reverse RmTBI-induced telomere shortening and behavioral deficits. Male and female Sprague-Dawley rats were orally administered TA-65 or a placebo substance for 30 consecutive days [postnatal day (P) 25-55]. Following the injury protocol (mTBIs on P33, 36, and 40), rats went through a behavioral test battery designed to examine symptomologies commonly associated with mTBI (balance and motor coordination, exploratory behavior, short-term working memory, and anxiety- and depressive-like behaviors). TL in ear and brain tissue (prefrontal cortex and hippocampus) and relative expression of TERT and Tep1 via qPCR were assessed 15 days following the last injury. We observed a heterogenous response between males and females, with TA65 administration resulting in increased mRNA expression of TERT and Tep1 in female rats that experienced RmTBI, which was accompanied by some functional recovery on motor behavior and footslips in the beam walk task and depressive-like behavior in the forced swim task.

Administration of diphenyl diselenide (PhSe)2 following repetitive mild traumatic brain injury exacerbates anxiety-like symptomology in a rat model.

Approximately 10-15 % of people that sustain mild traumatic brain injury (mTBI) develop post-concussive syndrome (PCS). PCS is a complex array of symptoms that can result in physical, cognitive and emotional impairments. Following mTBI, there are also complex changes in the oxidative stress system and engagement of the inflammatory system, within the brain. Diphenyl diselenide (PhSe)2 is an organoselenium compound which can play a role in anti-oxidant and anti-inflammatory activities. (PhSe)2 also has many interesting properties including anti-anxiety, anti-depressant and anti-nociception effects. We sought to determine if treatment with (PhSe)2 following repetitive mTBI could have mitigating effects on PCS. To investigate this, we induced mTBI or sham injuries using our lateral impact device in adolescent male and female Sprague Dawley rats and an hour later injected rats with vehicle, 10 mg/kg or 25 mg/kg (PhSe)2 i.p. Next, we conducted a behavioral assessment designed to assess PCS and then euthanized the animals to examine changes in gene expression and telomere length. (PhSe)2 decreased the time to cross the beam, distance travelled and time spent in the centre of the open field, time spent in the open arms of the elevated plus maze, the time investigating both objects in the novel context mismatch and time immobile in the forced swim. This anxiety-like symptomology resolved spontaneously between 10 and 12 days after the third mTBI. We found (PhSe)2 groups showed increased levels of TNF alpha and longer telomeres. We also found higher levels of GPX1 in the injured animals. Our results show that (PhSe)2 exacerbates anxiety-like symptomology in contrast to previous findings.

Repetitive Mild Traumatic Brain Injuries in Mice during Adolescence Cause Sexually Dimorphic Behavioral Deficits and Neuroinflammatory Dynamics.

Adolescent brain injuries have devastating impacts on lifelong health given that adolescence is a critical period for brain development. Adolescents are susceptible to mild traumatic brain injuries (mTBIs) acquired from collisions in contact sports, which are often sustained in a repetitive nature (repetitive mild traumatic brain injuries; RmTBIs), and cause compounding, sexually dimorphic neurological deficits. Neuroinflammation accompanies RmTBIs and may be a central driving force for chronic neurological decline. To date, the impact of neuroinflammation and sex-specific dynamics during adolescent RmTBIs has been understudied. A lateral impact model (LIM) was developed that mimics the biomechanical forces commonly experienced in human mTBIs. Here, we report novel sexually dimorphic neurobehavioral and -inflammatory responses using LIM to model adolescent RmTBIs. We first subjected adolescent male C57Bl/6 mice to one, three, or five RmTBIs at 24-h intervals and quantified neurobehavioral deficits, and brain volumetric and structural changes by magnetic resonance imaging. Five RmTBIs caused significant motor deficits, increased brain volume in cortex, hippocampus, and corpus callosum, and reduced white matter integrity in the corpus callosum. We then compared neurobehavioral deficits in adolescent male and female mice and observed sex-specific deficits in motor function, whereas both sexes had dysfunction in learning and memory. Flow cytometric quantification of neuroinflammatory responses revealed time- and sex-dependent infiltration of peripheral macrophages and T cells and male-specific decreases in microglia number. Using immunohistochemistry, we report specific microglia density decreases in male mice in the motor cortex and thalamus. We show novel neuroinflammatory responses after adolescent brain injuries that expands the current understanding of RmTBI pathophysiology in this critical neurodevelopmental period.

When Two Wrongs Make a Right: The Effect of Acute and Chronic Binge Drinking on Traumatic Brain Injury Outcomes in Young Adult Female Rats.

