The effect of environmental enrichment on substantia nigra gene expression after traumatic brain injury in rats

Environmental Enrichment for Stroke and Traumatic Brain Injury: Mechanisms and Translational Implications

Acquired brain injuries, such as ischemic stroke, intracerebral hemorrhage (ICH), and traumatic brain injury (TBI), can cause severe neurologic damage and even death. Unfortunately, currently, there are no effective and safe treatments to reduce the high disability and mortality rates associated with these brain injuries. However, environmental enrichment (EE) is an emerging approach to treating and rehabilitating acquired brain injuries by promoting motor, sensory, and social stimulation. Multiple preclinical studies have shown that EE benefits functional recovery, including improved motor and cognitive function and psychological benefits mediated by complex protective signaling pathways. This article provides an overview of the enriched environment protocols used in animal models of ischemic stroke, ICH, and TBI, as well as relevant clinical studies, with a particular focus on ischemic stroke. Additionally, we explored studies of animals with stroke and TBI exposed to EE alone or in combination with multiple drugs and other rehabilitation modalities. Finally, we discuss the potential clinical applications of EE in future brain rehabilitation therapy and the molecular and cellular changes caused by EE in rodents with stroke or TBI. This article aims to advance preclinical and clinical research on EE rehabilitation therapy for acquired brain injury. © 2024 American Physiological Society. Compr Physiol 14:5291-5323, 2024.

Transcriptional Profiling in a Novel Swine Model of Traumatic Brain Injury

Transcriptomic investigations of traumatic brain injury (TBI) can give us deep insights into the pathological and compensatory processes post-injury. Thus far, transcriptomic studies in TBI have mostly used microarrays and have focused on rodent models. However, a large animal model of TBI bears a much stronger resemblance to human TBI with regard to the anatomical details, mechanics of injury, genetics, and, possibly, molecular response. Because of the advantages of a large animal TBI model, we investigated the gene expression changes between injured and uninjured sides of pig cerebral cortex after TBI. Given acute inflammation that follows after TBI and the important role that immune response plays in neuroplasticity and recovery, we hypothesized that transcriptional changes involving immune function will be upregulated. Eight female 4-week-old piglets were injured on the right hemisphere with controlled cortical impact (CCI). At 5 days after TBI, pericontusional cortex tissues from the injured side and contralateral cortical tissues were collected. After RNA extraction, library preparation and sequencing as well as gene expression changes between the ipsi- and contralateral sides were compared. There were 6642 genes that were differentially expressed between the ipsi- and contralateral sides, and 1993 genes among them had at least 3-fold differences. Differentially expressed genes were enriched for biological processes related to immune system activation, regulation of immune response, and leukocyte activation. Many of the differentially expressed genes, such as CD4, CD86, IL1A, IL23R, and IL1R1, were major regulators of immune function. This study demonstrated some of the major transcriptional changes between the pericontusional and contralateral tissue at an acute time point after TBI in pigs.

LPS induces dopamine depletion and iron accumulation in substantia nigra in rat models of Parkinson's disease

OBJECTIVE

Intrapallidal inflammation may lead to the pathogenesis of Parkinson's disease. Pathological changes caused by lipopolysaccharide (LPS)-induced inflammation in Parkinson's disease rat models were largely unknown.

METHODS

Male Sprague-Dawley rat models were intra-globuspallidus injected with saline and lipopolysaccharide and divided into two groups, the control group and the LPS-stimulation group. The locomotor activity of the rat models was recorded for 4 consecutive weeks by trajectory analysis software for animal behavior. For the evaluation of pathological profiles, the expression levels of tyrosine hydroxylase and OX-42 in the substantia nigra tissues were detected by immunohistochemical staining. Also, the concentrations of dopamine at specific sites were detected through high-performance liquid chromatography. Perl's iron staining was used to evaluate iron accumulation in substantia nigra tissues.

RESULTS

LPS-stimulation reduced the locomotor capacity of the rat models compared with the control group. The density of tyrosine hydroxylase-positive cells was reduced and the secretion of striatal dopamine in the substantia nigra pars compacts was lower in the LPS group than it was in the control group. OX-42 positive microglia and ferritin levels were enhanced in the LPS group.

CONCLUSION

Intrapallidal inflammation by LPS induced dopamine depletion and iron accumulation in the substantia nigra of Parkinson's disease rat models. The management of cerebral inflammation might be pivotal for PD pathogenesis and prognosis.

