Abbreviated environmental enrichment confers neurobehavioral, cognitive, and histological benefits in brain-injured female 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.

Increasing Rigor of Preclinical Research to Maximize Opportunities for Translation

The use of animal models in pre-clinical research has significantly broadened our understanding of the pathologies that underlie traumatic brain injury (TBI)-induced damage and deficits. However, despite numerous pre-clinical studies reporting the identification of promising neurotherapeutics, translation of these therapies to clinical application has so far eluded the TBI research field. A concerted effort to address this lack of translatability is long overdue. Given the inherent heterogeneity of TBI and the replication crisis that continues to plague biomedical research, this is a complex task that will require a multifaceted approach centered around rigor and reproducibility. Here, we discuss the role of three primary focus areas for better aligning pre-clinical research with clinical TBI management. These focus areas are (1) reporting and standardization of protocols, (2) replication of prior knowledge including the confirmation of expected pharmacodynamics, and (3) the broad application of open science through inter-center collaboration and data sharing. We further discuss current efforts that are establishing the core framework needed for successfully addressing the translatability crisis of TBI.

Adipose-derived stem cell exosomes ameliorate traumatic brain injury through the NLRP3 signaling pathway

The exosomes of mesenchymal stem cells have immunoregulatory properties and can effectively mitigate secondary neuroinflammation due to traumatic brain injury (TBI). In this study, we found that adipose-derived stem cell exosomes (ADSCs-Exo) could reduce the inflammatory response after traumatic brain injury by reducing NLRP3 inflammasome secretion by microglial. ADSCs-Exo were monitored by Western blot and electron microscopy. An in-vitro lipopolysaccharide (LPS)-caused primary microglia model and a TBI rat model were constructed. Functional recovery was examined using the modified neurological severity score and foot fault tests. Inflammasome inactivation in LPS-stimulated microglial, ADSCs-Exo can reduce the secretion of interleukin (IL)-1β, IL-6 and tumor necrosis factor α. Compared with PBS-processed controls, the sensorimotor functional recovery was significantly improved by exosome treatment after injury at 14-35 days. Additionally, NLRP3 inflammasome was stimulated within 24 h after TBI. ADSCs-Exo application led to remarkable down-expression of NLRP3 and caspase-1. ADSCs-Exo can ameliorate LPS-induced inflammatory activation by reducing microglial pro-inflammatory cytokines. Moreover, the neuroprotective effect of ADSCs-Exo may be partially attributed to the inhibition thereof on the formation of NLRP3-mediated inflammasome. Such findings imply a potential function of ADSCs-Exo in treating TBI.

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.

The effect of thioredoxin-1 in a rat model of traumatic brain injury depending on diurnal variation

INTRODUCTION

Traumatic brain injury (TBI) is a public health concern with limited treatment options because it causes a cascade of side effects that are the leading cause of hospital death. Thioredoxin is an enzyme with neuroprotective properties such as antioxidant, antiapoptotic, immune response modulator, and neurogenic, among others; it has been considered a therapeutic target for treating many disorders.

METHODS

The controlled cortical impact (CCI) model was used to assess the effect of recombinant human thioredoxin 1 (rhTrx1) (1 μg/2 μL, intracortical) on rats subjected to TBI at two different times of the light-dark cycle (01:00 and 13:00 h). We analyzed the food intake, body weight loss, motor coordination, pain perception, and histology in specific hippocampus (CA1, CA2, CA3, and Dental Gyrus) and striatum (caudate-putamen) areas.

RESULTS

Body weight loss, reduced food intake, spontaneous pain, motor impairment, and neuronal damage in specific hippocampus and striatum regions are more evident in rats subjected to TBI in the light phase than in the dark phase of the cycle and in groups that did not receive rhTrx1 or minocycline (as positive control). Three days after TBI, there is a recovery in body weight, food intake, motor impairment, and pain, which is more pronounced in the rats subjected to TBI at the dark phase of the cycle and those that received rhTrx1 or minocycline.

CONCLUSIONS

Knowing the time of day a TBI occurs in connection to the neuroprotective mechanisms of the immune response in diurnal variation and the usage of the Trx1 protein might have a beneficial therapeutic impact in promoting quick recovery after a TBI.

