Brain injury results in lower levels of melatonin receptors subtypes MT1 and MT2

Sex Differences in Sleep Architecture After Traumatic Brain Injury: Potential Implications on Short-Term Episodic Memory and Recovery

Sleep-wake disturbances (SWDs) are common after TBI and often extend into the chronic phase of recovery. Such disturbances in sleep can lead to deficits in executive functioning, attention, and memory consolidation, which may ultimately impact the recovery process. We examined whether SWDs post-TBI were associated with morbidity during the post-acute period. Particular attention was placed on the impact of sleep architecture on learning and memory. Because women are more likely to report SWDs, we examined sex as a biological variable. We also examined subjective quality of life, depression, and disability levels. Data were retrospectively analyzed for 57 TBI patients who underwent an overnight polysomnography. Medical records were reviewed to determine cognitive and functional status during the period of the sleep evaluation. Consideration was given to medications, owing to the fact that a high number of these are likely to have secondary influences on sleep characteristics. Women showed higher levels of disability and reported more depression and lower quality of life. A sex-dependent disruption in sleep architecture was observed, with women having lower percent time in REM sleep. An association between percent time in REM and better episodic memory scores was found. Melatonin utilization had a positive impact on REM duration. Improvements in understanding the impact of sleep-wake disturbances on post-TBI outcome will aid in defining targeted interventions for this population. Findings from this study support the hypothesis that decreases in REM sleep may contribute to chronic disability and underlie the importance of considering sex differences when addressing sleep.

Traumatic Brain Injury, Sleep, and Melatonin-Intrinsic Changes with Therapeutic Potential

Traumatic brain injury (TBI) is one of the most prevalent causes of morbidity in the United States and is associated with numerous chronic sequelae long after the point of injury. One of the most common long-term complaints in patients with TBI is sleep dysfunction. It is reported that alterations in melatonin follow TBI and may be linked with various sleep and circadian disorders directly (via cellular signaling) or indirectly (via free radicals and inflammatory signaling). Work over the past two decades has contributed to our understanding of the role of melatonin as a sleep regulator and neuroprotective anti-inflammatory agent. Although there is increasing interest in the treatment of insomnia following TBI, a lack of standardization and rigor in melatonin research has left behind a trail of non-generalizable data and ambiguous treatment recommendations. This narrative review describes the underlying biochemical properties of melatonin as they are relevant to TBI. We also discuss potential benefits and a path forward regarding the therapeutic management of TBI with melatonin treatment, including its role as a neuroprotectant, a somnogen, and a modulator of the circadian rhythm.

Blast Exposure Dysregulates Nighttime Melatonin Synthesis and Signaling in the Pineal Gland: A Potential Mechanism of Blast-Induced Sleep Disruptions

Blast-induced traumatic brain injury (bTBI) frequently results in sleep-wake disturbances. However, limited studies have investigated the molecular signaling mechanisms underlying these sleep disturbances, and potentially efficacious therapies are lacking. We investigated the levels of melatonin and genes involved in melatonin synthesis pathway in the pineal glands of Sprague Dawley rats exposed to single and tightly coupled repeated blasts during the night and daytime. Rats were exposed to single and tightly coupled repeated blasts using an advanced blast simulator. The plasma, cerebrospinal fluid (CSF), and pineal gland were collected at 6 h, 24 h, or 1 month postblast at two different time points: one during the day (1000 h) and one at night (2200 h). Differential expressions of genes involved in pineal melatonin synthesis were quantified using quantitative real-time polymerase chain reaction (qRT-PCR). Plasma and CSF melatonin levels were assessed using a commercial melatonin ELISA kit. The plasma and CSF melatonin levels showed statistically significant decreases at 6 h and 24 h in the blast-exposed rats euthanized in the night (in dim light), with no significant alterations noted in rats euthanized in the morning (daylight) at all three-time points. Blast-exposed rats showed statistically significant decreases in Tph1, Aanat, Asmt, and Mtnr1b mRNA levels, along with increased Tph2 mRNA, in the pineal gland samples collected at night at 6 h and 24 h. No significant changes in the mRNA levels of these genes were noted at 1 month. These findings imply that the melatonin circadian rhythm is disrupted following blast exposure, which may be a factor in the sleep disturbances that blast victims frequently experience.