Impact of Traumatic Brain Injury on Dopaminergic Transmission

Brain trauma is often associated with severe morbidity and is a major public health concern. Even when injury is mild and no obvious anatomic disruption is seen, many individuals suffer disabling neuropsychological impairments such as memory loss, mood dysfunction, substance abuse, and adjustment disorder. These changes may be related to subtle disruption of neural circuits as well as functional changes at the neurotransmitter level. In particular, there is considerable evidence that dopamine (DA) physiology in the nigrostriatal and mesocorticolimbic pathways might be impaired after traumatic brain injury (TBI). Alterations in DA levels can lead to oxidative stress and cellular dysfunction, and DA plays an important role in central nervous system inflammation. Therapeutic targeting of DA pathways may offer benefits for both neuronal survival and functional outcome after TBI. The purpose of this review is to discuss the role of DA pathology in acute TBI and the potential impact of therapies that target these systems for the treatment of TBI.

Minocycline blocks traumatic brain injury-induced alcohol consumption and nucleus accumbens inflammation in adolescent male mice

Alcohol use is a well characterized risk factor for traumatic brain injury (TBI); however, emerging clinical and experimental research suggests that TBI may also be an independent risk factor for the development of alcohol use disorders. In particular, TBIs incurred early in life predict the development of problem alcohol use and increase vulnerability to neuroinflammation as a consequence of alcohol use. Critically, the neuroinflammatory response to alcohol, mediated in large part by microglia, may also function as a driver of further alcohol use. Here, we tested the hypothesis that TBI increases alcohol consumption through microglia-mediated neuroinflammation. Mice were injured as juveniles and alcohol consumption and preference were assessed in a free-choice voluntary drinking paradigm in adolescence. TBI increased alcohol consumption; however, treatment with minocycline, an inhibitor of microglial activation, reduced alcohol intake in TBI mice to sham levels. Moreover, a single injection of ethanol (2 g/kg) significantly increased microglial activation in the nucleus accumbens and microglial expression of the proinflammatory cytokine IL-1β in TBI, but not sham or minocycline-treated, mice. Our data implicate TBI-induced microglial activation as a possible mechanism for the development of alcohol use disorders.

Environmental Enrichment Mitigates Deficits after Repetitive Mild Traumatic Brain Injury

Although environmental enrichment has been shown to improve functional and histologic outcomes in pre-clinical moderate-to-severe traumatic brain injury (TBI), there are a paucity of pre-clinical data regarding enrichment strategies in the setting of repetitive mild traumatic brain injury (rmTBI). Given the vast numbers of athletes and those in the military who sustain rmTBI, the mounting evidence of the long-term and progressive sequelae of rmTBI, and the lack of targeted therapies to mitigate these sequelae, successful enrichment interventions in rmTBI could have large public health significance. Here, we evaluated enrichment strategies in an established pre-clinical rmTBI model. Seventy-one male C57BL/6 mice were randomized to two different housing conditions, environmental enrichment (EE) or normal condition (NC), then subjected to rmTBI injury (seven injuries in 9 days) or sham injury (anesthesia only). Functional outcomes in all four groups (NC-TBI, EE-TBI, NC-sham, and EE-sham) were assessed by motor, exploratory/anxiety, and mnemonic behavioral tests. At the synaptic level, N-methyl d-aspartate receptor (NMDAR) subunit expression of phosphorylated glutamate receptor 1 (GluR1), phosphorylated Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), and calpain were evaluated by western blot. Compared to injured NC-TBI mice, EE-TBI mice had improved memory and decreased anxiety and exploratory activity post-injury. Treatment with enrichment also corresponded to normal NMDAR subunit expression, decreased GluR1 phosphorylation, decreased phosphorylated CaMKII, and normal calpain expression post-rmTBI. These data suggest that enrichment strategies may improve functional outcomes and mitigate synaptic changes post-rmTBI. Given that enrichment strategies are feasible in the clinical setting, particularly for athletes and soldiers for whom the risk of repetitive injury is greatest, these data suggest that clinical trials may be warranted.

