Time window for voluntary exercise-induced increases in hippocampal neuroplasticity molecules after traumatic brain injury is severity dependent

Found in translation: Understanding the biology and behavior of experimental traumatic brain injury

The aim of this review is to discuss in greater detail the topics covered in the recent symposium entitled "Traumatic brain injury: laboratory and clinical perspectives," presented at the 2014 International Behavioral Neuroscience Society annual meeting. Herein, we review contemporary laboratory models of traumatic brain injury (TBI) including common assays for sensorimotor and cognitive behavior. New modalities to evaluate social behavior after injury to the developing brain, as well as the attentional set-shifting test (AST) as a measure of executive function in TBI, will be highlighted. Environmental enrichment (EE) will be discussed as a preclinical model of neurorehabilitation, and finally, an evidence-based approach to sports-related concussion will be considered. The review consists predominantly of published data, but some discussion of ongoing or future directions is provided.

The Benefits of Exercise on Structural and Functional Plasticity in the Rodent Hippocampus of Different Disease Models

In this review, the benefits of physical exercise on structural and functional plasticity in the hippocampus are discussed. The evidence is clear that voluntary exercise in rats and mice can lead to increases in hippocampal neurogenesis and enhanced synaptic plasticity which ultimately result in improved performance in hippocampal-dependent tasks. Furthermore, in models of neurological disorders, including fetal alcohol spectrum disorders, traumatic brain injury, stroke, and neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's disease exercise can also elicit beneficial effects on hippocampal function. Ultimately this review highlights the multiple benefits of exercise on hippocampal function in both the healthy and the diseased brain.

The Effects of Exercise on Cognitive Recovery after Acquired Brain Injury in Animal Models: A Systematic Review

The objective of the present paper is to review the current status of exercise as a tool to promote cognitive rehabilitation after acquired brain injury (ABI) in animal model-based research. Searches were conducted on the PubMed, Scopus, and psycINFO databases in February 2014. Search strings used were: exercise (and) animal model (or) rodent (or) rat (and) traumatic brain injury (or) cerebral ischemia (or) brain irradiation. Studies were selected if they were (1) in English, (2) used adult animals subjected to acquired brain injury, (3) used exercise as an intervention tool after inflicted injury, (4) used exercise paradigms demanding movement of all extremities, (5) had exercise intervention effects that could be distinguished from other potential intervention effects, and (6) contained at least one measure of cognitive and/or emotional function. Out of 2308 hits, 22 publications fulfilled the criteria. The studies were examined relative to cognitive effects associated with three themes: exercise type (forced or voluntary), timing of exercise (early or late), and dose-related factors (intensity, duration, etc.). The studies indicate that exercise in many cases can promote cognitive recovery after brain injury. However, the optimal parameters to ensure cognitive rehabilitation efficacy still elude us, due to considerable methodological variations between studies.

The new neurometabolic cascade of concussion

Since the original descriptions of postconcussive pathophysiology, there has been a significant increase in interest and ongoing research to study the biological underpinnings of concussion. The initial ionic flux and glutamate release result in significant energy demands and a period of metabolic crisis for the injured brain. These physiological perturbations can now be linked to clinical characteristics of concussion, including migrainous symptoms, vulnerability to repeat injury, and cognitive impairment. Furthermore, advanced neuroimaging now allows a research window to monitor postconcussion pathophysiology in humans noninvasively. There is also increasing concern about the risk for chronic or even progressive neurobehavioral impairment after concussion/mild traumatic brain injury. Critical studies are underway to better link the acute pathobiology of concussion with potential mechanisms of chronic cell death, dysfunction, and neurodegeneration. This "new and improved" article summarizes in a translational fashion and updates what is known about the acute neurometabolic changes after concussive brain injury. Furthermore, new connections are proposed between this neurobiology and early clinical symptoms as well as to cellular processes that may underlie long-term impairment.

Effects of exercise on brain functions in diabetic animal models

Human life span has dramatically increased over several decades, and the quality of life has been considered to be equally important. However, diabetes mellitus (DM) characterized by problems related to insulin secretion and recognition has become a serious health problem in recent years that threatens human health by causing decline in brain functions and finally leading to neurodegenerative diseases. Exercise is recognized as an effective therapy for DM without medication administration. Exercise studies using experimental animals are a suitable option to overcome this drawback, and animal studies have improved continuously according to the needs of the experimenters. Since brain health is the most significant factor in human life, it is very important to assess brain functions according to the different exercise conditions using experimental animal models. Generally, there are two types of DM; insulin-dependent type 1 DM and an insulin-independent type 2 DM (T2DM); however, the author will mostly discuss brain functions in T2DM animal models in this review. Additionally, many physiopathologic alterations are caused in the brain by DM such as increased adiposity, inflammation, hormonal dysregulation, uncontrolled hyperphagia, insulin and leptin resistance, and dysregulation of neurotransmitters and declined neurogenesis in the hippocampus and we describe how exercise corrects these alterations in animal models. The results of changes in the brain environment differ according to voluntary, involuntary running exercises and resistance exercise, and gender in the animal studies. These factors have been mentioned in this review, and this review will be a good reference for studying how exercise can be used with therapy for treating DM.

Repetitive concussions in adolescent athletes - translating clinical and experimental research into perspectives on rehabilitation strategies

Sports-related concussions are particularly common during adolescence, a time when even mild brain injuries may disrupt ongoing brain maturation and result in long-term complications. A recent focus on the consequences of repetitive concussions among professional athletes has prompted the development of several new experimental models in rodents, as well as the revision of guidelines for best management of sports concussions. Here, we consider the utility of rodent models to understand the functional consequences and pathobiology of concussions in the developing brain, identifying the unique behavioral and pathological signatures of concussive brain injuries. The impact of repetitive concussions on behavioral consequences and injury progression is also addressed. In particular, we focus on the epidemiological, clinical, and experimental evidence underlying current recommendations for physical and cognitive rest after concussion, and highlight key areas in which further research is needed. Lastly, we consider how best to promote recovery after injury, recognizing that optimally timed, activity-based rehabilitative strategies may hold promise for the adolescent athlete who has sustained single or repetitive concussions. The purpose of this review is to inform the clinical research community as it strives to develop and optimize evidence-based guidelines for the concussed adolescent, in terms of both acute and long-term management.