Neuro-Inflammation Modulation and Post-Traumatic Brain Injury Lesions: From Bench to Bed-Side

Head trauma is the most common cause of disability in young adults. Known as a silent epidemic, it can cause a mosaic of symptoms, whether neurological (sensory-motor deficits), psychiatric (depressive and anxiety symptoms), or somatic (vertigo, tinnitus, phosphenes). Furthermore, cranial trauma (CT) in children presents several particularities in terms of epidemiology, mechanism, and physiopathology-notably linked to the attack of an immature organ. As in adults, head trauma in children can have lifelong repercussions and can cause social and family isolation, difficulties at school, and, later, socio-professional adversity. Improving management of the pre-hospital and rehabilitation course of these patients reduces secondary morbidity and mortality, but often not without long-term disability. One hypothesized contributor to this process is chronic neuroinflammation, which could accompany primary lesions and facilitate their development into tertiary lesions. Neuroinflammation is a complex process involving different actors such as glial cells (astrocytes, microglia, oligodendrocytes), the permeability of the blood-brain barrier, excitotoxicity, production of oxygen derivatives, cytokine release, tissue damage, and neuronal death. Several studies have investigated the effect of various treatments on the neuroinflammatory response in traumatic brain injury in vitro and in animal and human models. The aim of this review is to examine the various anti-inflammatory therapies that have been implemented.

Melatonin in Traumatic Brain Injury and Cognition

Traumatic brain injury (TBI) is a leading cause of long-term disability and mortality in young adults. The devastating effects of TBI on emotion regulation, executive functioning, and cognition have been well-established, and recent research links TBI as a risk factor for neurodegenerative diseases such as Alzheimer’s disease. Despite an increased focus on the long-term cognitive dysfunction associated with TBI, research into potential treatments has not yet generated consistent successful results in human subjects. Many foundational studies have analyzed the cellular and molecular events involved in the inflammatory and healing processes following TBI, enhancing our understanding of the mechanisms that may contribute to the progression of dementia and cognitive decline in these patients. In this review, we will discuss the emergent research on melatonin within the framework of neuroinflammation and oxidative stress resulting from TBI and possibly preventing further sequelae such as Alzheimer’s disease.

A literature review was conducted using standard search strategies to query the PubMed database. The following search terms were used with qualifiers of various combinations: TBI, traumatic brain injury, melatonin, treatment, dementia, Alzheimer’s, cognition, and neurodegeneration. Selected studies included meta-analyses, literature reviews, and randomized controlled trials (RCT) that evaluated melatonin’s role as a potential therapy to prevent post-TBI neurodegeneration, specifically the development of dementia and deficits in memory and cognition. Three independent reviewers assessed all articles for eligibility. After assessment for eligibility, 11 total studies were included.

Much of the available data on melatonin in TBI has highlighted its significant neuroprotective and antiinflammatory effects, which can be significant in fighting against the neuroinflammatory processes indicated in neurodegeneration. In animal models, immunohistochemistry and histopathology have allowed researchers to study measures of cell injury such as inflammatory cytokines, edema, and markers of oxidative stress. Though the effects of melatonin in TBI appear to be mediated through mostly indirect mechanisms on inflammatory processes, some research has explored potential mechanisms that could be specific to melatonin.

Animal model studies support that melatonin treatment after TBI significantly improves cognition and behavioral outcomes. However, clinical studies with human subjects are scarce. Beyond the apparent general antiinflammatory and antioxidant actions of melatonin, a review of the evidence identified some preliminary research that has suggested the significance of melatonin receptors specifically in TBI. While there is some evidence to suggest that melatonin is able to reduce post-TBI cognitive decline as measured by subject performance on memory tasks, there is a lack of longitudinal data on whether melatonin decreases the risk of developing dementia after TBI. Considering melatonin therapy’s promising preclinical data, favorable safety profile, and accessibility, further studies are warranted to assess the effects of melatonin as a post-TBI therapy on human subjects.

