The Effect of Traumatic Brain Injury on Sleep Architecture and Circadian Rhythms in Mice—A Comparison of High-Frequency Head Impact and Controlled Cortical Injury

Traumatic brain injury and sleep in military and veteran populations: A literature review

BACKGROUND

Traumatic brain injury (TBI) is a hallmark of wartime injury and is related to numerous sleep wake disorders (SWD), which persist long term in veterans. Current knowledge gaps in pathophysiology have hindered advances in diagnosis and treatment.

OBJECTIVE

We reviewed TBI SWD pathophysiology, comorbidities, diagnosis and treatment that have emerged over the past two decades.

METHODS

We conducted a literature review of English language publications evaluating sleep disorders (obstructive sleep apnea, insomnia, hypersomnia, parasomnias, restless legs syndrome and periodic limb movement disorder) and TBI published since 2000. We excluded studies that were not specifically evaluating TBI populations.

RESULTS

Highlighted areas of interest and knowledge gaps were identified in TBI pathophysiology and mechanisms of sleep disruption, a comparison of TBI SWD and post-traumatic stress disorder SWD. The role of TBI and glymphatic biomarkers and management strategies for TBI SWD will also be discussed.

CONCLUSION

Our understanding of the pathophysiologic underpinnings of TBI and sleep health, particularly at the basic science level, is limited. Developing an understanding of biomarkers, neuroimaging, and mixed-methods research in comorbid TBI SWD holds the greatest promise to advance our ability to diagnose and monitor response to therapy in this vulnerable population.

Traumatic brain injury-induced disruption of the circadian clock

Disturbances in the circadian rhythm have been reported in patients following traumatic brain injury (TBI). However, the rhythmic expression of circadian genes in peripheral blood leukocytes (PBL) following TBI has not yet been studied. The messenger ribonucleic acid (mRNA) expression of period 1 (Per1), Per2, Per3, cryptochrome 1 (Cry1), Cry2, brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 (Bmal1), and circadian locomotor output cycles kaput (Clock) was quantified in PBLs from sham-operated rats and rats with acute subdural hematoma (ASDH) over a 48-h period. The rectal temperature of the animals was measured every 4 h over 2 days. The mesor, rhythm, amplitude, and acrophase were estimated using cosinor analysis. Cosinor analysis revealed that Per2, Cry1, and Bmal1 mRNAs were rhythmically expressed in the PBLs of sham-operated rats. In contrast, fluctuations in rhythmic expression were not observed following ASDH. The rectal temperature of sham-operated rats also exhibited rhythmicity. ASDH rats had a disrupted rectal temperature rhythm, a diminished amplitude, and an acrophase shift. TBI with ASDH results in dysregulated expression of some circadian genes and changes in body temperature rhythm. Further research is required to understand the pathophysiology of altered circadian networks following TBI. KEY MESSAGES: First to investigate the mRNA expression of circadian genes in PBLs of ASDH rats. ASDH rats had disrupted rhythmicity of Per2, Cry1, and Bmal1 mRNA expression. Cosinor analysis showed that ASDH rats had a disrupted rectal temperature rhythm.

Sleep, inflammation, and hemodynamics in rodent models of traumatic brain injury

Traumatic brain injury (TBI) can induce dysregulation of sleep. Sleep disturbances include hypersomnia and hyposomnia, sleep fragmentation, difficulty falling asleep, and altered electroencephalograms. TBI results in inflammation and altered hemodynamics, such as changes in blood brain barrier permeability and cerebral blood flow. Both inflammation and altered hemodynamics, which are known sleep regulators, contribute to sleep impairments post-TBI. TBIs are heterogenous in cause and biomechanics, which leads to different molecular and symptomatic outcomes. Animal models of TBI have been developed to model the heterogeneity of TBIs observed in the clinic. This review discusses the intricate relationship between sleep, inflammation, and hemodynamics in pre-clinical rodent models of TBI.

Investigation of effects of Circadian Rhythm in Sport: A bibliometric analysis

PURPOSE

This study conducted a bibliometric analysis of the literature on circadian rhythms and sports to identify research trends, knowledge gaps, and future directions.

METHODS

A total of 301 manuscripts, including 245 articles and 56 reviews, were extracted from the Web of Science Core Collection (WoSCC) database, and the bibliometric analysis was performed using VOSviewer 1.6.16.

RESULTS

The analysis revealed a continuous increase in the volume of literature on circadian rhythms and sports over the past 38 years, with a focus on the effects of circadian rhythms on physical performance, sleep quality, and jet lag. The study identified 1107 authors who have contributed to this field, with the highest number of publications from Reilly T, Chtourou H, and Atkinson G. The publications were from 512 institutions in 59 countries/regions, with Liverpool John Moores University, University of Sfax, and Manouba University being the leading institutions. The USA, UK, and Australia had the largest number of publications. The top 3 journals were Chronobiology International, Biological Rhythm Research, and Sports Medicine.