Factors affecting increased risk for substance use disorders following traumatic brain injury: What we can learn from animal models

Recent studies have helped identify multiple factors affecting increased risk for substance use disorders (SUDs) following traumatic brain injury (TBI). These factors include age at the time of injury, repetitive injury and TBI severity, neurocircuits, neurotransmitter systems, neuroinflammation, and sex differences. This review will address each of these factors by discussing 1) the clinical and preclinical data identifying patient populations at greatest risk for SUDs post-TBI, 2) TBI-related neuropathology in discrete brain regions heavily implicated in SUDs, and 3) the effects of TBI on molecular mechanisms that may drive substance abuse behavior, like dopaminergic and glutamatergic transmission or neuroimmune signaling in mesolimbic regions of the brain. Although these studies have laid the groundwork for identifying factors that affect risk of SUDs post-TBI, additional studies are required. Notably, preclinical models have been shown to recapitulate many of the behavioral, cellular, and neurochemical features of SUDs and TBI. Therefore, these models are well suited for answering important questions that remain in future investigations.

Where Environment Meets Cognition: A Focus on Two Developmental Intellectual Disability Disorders

One of the most challenging questions in neuroscience is to dissect how learning and memory, the foundational pillars of cognition, are grounded in stable, yet plastic, gene expression states. All known epigenetic mechanisms such as DNA methylation and hydroxymethylation, histone modifications, chromatin remodelling, and noncoding RNAs regulate brain gene expression, both during neurodevelopment and in the adult brain in processes related to cognition. On the other hand, alterations in the various components of the epigenetic machinery have been linked to well-known causes of intellectual disability disorders (IDDs). Two examples are Down Syndrome (DS) and Fragile X Syndrome (FXS), where global and local epigenetic alterations lead to impairments in synaptic plasticity, memory, and learning. Since epigenetic modifications are reversible, it is theoretically possible to use epigenetic drugs as cognitive enhancers for the treatment of IDDs. Epigenetic treatments act in a context specific manner, targeting different regions based on cell and state specific chromatin accessibility, facilitating the establishment of the lost balance. Here, we discuss epigenetic studies of IDDs, focusing on DS and FXS, and the use of epidrugs in combinatorial therapies for IDDs.

Adolescent Traumatic Brain Injury Induces Chronic Mesolimbic Neuroinflammation with Concurrent Enhancement in the Rewarding Effects of Cocaine in Mice during Adulthood

Clinical psychiatric disorders of depression, anxiety, and substance abuse are most prevalent after traumatic brain injury (TBI). Pre-clinical research has focused on depression and anxiety post-injury; however, virtually no data exist examining whether the preference for illicit drugs is affected by traumatic injury in the developing adolescent brain. Using the controlled cortical impact (CCI) model of TBI and the conditioned place preference (CPP) assay, we tested the underlying hypothesis that brain injury during adolescence exacerbates the rewarding properties of cocaine in adulthood possibly through an active inflammatory status in the mesolimbic pathway. Six-week old, C57BL/6 mice sustained a single CCI-TBI to the right somatosensory cortex. CPP experiments with cocaine began 2 weeks post-TBI. Animals receiving cocaine displayed significant place preference shifts compared to saline controls. Further, within the cocaine-experienced cohort, moderate CCI-TBI during adolescence significantly increased the preference shift in adulthood when compared to naïve controls. Additionally, persistent neuroinflammatory responses were observed in the cortex, nucleus accumbens (NAc), and ventral tegmental area post-CCI-TBI. Significant increases in both astrocytic, glial fibrillary acidic protein, and microglial, ionization basic acid 1, markers were observed in the NAc at the end of CPP testing. Moreover, analysis using focused array gene expression panels identified the upregulation of numerous inflammatory genes in moderate CCI-TBI animals, compared to naïve controls, both in the cortex and NAc at 2 weeks post-TBI, before onset of cocaine administration. These results suggest that sustaining moderate TBI during adolescence may augment the rewarding effects of psychostimulants in adulthood, possibly by induction of chronic mesolimbic neuroinflammation.

The Therapeutic Efficacy of Environmental Enrichment and Methylphenidate Alone and in Combination after Controlled Cortical Impact Injury