Alcohol is the most commonly abused drug by young adults across North America. Although alcohol consumption itself incurs a risk of neurological damage, it is also a significant risk factor for traumatic brain injury (TBI). TBI among young adults is described as a modern healthcare epidemic. The drastic changes occurring within their neurological networks put young adults at greater risk for developing long-term post-traumatic deficits. Contradictory findings have been indicated regarding the effects of alcohol consumption on TBI outcomes in adults, with some studies demonstrating detrimental effects, whereas others suggest neuroprotective abilities. However, little is known about the effects of alcohol consumption on TBI outcomes during the sensitive stage of early adulthood. Young adult female Sprague-Dawley rats were randomly assigned to one of six experimental conditions: Pre-injury alcohol+TBI; Pre-injury alcohol+Sham; Pre- and Post-injury alcohol+TBI; Pre- and Post-injury alcohol+Sham; No alcohol+TBI; No alcohol+Sham. Alcohol consumption groups received an amount of 10% v/v ethanol solution based on the animals' weight. Following the injury, the rats were subjected to a behavioral test battery to assess post-concussive symptomology. Overall, chronic binge drinking significantly improved TBI outcomes related to motor coordination and balance, whereas binge drinking in general significantly decreased anxiety-like behaviors. Additionally, in many cases, chronic binge drinking appears to return the TBI animal's behavioral outcomes to levels comparable to those of the no alcohol sham animals. Thus, the results suggest that alcohol may exhibit neuroprotective abilities in the context of early adulthood TBI.

Examining the Progressive Behavior and Neuropathological Outcomes Associated with Chronic Repetitive Mild Traumatic Brain Injury in Rats.

While the physical and behavioral symptomologies associated with a single mild traumatic brain injury (mTBI) are typically transient, repetitive mTBIs (RmTBI) have been associated with persisting neurological deficits. Therefore, this study examined the progressive changes in behavior and the neuropathological outcomes associated with chronic RmTBI through adolescence and adulthood in male and female Sprague Dawley rats. Rats experienced 2 mTBIs/week for 15 weeks and were periodically tested for changes in motor behavior, cognitive function, emotional disturbances, and aggression. Brain tissue was examined for neuropathological changes in ventricle size and presentation of Iba1 and GFAP. We did not see progressively worse behavioral impairments with the accumulation of injuries or time, but did find evidence for neurological and functional change (motor disturbance, reduced exploration, reduced aggression, alteration in depressive-like behavior, deficits in short-term working memory). Neuropathological assessment of RmTBI animals identified an increase in ventricle size, prolonged changes in GFAP, and sex differences in Iba1, in the corpus callosum, thalamus, and medial prefrontal cortex. Telomere length reduced exponentially as the injury load increased. Overall, chronic RmTBI did not result in accumulating behavioral impairment, and there is a need to further investigate progressive behavioral changes associated with repeated injuries in adolescence and young adulthood.

Living in fear: Low-cost avoidance maintains low-level threat.

BACKGROUND AND OBJECTIVES: Excessive avoidance of potential threat is a hallmark of anxiety and is thought to maintain fear by preserving the perceived high-threat value of avoided situations. Previous research has shown that the availability of avoidance maintains low-level threat. Here, we investigated whether an opportunity to engage in avoidance in the presence of a low-threat value safety cue would maintain its perceived threat value when avoidance was unavailable. METHODS: In a threat conditioning procedure, one conditional danger stimulus (CS+; A+) was followed by an aversive unconditioned stimulus (US; electric shock), and two safety stimuli (CS-; B- and C-) were never followed by the US. Next, clicking a button present during A+ avoided the scheduled US. Avoidance was then made available during C- for participants in the Experimental group but not in the Control group. In the test, all stimuli were presented without the opportunity to avoid. Threat expectancy, eyeblink startle electromyography (EMG), and skin conductance responses (SCRs) were measured. RESULTS: Findings showed an increase in threat expectancy for only C- in the Experimental group during the test phase following avoidance learning to similar levels as during threat conditioning. Compared to the Control group, threat expectancy for both B- and C- remained higher in Experimental group. SCR and startle EMG data did not corroborate these findings. LIMITATIONS: Further research is needed to test the commonly held clinical assumption that avoidance can increase threat value. CONCLUSIONS: Low-cost avoidance maintains low-threat value of safety cues.

Investigating the Role of the Hypothalamus in Outcomes to Repetitive Mild Traumatic Brain Injury: Neonatal Monosodium Glutamate Does Not Exacerbate Deficits.

Repetitive mild traumatic brain injury (RmTBI) is a prevalent and costly head injury particularly among adolescents. These injuries may result in long-term consequences, especially during this critical period of development. Insomnia and sleeping difficulties are frequently reported following RmTBI and greatly impair recovery. We sought to develop an animal model of exacerbated deficits following RmTBI by disrupting the hypothalamic circadian system. To accomplish this, we conducted RmTBI on adolescent rats that had received neonatal injections of monosodium glutamate (MSG), a known hypothalamic neurotoxin. We then examined behavioral, circadian, and epigenetic changes. MSG treated rats showed lower anxiety-like behaviors and displayed poor short-term working memory. We also showed changes in the morphology of the circadian clock in the suprachiasmatic nucleus (SCN) vasoactive intestinal polypeptide (VIP) immunostaining. VIP optical density in the SCN increased with MSG but decreased with RmTBI. There were changes in the expression of the clock genes and upregulation of the orexin receptors in response to RmTBI. MSG treated rats had longer telomere lengths than controls. Finally, although both MSG and RmTBI alone produced attenuated circadian amplitudes of activity and body temperature, exacerbated deficits were not identified in animals that received MSG and RmTBI. In sum, both MSG and RmTBI can alter behavior, circadian rhythm amplitude, SCN morphology, and gene expression independently, but the effects do not appear to be additive. Specific damage in the hypothalamus and SCN should be considered when patients experience sleeping problems following RmTBI, as this may improve therapeutic strategies.