Sudden infant death syndrome: Melatonin, serotonin, and CD34 factor as possible diagnostic markers and prophylactic targets

Sudden infant death syndrome (SIDS) is one of the primary causes of death of infants in the first year of life. According to the WHO's data, the global infant mortality rate is 0.64-2 per 1,000 live-born children. Molecular and cellular aspects of SIDS development have not been identified so far. The purpose of this paper is to verify and analyze the expression of melatonin 1 and 2 receptors, serotonin (as a melatonin precursor), and CD34 molecules (as hematopoietic and endothelial markers of cardiovascular damage) in the medulla, heart, and aorta in infants who died from SIDS. An immunohistochemical method was used to investigate samples of medulla, heart, and aorta tissues of infants 3 to 9 months of age who died from SIDS. The control group included children who died from accidents. It has been shown that the expression of melatonin receptors as well as serotonin and CD34 angiogenesis markers in tissues of the medulla, heart, and aorta of infants who died from SIDS is statistically lower as compared with their expression in the same tissues in children who died from accidents. The obtained data help to clarify in detail the role of melatonin and such signaling molecules as serotonin and CD34 in SIDS pathogenesis, which can open new prospects for devising novel methods for predictive diagnosis of development and targeted prophylaxis of SIDS.

Deletion of ferritin H in neurons counteracts the protective effect of melatonin against traumatic brain injury-induced ferroptosis

Accumulating evidence demonstrates that ferroptosis may be important in the pathophysiological process of traumatic brain injury (TBI). As a major hormone of the pineal gland, melatonin exerts many beneficial effects on TBI, but there is no information regarding the effects of melatonin on ferroptosis after TBI. As expected, TBI resulted in the time-course changes of ferroptosis-related molecules expression and iron accumulation in the ipsilateral cortex. Importantly, we found that treating with melatonin potently rescued TBI induced the changes mentioned above and improved functional deficits versus vehicle. Similar results were obtained with a ferroptosis inhibitor, liproxstatin-1. Moreover, the protective effect of melatonin is likely dependent on melatonin receptor 1B (MT2). Although ferritin plays a vital role in iron metabolism by storing excess cellular iron, its precise function in the brain, and whether it involves melatonin's neuroprotection remain unexplored. Considering ferritin H (Fth) is expressed predominantly in the neurons and global loss of Fth in mice induces early embryonic lethality, we then generated neuron-specific Fth conditional knockout (Fth-KO) mice, which are viable and fertile but have altered iron metabolism. In addition, Fth-KO mice were more susceptible to ferroptosis after TBI, and the neuroprotection by melatonin was largely abolished in Fth-KO mice. In vitro siFth experiments further confirmed the results mentioned above. Taken together, these data indicate that melatonin produces cerebroprotection, at least partly by inhibiting neuronal Fth-mediated ferroptosis following TBI, supporting the notion that melatonin is an excellent ferroptosis inhibitor and its anti-ferroptosis provides a potential therapeutic target for treating TBI.

Melatonin Attenuates Anoxia/Reoxygenation Injury by Inhibiting Excessive Mitophagy Through the MT2/SIRT3/FoxO3a Signaling Pathway in H9c2 Cells

Purpose

Autophagy caused by ischemia/reperfusion (I/R) increases the extent of cardiomyocyte damage. Melatonin (Mel) diminishes cardiac injury through regulating autophagy and mitochondrial dynamics. However, illustrating the specific role of mitophagy in the cardioprotective effects of melatonin remains a challenge. The aim of our research was to investigate the impact and underlying mechanisms of melatonin in connection with mitophagy during anoxia/reoxygenation (A/R) injury in H9c2 cells.

Methods

H9c2 cells were pretreated with melatonin with or without the melatonin membrane receptor 2 (MT2) antagonist 4-P-PDOT, the MT2 agonist IIK7 and the sirtuin 3 (SIRT3) inhibitor 3-TYP for 4 hours and then subjected to A/R injury. Cell viability, cellular apoptosis, necrosis levels and oxidative markers were assessed. The expression of SIRT3 and forkhead box O3a (FoxO3a), mitochondrial function and the levels of mitophagy-related proteins were also evaluated.

Results

A/R injury provoked enhanced mitophagy in H9c2 myocytes. In addition, increased mitophagy was correlated with decreased cellular viability, increased oxidative stress and mitochondrial dysfunction in H9c2 cells. However, melatonin pretreatment notably increased cell survival and decreased cell apoptosis and oxidative response after A/R injury, accompanied by restored mitochondrial function. The inhibition of excessive mitophagy is involved in the cardioprotective effects of melatonin, as shown by the decreased expression of the mitophagy-related molecules Parkin, Beclin1, and BCL2-interacting protein 3-like (BNIP3L, best known as NIX) and decreased light chain 3 II/light chain 3 I (LC3 II/LC3 I) ratio and upregulation of p62 expression. Moreover, the decreased expression of SIRT3 and FoxO3a in A/R-injured H9c2 cells was abrogated by melatonin, but these beneficial effects were attenuated by the MT2 antagonist 4-P-PDOT or the SIRT3 inhibitor 3-TYP and enhanced by the MT2 agonist IIK7.

