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

Real-world environmental enrichment rehabilitation paradigm in people with severe traumatic brain injury: a pilot feasibility study

BACKGROUND

The use of Environmental Enrichment (EE) has been widely studied in animal models. However, the application of the same in humans is limited to rehabilitation settings.

OBJECTIVE

To investigate the feasibility of a community-based EE paradigm in adults with brain injury.

METHODS

Six individuals diagnosed with traumatic brain injury enrolled in the study. The Go Baby Go Café instrumented with a body weight harness system, provided physical and social enrichment as participants performed functional tasks for 2 hours, three times a week, for 2 months. Feasibility and safety outcomes were recorded throughout sessions. Clinical measures including 10-meter walk, timed up and go, jebsen hand function, 6-minute walk, and trail making tests were obtained pre and post intervention.

RESULTS

All participants completed the study. The attendance was 100% and adherence was 87%. Positive changes in clinical measures were statistically significant for the timed up and go (p = 0.0175), TUG-cognitive (p = 0.0064), 10-meter walk (p = 0.0428), six-minute walk (p = 0.0196), TMT-A (p = 0.034). Changes in JHFT were not significant (p = 0.0506), with one subject recording values counter to the trend.

CONCLUSION

The Café was a comprehensive EE-based intervention that was feasible, safe, and has the potential to enhance motor and cognitive function in individuals with brain injury.

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.

Environmental modifications to rehabilitate social behavior deficits after acquired brain injury: What is the evidence?

Social behavior deficits are a common, debilitating consequence of traumatic brain injury and stroke, particularly when sustained during childhood. Numerous factors influence the manifestation of social problems after acquired brain injuries, raising the question of whether environmental manipulations can minimize or prevent such deficits. Here, we examine both clinical and preclinical evidence addressing this question, with a particular focus on environmental enrichment paradigms and differing housing conditions. We aimed to understand whether environmental manipulations can ameliorate injury-induced social behavior deficits. In summary, promising data from experimental models supports a beneficial role of environmental enrichment on social behavior. However, limited studies have considered social outcomes in the chronic setting, and few studies have addressed the social context specifically as an important component of the post-injury environment. Clinically, limited high-caliber evidence supports the use of specific interventions for social deficits after acquired brain injuries. An improved understanding of how the post-injury environment interacts with the injured brain, particularly during development, is needed to validate the implementation of rehabilitative interventions that involve manipulating an individuals' environment.

Enriching adult male rats prior to traumatic brain injury does not attenuate neurobehavioral or histological deficits

Environmental enrichment (EE) confers significant increases in neurobehavioral and cognitive recovery and decreases histological damage in various models of traumatic brain injury (TBI). However, despite EE's pervasiveness, little is known regarding its prophylactic potential. Thus, the goal of the current study was to determine whether enriching rats prior to a controlled cortical impact exerts protection as evidenced by attenuated injury-induced neurobehavioral and histological deficits relative to rats without prior EE. The hypothesis was that enrichment prior to TBI would be protective. After two weeks of EE or standard (STD) housing, anesthetized adult male rats received either a controlled cortical impact (2.8 mm deformation at 4 m/s) or sham injury and then were placed in EE or STD conditions. Motor (beam-walk) and cognitive (spatial learning) performance were assessed on post-operative days 1-5 and 14-18, respectively. Cortical lesion volume was quantified on day 21. The group that was housed in STD conditions before TBI and received post-injury EE performed significantly better in motor, cognitive, and histological outcomes vs. both groups in STD conditions regardless of whether having received pre-injury EE or not (p < 0.05). That no differences in any endpoint were revealed between the two STD-housed groups after TBI suggests that enriching rats prior to TBI does not attenuate neurobehavioral or histological deficits and therefore does not support the hypothesis.

Milnacipran Ameliorates Executive Function Impairments following Frontal Lobe Traumatic Brain Injury in Male Rats: A Multimodal Behavioral Assessment