CONCLUSION

Despite the increase in research, there are still several underexplored areas, such as the effects of circadian rhythms on cognitive and emotional processes in sports, the role of individual differences in circadian rhythms on sports outcomes, and the potential applications of circadian interventions for sports performance optimization. Future research should address these gaps to advance our understanding of the complex relationship between circadian rhythms and sports.

Microglial Nogo delays recovery following traumatic brain injury in mice

Nogo-A, B, and C are well described members of the reticulon family of proteins, most well known for their negative regulatory effects on central nervous system (CNS) neurite outgrowth and repair following injury. Recent research indicates a relationship between Nogo-proteins and inflammation. Microglia, the brain's immune cells and inflammation-competent compartment, express Nogo protein, although specific roles of the Nogo in these cells is understudied. To examine inflammation-related effects of Nogo, we generated a microglial-specific inducible Nogo KO (MinoKO) mouse and challenged the mouse with a controlled cortical impact (CCI) traumatic brain injury (TBI). Histological analysis shows no difference in brain lesion sizes between MinoKO-CCI and Control-CCI mice, although MinoKO-CCI mice do not exhibit the levels of ipsilateral lateral ventricle enlargement as injury matched controls. Microglial Nogo-KO results in decreased lateral ventricle enlargement, microglial and astrocyte immunoreactivity, and increased microglial morphological complexity compared to injury matched controls, suggesting decreased tissue inflammation. Behaviorally, healthy MinoKO mice do not differ from control mice, but automated tracking of movement around the home cage and stereotypic behavior, such as grooming and eating (termed cage "activation"), following CCI is significantly elevated. Asymmetrical motor function, a deficit typical of unilaterally brain lesioned rodents, was not detected in CCI injured MinoKO mice, while the phenomenon was present in CCI injured controls 1-week post-injury. Overall, our studies show microglial Nogo as a negative regulator of recovery following brain injury. To date, this is the first evaluation of the roles microglial specific Nogo in a rodent injury model.

Traumatic brain injury induces an adaptive immune response in the meningeal transcriptome that is amplified by aging

Traumatic Brain Injury (TBI) is a major cause of disability and mortality, particularly among the elderly, yet our mechanistic understanding of how age renders the post-traumatic brain vulnerable to poor clinical outcomes and susceptible to neurological disease remains poorly understood. It is well established that dysregulated and sustained immune responses contribute to negative outcomes after TBI, however our understanding of the interactions between central and peripheral immune reservoirs is still unclear. The meninges serve as the interface between the brain and the immune system, facilitating important bi-directional roles in healthy and disease settings. It has been previously shown that disruption of this system exacerbates inflammation in age related neurodegenerative disorders such as Alzheimer's disease, however we have an incomplete understanding of how the meningeal compartment influences immune responses after TBI. Here, we examine the meningeal tissue and its response to brain injury in young (3-months) and aged (18-months) mice. Utilizing a bioinformatic approach, high-throughput RNA sequencing demonstrates alterations in the meningeal transcriptome at sub-acute (7-days) and chronic (1 month) timepoints after injury. We find that age alone chronically exacerbates immunoglobulin production and B cell responses. After TBI, adaptive immune response genes are up-regulated in a temporal manner, with genes involved in T cell responses elevated sub-acutely, followed by increases in B cell related genes at chronic time points after injury. Pro-inflammatory cytokines are also implicated as contributing to the immune response in the meninges, with ingenuity pathway analysis identifying interferons as master regulators in aged mice compared to young mice following TBI. Collectively these data demonstrate the temporal series of meningeal specific signatures, providing insights into how age leads to worse neuroinflammatory outcomes in TBI.

Repetitive mild traumatic brain injury alters central and peripheral clock gene expression in the adolescent rat

Mild traumatic brain injury (mTBI) or concussion is a common injury worldwide leading to substantial medical costs and a high burden on society. In adolescents, falls and sports related trauma are often the causes of mTBI. Importantly, critical brain growth and development occurs during this sensitive period making the prospect of a brain injury a worrying phenomenon. Upwards of 70% of patients report circadian disruption following these injuries and this has been shown to impede recovery. Therefore, we sought to determine if core circadian clock gene expression was disrupted in rat model of repetitive mTBI (RmTBI). Male and female adolescent rats (n = 129) received sham or RmTBI. The animals were then euthanized at different times throughout the day and night. Tissue from the hypothalamus, cerebellum, hippocampus, liver, and small intestine were evaluated for the expression of per1, per2, cry1, clock, bmal1 and rev-erb-α. We found most clock genes varied across the day/night indicating circadian expression patterns. In the hypothalamus we found RmTBI altered the expression of cry1 and bmal1 in addition to sex differences in per2, cry1, clock, bmal1 and rev-erb- α. In the cerebellum, per1, per2, cry1, clock, bmal1 and rev-erb-α rhythms were all knocked out by RmTBI in addition to sex differences in cry1, clock and bmal1 expression. We also detected a significant decrease in overall expression of all clock genes in males in the middle of the night. In the hippocampus we found that RmTBI changed the rhythm of rev-erb-α expression in addition to sex differences in bmal1 expression. In the liver we detected strong rhythms in all genes examined, however only per2 expression was knocked out by RmTBI, in addition we also detected sex differences in per2 and cry1. We also detected an overall decrease in female clock gene expression in the early night. In the small intestine, RmTBI altered cry1 expression and there were sex differences in rev-erb-α. These results indicate that RmTBI alters core circadian clock gene expression in the central and peripheral nervous system in a time, tissue and sex dependent manner. This may be disrupting important phase relationships between the brain and peripheral nervous system and contributing to post-injury symptomology and also highlights the importance for time and sex dependent assessment of injury outcomes.