Environmental enrichment (EE) and methylphenidate (MPH) independently confer significant benefit to behavioral recovery after controlled cortical impact (CCI) injury. Given that combinational therapies may be more clinically translatable than monotherapies, the aim of the current study was to test the hypothesis that a combined treatment regimen of EE and MPH would provide greater therapeutic efficacy than either one alone. Anesthetized adult male rats received either a CCI of moderate severity or sham injury and were then randomly assigned to EE or standard (STD) housing where they received either intraperitoneal (ip) MPH (5 mg/kg) or vehicle (VEH; 1.0 mL/kg; ip) beginning 24 h after injury and once daily for 19 days. Motor and cognitive assessments were conducted on post-injury days 1-5 and 14-19, respectively. No differences were observed in sham controls regardless of treatments, and thus their data were pooled. The traumatic brain injury (TBI)+EE+VEH and TBI+EE+MPH groups exhibited enhanced beam balance and beam walk performance relative to the TBI+STD+VEH group (p < 0.05), but did not differ from one another (p > 0.05). No effect of MPH treatment alone was observed in either motor task. In contrast, MPH improved spatial learning and memory when presented alone and also when combined with EE relative to VEH-treated STD controls (p < 0.05). In addition, both EE groups performed significantly better than the TBI+STD+MPH group (p < 0.05), but did not differ from one another (p > 0.05). These data replicate previous findings that both EE and MPH confer cognitive benefits after TBI and extend the findings by revealing that combining EE and MPH does not produce effects greater than either treatment alone, which does not support the hypothesis. The lack of an additive effect may be because of the robustness of the EE.

The Controlled Cortical Impact Model of Experimental Brain Trauma: Overview, Research Applications, and Protocol

Controlled cortical impact (CCI) is a commonly used and highly regarded model of brain trauma that uses a pneumatically or electromagnetically controlled piston to induce reproducible and well-controlled injury. The CCI model was originally used in ferrets and it has since been scaled for use in many other species. This chapter will describe the historical development of the CCI model, compare and contrast the pneumatic and electromagnetic models, and summarize key short- and long-term consequences of TBI that have been gleaned using this model. In accordance with the recent efforts to promote high-quality evidence through the reporting of common data elements (CDEs), relevant study details-that should be reported in CCI studies-will be noted.

Catecholaminergic based therapies for functional recovery after TBI

Among the many pathophysiologic consequences of traumatic brain injury are changes in catecholamines, including dopamine, epinephrine, and norepinephrine. In the context of TBI, dopamine is the one most extensively studied, though some research exploring epinephrine and norepinephrine have also been published. The purpose of this review is to summarize the evidence surrounding use of drugs that target the catecholaminergic system on pathophysiological and functional outcomes of TBI using published evidence from pre-clinical and clinical brain injury studies. Evidence of the effects of specific drugs that target catecholamines as agonists or antagonists will be discussed. Taken together, available evidence suggests that therapies targeting the catecholaminergic system may attenuate functional deficits after TBI. Notably, it is fairly common for TBI patients to be treated with catecholamine agonists for either physiological symptoms of TBI (e.g. altered cerebral perfusion pressures) or a co-occuring condition (e.g. shock), or cognitive symptoms (e.g. attentional and arousal deficits). Previous clinical trials are limited by methodological limitations, failure to replicate findings, challenges translating therapies to clinical practice, the complexity or lack of specificity of catecholamine receptors, as well as potentially counfounding effects of personal and genetic factors. Overall, there is a need for additional research evidence, along with a need for systematic dissemination of important study details and results as outlined in the common data elements published by the National Institute of Neurological Diseases and Stroke. Ultimately, a better understanding of catecholamines in the context of TBI may lead to therapeutic advancements. This article is part of a Special Issue entitled SI:Brain injury and recovery.

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.

Expression of three topologically distinct membrane proteins elicits unique stress response pathways in the yeast Saccharomyces cerevisiae

Misfolded membrane proteins are retained in the endoplasmic reticulum (ER) and are subject to ER-associated degradation, which clears the secretory pathway of potentially toxic species. While the transcriptional response to environmental stressors has been extensively studied, limited data exist describing the cellular response to misfolded membrane proteins. To this end, we expressed and then compared the transcriptional profiles elicited by the synthesis of three ER retained, misfolded ion channels: The α-subunit of the epithelial sodium channel, ENaC, the cystic fibrosis transmembrane conductance regulator, CFTR, and an inwardly rectifying potassium channel, Kir2.1, which vary in their mass, membrane topologies, and quaternary structures. To examine transcriptional profiles in a null background, the proteins were expressed in yeast, which was previously used to examine the degradation requirements for each substrate. Surprisingly, the proteins failed to induce a canonical unfolded protein response or heat shock response, although messages encoding several cytosolic and ER lumenal protein folding factors rose when αENaC or CFTR was expressed. In contrast, the levels of these genes were unaltered by Kir2.1 expression; instead, the yeast iron regulon was activated. Nevertheless, a significant number of genes that respond to various environmental stressors were upregulated by all three substrates, and compared with previous microarray data we deduced the existence of a group of genes that reflect a novel misfolded membrane protein response. These data indicate that aberrant proteins in the ER elicit profound yet unique cellular responses.