Conclusion

These results indicate that melatonin protects H9c2 cells during A/R injury through suppressing excessive mitophagy by activating the MT2/SIRT3/FoxO3a pathway. Melatonin may be a useful candidate for alleviating myocardial ischemia/reperfusion (MI/R) injury in the future, and the MT2 receptor might become a therapeutic target.

Repositioning of an anti-depressant drug, agomelatine as therapy for brain injury induced by craniotomy

Traumatic brain injury (TBI) leads to the disruption of blood-brain barrier integrity and therefore results in increased brain water content (brain edema). Brain edema is a significant factor for increased intracranial pressure (ICP), which ultimately causes functional disability and death. The decompressive craniotomy (DC) is a surgical procedure widely used for treating increased ICP following TBI. The life-saving craniotomy itself results in brain injury. The objective of this study is to investigate the effect of agomelatine against craniotomy induced brain injury. The craniotomy was performed by a variable speed micro-motor dental driller of 0.8 mm drill bit. The present study, in addition to blood-brain permeability, brain water content (edema) and histological examination of the brain, also estimated locomotor activity, oxidant, and antioxidant parameters. Results show that the craniotomy induced increase in the blood-brain barrier permeability, brain water content (edema), oxidative stress (lipid peroxide and nitric oxide) and impaired antioxidant mechanisms (superoxide dismutase, catalase, and reduced glutathione) in rats. The craniotomy was also found to increase neuronal cell death indicated by augmented chromatolysis and impaired locomotor activity. Administration of agomelatine after the craniotomy ameliorated histopathological, neurochemical and behavioral consequences of craniotomy. Thus agomelatine is effective against brain injury caused by craniotomy.

Advances in Characterizing Recently-Identified Molecular Actions of Melatonin: Clinical Implications

Melatonin, N-acetyl-5-methoxy-tryptamine, was discovered to be a product of serotonin metabolism in the mammalian pineal gland where its synthesis is under control of the light:dark cycle. Besides its regulatory pathway involving ganglion cells in the retina, the neural connections between the eyes and the pineal gland include the master circadian clock, the suprachiasmatic nuclei, and the central and peripheral nervous systems. Since pineal melatonin is released into the blood and into the cerebrospinal fluid, it has access to every cell in an organism and it mediates system-wide effects. Subsequently, melatonin was found in several extrapineal organs and, more recently, perhaps in every cell of every organ. In contrast to the pinealocytes, non-pineal cells do not discharge melatonin into the blood; rather it is used locally in an intracrine, autocrine, or paracrine manner. Melatonin levels in non-pineal cells do not exhibit a circadian rhythm and do not depend on circulating melatonin concentrations although when animals are treated with exogenous melatonin it is taken up by presumably all cells. Mitochondria are the presumed site of melatonin synthesis in all cells; the enzymatic machinery for melatonin synthesis has been identified in mitochondria. The association of melatonin with mitochondria, because of its ability to inhibit oxidative stress, is very fortuitous since these organelles are a major site of damaging reactive oxygen species generation. In this review, some of the actions of non-pineal-derived melatonin are discussed in terms of cellular and subcellular physiology.

Melatonin in Synaptic Impairments of Alzheimer's Disease

Alzheimer's disease (AD) underlies dementia for millions of people worldwide with no effective treatment. The dementia of AD is thought stem from the impairments of the synapses because of their critical roles in cognition. Melatonin is a neurohormone mainly released by the pineal gland in a circadian manner and it regulates brain functions in various manners. It is reported that both the melatonin deficit and synaptic impairments are present in the very early stage of AD and strongly contribute to the progress of AD. In the mammalian brains, the effects of melatonin are mainly relayed by two of its receptors, melatonin receptor type 1a (MT1) and 1b (MT2). To have a clear idea on the roles of melatonin in synaptic impairments of AD, this review discussed the actions of melatonin and its receptors in the stabilization of synapses, modulation of long-term potentiation, as well as their contributions in the transmissions of glutamatergic, GABAergic and dopaminergic synapses, which are the three main types of synapses relevant to the synaptic strength. The synaptic protective roles of melatonin in AD treatment were also summarized. Regarding its protective roles against amyloid-β neurotoxicity, tau hyperphosphorylation, oxygenation, inflammation as well as synaptic dysfunctions, melatonin may be an ideal therapeutic agent against AD at early stage.