Persistent hypersomnia following repetitive mild experimental traumatic brain injury: Roles of chronic stress and sex differences

Traumatic brain injury (TBI) is often more complicated than a single head injury. An extreme example of this point may be military service members who experience a spectrum of exposures over a prolonged period under stressful conditions. Understanding the effects of complex exposures can inform evaluation and care to prevent persistent symptoms. We designed a longitudinal series of non-invasive procedures in adult mice to evaluate the effects of prolonged mild stress and head injury exposures. We assessed anxiety, depression, and sleep-wake dysfunction as symptoms that impact long-term outcomes after mild TBI. Unpredictable chronic mild stress (UCMS) was generated from a varied sequence of environmental stressors distributed within each of 21 days. Subsequently, mice received a mild blast combined with closed-head mild TBI on 5 days at 24-h intervals. In males and females, UCMS induced anxiety without depressive behavior. A major finding was reproducible sleep-wake dysfunction through 6- to 12-month time points in male mice that received UCMS with repetitive blast plus TBI events, or surprisingly after just UCMS alone. Specifically, male mice exhibited hypersomnia with increased sleep during the active/dark phase and fragmentation of longer wake bouts. Sleep-wake dysfunction was not found with TBI events alone, and hypersomnia was not found in females under any conditions. These results identify prolonged stress and sex differences as important considerations for sleep-wake dysfunction. Furthermore, this reproducible hypersomnia with impaired wakefulness is similar to the excessive daytime sleepiness reported in patients, including patients with TBI, which warrants further clinical screening, care, and treatment development.

M1M2: Deep-Learning-Based Real-Time Emotion Recognition from Neural Activity

Emotion recognition, or the ability of computers to interpret people's emotional states, is a very active research area with vast applications to improve people's lives. However, most image-based emotion recognition techniques are flawed, as humans can intentionally hide their emotions by changing facial expressions. Consequently, brain signals are being used to detect human emotions with improved accuracy, but most proposed systems demonstrate poor performance as EEG signals are difficult to classify using standard machine learning and deep learning techniques. This paper proposes two convolutional neural network (CNN) models (M1: heavily parameterized CNN model and M2: lightly parameterized CNN model) coupled with elegant feature extraction methods for effective recognition. In this study, the most popular EEG benchmark dataset, the DEAP, is utilized with two of its labels, valence, and arousal, for binary classification. We use Fast Fourier Transformation to extract the frequency domain features, convolutional layers for deep features, and complementary features to represent the dataset. The M1 and M2 CNN models achieve nearly perfect accuracy of 99.89% and 99.22%, respectively, which outperform every previous state-of-the-art model. We empirically demonstrate that the M2 model requires only 2 seconds of EEG signal for 99.22% accuracy, and it can achieve over 96% accuracy with only 125 milliseconds of EEG data for valence classification. Moreover, the proposed M2 model achieves 96.8% accuracy on valence using only 10% of the training dataset, demonstrating our proposed system's effectiveness. Documented implementation codes for every experiment are published for reproducibility.

Sequential Isolation of Microglia and Astrocytes from Young and Aged Adult Mouse Brains for Downstream Transcriptomic Analysis

In aging, the brain is more vulnerable to injury and neurodegenerative disease, but the mechanisms responsible are largely unknown. Evidence now suggests that neuroinflammation, mediated by resident brain astrocyte and microglia populations, are key players in the generation of inflammatory responses and may influence both age related processes and the initiation/progression of neurodegeneration. Consequently, targeting these cell types individually and collectively may aid in the development of novel disease-modifying therapies. We have optimized and characterized a protocol for the effective sequential isolation of both microglia and astrocytes from the adult mouse brain in young and aged mice. We demonstrate a technique for the sequential isolation of these immune cells by using magnetic beads technology, optimized to increase yield and limit potential artifacts in downstream transcriptomic applications, including RNA-sequencing pipelines. This technique is versatile, cost-effective, and reliable for the study of responses within the same biological context, simultaneously being advantageous in reducing mice numbers required to assess cellular responses in normal and age-related pathological conditions.