Traumatic brain injuries (TBIs) affect more than 10 million patients annually worldwide, causing long-term cognitive and psychosocial impairments. Frontal lobe TBIs commonly impair executive function, but laboratory models typically focus primarily on spatial learning and declarative memory. We implemented a multi-modal approach for clinically relevant cognitive-behavioral assessments of frontal lobe function in rats with TBI and assessed treatment benefits of the serotonin-norepinephrine reuptake inhibitor, milnacipran (MLN). Two attentional set-shifting tasks (AST) evaluated cognitive flexibility via the rats' ability to locate food-based rewards by learning, unlearning, and relearning sequential rule sets with shifting salient cues. Adult male rats reached stable pre-injury operant AST (oAST) performance in 3-4 weeks, then were isoflurane-anesthetized, subjected to a unilateral frontal lobe controlled cortical impact (2.4 mm depth, 4 m/sec velocity) or Sham injury, and randomized to treatment conditions. Milnacipran (30 mg/kg/day) or vehicle (VEH; 10% ethanol in saline) was administered intraperitoneally via implanted osmotic minipumps (continuous infusions post-surgery, 60 μL/h). Rats had a 10-day recovery post-TBI/Sham before performing light/location-based oAST for 10 days and, subsequently, odor/media-based digging AST (dAST) on the last test day (26-27 days post-injury) before sacrifice. Both AST tests revealed significant deficits in TBI+VEH rats, seen as elevated total trials and errors (p < 0.05), which generally normalized in MLN-treated rats (p < 0.05). This first simultaneous dual AST assessment demonstrates oAST and dAST are sufficiently sensitive and robust to detect subtle attentional and cognitive flexibility executive impairments after frontal lobe TBI in rats. Chronic MLN administration shows promise for attenuation of post-TBI executive function deficits, thus meriting further investigation.

Chronic unpredictable stress during adolescence protects against adult traumatic brain injury-induced affective and cognitive deficits

Pre-clinical early-life stress paradigms model early adverse events in humans. However, the long-term behavioral consequences of early-life adversities after traumatic brain injury (TBI) in adults have not been examined. In addition, endocannabinoids may protect against TBI neuropathology. Hence, the current study assessed the effects of adverse stress during adolescence on emotional and cognitive performance in rats sustaining a TBI as adults, and how cannabinoid receptor 1 (CB1) activation impacts the outcome. On postnatal days (PND) 30-60, adolescent male rats were exposed to four weeks of chronic unpredictable stress (CUS), followed by four weeks of no stress (PND 60-90), or no stress at any time (Control), and then anesthetized and provided a cortical impact of moderate severity (2.8 mm tissue deformation at 4 m/s) or sham injury. TBI and Sham rats (CUS and Control) were administered either arachidonyl-2'-chloroethylamide (ACEA; 1 mg/kg, i.p.), a CB1 receptor agonist, or vehicle (VEH; 1 mL/kg, i.p.) immediately after surgery and once daily for 7 days. Anxiety-like behavior was assessed in an open field test (OFT) and learning and memory in novel object recognition (NOR) and Morris water maze (MWM) tasks. No differences were revealed among the Sham groups in any behavioral assessment and thus the groups were pooled. In the ACEA and VEH-treated TBI groups, CUS increased exploration in the OFT, enhanced NOR focus, and decreased the time to reach the escape platform in the MWM, suggesting decreased anxiety and enhanced learning and memory relative to the Control group receiving VEH (p < 0.05). ACEA also enhanced NOR and MWM performance in the Control + TBI group (p < 0.05). These data suggest that 4 weeks of CUS provided during adolescence may provide protection against TBI acquired during adulthood and/or induce adaptive behavioral responses. Moreover, CB1 receptor agonism produces benefits after TBI independent of CUS protection.

Environmental Complexity and Research Outcomes

Environmental complexity is an experimental paradigm as well as a potential part of animals' everyday housing experiences. In experimental uses, researchers add complexity to stimulate brain development, delay degenerative brain changes, elicit more naturalistic behaviors, and test learning and memory. Complexity can exacerbate or mitigate behavioral problems, give animals a sense of control, and allow for expression of highly driven, species-typical behaviors that can improve animal welfare. Complex environments should be designed thoughtfully with the animal's natural behaviors in mind, reported faithfully in the literature, and evaluated carefully for unexpected effects.

Hydrogen Sulfide Alleviates Anxiety, Motor, and Cognitive Dysfunctions in Rats with Maternal Hyperhomocysteinemia via Mitigation of Oxidative Stress

Hydrogen sulfide (H₂S) is endogenously produced from sulfur containing amino acids, including homocysteine and exerts neuroprotective effects. An increase of homocysteine during pregnancy impairs fetal growth and development of the offspring due to severe oxidative stress. We analyzed the effects of the H₂S donor—sodium hydrosulfide (NaHS) administered to female rats with hyperhomocysteinemia (hHcy) on behavioral impairments and levels of oxidative stress of their offspring. Rats born from females fed with control or high methionine diet, with or without H₂S donor injections were investigated. Rats with maternal hHcy exhibit increased levels of total locomotor activity and anxiety, decreased muscle endurance and motor coordination, abnormalities of fine motor control, as well as reduced spatial memory and learning. Oxidative stress in brain tissues measured by activity of glutathione peroxidases and the level of malondialdehyde was higher in rats with maternal hHcy. Concentrations of H₂S and the activity and expression of the H₂S generating enzyme—cystathionine-beta synthase—were lower compared to the control group. Administration of the H₂S donor to females with hHcy during pregnancy prevented behavioral alterations and oxidative stress of their offspring. The acquisition of behavioral together with biochemical studies will add to our knowledge about homocysteine neurotoxicity and proposes H₂S as a potential agent for therapy of hHcy associated disorders.