The multiple protective roles and molecular mechanisms of melatonin and its precursor N-acetylserotonin in targeting brain injury and liver damage and in maintaining bone health

Melatonin is a neurohormone associated with sleep and wakefulness and is mainly produced by the pineal gland. Numerous physiological functions of melatonin have been demonstrated including anti-inflammation, suppressing neoplastic growth, circadian and endocrine rhythm regulation, and its potent antioxidant activity as well as its role in regeneration of various tissues including the nervous system, liver, bone, kidney, bladder, skin, and muscle, among others. In this review, we summarize the recent advances related to the multiple protective roles of melatonin receptor agonists, melatonin and N-acetylserotonin (NAS), in brain injury, liver damage, and bone health. Brain injury, including traumatic brain injury, ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, and newborn perinatal hypoxia-ischemia encephalopathy, is a major cause of mortality and disability. Liver disease causes serious public health problems and various factors including alcohol, chemical pollutants, and drugs induce hepatic damage. Osteoporosis is the most common bone disease in humans. Due in part to an aging population, both the cost of care of fracture patients and the annual fracture rate have increased steadily. Despite the discrepancy in the pathophysiological processes of these disorders, time frames and severity, they may share several common molecular mechanisms. Oxidative stress is considered to be a critical factor in these pathogeneses. We update the current state of knowledge related to the molecular processes, mainly including anti-oxidative stress, anti-apoptosis, autophagy dysfunction, and anti-inflammation as well as other properties of melatonin and NAS. Particularly, the abilities of melatonin and NAS to directly scavenge oxygen-centered radicals and toxic reactive oxygen species, and indirectly act through antioxidant enzymes are disscussed. In this review, we summarize the similarities and differences in the protection provided by melatonin and/or NAS in brain, liver and bone damage. We analyze the involvement of melatonin receptor 1A (MT1), melatonin receptor 1B (MT2), and melatonin receptor 1C (MT3) in the protection of melatonin and/or NAS. Additionally, we evaluate their potential clinical applications. The multiple mechanisms of action and multiple organ-targeted properties of melatonin and NAS may contribute to development of promising therapies for clinical trials.

Ubiquitin-Specific Peptidase 10 (USP10) Inhibits Hepatic Steatosis, Insulin Resistance, and Inflammation Through Sirt6

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, insulin resistance and inflammation, and the pathogenic mechanism of NAFLD is poorly understood. Ubiquitin-specific peptidase 10 (USP10), a member of the ubiquitin-specific protease family, is involved in environmental stress responses, tumor growth, inflammation, and cellular metabolism. However, the role of USP10 in hepatic steatosis, insulin resistance, and inflammation remains largely unexplored. USP10 expression was detected in livers of patients with NAFLD, mice with high-fat diet (HFD)-induced obesity, and genetically obese (ob/ob) mice, as well as in palmitate-induced hepatocytes. The function of USP10 in hepatic steatosis, insulin resistance, and inflammation was investigated using hepatocyte-specific USP10 deficiency or overexpression in mice induced by HFD treatment or genetic defect. The molecular mechanisms underlying USP10-regulated hepatic steatosis were further investigated in HFD-treated mice. USP10 expression was significantly decreased in the fatty livers of NAFLD patients and obese mice and in palmitate-treated hepatocytes. USP10 deficiency exacerbated the metabolic dysfunction induced by HFD treatment for 12 weeks. Conversely, USP10 overexpression significantly suppressed metabolic dysfunction in mice after HFD treatment and inhibited the development of NAFLD in ob/ob mice. Further investigation indicated that USP10 regulates hepatic steatosis by interacting with Sirt6 and inhibiting its ubiquitination and degradation. Sirt6 overexpression markedly ameliorated the effects of USP10 deficiency in hepatic steatosis, insulin resistance, and inflammation. Conversely, Sirt6 deficiency decreased the ameliorative effects of USP10 overexpression in response to HFD treatment. Conclusion: USP10 inhibits hepatic steatosis, insulin resistance, and inflammation through Sirt6.