Long-lasting suppression of acoustic startle response after mild traumatic brain injury

Acoustic startle response (ASR) is a defensive reflex that is largely ignored unless greatly exaggerated. ASR is suppressed after moderate and severe traumatic brain injury (TBI), but the effect of mild TBI (mTBI) on ASR has not been investigated. Because the neural circuitry for ASR resides in the pons in all mammals, ASR may be a good measure of brainstem function after mTBI. The present study assessed ASR in Sprague-Dawley rats after mTBI using lateral fluid percussion and compared these effects to those on spatial working memory. mTBI caused a profound, long-lasting suppression of ASR. Both probability of emitting a startle and startle amplitude were diminished. ASR suppression was observed as soon as 1 day after injury and remained suppressed for the duration of the study (21 days after injury). No indication of recovery was observed. mTBI also impaired spatial working memory. In contrast to the suppression of ASR, working memory impairment was transient; memory was impaired 1 and 7 days after injury, but recovered by 21 days. The long-lasting suppression of ASR suggests long-term dysfunction of brainstem neural circuits at a time when forebrain neural circuits responsible for spatial working memory have recovered. These results have important implications for return-to-activity decisions because recovery of cognitive impairments plays an important role in these decisions.

Combining Multiple Types of Motor Rehabilitation Enhances Skilled Forelimb Use Following Experimental Traumatic Brain Injury in Rats

BACKGROUND

Neuroplasticity and neurorehabilitation have been extensively studied in animal models of stroke to guide clinical rehabilitation of stroke patients. Similar studies focused on traumatic brain injury (TBI) are lacking.

OBJECTIVE

The current study was designed to examine the effects of individual and combined rehabilitative approaches, previously shown to be beneficial following stroke, in an animal model of moderate/severe TBI, the controlled cortical impact (CCI).

METHODS

Rats received a unilateral CCI, followed by reach training, voluntary exercise, or unimpaired forelimb constraint, alone or in combination. Forelimb function was assessed at different time points post-CCI by tests of skilled reaching, motor coordination, and asymmetrical limb use.

RESULTS

Following CCI, skilled reaching and motor coordination were significantly enhanced by combinations of rehabilitation strategies, not by individual approaches. The return of symmetrical limb use benefited from forelimb constraint alone. None of the rehabilitation strategies affected the size of injury, suggesting that enhanced behavioral function was not a result of neuroprotection.

CONCLUSIONS

The current study has provided evidence that individual rehabilitation strategies shown to be beneficial in animal models of stroke are not similarly sufficient to enhance behavioral outcome in a model of TBI. Motor rehabilitation strategies for TBI patients may need to be more intense and varied. Future basic science studies exploring the underlying mechanisms of combined rehabilitation approaches in TBI as well as clinical studies comparing rehabilitation approaches for stroke versus TBI would prove fruitful.

Ice Hockey Summit II: zero tolerance for head hits and fighting

OBJECTIVE

To present currently known basic science and on-ice influences of sport-related concussion (SRC) in hockey, building on the Ice Hockey Summit I action plan (2011) to reduce SRC.

METHODS

The prior summit proceedings included an action plan intended to reduce SRC. As such, the proceedings from Summit I served as a point of departure, for the science and discussion held during Summit II (Mayo Clinic, Rochester MN, October 2013). Summit II focused on (1) Basic Science of Concussions in Ice Hockey: Taking Science Forward; (2) Acute and Chronic Concussion Care: Making a Difference; (3) Preventing Concussions via Behavior, Rules, Education and Measuring Effectiveness; (4) Updates in Equipment: their Relationship to Industry Standards; and (5) Policies and Plans at State, National and Federal Levels to reduce SRC. Action strategies derived from the presentations and discussion described in these sectors were subsequently voted on for purposes of prioritization. The following proceedings include knowledge and research shared by invited faculty, many of whom are health care providers and clinical investigators.

RESULTS

The Summit II evidence-based action plan emphasizes the rapidly evolving scientific content of hockey SRC. It includes the most highly prioritized strategies voted on for implementation to decrease concussion.

CONCLUSIONS

The highest priority action items identified from the Summit includes the following: (1) eliminate head hits from all levels of ice hockey, (2) change body-checking policies, and (3) eliminate fighting in all amateur and professional hockey.

Pediatric issues in sports concussions

PURPOSE OF REVIEW

Sports-related concussions are receiving increasing attention in both the lay press and medical literature. While most media attention has been on high-profile collegiate or professional athletes, the vast majority of individuals participating in contact and collision sports are adolescents and children. This review provides a practical approach toward youth sports-related concussion with a foundation in the recent guidelines, but including specific considerations when applying these management principles to children and adolescents.

RECENT FINDINGS

Objective measurement of early signs and symptoms is challenging in younger patients, and many commonly used assessment tools await rigorous validation for younger patients. Excellent evidence-based guidelines exist for CT evaluation of mild traumatic brain injury presenting to the emergency department. Evidence suggests that recovery from sports-related concussion takes longer in high school athletes compared with collegiate or professionals; however, rigorous studies below high school age are still lacking.

SUMMARY

Proper care for concussion in youth requires a delicate balance of clinical skills, age-appropriate assessment, and individualized management to achieve optimal outcomes.

Cerebrovascular regulation, exercise, and mild traumatic brain injury

A substantial number of people who sustain a mild traumatic brain injury report persistent symptoms. Most common among these symptoms are headache, dizziness, and cognitive difficulties. One possible contributor to sustained symptoms may be compromised cerebrovascular regulation. In addition to injury-related cerebrovascular dysfunction, it is possible that prolonged rest after mild traumatic brain injury leads to deconditioning that may induce physiologic changes in cerebral blood flow control that contributes to persistent symptoms in some people. There is some evidence that exercise training may reduce symptoms perhaps because it engages an array of cerebrovascular regulatory mechanisms. Unfortunately, there is very little work on the degree of impairment in cerebrovascular control that may exist in patients with mild traumatic brain injury, and there are no published studies on the subacute phase of recovery from this injury. This review aims to integrate the current knowledge of cerebrovascular mechanisms that might underlie persistent symptoms and seeks to synthesize these data in the context of exploring aerobic exercise as a feasible intervention to treat the underlying pathophysiology.