Environmental enrichment improves cognitive symptoms and pathological features in a focal model of cortical damage of multiple sclerosis

Multiple Sclerosis (MS) is a neuroinflammatory disease affecting white and grey matter, it is characterized by demyelination, axonal degeneration along with loss of motor, sensitive and cognitive functions. MS is a heterogeneous disease that displays different clinical courses: relapsing/remitting MS (RRMS), and MS progressive forms: primary progressive (PPMS) and secondary progressive (SPMS). Cortical damage in the progressive MS forms has considerable clinical relevance due to its association with cognitive impairment and disability progression in patients. One treatment is available for the progressive forms of the disease, but none are specific for cognitive deficits. We developed an animal model that reflects most of the characteristics of the cortical damage, such as cortical neuroinflammation, demyelination, neurodegeneration and meningeal inflammation, which was associated with cognitive impairment. Cognitive rehabilitation, exercise and social support have begun to be evaluated in patients and animal models of neurodegenerative diseases. Environmental enrichment (EE) provides exercise as well as cognitive and social stimulation. EE has been demonstrated to exert positive effects on cognitive domains, such as learning and memory, and improving anxiety-like symptoms. We proposed to study the effect of EE on peripherally stimulated cortical lesion induced by the long term expression of interleukin IL-1β (IL-1β) in adult rats. Here, we demonstrated that EE: 1) reduces the peripheral inflammatory response to the stimulus, 2) ameliorates cognitive deficits and anxiety-like symptoms, 3) modulates neurodegeneration, demyelination and glial activation, 4) regulates neuroinflammation by reducing the expression of pro-inflammatory cytokines and enhancing the expression of anti-inflammatory ones. Our findings correlate with the fact that EE housing could be considered an effective non- pharmacological therapeutic agent that can synergistically aid in the rehabilitation of the disease.

Stem cells technology: a powerful tool behind new brain treatments

Stem cell research has recently become a hot research topic in biomedical research due to the foreseen unlimited potential of stem cells in tissue engineering and regenerative medicine. For many years, medicine has been facing intense challenges, such as an insufficient number of organ donations that is preventing clinicians to fulfill the increasing needs. To try and overcome this regrettable matter, research has been aiming at developing strategies to facilitate the in vitro culture and study of stem cells as a tool for tissue regeneration. Meanwhile, new developments in the microfluidics technology brought forward emerging cell culture applications that are currently allowing for a better chemical and physical control of cellular microenvironment. This review presents the latest developments in stem cell research that brought new therapies to the clinics and how the convergence of the microfluidics technology with stem cell research can have positive outcomes on the fields of regenerative medicine and high-throughput screening. These advances will bring new translational solutions for drug discovery and will upgrade in vitro cell culture to a new level of accuracy and performance. We hope this review will provide new insights into the understanding of new brain treatments from the perspective of stem cell technology especially regarding regenerative medicine and tissue engineering.

Enhancing and Extending Biological Performance and Resilience

Human performance, endurance, and resilience have biological limits that are genetically and epigenetically predetermined but perhaps not yet optimized. There are few systematic, rigorous studies on how to raise these limits and reach the true maxima. Achieving this goal might accelerate translation of the theoretical concepts of conditioning, hormesis, and stress adaptation into technological advancements. In 2017, an Air Force-sponsored conference was held at the University of Massachusetts for discipline experts to display data showing that the amplitude and duration of biological performance might be magnified and to discuss whether there might be harmful consequences of exceeding typical maxima. The charge of the workshop was "to examine and discuss and, if possible, recommend approaches to control and exploit endogenous defense mechanisms to enhance the structure and function of biological tissues." The goal of this white paper is to fulfill and extend this workshop charge. First, a few of the established methods to exploit endogenous defense mechanisms are described, based on workshop presentations. Next, the white paper accomplishes the following goals to provide: (1) synthesis and critical analysis of concepts across some of the published work on endogenous defenses, (2) generation of new ideas on augmenting biological performance and resilience, and (3) specific recommendations for researchers to not only examine a wider range of stimulus doses but to also systematically modify the temporal dimension in stimulus inputs (timing, number, frequency, and duration of exposures) and in measurement outputs (interval until assay end point, and lifespan). Thus, a path forward is proposed for researchers hoping to optimize protocols that support human health and longevity, whether in civilians, soldiers, athletes, or the elderly patients. The long-term goal of these specific recommendations is to accelerate the discovery of practical methods to conquer what were once considered intractable constraints on performance maxima.

