Increased Cortical Gamma-Aminobutyric Acid Precedes Incomplete Extinction of Conditioned Fear and Increased Hippocampal Excitatory Tone in a Mouse Model of Mild Traumatic Brain Injury

Uninterrupted in vivo cerebral microdialysis measures of the acute neurochemical response to a single or repeated concussion in a rat model combining force and rotation

Altered extracellular amino acid concentrations following concussion or mild traumatic brain injury can result in delayed neuronal damage through overactivation of NMDA glutamatergic receptors. However, the consequences of repeated concussions prior to complete recovery are not well understood. In this study, we utilized in vivo cerebral microdialysis and a weight-drop model to investigate the acute neurochemical response to single and repeated concussions in adult rats that were fully conscious. A microdialysis probe was inserted into the hippocampus and remained in place during impact. Primary outcomes included concentrations of glutamate, GABA, taurine, glycine, glutamine, and serine, while secondary outcomes were righting times and excitotoxic indices. Compared to sham injury, the first concussion resulted in significant increases in glutamate, GABA, taurine, and glycine levels, longer righting times, and higher excitotoxic indices. Following the second concussion, righting times were significantly longer, suggesting cumulative effects of repeated concussion while only partial increases were observed in glutamate and taurine levels. GABA and glycine levels, and excitotoxic indices were comparable to sham injury. These findings suggest that single and repeated concussions may induce acute increases in several amino acids, while repeated concussions could exacerbate neurological symptoms despite less pronounced neurochemical changes.

Mechanistic and therapeutic relationships of traumatic brain injury and γ-amino-butyric acid (GABA)

Traumatic brain injury (TBI) is a highly prevalent medical condition for which no medications specific for the prophylaxis or treatment of the condition as a whole exist. The spectrum of symptoms includes coma, headache, seizures, cognitive impairment, depression, and anxiety. Although it has been known for years that the inhibitory neurotransmitter γ-amino-butyric acid (GABA) is involved in TBI, no novel therapeutics based upon this mechanism have been introduced into clinical practice. We review the neuroanatomical, neurophysiological, neurochemical, and neuropharmacological relationships of GABA neurotransmission to TBI with a view toward new potential GABA-based medicines. The long-standing idea that excitatory and inhibitory (GABA and others) balances are disrupted by TBI is supported by the experimental data but has failed to invent novel methods of restoring this balance. The slow progress in advancing new treatments is due to the complexity of the disorder that encompasses multiple dynamically interacting biological processes including hemodynamic and metabolic systems, neurodegeneration and neurogenesis, major disruptions in neural networks and axons, frank brain lesions, and a multitude of symptoms that have differential neuronal and neurohormonal regulatory mechanisms. Although the current and ongoing clinical studies include GABAergic drugs, no novel GABA compounds are being explored. It is suggested that filling the gap in understanding the roles played by specific GABAA receptor configurations within specific neuronal circuits could help define new therapeutic approaches. Further research into the temporal and spatial delivery of GABA modulators should also be useful. Along with GABA modulation, research into the sequencing of GABA and non-GABA treatments will be needed.

The neural circuits and molecular mechanisms underlying fear dysregulation in posttraumatic stress disorder

Post-traumatic stress disorder (PTSD) is a stress-associated complex and debilitating psychiatric disorder due to an imbalance of neurotransmitters in response to traumatic events or fear. PTSD is characterized by re-experiencing, avoidance behavior, hyperarousal, negative emotions, insomnia, personality changes, and memory problems following exposure to severe trauma. However, the biological mechanisms and symptomatology underlying this disorder are still largely unknown or poorly understood. Considerable evidence shows that PTSD results from a dysfunction in highly conserved brain systems involved in regulating stress, anxiety, fear, and reward circuitry. This review provides a contemporary update about PTSD, including new data from the clinical and preclinical literature on stress, PTSD, and fear memory consolidation and extinction processes. First, we present an overview of well-established laboratory models of PTSD and discuss their clinical translational value for finding various treatments for PTSD. We then highlight the research progress on the neural circuits of fear and extinction-related behavior, including the prefrontal cortex, hippocampus, and amygdala. We further describe different molecular mechanisms, including GABAergic, glutamatergic, cholinergic, and neurotropic signaling, responsible for the structural and functional changes during fear acquisition and fear extinction processes in PTSD.