Pre and post-injury environmental enrichment effects functional recovery following medial frontal cortical contusion injury in rats

The rodent has been the preferred research model for evaluating the mechanisms related to, and potential treatments for, traumatic brain injury (TBI). Many therapies previously determined to be effective in pre-clinical investigations have failed to show the same effectiveness in clinical trials. The environment a rodent is housed in plays an important role in brain and behavioral development. Housing rodents in non-enriched environments significantly alters the development of the rodent brain and its behavioral profile, negatively impacting the ecological validity of the rodent model. This investigation employed 113 male Long-Evans rats assigned to either an enriched environment (EE) or standard environment (SE) from post-natal day 25. At four months of age, rats received either a controlled cortical impact (CCI) to the medial frontal cortex (mFC) or sham injury. Rats assigned to EE or SE pre-injury were re-assigned to remain in, or switch to, EE or SE post-injury. The open-field test (OFT), vermicelli handling test (VHT) Morris water maze (MWM), and rotor-rod (RR), were used to evaluate the animals response to TBI. The data from the current investigation indicates that the performance of TBI rats assigned to pre-injury EE was improved on the MWM compared to the TBI rats assigned to pre-injury SE. However, those that were reared in the EE performed better on the MWM if placed into a SE post-injury as compared to those placed into the EE after insult. The TBI and sham groups that were raised, and remained, in the SE performed worse than any of the EE groups on the RR. TBI rats that were placed in the EE had larger cortices and more cells in the hippocampus than the TBI rats housed in the SE. These data strongly suggest that the pre-injury housing environment should be considered as investigators refine pre-clinical models of TBI.

Use it and/or lose it-experience effects on brain remodeling across time after stroke

The process of brain remodeling after stroke is time- and neural activity-dependent, and the latter makes it inherently sensitive to behavioral experiences. This generally supports targeting early dynamic periods of post-stroke neural remodeling with rehabilitative training (RT). However, the specific neural events that optimize RT effects are unclear and, as such, cannot be precisely targeted. Here we review evidence for, potential mechanisms of, and ongoing knowledge gaps surrounding time-sensitivities in RT efficacy, with a focus on findings from animal models of upper extremity RT. The reorganization of neural connectivity after stroke is a complex multiphasic process interacting with glial and vascular changes. Behavioral manipulations can impact numerous elements of this process to affect function. RT efficacy varies both with onset time and its timing relative to the development of compensatory strategies with the less-affected (nonparetic) hand. Earlier RT may not only capitalize on a dynamic period of brain remodeling but also counter a tendency for compensatory strategies to stamp-in suboptimal reorganization patterns. However, there is considerable variability across injuries and individuals in brain remodeling responses, and some early behavioral manipulations worsen function. The optimal timing of RT may remain unpredictable without clarification of the cellular events underlying time-sensitivities in its effects.

Using the olfactory system as an in vivo model to study traumatic brain injury and repair

Loss of olfactory function is an early indicator of traumatic brain injury (TBI). The regenerative capacity and well-defined neural maps of the mammalian olfactory system enable investigations into the degeneration and recovery of neural circuits after injury. Here, we introduce a unique olfactory-based model of TBI that reproduces many hallmarks associated with human brain trauma. We performed a unilateral penetrating impact to the mouse olfactory bulb and observed a significant loss of olfactory sensory neurons (OSNs) in the olfactory epithelium (OE) ipsilateral to the injury, but not contralateral. By comparison, we detected the injury markers p75(NTR), β-APP, and activated caspase-3 in both the ipsi- and contralateral OE. In the olfactory bulb (OB), we observed a graded cell loss, with ipsilateral showing a greater reduction than contralateral and both significantly less than sham. Similar to OE, injury markers in the OB were primarily detected on the ipsilateral side, but also observed contralaterally. Behavioral experiments measured 4 days after impact also demonstrated loss of olfactory function, yet following a 30-day recovery period, we observed a significant improvement in olfactory function and partial recovery of olfactory circuitry, despite the persistence of TBI markers. Interestingly, by using the M71-IRES-tauLacZ reporter line to track OSN organization, we further determined that inducing neural activity during the recovery period with intense odor conditioning did not enhance the recovery process. Together, these data establish the mouse olfactory system as a new model to study TBI, serving as a platform to understand neural disruption and the potential for circuit restoration.

Scale and pattern of atrophy in the chronic stages of moderate-severe TBI

BACKGROUND

Moderate-severe traumatic brain injury (TBI) is increasingly being understood as a progressive disorder, with growing evidence of reduced brain volume and white matter (WM) integrity as well as lesion expansion in the chronic phases of injury. The scale of these losses has yet to be investigated, and pattern of change across structures has received limited attention.

OBJECTIVES

(1) To measure the percentage of patients in our TBI sample showing atrophy from 5 to 20 months post-injury in the whole brain and in structures with known vulnerability to acute TBI, and (2) To examine relative vulnerability and patterns of volume loss across structures.

METHODS

Fifty-six TBI patients [complicated mild to severe, with mean Glasgow Coma Scale (GCS) in severe range] underwent MRI at, on average, 5 and 20 months post-injury; 12 healthy controls underwent MRI twice, with a mean gap between scans of 25.4 months. Mean monthly percent volume change was computed for whole brain (ventricle-to-brain ratio; VBR), corpus callosum (CC), and right and left hippocampi (HPC).

RESULTS

(1) Using a threshold of 2 z-scores below controls, 96% of patients showed atrophy across time points in at least one region; 75% showed atrophy in at least 3 of the 4 regions measured. (2) There were no significant differences in the proportion of patients who showed atrophy across structures. For those showing decline in VBR, there was a significant association with both the CC and the right HPC (P < 0.05 for both comparisons). There were also significant associations between those showing decline in (i) right and left HPC (P < 0.05); (ii) all combinations of genu, body and splenium of the CC (P < 0.05), and (iii) head and tail of the right HPC (P < 0.05 all sub-structure comparisons).