Modulating chronic outcomes after pediatric traumatic brain injury: Distinct effects of social and environmental enrichment

Impairments in social and cognitive function are a common consequence of pediatric traumatic brain injury (TBI). Rehabilitation has the potential to promote optimal behavioral recovery. Here, we evaluated whether an enhanced social and/or cognitive environment could improve long-term outcomes in a preclinical model of pediatric TBI. Male C57Bl/6 J mice received a moderately-severe TBI or sham procedure at postnatal day 21. After one week, mice were randomized to different social conditions (minimal socialization, n = 2/cage; or social grouping, n = 6/cage), and housing conditions (standard cage, or environmental enrichment (EE), incorporating sensory, motor, and cognitive stimuli). After 8 weeks, neurobehavioral outcomes were assessed, followed by post-mortem neuropathology. We found that TBI mice exhibited hyperactivity, spatial memory deficits, reduced anxiety-like behavior, and reduced sensorimotor performance compared to age-matched sham controls. Pro-social and sociosexual behaviors were also reduced in TBI mice. EE increased sensorimotor performance, and the duration of sociosexual interactions. Conversely, social housing reduced hyperactivity and altered anxiety-like behavior in TBI mice, and reduced same-sex social investigation. TBI mice showed impaired spatial memory retention, except for TBI mice exposed to both EE and group housing. In the brain, while TBI led to significant regional tissue atrophy, social housing had modest neuroprotective effects on hippocampal volumes, neurogenesis, and oligodendrocyte progenitor numbers. In conclusion, manipulation of the post-injury environment has benefit for chronic behavioral outcomes, but the benefits are specific to the type of enrichment available. This study improves understanding of modifiable factors that may be harnessed to optimize long-term outcomes for survivors of early-life TBI.

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.

Environmental enrichment improves traumatic brain injury-induced behavioral phenotype and associated neurodegenerative process

Traumatic brain injury (TBI) causes persistent cognitive impairment and neurodegeneration. Environmental enrichment (EE) refers to a housing condition that promotes sensory and social stimulation and improves cognition and motor performance but the underlying mechanisms responsible for such beneficial effects are not well defined. In this study, anesthetized adult rats received either a moderate-to-severe controlled cortical impact (CCI) or sham surgery and then were housed in either EE or standard conditions. The results showed a significant increase in protein nitration and oxidation of lipids, impaired cognition and motor performance, and augmented N-methyl-d-aspartate receptor subtype-1 (NMDAR1) levels. However, EE initiated 24 h after CCI resulted in reduced oxidative insult and microglial activation and significant improvement in beam-balance/walk performance and both spatial learning and memory. We hypothesize that following TBI there is an upstream activation of NMDAR that promotes oxidative insult and an inflammatory response, thereby resulting in impaired behavioral functioning but EE may exert a neuroprotective effect via sustained downregulation of NMDAR1.

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.

A combined therapeutic regimen of citalopram and environmental enrichment ameliorates attentional set-shifting performance after brain trauma

Traumatic brain injuries (TBI) have led to lasting deficits for an estimated 5.3 million American patients. Effective therapies for these patients remain scarce and each of the clinical trials stemming from success in experimental models has failed. We believe that the failures may be, in part, due to the lack of preclinical assessment of cognitive domains that widely affect clinical TBI. Specifically, the behavioral tasks in the TBI literature often do not focus on common executive impairments related to the frontal lobe such as cognitive flexibility. In previous work, we have demonstrated that the attentional set-shifting test (AST), a task analogous to the clinically-employed Wisconsin Card Sorting Test (WCST), could be used to identify cognitive flexibility impairments following controlled cortical impact (CCI) injury. In this study, we hypothesized that both the administration of the antidepressant drug citalopram (CIT) and exposure to a preclinical model of neurorehabilitation, environmental enrichment (EE), would attenuate cognitive performance deficits on AST when provided alone and lead to greater benefits when administered in combination. Adult male rats were subjected to a moderate-severe CCI or sham injury. Rats were randomly divided into experimental groups that included surgical injury, drug therapy, and housing condition. We observed that both CIT and EE provided significant cognitive recovery when administered alone and reversal learning performance recovery increased the most when the therapies were combined (p < 0.05). Ongoing studies continue to evaluate novel ways of assessing more clinically relevant measurements of high order cognitive TBI-related impairments in the rat model.