Examining the long-term effects of traumatic brain injury on fear extinction in male rats

There is a strong association between traumatic brain injuries (TBIs) and the development of psychiatric disorders, including post-traumatic stress disorder (PTSD). Exposure-based therapy is a first-line intervention for individuals who suffer from PTSD and other anxiety-related disorders; however, up to 50% of individuals with PTSD do not respond well to this approach. Fear extinction, a core mechanism underlying exposure-based therapy, is a procedure in which a repeated presentation of a conditioned stimulus in the absence of an unconditioned stimulus leads to a decrease in fear expression, and is a useful tool to better understand exposure-based therapy. Identifying predictors of extinction would be useful in developing alternative treatments for the non-responders. We recently found that CO₂ reactivity predicts extinction phenotypes in rats, likely through the activation of orexin receptors in the lateral hypothalamus. While studies have reported mixed results in extinction of fear after TBI, none have examined the long-term durability of this phenotype in the more chronically injured brain. Here we tested the hypothesis that TBI results in a long-term deficit in fear extinction, and that CO₂ reactivity would be predictive of this extinction phenotype. Isoflurane-anesthetized adult male rats received TBI (n = 59) (produced by a controlled cortical impactor) or sham surgery (n = 29). One month post-injury or sham surgery, rats underwent a CO₂ or air challenge, followed by fear conditioning, extinction, and fear expression testing. TBI rats exposed to CO₂ (TBI-CO₂) showed no difference during extinction or fear expression relative to shams exposed to CO₂ (sham-CO₂). However, TBI-CO₂ rats, showed significantly better fear expression than TBI rats exposed to air (TBI-air). In contrast to previous findings, we observed no relationship between CO₂ reactivity and post-extinction fear expression in either the sham or TBI rats. However, compared to the previously observed naïve sample, we observed more variability in post-extinction fear expression but a very similar distribution of CO₂ reactivity in the current sample. Isoflurane anesthesia may lead to interoceptive threat habituation, possibly via action on orexin receptors in the lateral hypothalamus, and may interact with CO₂ exposure, resulting in enhanced extinction. Future work will directly test this possibility.

Involvement of the GABAergic system in PTSD and its therapeutic significance

The neurobiological mechanism of post-traumatic stress disorder (PTSD) is poorly understood. The inhibition of GABA neurons, especially in the amygdala, is crucial for the precise regulation of the consolidation, expression, and extinction of fear conditioning. The GABAergic system is involved in the pathophysiological process of PTSD, with several studies demonstrating that the function of the GABAergic system decreases in PTSD patients. This paper reviews the preclinical and clinical studies, neuroimaging techniques, and pharmacological studies of the GABAergic system in PTSD and summarizes the role of the GABAergic system in PTSD. Understanding the role of the GABAergic system in PTSD and searching for new drug targets will be helpful in the treatment of PTSD.

Macromolecular-Suppressed GABA-Edited MR Spectroscopy in the Posterior Cingulate Cortex of Patients With Acute Mild Traumatic Brain Injury

BACKGROUND

Mild traumatic brain injury (mTBI) causes a number of molecular and cellular alterations. There is evidence of an imbalance between the main excitatory (glutamate, Glu) and the main inhibitory (gamma-aminobutyric acid [GABA]) neurotransmitters following mTBI. In vivo human GABA-Glu balance studies following mTBI are sparse.

PURPOSE

To investigate the effect of acute mTBI on the GABA concentration measured in the posterior cingulate cortex (PCC) of pediatric patients by using the macromolecular (MM)-suppressed GABA J-editing technique.

STUDY TYPE

Prospective patient and phantom.

PARTICIPANTS

A total of 14 pediatric patients (mean age 16.0 ± 1.7) with acute mTBI (<3 days after trauma; Glasgow Coma Scale 15) and 16 healthy volunteers (mean age 16.9 ± 2.8). Phantom: 524 cm³ sphere containing 10 mM glycine, 10 mM GABA.

FIELD STRENGTH/SEQUENCE

A 3 T, MEGA-PRESS pulse sequence.

ASSESSMENT

GABA spectra were processed in Gannet software. MM-suppressed GABA editing efficiency was derived from the phantom study. Absolute GABA and glutamate + glutamine (Glx) concentrations were quantified using different types of correction and compared between groups. N-acetyl aspartate (NAA) and choline (Cho) levels relative to tCr were also compared.

STATISTICAL TESTS

Shapiro-Wilk test, Mann-Whitney U test, Student t-test, Pearson or Spearman correlations. P < 0.01 was considered statistically significant.

RESULTS

The MM-suppressed GABA editing efficiency was 0.63. GABA signal fit error was <16% for all participants. The GABA concentration in the PCC of the mTBI group was significantly different from that in healthy controls: GABA/tCr was higher by 27%, absolute GABA concentration with different types of correction was higher by ≈17%. No significant differences were observed in Glx concentrations (P ≥ 0.32) or in Glx/tCr (P ≥ 0.1), NAA/tCr (P = 0.55), and Cho/tCr levels (P = 0.85).

DATA CONCLUSION

We report an increase in the GABA concentration in the PCC region in acute mTBI pediatric patients. This may suggest activation of GABA synthesis and impairment of the GABAergic system after acute mTBI.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 1.