CONCLUSIONS

Atrophy in chronic TBI is robust, and the CC, right HPC and left HPC appear equally vulnerable. Significant associations between the right and left HPC, and within substructures of the CC and right HPC, raise the possibility of common mechanisms for these regions, including transneuronal degeneration. Given the 96% incidence rate of atrophy, a genetic explanation is unlikely to explain all findings. Multiple and possibly synergistic mechanisms may explain findings. Atrophy has been associated with poorer functional outcomes, but recent findings suggest there is potential to offset this. A better, understanding of the underlying mechanisms could permit targeted therapy enabling better long-term outcomes.

Exercise modifies amphetamine relapse: behavioral and oxidative markers in rats

Exercise has been reported to attenuate rewarding symptoms related to addictive drugs mainly by affecting the brain neuroplasticity and neurotransmission. In this study, we investigated the influence of physical exercise on the behavioral and enzymatic status related to drug relapse in rats. Animals were primarily treated with amphetamine (AMPH; 4.0 mg/kg, i.p.) or vehicle (C; NaCl 0.9% solution) in the conditioned place preference (CPP) paradigm for 14 days. Half of each experimental group was then submitted to swimming sessions (60 min/day, 5 days/week) for 5 weeks. Animals were re-exposed to AMPH- or vehicle-CPP paradigm for another 3 days, in order to observe drug relapse and anxiety-like symptoms, which were observed 24h after AMPH reconditioning in CPP, and elevated plus maze (EPM), respectively, and brain biochemical evaluations were carried out subsequently. While AMPH was related to place preference and anxiety, indicating drug addiction and abstinence symptoms, respectively, physical activity was able to prevent relapse symptoms after AMPH reconditioning, as observed through consecutive decreased CPP and anxiety-like symptoms. In addition, AMPH exposure increased reactive species (RS) generation and protein carbonyl (PC) levels together with decreased activity of catalase- and Na(+)K(+)-ATPase in hippocampus. On the other hand, while all AMPH-induced effects were prevented by physical activity, there was a negative correlation between PC levels (r=0.65; p<0.003) and CAT activity, and a positive correlation between RS generation and PC levels (r=0.54; r=0.52, p<0.05) with AMPH-CPP after exercise. These results indicate that exercise has a clear beneficial influence on the prevention of psychostimulant drug relapse.

Neuroprotective strategies for traumatic brain injury: improving clinical translation

Traumatic brain injury (TBI) induces secondary biochemical changes that contribute to delayed neuroinflammation, neuronal cell death, and neurological dysfunction. Attenuating such secondary injury has provided the conceptual basis for neuroprotective treatments. Despite strong experimental data, more than 30 clinical trials of neuroprotection in TBI patients have failed. In part, these failures likely reflect methodological differences between the clinical and animal studies, as well as inadequate pre-clinical evaluation and/or trial design problems. However, recent changes in experimental approach and advances in clinical trial methodology have raised the potential for successful clinical translation. Here we critically analyze the current limitations and translational opportunities for developing successful neuroprotective therapies for TBI.

Current practices of the child neurologist in managing sports concussion

Given the 2010 position statement issued by the American Academy of Neurology that neurologists be consulted on return-to-play decisions following a concussion, we surveyed members of the Child Neurology Society to asses clinical practice management of concussion among child neurologists. Among the 239 respondents, the majority continued to rely on the American Academy of Neurology's 1997 Practice Parameter to guide their decision-making process. Although the 2008 consensus statement from the Third International Conference on Concussion in Sport (Zurich Guidelines) is currently considered the most up-to-date guideline, few respondents relied exclusively on this guideline. More respondents who completed continuing medical education on concussion reported making clinical decisions based on the Zurich guidelines. The finding that child neurologists who completed continuing medical education had a greater familiarity with the more recently proposed consensus-based concussion guidelines supports the development of additional education in sports concussion at all levels of child neurology training.

Recovery of stress response coincides with responsiveness to voluntary exercise after traumatic brain injury

We have recently shown that there is a heightened stress response after a mild traumatic brain injury (TBI) during the first 2 post-injury weeks. This corresponds to the same post-injury period when exercise does not increase brain-derived neurotrophic factor (BDNF) and autonomic dysfunction becomes evident with exercise. Here we determined stress and autonomic responses to voluntary and forced exercise at a post-injury time window when exercise has been found to elicit beneficial effects. Rats underwent a mild fluid percussion injury and were exercised at post-injury days 28-32 and 35-39. Cardiac and temperature autonomic function were evaluated. Hippocampal tissue was obtained immediately after exercise for analysis of BDNF. In contrast to the sub-acute period, corticosterone and adrenocorticotropic hormone responses to exercise were normalized in the TBI group. Irrespective of injury, forced exercise markedly stimulated the corticotrophic axis and did not increase BDNF. BDNF levels were increased with voluntary exercise in all animals. Rats exposed to forced exercise had lower activity levels during periods of non-exercise. This effect was more pronounced in the TBI rats. Cardiac and temperature autonomic responses to delayed exercise also recuperated. Rats with TBI that underwent forced exercise, however, had higher core body temperatures during experimental manipulations, thus suggesting that exposure to a potent stressor facilitates responsiveness to environmental stimulations.

Elevated MMP-9 in the lumbar cord early after thoracic spinal cord injury impedes motor relearning in mice

Spinal cord injury results in distant pathology around putative locomotor networks that may jeopardize the recovery of locomotion. We previously showed that activated microglia and increased cytokine expression extend at least 10 segments below the injury to influence sensory function. Matrix metalloproteinase-9 (MMP-9) is a potent regulator of acute neuroinflammation. Whether MMP-9 is produced remote to the injury or influences locomotor plasticity remains unexamined. Therefore, we characterized the lumbar enlargement after a T9 spinal cord injury in C57BL/6 (wild-type [WT]) and MMP-9-null (knock-out [KO]) mice. Within 24 h, resident microglia displayed an activated phenotype alongside increased expression of progelatinase MMP-3 in WT mice. By 7 d, increases in active MMP-9 around lumbar vasculature and production of proinflammatory TNF-α were evident. Deletion of MMP-9 attenuated remote microglial activation and restored TNF-α expression to homeostatic levels. To determine whether MMP-9 impedes locomotor plasticity, we delivered lumbar-focused treadmill training in WT and KO mice during early (2-9 d) or late (35-42 d) phases of recovery. Robust behavioral improvements were observed by 7 d, when only trained KO mice stepped in the open field. Locomotor improvements were retained for 4 weeks as identified using state of the art mouse kinematics. Neither training nor MMP-9 depletion alone promoted recovery. The same intervention delivered late was ineffective, suggesting that lesion site sparing is insufficient to facilitate activity-based training and recovery. Our work suggests that by attenuating remote mechanisms of inflammation, acute treadmill training can harness endogenous spinal plasticity to promote robust recovery.