Evaluating rodent motor functions: Which tests to choose?

Damage to the motor cortex induced by stroke or traumatic brain injury (TBI) can result in chronic motor deficits. For the development and improvement of therapies, animal models which possess symptoms comparable to the clinical population are used. However, the use of experimental animals raises valid ethical and methodological concerns. To decrease discomfort by experimental procedures and to increase the quality of results, non-invasive and sensitive rodent motor tests are needed. A broad variety of rodent motor tests are available to determine deficits after stroke or TBI. The current review describes and evaluates motor tests that fall into three categories: Tests to evaluate fine motor skills and grip strength, tests for gait and inter-limb coordination and neurological deficit scores. In this review, we share our thoughts on standardized data presentation to increase data comparability between studies. We also critically evaluate current methods and provide recommendations for choosing the best behavioral test for a new research line.

Understanding the Mechanisms of Recovery and/or Compensation following Injury

Injury due to stroke and traumatic brain injury result in significant long-term effects upon behavioral functioning. One central question to rehabilitation research is whether the nature of behavioral improvement observed is due to recovery or the development of compensatory mechanisms. The nature of functional improvement can be viewed from the perspective of behavioral changes or changes in neuroanatomical plasticity that follows. Research suggests that these changes correspond to each other in a bidirectional manner. Mechanisms surrounding phenomena like neural plasticity may offer an opportunity to explain how variables such as experience can impact improvement and influence the definition of recovery. What is more, the intensity of the rehabilitative experiences may influence the ability to recover function and support functional improvement of behavior. All of this impacts how researchers, clinicians, and medical professionals utilize rehabilitation.

Housing Complexity Alters GFAP-Immunoreactive Astrocyte Morphology in the Rat Dentate Gyrus

Rats used in research are typically housed singly in cages with limited sensory stimulation. There is substantial evidence that housing rats in these conditions lead to numerous neuroanatomical and behavioral abnormalities. Alternatively, rats can be housed in an enriched environment in which rats are housed in groups and given room for exercise and exploration. Enriched environments result in considerable neuroplasticity in the rodent brain. In the dentate gyrus of the hippocampus, enriched environments evoke especially profound neural changes, including increases in the number of neurons and the number of dendritic spines. However, whether changes in astrocytes, a type of glia increasingly implicated in mediating neuroplasticity, are concurrent with these neural changes remains to be investigated. In order to assess morphological changes among astrocytes of the rat dentate gyrus, piSeeDB was used to optically clear 250 μm sections of tissue labeled using GFAP immunohistochemistry. Confocal imaging and image analysis were then used to measure astrocyte morphology. Astrocytes from animals housed in EE demonstrated a reduced distance between filament branch points. Furthermore, the most complex astrocytes were significantly more complex among animals housed in EE compared to standard environments.

Enduring effects of post-weaning rearing condition on depressive- and anxiety-like behaviors and motor activity in male rats

Environmental manipulation at early critical periods could have long-lasting effects. In spite of the great interest in the biological effects of the environmental condition so far, its long-lasting effects are less documented. This study looks at the enduring effects of rearing condition on tasks that measure affective responses and exploratory behavior in male Wistar rats. The animals were reared from weaning to adulthood in an enriched environment, standard laboratory condition, or isolated condition. Then, all rats were housed in standard laboratory cages to provide a common environment, and successively exposed to different tests between 0 and 11 weeks post-manipulation. The open field test indicated a more efficient exploratory behavior in the enriched group, and an enhanced spontaneous motor activity in both standard and isolated groups. In addition, rats reared in standard condition showed heightened motor activity in forced swimming test and elevated plus maze. Forced swimming test showed an antidepressive-like effect in the enriched environment group by increased climbing behavior. In respect to the anxiety behavior, environmental enrichment improved threat detection ability. It is concluded that rearing condition from weaning to adulthood has important and long-lasting effects on depressive- and anxiety-like and exploratory behaviors as well as motor activity.