The role of the stress system in recovery after traumatic brain injury: A tribute to Bruce S. McEwen

Traumatic brain injury (TBI) represents a major public health concern. Although the majority of individuals that suffer mild-moderate TBI recover relatively quickly, a substantial subset of individuals experiences prolonged and debilitating symptoms. An exacerbated response to physiological and psychological stressors after TBI may mediate poor functional recovery. Individuals with TBI can suffer from poor stress tolerance, impairments in the ability to evaluate stressors, and poor initiation (and cessation) of neuroendocrine stress responses, all of which can exacerbate TBI-mediated dysfunction. Here, we pay tribute to the pioneering neuroendocrinologist Dr. Bruce McEwen by discussing the ways in which his work on stress physiology and allostatic loading impacts the TBI patient population both before and after their injuries. Specifically, we will discuss the modulatory role of hypothalamic-pituitary-adrenal axis responses immediately after TBI and later in recovery. We will also consider the impact of stressors and stress responses in promoting post-concussive syndrome and post-traumatic stress disorders, two common sequelae of TBI. Finally, we will explore the role of early life stressors, prior to brain injuries, as modulators of injury outcomes.

Repetitive mild traumatic brain injury induces persistent alterations in spontaneous synaptic activity of hippocampal CA1 pyramidal neurons

Mild traumatic brain injury (mTBI) or concussion is the most common form of TBI which frequently results in persistent cognitive impairments and memory deficits in affected individuals [1]. Although most studies have investigated the role of hippocampal synaptic dysfunction in earlier time points following a single injury, the long-lasting effects of mTBI on hippocampal synaptic transmission following multiple brain concussions have not been well-elucidated. Using a repetitive closed head injury (3XCHI) mouse model of mTBI, we examined the alteration of spontaneous synaptic transmission onto hippocampal CA1 pyramidal neurons by recording spontaneous excitatory AMPA receptor (AMPAR)- and inhibitory GABA_AR-mediated postsynaptic currents (sEPSCs and sIPSCs, respectively) in adult male mice 2-weeks following the injury. We found that mTBI potentiated postsynaptic excitatory AMPAR synaptic function while depressed postsynaptic inhibitory GABA_AR synaptic function in CA1 pyramidal neurons. Additionally, mTBI slowed the decay time of AMPAR currents while shortened the decay time of GABA_AR currents suggesting changes in AMPAR and GABA_AR subunit composition by mTBI. On the other hand, mTBI reduced the frequency of sEPSCs while enhanced the frequency of sIPSCs resulting in a lower ratio of sEPSC/sIPSC frequency in CA1 pyramidal neurons of mTBI animals compared to sham animals. Altogether, our results suggest that mTBI induces persistent postsynaptic modifications in AMPAR and GABA_AR function and their synaptic composition in CA1 neurons while triggering a compensatory shift in excitation/inhibition (E/I) balance of presynaptic drives towards more inhibitory synaptic drive to hippocampal CA1 cells. The persistent mTBI-induced CA1 synaptic dysfunction and E/I imbalance could contribute to deficits in hippocampal plasticity that underlies long-term hippocampal-dependent learning and memory deficits in mTBI patients long after the initial injury.

Repeated blast mild traumatic brain injury and oxycodone self-administration produce interactive effects on neuroimaging outcomes

Traumatic brain injury (TBI) and drug addiction are common comorbidities, but it is unknown if the neurological sequelae of TBI contribute to this relationship. We have previously reported elevated oxycodone seeking after drug self-administration in rats that received repeated blast TBI (rbTBI). TBI and exposure to drugs of abuse can each change structural and functional neuroimaging outcomes, but it is unknown if there are interactive effects of injury and drug exposure. To determine the effects of TBI and oxycodone exposure, we subjected rats to rbTBI and oxycodone self-administration and measured drug seeking and several neuroimaging measures. We found interactive effects of rbTBI and oxycodone on fractional anisotropy (FA) in the nucleus accumbens (NAc) and that FA in the medial prefrontal cortex (mPFC) was correlated with drug seeking. We also found an interactive effect of injury and drug on widespread functional connectivity and regional homogeneity of the blood oxygen level dependent (BOLD) response, and that intra-hemispheric functional connectivity in the infralimbic medial prefrontal cortex positively correlated with drug seeking. In conclusion, rbTBI and oxycodone self-administration had interactive effects on structural and functional magnetic resonance imaging (MRI) measures, and correlational effects were found between some of these measures and drug seeking. These data support the hypothesis that TBI and opioid exposure produce neuroadaptations that contribute to addiction liability.

A review of the pathology and treatment of TBI and PTSD

This literature review focuses on the underlying pathophysiology of TBI and PTSD symptoms, while also examining the plethora of stem cell treatment options to ameliorate these neuronal and functional changes. As more veterans return suffering from TBI and/or PTSD, it is vital that researchers discover novel therapies to mitigate the detrimental symptoms of both diagnoses. A variety of stem cell treatments have been studied and offer hopeful options for TBI and PTSD recovery.