Intranasally Administered L-Myc-Immortalized Human Neural Stem Cells Migrate to Primary and Distal Sites of Damage after Cortical Impact and Enhance Spatial Learning

As the success of stem cell-based therapies is contingent on efficient cell delivery to damaged areas, neural stem cells (NSCs) have promising therapeutic potential because they inherently migrate to sites of central nervous system (CNS) damage. To explore the possibility of NSC-based therapy after traumatic brain injury (TBI), isoflurane-anesthetized adult male rats received a controlled cortical impact (CCI) of moderate severity (2.8 mm deformation at 4 m/s) or sham injury (i.e., no cortical impact). Beginning 1-week post-injury, the rats were immunosuppressed and 1 × 106 human NSCs (LM-NS008.GFP.fLuc) or vehicle (VEH) (2% human serum albumen) were administered intranasally (IN) on post-operative days 7, 9, 11, 13, 15, and 17. To evaluate the spatial distributions of the LM-NSC008 cells, half of the rats were euthanized on day 25, one day after completion of the cognitive task, and the other half were euthanized on day 46. 1 mm thick brain sections were optically cleared (CLARITY), and volumes were imaged by confocal microscopy. In addition, LM-NSC008 cell migration to the TBI site by immunohistochemistry for human-specific Nestin was observed at day 39. Acquisition of spatial learning was assessed in a well-established Morris water maze task on six successive days beginning on post-injury day 18. IN administration of LM-NSC008 cells after TBI (TBI + NSC) significantly facilitated spatial learning relative to TBI + VEH rats (p < 0.05) and had no effect on sham + NSC rats. Overall, these data indicate that IN-administered LM-NSC008 cells migrate to sites of TBI damage and that their presence correlates with cognitive improvement. Future studies will expand on these preliminary findings by evaluating other LM-NSC008 cell dosing paradigms and evaluating mechanisms by which LM-NSC008 cells contribute to cognitive recovery.

Preclinical neurorehabilitation with environmental enrichment confers cognitive and histological benefits in a model of pediatric asphyxial cardiac arrest

Pediatric asphyxial cardiac arrest (ACA) often leaves children with physical, cognitive, and emotional disabilities that affect overall quality of life, yet rehabilitation is neither routinely nor systematically provided. Environmental enrichment (EE) is considered a preclinical model of neurorehabilitation and thus we sought to investigate its efficacy in our established model of pediatric ACA. Male Sprague-Dawley rat pups (post-natal day 16-18) were randomly assigned to ACA (9.5 min) or Sham injury. After resuscitation, the rats were assigned to 21 days of EE or standard (STD) housing during which time motor, cognitive, and anxiety-like (i.e., affective) outcomes were assessed. Hippocampal CA1 cells were quantified on post-operative day-22. Both ACA + STD and ACA + EE performed worse on beam-balance vs. Sham controls (p < 0.05) and did not differ from one another overall (p > 0.05); however, a single day analysis on the last day of testing revealed that the ACA + EE group performed better than the ACA + STD group (p < 0.05) and did not differ from the Sham controls (p > 0.05). Both Sham groups performed better than ACA + STD (p < 0.05) but did not differ from ACA + EE (p > 0.05) in the open field test. Spatial learning and declarative memory were improved and CA1 neuronal loss was attenuated in the ACA + EE vs. ACA + STD group (p < 0.05). Collectively, the data suggest that providing rehabilitation after pediatric ACA can reduce histopathology and improve motor and cognitive ability.

Disruption of basal forebrain cholinergic neurons after traumatic brain injury does not compromise environmental enrichment-mediated cognitive benefits

Environmental enrichment (EE) attenuates traumatic brain injury (TBI)-induced loss of medial septal (MS) choline acetyltransferase (ChAT)-cells and enhances spatial learning and memory vs. standard (STD) housing. Whether basal forebrain cholinergic neurons (BFCNs) are important mediators of EE-induced benefits after TBI requires further investigation. Anesthetized female rats were randomly assigned to intraseptal infusions of the immunotoxin 192-IgG-saporin (SAP; 0.22 μg in 1.0 μL) or vehicle (VEH; 1.0 μL IgG) followed immediately by a cortical impact (2.8 mm deformation depth at 4 m/s) or sham injury and divided into EE and STD housing. Spatial learning and memory retention were assessed on post-operative days 14-19. MS ChAT⁺ cells were quantified at 3 weeks. SAP significantly reduced ChAT⁺ cells in both the EE and STD groups. Cognitive performance was improved in the EE groups, regardless of VEH or SAP infusion, vs. the STD-housed groups (p's < 0.05). No cognitive differences were revealed between the TBI + EE + SAP and TBI + EE + VEH groups (p > 0.05) or between the TBI + STD + SAP and TBI + STD + VEH groups (p > 0.05). These data show that despite significant MS ChAT⁺ cell loss, the EE-mediated benefit in cognitive recovery is not compromised.