Amantadine preserves dopamine level and attenuates depression-like behavior induced by traumatic brain injury in rats

Traumatic brain injury (TBI) often results in multiple neuropsychiatric sequelae, including cognitive, emotional, and behavioral problems. Among them, depression is a common psychiatric symptom, and links to poorer recovery. Amantadine, as an antiparkinsonian, increases dopamine release, and blocks dopamine reuptake, but has recently received attention for its effectiveness as an antidepressant. In the present study, we first induced a post-TBI depression rat model to probe the efficacy of amantadine therapy in reducing post-TBI depression. The DA concentration in the striatum of the injured rats, as well as the degeneration and apoptosis of dopaminergic neurons in the substantia nigra (SN), were checked along with the depression-like behavior. The results showed that amantadine therapy could significantly ameliorate the depression-like behavior, improving the DA level in the striatum and decreasing the degeneration and apoptosis of dopaminergic neurons in the SN. The results indicated that the anti-depression effect may result from the increase of extracellular DA concentration in the striatum and/or the indirect neuroprotection on the dopaminergic neurons in the SN. We conclude that DA plays a critical role in post-TBI depression, and that amantadine shows its potential value in anti-depression treatment for TBI.

Environmental enrichment as a viable neurorehabilitation strategy for experimental traumatic brain injury

Environmental enrichment (EE) emerged as a robust independent variable capable of influencing behavioral outcome in experimental studies after the fortuitous observation by renowned neuropsychologist Donald O. Hebb that rats raised as pets in his home performed markedly better on problem-solving tasks than those kept in the laboratory. In the subsequent years, numerous studies ensued demonstrating that EE was also capable of inducing neuroplasticity in normal (i.e., noninjured) rats. These behavioral and neural alterations provided the impetus for investigating EE as a potential therapy for traumatic brain injury (TBI), which, over the past two decades, has resulted in several reports. Hence, the aim of this review is to integrate the findings and present the current state of EE as a viable neurorehabilitation strategy for TBI. Using the specific key term searches "traumatic brain injury" and "environmental enrichment" or "enriched environment," 30 and 30 experimental TBI articles were identified by PubMed and Scopus, respectively. Of these, 27 articles were common to both search engines. An additional article was found on PubMed using the key terms "enriched environment" and "fluid percussion." A review of the bibliographies in the 34 articles did not yield additional citations. The overwhelming consensus of the 34 publications is that EE benefits behavioral and histological outcome after brain injury produced by various models. Further, the enhancements are observed in male and female as well as adult and pediatric rats and mice. Taken together, these cumulative findings provide strong support for EE as a generalized and robust preclinical model of neurorehabilitation. However, to further enhance the model and to more accurately mimic the clinic, future studies should continue to evaluate EE during more rehabilitation-relevant conditions, such as delayed and shorter time periods, as well as in combination with other therapeutic approaches, as we have been doing for the past few years.

Traumatic brain injury and post-acute decline: what role does environmental enrichment play? A scoping review

Objectives: While a growing number of studies provide evidence of neural and cognitive decline in traumatic brain injury (TBI) survivors during the post-acute stages of injury, there is limited research as of yet on environmental factors that may influence this decline. The purposes of this paper, therefore, are to (1) examine evidence that environmental enrichment (EE) can influence long-term outcome following TBI, and (2) examine the nature of post-acute environments, whether they vary in degree of EE, and what impact these variations have on outcomes.

Methods: We conducted a scoping review to identify studies on EE in animals and humans, and post-discharge experiences that relate to barriers to recovery.

Results: One hundred and twenty-three articles that met inclusion criteria demonstrated the benefits of EE on brain and behavior in healthy and brain-injured animals and humans. Nineteen papers on post-discharge experiences revealed that variables such as insurance coverage, financial, and social support, home therapy, and transition from hospital to home, can have an impact on clinical outcomes.

Conclusion: There is evidence to suggest that lack of EE, whether from lack of resources or limited ability to engage in such environments, may play a role in post-acute cognitive and neural decline. Maximizing EE in the post-acute stages of TBI may improve long-term outcomes for the individual, their family and society.