Efficacy of prophylactic versus therapeutic administration of the NMDA receptor antagonist MK-801 on the acute neurochemical response to a concussion in a rat model combining force and rotation

OBJECTIVE

Alterations in amino acid concentrations are a major contributor to the persistent neurological and behavioral effects induced by concussions and mild traumatic brain injuries (TBIs). Glutamate, the most abundant excitatory amino acid in the CNS, has a major role in the pathophysiological process of concussion. The indiscriminate liberation of glutamate immediately after a concussion triggers an excitotoxic response that leads to cell death, neuronal damage, and the dysfunction of surviving neurons, largely by overactivation of N-methyl-d-aspartate (NMDA) glutamatergic receptors. The aim of the present study was to investigate the efficacy of prophylactic versus therapeutic administration of MK-801, a promising NMDA receptor antagonist, on the acute changes in amino acid extracellular concentrations involved in excitotoxicity resulting from a concussive trauma.

METHODS

The immediate neurochemical response to a concussion cannot be characterized in humans. Therefore, the authors used their previously validated combination of a weight-drop concussion rat model and in vivo cerebral microdialysis. The microdialysis probe was inserted inside the hippocampus and left inserted at impact to allow uninterrupted sampling of amino acids of interest immediately after concussion. The primary outcome included amino acid concentrations and the secondary outcome included righting time. Samples were taken in 10-minute increments for 60 minutes before, during, and 60 minutes after impact, and analyzed for glutamate, gamma-aminobutyric acid, taurine, glycine, glutamine, and serine using high-performance liquid chromatography. Righting time was acquired as a neurological restoration indicator. Physiological saline or 10 mg/kg MK-801 was administrated intraperitoneally 60 minutes before or immediately following induction of sham injury or concussion.

RESULTS

Following induction of concussion, glutamate, taurine, and glycine levels as well as righting times in cases from the MK-801 treatment group were comparable to those of vehicle-treated animals. In contrast, righting times and amino acid concentrations observed within the first 10 minutes after induction of concussion in cases assigned to the MK-801 prophylaxis group were comparable to those of sham-injured animals.

CONCLUSIONS

These results suggest that presynaptic actions and peak availability of MK-801 following prophylactic administration significantly inhibit the immediate and indiscriminate release of glutamate, taurine, and glycine in extracellular fluid after a concussion.

Repetitive Mild Traumatic Brain Injury in Rats Impairs Cognition, Enhances Prefrontal Cortex Neuronal Activity, and Reduces Pre-synaptic Mitochondrial Function

A major hurdle preventing effective interventions for patients with mild traumatic brain injury (mTBI) is the lack of known mechanisms for the long-term cognitive impairment that follows mTBI. The closed head impact model of repeated engineered rotational acceleration (rCHIMERA), a non-surgical animal model of repeated mTBI (rmTBI), mimics key features of rmTBI in humans. Using the rCHIMERA in rats, this study was designed to characterize rmTBI-induced behavioral disruption, underlying electrophysiological changes in the medial prefrontal cortex (mPFC), and associated mitochondrial dysfunction. Rats received 6 closed-head impacts over 2 days at 2 Joules of energy. Behavioral testing included automated analysis of behavior in open field and home-cage environments, rotarod test for motor skills, novel object recognition, and fear conditioning. Following rmTBI, rats spent less time grooming and less time in the center of the open field arena. Rats in their home cage had reduced inactivity time 1 week after mTBI and increased exploration time 1 month after injury. Impaired associative fear learning and memory in fear conditioning test, and reduced short-term memory in novel object recognition test were found 4 weeks after rmTBI. Single-unit in vivo recordings showed increased neuronal activity in the mPFC after rmTBI, partially attributable to neuronal disinhibition from reduced inhibitory synaptic transmission, possibly secondary to impaired mitochondrial function. These findings help validate this rat rmTBI model as replicating clinical features, and point to impaired mitochondrial functions after injury as causing imbalanced synaptic transmission and consequent impaired long-term cognitive dysfunction.

Region-Dependent Modulation of Neural Plasticity in Limbic Structures Early after Traumatic Brain Injury