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.

Environmental enrichment and amantadine confer individual but nonadditive enhancements in motor and spatial learning after controlled cortical impact injury

Environmental enrichment (EE) and amantadine (AMT) enhance motor and cognitive outcome after experimental traumatic brain injury (TBI). However, there are no data on the effects of combining these two therapies. Hence, the aim of the current study was to combine EE and AMT after TBI to determine if their net effect further enhances motor and cognitive performance. Anesthetized adult male rats received either a cortical impact of moderate severity or sham injury and then were randomly assigned to EE or standard (STD) housing and once daily administration of AMT (20 mg/kg; i.p.) or saline vehicle (VEH, 1 mL/kg; i.p.) beginning 24 h after injury for 19 days. Motor and cognitive function were assessed on post-surgical days 1-5 and 14-19, respectively. Cortical lesion volume was quantified on day 21. There were no statistical differences among the sham groups regardless of therapy, so the data were pooled. EE, AMT, and their combination (EE + AMT) improved beam-balance, but only EE and EE + AMT enhanced beam-walking. All three treatment paradigms improved spatial learning and memory relative to the VEH-treated STD controls (p < 0.05). No differences were revealed between the EE groups, regardless of treatment, but both were better than the AMT-treated STD group on beam-walking and spatial learning (p < 0.05). Both EE groups equally reduced cortical lesion volume relative to the STD-housed AMT and VEH groups (p < 0.05). The results indicate that although beneficial on their own, EE + AMT do not provide additional benefits after TBI. It is important to note that the lack of additive effects using the current treatment and behavioral protocols does not detract from the benefits of each individual therapy. The findings provide insight for future combination studies.

Aripiprazole and environmental enrichment independently improve functional outcome after cortical impact injury in adult male rats, but their combination does not yield additional benefits

Typical antipsychotic drugs (APDs) with D₂antagonistic properties impede functional outcome after experimental traumatic brain injury (TBI) and reduce the effectiveness of environmental enrichment (EE). Here we test the hypothesis that aripiprazole (ARIP), an atypical APD with partial D₂and 5-HT_1Areceptor agonist activities will improve recovery after TBI and when combined with EE will further enhance the benefits. Anesthetized adult male rats received either a controlled cortical impact of moderate severity or sham injury and then were randomly assigned to EE or standard (STD) housing and once daily intraperitoneal injections of ARIP (0.1 mg/kg) or vehicle (VEH; 1.0 mL/kg) beginning 24 h after injury for 19 days. Motor (beam-walking time and beam-walk score) and cognitive (acquisition of spatial learning and memory) outcomes were assessed on post-operative days 1-5 and 14-19, respectively. Cortical lesion volume was quantified on day 21. There were no statistical differences among the sham groups, regardless of housing or treatment, so the data were pooled. The SHAM group performed better than all TBI groups on motor and spatial learning (p < 0.05) but did not differ from either EE group on memory retention. Regarding TBI, both EE groups improved motor and cognitive outcomes vs. the VEH-treated STD group (p < 0.05) but did not differ from one another (p > 0.05). The ARIP-treated STD group performed better than the VEH-treated STD group on beam-walk score and spatial learning (p < 0.05), but not beam-walking time or memory retention (p > 0.05). Cortical lesion volume was smaller in all treated groups compared to the TBI + STD + VEH group (p < 0.05). The data replicate previous work and extend the findings by demonstrating that 1) ARIP promotes recovery after TBI, but combining treatments does not yield additional benefits, which is contrary to the hypothesis, and 2) unlike APDs that exhibit D₂ receptor antagonism, ARIP does not impede rehabilitation (i.e., EE).

Intermittent Administration of Haloperidol after Cortical Impact Injury Neither Impedes Spontaneous Recovery Nor Attenuates the Efficacy of Environmental Enrichment