The effect of different intensities of treadmill exercise on cognitive function deficit following a severe controlled cortical impact in rats

Exercise has been proposed for the treatment of traumatic brain injury (TBI). However, the proper intensity of exercise in the early phase following a severe TBI is largely unknown. To compare two different treadmill exercise intensities on the cognitive function following a severe TBI in its early phase, rats experienced a controlled cortical impact (CCI) and were forced to treadmill exercise for 14 days. The results revealed that the rats in the low intensity exercise group had a shorter latency to locate a platform and a significantly better improvement in spatial memory in the Morris water maze (MWM) compared to the control group (p < 0.05). The high intensity exercise group showed a longer latency and a mild improvement in spatial memory compared to the control group rats in the MWM; however, this difference was not statistically significant (p > 0.05). The brain-derived neurotrophic factor (BDNF) and p-CREB protein levels in the contralateral hippocampus were increased significantly in the low intensity exercise group. Our results suggest that 2 weeks of low intensity of treadmill exercise is beneficial for improving cognitive function and increasing hippocampal BDNF expression after a severe TBI in its early phase.

Treadmill exercise protects against pentylenetetrazol-induced seizures and oxidative stress after traumatic brain injury

Traumatic brain injury (TBI) is a major cause of acquired epilepsy, and significant resources are required to develop a better understanding of the pathologic mechanism as targets for potential therapies. Thus, we decided to investigate whether physical exercise after fluid percussion injury (FPI) protects from oxidative and neurochemical alterations as well as from behavioral electroencephalographic (EEG) seizures induced by subeffective convulsive doses of pentylenetetrazol (PTZ; 35 mg/kg). Behavioral and EEG recordings revealed that treadmill physical training increased latency to first clonic and tonic-clonic seizures, attenuated the duration of generalized seizures, and protected against the increase of PTZ-induced Racine scale 5 weeks after neuronal injury. EEG recordings also revealed that physical exercise prevented PTZ-induced amplitude increase in TBI animals. Neurochemical analysis showed that exercise training increased glutathione/oxidized glutathione ratio and glutathione levels per se. Exercise training was also effective against alterations in the redox status, herein characterized by lipid peroxidation (thiobarbituric acid reactive substances), protein carbonyl increase, as well as the inhibition of superoxide dismutase and Na⁺,K⁺-ATPase activities after FPI. On the other hand, histologic analysis with hematoxylin and eosin revealed that FPI induced moderate neuronal damage in cerebral cortex 4 weeks after injury and that physical exercise did not protect against neuronal injury. These data suggest that the ability of physical exercise to reduce FPI-induced seizures is not related to its protection against neuronal damage; however, the effective protection of selected targets, such as Na⁺/K⁺-ATPase elicited by physical exercise, may represent a new line of treatment for post-traumatic seizure susceptibility.

Exercise facilitates the action of dietary DHA on functional recovery after brain trauma

The abilities of docosahexaenoic acid (DHA) and exercise to counteract cognitive decay after traumatic brain injury (TBI) is getting increasing recognition; however, the possibility that these actions can be complementary remains just as an intriguing possibility. Here we have examined the likelihood that the combination of diet and exercise has the added potential to facilitate functional recovery following TBI. Rats received mild fluid percussion injury (mFPI) or sham injury and then were maintained on a diet high in DHA (1.2% DHA) with or without voluntary exercise for 12days. We found that FPI reduced DHA content in the brain, which was accompanied by increased levels of lipid peroxidation assessed using 4-hydroxy-2-hexenal (4-HHE). FPI reduced the enzymes acyl-CoA oxidase 1 (Acox1) and 17β-hydroxysteroid dehydrogenase type 4 (17β-HSD4), and the calcium-independent phospholipases A2 (iPLA2), which are involved in metabolism of membrane phospholipids. FPI reduced levels of syntaxin-3 (STX-3), involved in the action of membrane DHA on synaptic membrane expansion, and also reduced brain-derived neurotrophic factor (BDNF) signaling through its tyrosine kinase B (TrkB) receptor. These effects of FPI were optimally counteracted by the combination of DHA and exercise. Our results support the possibility that the complementary action of exercise is exerted on restoring membrane homeostasis after TBI, which is necessary for supporting synaptic plasticity and cognition. It is our contention that strategies that take advantage of the combined applications of diet and exercise may have additional effects to the injured brain.

Poorer physical fitness is associated with reduced structural brain integrity in heart failure

OBJECTIVE

Physical fitness is an important correlate of structural and functional integrity of the brain in healthy adults. In heart failure (HF) patients, poor physical fitness may contribute to cognitive dysfunction and we examined the unique contribution of physical fitness to brain structural integrity among patients with HF.

METHODS

Sixty-nine HF patients performed the Modified Mini Mental State examination (3MS) and underwent brain magnetic resonance imaging. All participants completed the 2-minute step test (2MST), a brief measure of physical fitness. We examined the associations between cognitive performance, physical fitness, and three indices of global brain integrity: total cortical gray matter volume, total white matter volume, and whole brain cortical thickness.

RESULTS

Regression analyses adjusting for demographic characteristics, medical variables (e.g., left ventricular ejection fraction), and intracranial volume revealed reduced performance on the 2MST were associated with decreased gray matter volume and thinner cortex (p<.05). Follow up analyses showed that reduced gray matter volume and decreased cortical thickness were associated with poorer 3MS scores (p<.05).