Traumatic brain injury (TBI)-induced disruptions in synaptic function within brain regions and across networks in the limbic system may underlie a vulnerability for maladaptive plasticity and contribute to behavioral comorbidities. In this study we measured how synaptic proteins respond to lateral fluid percussion injury (FPI) brain regions known to regulate emotion and memory, including the basolateral amygdala (BLA), dorsal and ventral hippocampus (DH, VH), and medial prefrontal cortex (PFC). We investigated proteins involved in regulating plasticity, including synaptic glutamatergic a-amino-3-hydroxy5-methyl-4-isoxazolepropionic acid (AMPA; GluA1, GluA2) and N-methyl-D-aspartate (NMDA; NR1, NR2A, NR2B) receptor subunits as well as inhibitory gamma-aminobutyric acid (GABA) synthetic enzymes (GAD67, GAD65) via western blot. Adult male rats received a mild-moderate lateral FPI or sham surgery and ipsi- and contralateral BLA, DH, VH, and PFC were collected 6 h, 24 h, 48 h, and 7 days post-injury. In the ipsilateral BLA, there was a significant decrease in NR1 and GluA2 24 h after injury, whereas NR2A and NR2B were increased in the contralateral BLA at 48 h compared with sham. GAD67 was increased ipsilaterally at 24 h, but decreased contralaterally at 48 h in the BLA. In the DH, both NMDA (NR2A, NR2B) and GABA-synthetic (GAD65, GAD67) proteins were increased acutely at 6 h compared with sham. GAD67 was also robustly increased in the ipsilateral VH at 6 h. In the contralateral VH, NR2A significantly increased between 6 h and 24 h after FPI, whereas GAD65 was decreased across the same time-points in the contralateral VH. In the medial PFC at 24 h we saw bilateral increases in GAD67 and a contralateral decrease in GluA1. Later, there was a significant decrease in GAD67 in contralateral PFC from 48 h to 7 days post-injury. Collectively, these data suggest that lateral FPI causes a dynamic homeostatic response across limbic networks, leading to an imbalance of the proteins involved in plasticity in neural systems underlying cognitive and emotional regulation.

Translational neuroimaging in mild traumatic brain injury

Traumatic brain injuries (TBIs) are common with an estimated 27.1 million cases per year. Approximately 80% of TBIs are categorized as mild TBI (mTBI) based on initial symptom presentation. While in most individuals, symptoms resolve within days to weeks, in some, symptoms become chronic. Advanced neuroimaging has the potential to characterize brain morphometric, microstructural, biochemical, and metabolic abnormalities following mTBI. However, translational studies are needed for the interpretation of neuroimaging findings in humans with respect to the underlying pathophysiological processes, and, ultimately, for developing novel and more targeted treatment options. In this review, we introduce the most commonly used animal models for the study of mTBI. We then summarize the neuroimaging findings in humans and animals after mTBI and, wherever applicable, the translational aspects of studies available today. Finally, we highlight the importance of translational approaches and outline future perspectives in the field of translational neuroimaging in mTBI.

Neural Markers of Vulnerability to Anxiety Outcomes after Traumatic Brain Injury

Anxiety outcomes after traumatic brain injury (TBI) are complex, and the underlying neural mechanisms are poorly understood. Here, we developed a multi-dimensional behavioral profiling approach to investigate anxiety-like outcomes in mice that takes into account individual variability. Departing from the tradition of comparing outcomes in TBI versus sham groups, we identified a subgroup within the TBI group that is vulnerable to anxiety dysfunction, and present increased exploration of the anxiogenic zone compared to sham controls or resilient injured animals, by applying dimensionality reduction, clustering, and post hoc validation to behavioral data obtained from multiple assays for anxiety at several post-injury time points. These vulnerable animals expressed distinct molecular profiles in the corticolimbic network, with downregulation in gamma-aminobutyric acid and glutamate and upregulation in neuropeptide Y markers. Indeed, among vulnerable animals, not resilient or sham controls, severity of anxiety-related outcomes correlated strongly with expression of molecular markers. Our results establish a foundational approach, with predictive power, for reliably identifying maladaptive anxiety outcomes after TBI and uncovering neural signatures of vulnerability to anxiety.

Inhibiting α5 Subunit-Containing γ-Aminobutyric Acid Type A Receptors Attenuates Cognitive Deficits After Traumatic Brain Injury

OBJECTIVES

Cognitive deficits after traumatic brain injury are a leading cause of disability worldwide, yet no effective pharmacologic treatments exist to improve cognition. Traumatic brain injury increases proinflammatory cytokines, which trigger excess function of α5 subunit-containing γ-aminobutyric acid type A receptors. In several models of brain injury, drugs that inhibit α5 subunit-containing γ-aminobutyric acid type A receptor function improve cognitive performance. Thus, we postulated that inhibiting α5 subunit-containing γ-aminobutyric acid type A receptors would improve cognitive performance after traumatic brain injury. In addition, because traumatic brain injury reduces long-term potentiation in the hippocampus, a cellular correlate of memory, we studied whether inhibition of α5 subunit-containing γ-aminobutyric acid type A receptors attenuated deficits in long-term potentiation after traumatic brain injury.

DESIGN

Experimental animal study.

SETTING

Research laboratory.

SUBJECTS

Adult male mice and hippocampal brain slices.

INTERVENTIONS

Anesthetized mice were subjected to traumatic brain injury with a closed-head, free-weight drop method. One week later, the mice were treated with L-655,708 (0.5 mg/kg), an inhibitor that is selective for α5 subunit-containing γ-aminobutyric acid type A receptors, 30 minutes before undergoing behavioral testing. Problem-solving abilities were assessed using the puzzle box assay, and memory performance was studied with novel object recognition and object place recognition assays. In addition, hippocampal slices were prepared 1 week after traumatic brain injury, and long-term potentiation was studied using field recordings in the cornu Ammonis 1 region of slices that were perfused with L-655,708 (100 nM).