Extended Combined Neonatal Treatment With Erythropoietin Plus Melatonin Prevents Posthemorrhagic Hydrocephalus of Prematurity in Rats

Posthemorrhagic hydrocephalus of prematurity (PHHP) remains a global challenge. Early preterm infants (<32 weeks gestation), particularly those exposed to chorioamnionitis (CAM), are prone to intraventricular hemorrhage (IVH) and PHHP. We established an age-appropriate, preclinical model of PHHP with progressive macrocephaly and ventriculomegaly to test whether non-surgical neonatal treatment could modulate PHHP. We combined prenatal CAM and postnatal day 1 (P1, equivalent to 30 weeks human gestation) IVH in rats, and administered systemic erythropoietin (EPO) plus melatonin (MLT), or vehicle, from P2 to P10. CAM-IVH rats developed progressive macrocephaly through P21. Macrocephaly was accompanied by ventriculomegaly at P5 (histology), and P21 (ex vivo MRI). CAM-IVH rats showed impaired performance of cliff aversion, a neonatal neurodevelopmental test. Neonatal EPO+MLT treatment prevented macrocephaly and cliff aversion impairment, and significantly reduced ventriculomegaly. EPO+MLT treatment prevented matted or missing ependymal motile cilia observed in vehicle-treated CAM-IVH rats. EPO+MLT treatment also normalized ependymal yes-associated protein (YAP) mRNA levels, and reduced ependymal GFAP-immunolabeling. Vehicle-treated CAM-IVH rats exhibited loss of microstructural integrity on diffusion tensor imaging, which was normalized in EPO+MLT-treated CAM-IVH rats. In summary, combined prenatal systemic inflammation plus early postnatal IVH caused progressive macrocephaly, ventriculomegaly and delayed development of cliff aversion reminiscent of PHHP. Neonatal systemic EPO+MLT treatment prevented multiple hallmarks of PHHP, consistent with a clinically viable, non-surgical treatment strategy.

Sleep, Sleep Disorders, and Circadian Health following Mild Traumatic Brain Injury in Adults: Review and Research Agenda

A rapidly expanding scientific literature supports the frequent co-occurrence of sleep and circadian disturbances following mild traumatic brain injury (mTBI). Although many questions remain unanswered, the preponderance of evidence suggests that sleep and circadian disorders can result from mTBI. Among those with mTBI, sleep disturbances and clinical sleep and circadian disorders contribute to the morbidity and long-term sequelae across domains of functional outcomes and quality of life. Specifically, along with deterioration of neurocognitive performance, insufficient and disturbed sleep can precede, exacerbate, or perpetuate many of the other common sequelae of mTBI, including depression, post-traumatic stress disorder, and chronic pain. Further, sleep and mTBI share neurophysiologic and neuroanatomic mechanisms that likely bear directly on success of rehabilitation following mTBI. For these reasons, focus on disturbed sleep as a modifiable treatment target has high likelihood of improving outcomes in mTBI. Here, we review relevant literature and present a research agenda to 1) advance understanding of the reciprocal relationships between sleep and circadian factors and mTBI sequelae and 2) advance rapidly the development of sleep-related treatments in this population.

Mini Review of Controlled Cortical Impact: A Well-Suited Device for Concussion Research

Mild traumatic brain injury (mTBI) is increasingly recognized as a significant public health problem which warrants additional research. Part of the effort to understand mTBI and concussion includes modeling in animals. Controlled cortical impact (CCI) is a commonly employed and well-characterized model of experimental TBI that has been utilized for three decades. Today, several commercially available pneumatic- and electromagnetic-CCI devices exist as do a variety of standard and custom injury induction tips. One of CCI's strengths is that it can be scaled to a number of common laboratory animals. Similarly, the CCI model can be used to produce graded TBI ranging from mild to severe. At the mild end of the injury spectrum, CCI has been applied in many ways, including to study open and closed head mTBI, repeated injuries, and the long-term deficits associated with mTBI and concussion. The purpose of this mini-review is to introduce the CCI model, discuss ways the model can be applied to study mTBI and concussion, and compare CCI to alternative pre-clinical TBI models.