CONCLUSIONS

Poor physical fitness is common in HF and associated with reduced structural brain integrity. Prospective studies are needed to elucidate underlying mechanisms for the influence of physical fitness on brain health in HF.

Inhibition of Nogo-66 receptor 1 enhances recovery of cognitive function after traumatic brain injury in mice

Central nervous system (CNS) axons recover poorly following injury because of the expression of myelin-derived inhibitors of axonal outgrowth such as Nogo, myelin-associated glycoprotein (MAG), and oligodendrocyte-myelin glycoprotein (OMgp), all of which bind to the Nogo-66 receptor 1 (NgR1). Herein we examine the role of NgR1 in the recovery of motor and cognitive function after traumatic brain injury (TBI) using a controlled cortical impact (CCI) model in NgR1 knockout (KO) and wild-type (WT) mice. Four weeks post-injury, scores on the Novel Object Recognition test were significantly increased in NgR1 KO mice compared with WT mice (p<0.05), but motor behavior test scores did not differ significantly between the two groups. Nissl staining showed that NgR1 KO mice had less brain injury volume 2 weeks after CCI (p<0.05). Histological analysis revealed more doublecortin (DCX+) cells (p<0.01) and more Ki-67+ cells in the contralateral dentate gyrus (DG) (p<0.05) 2 weeks after CCI in NgR1 KO mice than in WT. Furthermore, DCX+ cells still retained their longer processes in KO mice (p<0.01) 4 weeks following trauma. The number of bromodeoxyuridine (BrdU)+ cells did not differ between the two groups at 4 weeks post-trauma, but KO mice had higher numbers of cells that co-stained with NeuN, a marker of mature neurons. Increased transcription of growth-associated protein (GAP)-43 in both the injured and contralateral sides of the hippocampus (both p<0.05) was detected in NgR1 KO mice relative to WT. These data suggest that NgR1 negatively influences plasticity and cognitive recovery after TBI.

Late exercise reduces neuroinflammation and cognitive dysfunction after traumatic brain injury

Delayed secondary biochemical and cellular changes after traumatic brain injury continue for months to years, and are associated with chronic neuroinflammation and progressive neurodegeneration. Physical activity can reduce inflammation and facilitate recovery after brain injury. Here, we investigated the time-dependent effects, and underlying mechanisms of post-traumatic exercise initiation on outcome after moderate traumatic brain injury using a well-characterized mouse controlled cortical impact model. Late exercise initiation beginning at 5weeks after trauma, but not early initiation of exercise at 1week, significantly reduced working and retention memory impairment at 3months, and decreased lesion volume compared to non-exercise injury controls. Cognitive recovery was associated with attenuation of classical inflammatory pathways, activation of alternative inflammatory responses and enhancement of neurogenesis. In contrast, early initiation of exercise failed to alter behavioral recovery or lesion size, while increasing the neurotoxic pro-inflammatory responses. These data underscore the critical importance of timing of exercise initiation after trauma and its relation to neuroinflammation, and challenge the widely held view that effective neuroprotection requires early intervention.

Energy intake and exercise as determinants of brain health and vulnerability to injury and disease

Evolution favored individuals with superior cognitive and physical abilities under conditions of limited food sources, and brain function can therefore be optimized by intermittent dietary energy restriction (ER) and exercise. Such energetic challenges engage adaptive cellular stress-response signaling pathways in neurons involving neurotrophic factors, protein chaperones, DNA-repair proteins, autophagy, and mitochondrial biogenesis. By suppressing adaptive cellular stress responses, overeating and a sedentary lifestyle may increase the risk of Alzheimer's and Parkinson's diseases, stroke, and depression. Intense concerted efforts of governments, families, schools, and physicians will be required to successfully implement brain-healthy lifestyles that incorporate ER and exercise.

A pediatric perspective on concussion pathophysiology

PURPOSE OF REVIEW

According to recent Centers for Disease Control (CDC) data, the annual incidence of traumatic brain injury (TBI) in the United States is 1.6-3.2 million, of which the majority is classified as mild. Over half of these injuries occur in the pediatric population, and can often be attributed to a sports-related mechanism. Although postconcussion symptoms are usually short-lived, more lasting deficits can occur, which can be particularly disruptive to the developing brain. Recent literature detailing the pathophysiology of mild TBI (mTBI), with attention to pediatric studies, is presented.

RECENT FINDINGS

Although concussion generally does not produce any structural damage on conventional computed tomography (CT) or MRI, advanced neuroimaging modalities reveal microstructural and functional neurobiological changes. Diffuse axonal injury, metabolic impairment, alterations in neural activation and cerebral blood flow perturbations can occur and may contribute to acute symptomatology. Although these physiological changes usually recover to baseline in 7-10 days, sustaining recurrent injury before full recovery may increase the potential for persistent deficits.

SUMMARY

Understanding the pathophysiology of concussion in the pediatric population can potentially open therapeutic avenues to decrease symptom persistence and prevent further injury. Future studies in the pediatric population are necessary given the pathophysiologic differences between the developing and adult brains.

Early postinjury exercise reverses memory deficits and retards the progression of closed-head injury in mice

Closed-head injury (CHI) usually involves both physical damage of neurons and neuroinflammation. Although exercise promotes neuronal repair and suppresses neuroinflammation, CHI patients currently often remain resting during the post-traumatic period. This study aimed to investigate whether and how postinjury exercise benefited the brain structure and function in mice after CHI. Closed-head injury immediately caused an elevated neurological severity score, with rapid loss of object recognition memory, followed by progressive location-dependent brain damage (neuronal loss and activation of microglia in the cortex and hippocampus). An early exercise protocol at moderate intensity (starting 2 days postimpact and lasting for 7 or 14 days) effectively restored the object recognition memory and prevented the progressive neuronal loss and activation of microglia. However, if the exercise started 9 days postimpact, it was unable to recover recognition memory deficits. In parallel, early exercise intervention drastically promoted neurite regeneration, while late exercise intervention was much less effective. We also tested the possible involvement of brain-derived neurotrophic factor (BDNF) and mitogen-activated protein kinase phosphatase-1 (MKP-1) in the exercise-induced beneficial effects. Exercise gradually restored the impact-abolished hippocampal expression of BDNF and MPK-1, while oral administration of triptolide (a synthesis inhibitor of MKP-1 and an antagonist of nuclear factor-B) before each bout of exercise blocked the restorative effects of exercise on MKP-1 and recognition memory, as well as the exercise-induced retardation of neuronal loss. Although triptolide treatment alone inhibited activation of microglia and maintained neuronal numbers, it did not recover the injury-hampered recognition memory. Overall, moderate exercise shortly after CHI reversed the deficits in recognition memory and prevented the progression of brain injury.