MEASUREMENTS AND MAIN RESULTS

Traumatic brain injury increased the time required to solve difficult but not simple tasks in the puzzle box assay and impaired memory in the novel object recognition and object place recognition assays. L-655,708 improved both problem solving and memory in the traumatic brain injury mice. Traumatic brain injury reduced long-term potentiation in the hippocampal slices, and L-655,708 attenuated this reduction.

CONCLUSIONS

Pharmacologic inhibition of α5 subunit-containing γ-aminobutyric acid type A receptors attenuated cognitive deficits after traumatic brain injury and enhanced synaptic plasticity in hippocampal slices. Collectively, these results suggest that α5 subunit-containing γ-aminobutyric acid type A receptors are novel targets for pharmacologic treatment of traumatic brain injury-induced persistent cognitive deficits.

UPLC-ESI-IT-TOF-MS metabolomic study of the therapeutic effect of Xuefu Zhuyu decoction on rats with traumatic brain injury

It has been widely reported that Xuefu Zhuyu decoction (XFZYD), a traditional Chinese medicine, is effective in the treatment of traumatic brain injury (TBI). However, the mechanism of the therapeutic process is still not fully understood. Metabolomic technique can be used to explore the mechanisms underlying the treatment of TBI with XFZYD. The purpose of this work was to investigate the metabolic characteristics of blood samples from rats with and without XFZYD treatment and the dynamic changes in metabolite profiles on days 1, 3, 7, 14 and 21 after injury (within the severe phase of TBI) based on untargeted UPLC-ESI-IT-TOF-MS analysis. Pattern recognition, clustering analysis and metabolic pathway analysis were used to analyse the metabolomic data of three groups (a sham-operated group, a TBI model, and an XFZYD-treated TBI model). The results showed that XFZYD reversed the abnormalities in the levels of small-molecule metabolites (such as L-acetylcarnitine, L-tryptophan, indoleacrylic acid, γ-aminobutyric acid, hypotaurine, LysoPC(18:1)(11Z), creatine, L-phenylalanine and L-leucine) in TBI rats through six metabolic pathways (including phenylalanine, tyrosine and tryptophan biosynthesis; phenylalanine metabolism; valine, leucine and isoleucine biosynthesis; taurine and hypotaurine metabolism; tryptophan metabolism; and alanine, aspartate and glutamate metabolism) involved in the therapy process. XFZYD regulated the metabolic disorders of endogenous markers by the possible mechanisms of neuroprotection, energy metabolism, inflammatory response and oxidative stress. This study revealed the holistic and dynamic metabolic changes caused by XFZYD in rats with TBI and provided important research methods and approaches for exploring the multiple metabolites and metabolic pathways involved in the therapeutic effect of XFZYD on TBI.

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.

Repeated blast model of mild traumatic brain injury alters oxycodone self-administration and drug seeking

Each year, traumatic brain injuries (TBI) affect millions worldwide. Mild TBIs (mTBI) are the most prevalent and can lead to a range of neurobehavioral problems, including substance abuse. A single blast exposure, inducing mTBI alters the medial prefrontal cortex, an area implicated in addiction, for at least 30 days post injury in rats. Repeated blast exposures result in greater physiological and behavioral dysfunction than single exposure; however, the impact of repeated mTBI on addiction is unknown. In this study, the effect of mTBI on various stages of oxycodone use was examined. Male Sprague Dawley rats were exposed to a blast model of mTBI once per day for 3 days. Rats were trained to self-administer oxycodone during short (2 h) and long (6 h) access sessions. Following abstinence, rats underwent extinction and two cued reinstatement sessions. Sham and rbTBI rats had similar oxycodone intake, extinction responding and cued reinstatement of drug seeking. A second group of rats were trained to self-administer oxycodone with varying reinforcement schedules (fixed ratio (FR)-2 and FR-4). Under an FR-2 schedule, rbTBI-exposed rats earned fewer reinforcers than sham-exposed rats. During 10 extinction sessions, the rbTBI-exposed rats exhibited significantly more seeking for oxycodone than the sham-injured rats. There was a positive correlation between total oxycodone intake and day 1 extinction drug seeking in sham, but not in rbTBI-exposed rats. Together, this suggests that rbTBI-exposed rats are more sensitive to oxycodone-associated cues during reinstatement than sham-exposed rats and that rbTBI may disrupt the relationship between oxycodone intake and seeking.

Untangling PTSD and TBI: Challenges and Strategies in Clinical Care and Research

PURPOSE OF REVIEW

Traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) can result from similar injuries and can result in similar symptoms, such as problems with sleep, concentration, memory, and mood. Although PTSD and persistent sequelae due to a TBI (PST) have generally been viewed as pragmatically confounded but conceptually separable entities, we examine emerging evidence emphasizing the breadth of overlap in both clinical presentation and underlying pathophysiology between PST and PTSD.