Enhancement of cognitive function in models of brain disease through environmental enrichment and physical activity

This review will provide an overview of the non-drug based approaches that have been demonstrated to enhance cognitive function of the compromised brain, primarily focussed on the two most widely adopted paradigms of environmental enrichment and enhanced physical exercise. Environmental enrichment involves the generation of novelty and complexity in animal housing conditions which facilitates enhanced sensory and cognitive stimulation as well as physical activity. In a wide variety of animal models of brain disorders, environmental enrichment and exercise have been found to have beneficial effects, including cognitive enhancement, delayed disease onset, enhanced cellular plasticity and associated molecular processes. Potential cellular and molecular mechanisms will also be discussed, which have relevance for the future development of 'enviromimetics', drugs which could mimic or enhance the beneficial effects of environmental stimulation. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Differential effects of voluntary and forced exercise on stress responses after traumatic brain injury

Voluntary exercise increases levels of brain-derived neurotrophic factor (BDNF) after traumatic brain injury (TBI) when it occurs during a delayed time window. In contrast, acute post-TBI exercise does not increase BDNF. It is well known that increases in glucocorticoids suppress levels of BDNF. Moreover, recent work from our laboratory showed that there is a heightened stress response after fluid percussion injury (FPI). In order to determine if a heightened stress response is also observed with acute exercise, at post-injury days 0-4 and 7-11, corticosterone (CORT) and adrenocorticotropic hormone (ACTH) release were measured in rats running voluntarily or exposed to two daily 20-min periods of forced running wheel exercise. Forced, but not voluntary exercise, continuously elevated CORT. ACTH levels were initially elevated with forced exercise, but decreased by post-injury day 7 in the control, but not the FPI animals. As previously reported, voluntary exercise did not increase BDNF in the FPI group as it did in the control animals. Forced exercise did not increase levels of BDNF in any group. It did, however, decrease hippocampal glucocorticoid receptors in the control group. The results suggest that exercise regimens with strong stress responses may not be beneficial during the early post-injury period.

Effects of acute restraint-induced stress on glucocorticoid receptors and brain-derived neurotrophic factor after mild traumatic brain injury

We have previously reported that experimental mild traumatic brain injury results in increased sensitivity to stressful events during the first post-injury weeks, as determined by analyzing the hypothalamic-pituitary-adrenal (HPA) axis regulation following restraint-induced stress. This is the same time period when rehabilitative exercise has proven to be ineffective after a mild fluid-percussion injury (FPI). Here we evaluated effects of stress on neuroplasticity. Adult male rats underwent either an FPI or sham injury. Additional rats were only exposed to anesthesia. Rats were exposed to 30 min of restraint stress, followed by tail vein blood collection at post-injury days (PID) 1, 7, and 14. The response to dexamethasone (DEX) was also evaluated. Hippocampal tissue was collected 120 min after stress onset. Brain-derived neurotrophic factor (BDNF) along with glucocorticoid (GR) and mineralocorticoid (MR) receptors was determined by Western blot analysis. Results indicated injury-dependent changes in glucocorticoid and mineralocorticoid receptors that were influenced by the presence of dexamethasone. Control and FPI rats responded differentially to DEX in that GR increases after receiving the lower dose of DEX were longer lasting in the FPI group. A suppression of MR was found at PID 1 in vehicle-treated FPI and Sham groups. Decreases in the precursor form of BDNF were observed in different FPI groups at PIDs 7 and 14. These findings suggest that the increased sensitivity to stressful events during the first post-injury weeks, after a mild FPI, has an impact on hippocampal neuroplasticity.

Collaborative effects of diet and exercise on cognitive enhancement

Certain dietary factors, such as omega-3 fatty acids and curcumin, are reviewed in their context of stimulating molecular systems that serve synaptic function, while diets rich in saturated fats do the opposite. In turn, exercise, using similar mechanisms as healthy diets, displays healing effects on the brain such as counteracting the mental decline associated with age and facilitating functional recovery resulting from brain injury and disease. Diet and exercise are two noninvasive approaches that used together may enhance neural repair. Omega 3 fatty acids and curcumin elevate levels of molecules important for synaptic plasticity such as brain-derived neurotrophic factor (BDNF), thus benefiting normal brain function and recovery events following brain insults.

The influence of dietary factors in central nervous system plasticity and injury recovery

Although feeding is an essential component of life, it is only recently that the actions of foods on brain plasticity and function have been scrutinized. There is evidence that select dietary factors are important modifiers of brain plasticity and can have an impact on central nervous system health and disease. Results of new research indicate that dietary factors exert their effects by affecting molecular events related to the management of energy metabolism and synaptic plasticity. Recent study results show that select dietary factors have mechanisms similar to those of exercise, and that, in some cases, dietary factors can complement the action of exercise. Abundant research findings in animal models of central nervous system injury support the idea that nutrients can be taken in through whole foods and dietary supplements to reduce the consequences of neural damage. Therefore, exercise and dietary management appear as a noninvasive and effective strategy to help counteract neurologic and cognitive disorders.

The pathophysiology of concussions in youth

Mild traumatic brain injury, especially sport-related concussion, is common among young persons. Consequences of transient pathophysiologic dysfunction must be considered in the context of a developing or immature brain, as must the potential for an accumulation of damage with repeated exposure. This review summarizes the underlying neurometabolic cascade of concussion, with emphasis on the young brain in terms of acute pathophysiology, vulnerability, alterations in plasticity and activation, axonal injury, and cumulative risk from chronic, repetitive damage, and discusses their implications in the context of clinical care for the concussed youth, highlighting areas for future investigation.

Effects of forced running exercise on cognitive function and its relation to zinc homeostasis-related gene expression in rat hippocampus

Voluntary exercise has been implicated to be beneficial for overall health and cognitive function in both clinical and experimental studies, but little is presently known about forced physical exercise on cognition and underlying molecular mechanism. We have used real-time RT-PCR to analyze gene expression in hippocampus, in the presence and absence of physical exercise, during spatial learning of rats in the Morris water maze. Our results show distinct zinc homeostasis-related gene expression profiles associated with learning and memory. Rats with physical exercise (EXP) showed a significant up-regulation of mRNA expression of zinc transporter-2 (ZnT-2), ZnT-4, ZnT-5, ZnT-6, and ZnT-7, metallothionein-1 (MT-1)-MT-3, divalent cation transporter-1, and Zrt-Irt-like proteins-7 in hippocampus when compared with control rats. In addition, spatial learning ability was improved in EXP rats compared with that in control group. This study provides the first comparative view of zinc homeostasis-related gene expression in hippocampus following forced physical exercise. These results suggested that forced physical exercise may provide a simple means to maintain brain function and promote learning capacity. Results of this study also suggest that exercise mobilizes zinc homeostasis-related gene expression profiles that would be predicted to benefit brain plasticity processes.

Reflections of experience-expectant development in repair of the adult damaged brain

Behavioral experience has long been known to influence functional outcome after brain injury, but only recently has its pervasive role in the reorganization of the adult brain after damage become appreciated. We briefly review findings from animal models on the role of experience in shaping neuronal events after stroke-like injury. Experience-dependent neural plasticity can be enhanced or impaired by brain damage, depending upon injury parameters and timing. The neuronal growth response to some experiences is heightened due to interactions with denervation-induced plasticity. This includes compensatory behavioral strategies developed in response to functional impairments. Early behavioral experiences can constrain later experience-dependent plasticity, leading to suboptimal functional outcome. Time dependencies and facets of neural growth patterns are reminiscent of experience-expectant processes that shape brain development. As with sensitive periods in brain development, this process may establish behavioral patterns early after brain injury which are relatively resistant to later change.

Exercise-induced myokines and their role in chronic diseases

Physical inactivity has recently been identified as a major and independent risk factor for the development of dementia and cognitive decline. In addition to the effect of exercise with regard to protection against neurodegenerative diseases, it is well-established that physical inactivity increases the risk of type 2 diabetes, cardiovascular diseases (CVD), colon cancer and postmenopausal breast cancer. These diseases constitute a network of related diseases, also called "the diseasome of physical inactivity". In this review, physical inactivity is given the central role as an independent and strong risk factor for accumulation of visceral fat and consequently the activation of a network of systemic inflammatory pathways, which promote development of neurodegeneration as well as insulin resistance, atherosclerosis, and tumour growth. The recent finding that muscles produce and release myokines provides a conceptual basis for understanding some of the molecular mechanisms underlying organ cross talk, including muscle-fat cross talk. Accumulating data suggest that contracting skeletal muscles release myokines, which may work in a hormone-like fashion, exerting specific endocrine effects on visceral fat or mediating direct anti-inflammatory effects. Other myokines work locally within the muscle via paracrine mechanisms, exerting their effects on signalling pathways involved in fat oxidation.

The combined effects of exercise and foods in preventing neurological and cognitive disorders

OBJECTIVE

Exercise and select diets have important influences on health and plasticity of the nervous system, and the molecular mechanisms involved with these actions are starting to be elucidated. New evidence indicates that exercise, in combination with dietary factors, exerts its effects by affecting molecular events related to the management of energy metabolism and synaptic plasticity.

METHODS

Published studies in animals and humans describing the effects of exercise and diets in brain plasticity and cognitive abilities are discussed.

RESULTS

New evidence indicates that exercise and select diets exert their effects by affecting molecular events related to the management of energy metabolism and synaptic plasticity. An important instigator in the molecular machinery stimulated by exercise is brain-derived neurotrophic factor (BDNF), which acts at the interface of metabolism and plasticity.

CONCLUSIONS

Recent studies show that selected dietary factors share similar mechanisms with exercise, and in some cases they can complement the action of exercise. Therefore, exercise and dietary management appear as a non-invasive and effective strategy to counteract neurological and cognitive disorders.

Repeat traumatic brain injury in the developing brain

The Center for Disease Control estimates that there are 1.7 million brain injuries in the US each year with 51% of these injuries occurring during periods of cerebral development. Among this population there is a growing population of individuals with repeat traumatic brain injury (RTBI). While the exact incidence is unknown, estimates range from 5.6 to 36% of the TBI population. This review summarizes the clinical problems/challenges and experimental research models that currently exist. It is intended to reveal the critical areas that need to be addressed so that age-relevant clinical management guidelines can be established to protect this population.

Muscles and their myokines

In the past, the role of physical activity as a life-style modulating factor has been considered as that of a tool to balance energy intake. Although it is important to avoid obesity, physical inactivity should be discussed in a much broader context. There is accumulating epidemiological evidence that a physically active life plays an independent role in the protection against type 2 diabetes, cardiovascular diseases, cancer, dementia and even depression. For most of the last century, researchers sought a link between muscle contraction and humoral changes in the form of an 'exercise factor', which could be released from skeletal muscle during contraction and mediate some of the exercise-induced metabolic changes in other organs such as the liver and the adipose tissue. We have suggested that cytokines or other peptides that are produced, expressed and released by muscle fibres and exert autocrine, paracrine or endocrine effects should be classified as 'myokines'. Given that skeletal muscle is the largest organ in the human body, our discovery that contracting skeletal muscle secretes proteins sets a novel paradigm: skeletal muscle is an endocrine organ producing and releasing myokines, which work in a hormone-like fashion, exerting specific endocrine effects on other organs. Other myokines work via paracrine mechanisms, exerting local effects on signalling pathways involved in muscle metabolism. It has been suggested that myokines may contribute to exercise-induced protection against several chronic diseases.