RECENT FINDINGS

New evidence underscores the poor specificity of symptoms to etiology and emphasizes the potential, after both physical brain injury and traumatic stress, for changes in each of the three interacting systems that coordinate the body's response to the experience or expectation of major injury-the immune, endocrine, and neuromodulatory neurotransmitter systems. A view of PTSD and PST sharing common pathophysiologic elements related to the CNS response to acute injury or threat carries important implications for research and clinical care.

Pathophysiological Bases of Comorbidity: Traumatic Brain Injury and Post-Traumatic Stress Disorder

The high rates of traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) diagnoses encountered in recent years by the United States Veterans Affairs Healthcare System have increased public awareness and research investigation into these conditions. In this review, we analyze the neural mechanisms underlying the TBI/PTSD comorbidity. TBI and PTSD present with common neuropsychiatric symptoms including anxiety, irritability, insomnia, personality changes, and memory problems, and this overlap complicates diagnostic differentiation. Interestingly, both TBI and PTSD can be produced by overlapping pathophysiological changes that disrupt neural connections termed the "connectome." The neural disruptions shared by PTSD and TBI and the comorbid condition include asymmetrical white matter tract abnormalities and gray matter changes in the basolateral amygdala, hippocampus, and prefrontal cortex. These neural circuitry dysfunctions result in behavioral changes that include executive function and memory impairments, fear retention, fear extinction deficiencies, and other disturbances. Pathophysiological etiologies can be identified using experimental models of TBI, such as fluid percussion or blast injuries, and for PTSD, using models of fear conditioning, retention, and extinction. In both TBI and PTSD, there are discernible signs of neuroinflammation, excitotoxicity, and oxidative damage. These disturbances produce neuronal death and degeneration, axonal injury, and dendritic spine dysregulation and changes in neuronal morphology. In laboratory studies, various forms of pharmacological or psychological treatments are capable of reversing these detrimental processes and promoting axonal repair, dendritic remodeling, and neurocircuitry reorganization, resulting in behavioral and cognitive functional enhancements. Based on these mechanisms, novel neurorestorative therapeutics using anti-inflammatory, antioxidant, and anticonvulsant agents may promote better outcomes for comorbid TBI and PTSD.

Fear learning alterations after traumatic brain injury and their role in development of posttraumatic stress symptoms

BACKGROUND

It is unknown how traumatic brain injury (TBI) increases risk for posttraumatic stress disorder (PTSD). One potential mechanism is via alteration of fear-learning processes that could affect responses to trauma memories and cues. We utilized a prospective, longitudinal design to determine if TBI is associated with altered fear learning and extinction, and if fear processing mediates effects of TBI on PTSD symptom change.

METHODS

Eight hundred fifty two active-duty Marines and Navy Corpsmen were assessed before and after deployment. Assessments included TBI history, PTSD symptoms, combat trauma and deployment stress, and a fear-potentiated startle task of fear acquisition and extinction. Startle response and self-reported expectancy and anxiety served as measures of fear conditioning, and PTSD symptoms were measured with the Clinician-Administered PTSD Scale.

RESULTS

Individuals endorsing "multiple hit" exposure (both deployment TBI and a prior TBI) showed the strongest fear acquisition and highest fear expression compared to groups without multiple hits. Extinction did not differ across groups. Endorsing a deployment TBI was associated with higher anxiety to the fear cue compared to those without deployment TBI. The association of deployment TBI with increased postdeployment PTSD symptoms was mediated by postdeployment fear expression when recent prior-TBI exposure was included as a moderator. TBI associations with increased response to threat cues and PTSD symptoms remained when controlling for deployment trauma and postdeployment PTSD diagnosis.

CONCLUSIONS

Deployment TBI, and multiple-hit TBI in particular, are associated with increases in conditioned fear learning and expression that may contribute to risk for developing PTSD symptoms.

Severity of experimental traumatic brain injury modulates changes in concentrations of cerebral free amino acids

In this study, concentrations of free amino acids (FAA) and amino group containing compounds (AGCC) following graded diffuse traumatic brain injury (mild TBI, mTBI; severe TBI, sTBI) were evaluated. After 6, 12, 24, 48 and 120 hr aspartate (Asp), glutamate (Glu), asparagine (Asn), serine (Ser), glutamine (Gln), histidine (His), glycine (Gly), threonine (Thr), citrulline (Cit), arginine (Arg), alanine (Ala), taurine (Tau), γ‐aminobutyrate (GABA), tyrosine (Tyr), S‐adenosylhomocysteine (SAH), l‐cystathionine (l‐Cystat), valine (Val), methionine (Met), tryptophane (Trp), phenylalanine (Phe), isoleucine (Ile), leucine (Leu), ornithine (Orn), lysine (Lys), plus N‐acetylaspartate (NAA) were determined in whole brain extracts (n = 6 rats at each time for both TBI levels). Sham‐operated animals (n = 6) were used as controls. Results demonstrated that mTBI caused modest, transient changes in NAA, Asp, GABA, Gly, Arg. Following sTBI, animals showed profound, long‐lasting modifications of Glu, Gln, NAA, Asp, GABA, Ser, Gly, Ala, Arg, Citr, Tau, Met, SAH, l‐Cystat, Tyr and Phe. Increase in Glu and Gln, depletion of NAA and Asp increase, suggested a link between NAA hydrolysis and excitotoxicity after sTBI. Additionally, sTBI rats showed net imbalances of the Glu‐Gln/GABA cycle between neurons and astrocytes, and of the methyl‐cycle (demonstrated by decrease in Met, and increase in SAH and l‐Cystat), throughout the post‐injury period. Besides evidencing new potential targets for novel pharmacological treatments, these results suggest that the force acting on the brain tissue at the time of the impact is the main determinant of the reactions ignited and involving amino acid metabolism.

The Anti-Inflammatory Effects of Blueberries in an Animal Model of Post-Traumatic Stress Disorder (PTSD)

Post-traumatic stress disorder (PTSD) is a trauma and stressor-related disorder that results in a prolonged stress response. It is associated with increased oxidative stress and inflammation in the prefrontal cortex (PFC) and hippocampus (HC). The only approved therapy for PTSD is selective serotonin re-uptake inhibitors (SSRIs), but their efficacy is marginal. Recently, we demonstrated that over-production of norepinephrine (NE) as the possible reason for the lack of efficacy of SSRIs. Hence, there is a need for novel therapeutic approaches for the treatment of PTSD. In this study, we investigated the anti-inflammatory role of blueberries in modulating inflammatory markers and neurotransmitter levels in PTSD. Rats were fed either a blueberry enriched (2%) or a control diet. Rats were exposed to cats for one hour on days 1 and 11 of a 31-day schedule to simulate traumatic conditions. The rats were also subjected to psychosocial stress via daily cage cohort changes. At the end of the study, the rats were euthanized and the PFC and HC were isolated. Monoamines were measured by high-performance liquid chromatography. Reactive oxygen species (ROS), gene and protein expression levels of inflammatory cytokines were also measured. In our PTSD model, NE levels were increased and 5-HT levels were decreased when compared to control. In contrast, a blueberry enriched diet increased 5-HT without affecting NE levels. The rate limiting enzymes tyrosine hydroxylase and tryptophan hydroxylase were also studied and they confirmed our findings. The enhanced levels free radicals, gene and protein expression of inflammatory cytokines seen in the PTSD group were normalized with a blueberry enriched diet. Decreased anxiety in this group was shown by improved performance on the elevated plus-maze. These findings indicate blueberries can attenuate oxidative stress and inflammation and restore neurotransmitter imbalances in a rat model of PTSD.

Central HIV-1 Tat exposure elevates anxiety and fear conditioned responses of male mice concurrent with altered mu-opioid receptor-mediated G-protein activation and β-arrestin 2 activity in the forebrain

Co-exposure to opiates and HIV/HIV proteins results in enhanced CNS morphological and behavioral deficits in HIV(+) individuals and in animal models. Opiates with abuse liability, such as heroin and morphine, bind preferentially to and have pharmacological actions through μ-opioid-receptors (MORs). The mechanisms underlying opiate-HIV interactions are not understood. Exposure to the HIV-1 transactivator of transcription (Tat) protein causes neurodegenerative outcomes that parallel many aspects of the human disease. We have also observed that in vivo exposure to Tat results in apparent changes in morphine efficacy, and thus have hypothesized that HIV proteins might alter MOR activation. To test our hypothesis, MOR-mediated G-protein activation was determined in neuroAIDS-relevant forebrain regions of transgenic mice with inducible CNS expression of HIV-1 Tat. G-protein activation was assessed by MOR agonist-stimulated [(35)S]guanosine-5'-O-(3-thio)triphosphate ([(35)S]GTPγS) autoradiography in brain sections, and in concentration-effect curves of MOR agonist-stimulated [(35)S]GTPγS binding in membranes isolated from specific brain regions. Comparative studies were done using the MOR-selective agonist DAMGO ([D-Ala(2), N-MePhe(4), Gly-ol]-enkephalin) and a more clinically relevant agonist, morphine. Tat exposure reduced MOR-mediated G-protein activation in an agonist, time, and regionally dependent manner. Levels of the GPCR regulatory protein β-arrestin-2, which is involved in MOR desensitization, were found to be elevated in only one affected brain region, the amygdala; amygdalar β-arrestin-2 also showed a significantly increased association with MOR by co-immunoprecipitation, suggesting decreased availability of MOR. Interestingly, this correlated with changes in anxiety and fear-conditioned extinction, behaviors that have substantial amygdalar input. We propose that HIV-1 Tat alters the intrinsic capacity of MOR to signal in response to agonist binding, possibly via a mechanism involving altered expression and/or function of β-arrestin-2.