The administration of haloperidol (HAL) once-daily for 19 days after experimental traumatic brain injury (TBI) impedes recovery and attenuates the efficacy of environmental enrichment (EE). However, it is unknown how intermittent administration of HAL affects the recovery process when paired with EE. Addressing the uncertainty is relevant because daily HAL is not always warranted to manage TBI-induced agitation in the clinic, and indeed intermittent therapy may be a more common approach. Hence, the aim of the study was to test the hypothesis that intermittent HAL would neither impair recovery in standard (STD)-housed controls nor attenuate the efficacy of EE. Anesthetized adult male rats received a cortical impact or sham injury and then were housed in STD or EE conditions. Beginning 24 h later, HAL (0.5 mg/kg; intraperitoneally [i.p.]) was administered either once-daily for 19 days or once every other day, whereas vehicle (VEH; 1 mL/kg; i.p.) was administered once daily. Motor performance and cognition were assessed on post-injury days 1-5 and 14-19, respectively. Cortical lesion volume was quantified on day 21. SHAM controls performed better than all TBI groups on motor and spatial learning [p < 0.05], but did not differ from the TBI + EE + daily VEH group on memory retention [p > 0.05]. The TBI + EE + daily VEH and TBI + EE + intermittent HAL groups did not differ from one another on beam-walk or spatial learning [p > 0.05], and both performed better than all other TBI groups [p < 0.05]. In contrast, the TBI + STD + daily HAL group performed worse than all TBI groups on spatial learning [p < 0.05]. No difference in any endpoint was revealed between the TBI + STD + intermittent HAL and TBI + STD + daily VEH groups [p > 0.05]. The results support the hypothesis that HAL is not detrimental when provided intermittently. If translatable to the clinic, intermittent HAL may be used to control TBI-induced agitation without negatively affecting spontaneous recovery or rehabilitative efficacy.

Delayed and Abbreviated Environmental Enrichment after Brain Trauma Promotes Motor and Cognitive Recovery That Is Not Contingent on Increased Neurogenesis

Environmental enrichment (EE) confers motor and cognitive recovery in pre-clinical models of traumatic brain injury (TBI), and neurogenesis has been attributed to mediating the benefits. Whether that ascription is correct has not been fully investigated. Hence, the goal of the current study is to further clarify the possible role of learning-induced hippocampal neurogenesis on functional recovery after cortical impact or sham injury by utilizing two EE paradigms (i.e., early + continuous, initiated immediately after TBI and presented 24 h/day; and delayed + abbreviated, initiated 4 days after TBI for 6 h/day) and comparing them to one another as well as to standard (STD) housed controls. Motor and cognitive performance was assessed on post-operative Days 1-5 and 14-19, respectively, for the STD and early + continuous EE groups and on Days 4-8 and 17-22, for the delayed + abbreviated EE groups. Rats were injected with bromodeoxyuridine (BrdU, 500 mg/ kg; intraperitoneally) for 3 days (12 h apart) before cognitive training and sacrificed 1 week later for quantification of BrdU+ and doublecortin (DCX+) labeled cells. Both early + continuous and delayed + abbreviated EE promoted motor and cognitive recovery after TBI, relative to STD (p < 0.05), and did not differ from one another (p > 0.05). However, only early + continuous EE increased DCX+ cells beyond the level of STD-housed controls (p < 0.05). No effect of EE on non-injured controls was observed. Based on these data, two novel conclusions emerged. First, EE does not need to be provided early and continuously after TBI to confer benefits, which lends credence to the delayed + abbreviated EE paradigm as a relevant pre-clinical model of neurorehabilitation. Second, the functional recovery observed after TBI in the delayed + abbreviated EE paradigm is not contingent on increased hippocampal neurogenesis. Future studies will elucidate alternate viable mechanisms mediating the benefits induced by EE.

Systemic administration of donepezil attenuates the efficacy of environmental enrichment on neurobehavioral outcome after experimental traumatic brain injury

BACKGROUND

The acetylcholinesterase inhibitor (AChEI) donepezil (DON) is recommended as a potential treatment for cognition after clinical traumatic brain injury (TBI) and therefore may be prescribed as an adjunct therapy during rehabilitation. However, a dose-response study evaluating DON after a controlled cortical impact (CCI) injury in rats did not reveal cognitive benefits.

OBJECTIVE

The aim of this study was to determine the effect of DON on behavioral and histological outcome when combined with environmental enrichment (EE), a preclinical model of neurorehabilitation. It was hypothesized that the combined treatments would produce a synergistic effect yielding improved recovery over neurorehabilitation alone.

METHODS

Isoflurane-anesthetized adult male rats received a CCI or sham injury and then were randomly assigned to EE or standard (STD) housing plus systemic injections of DON (0.25 mg/kg) or vehicle (VEH; 1.0 mL/kg saline) once daily for 19 days beginning 24 hr after injury. Function was assessed by established motor and cognitive tests on post-injury days 1-5 and 14-19, respectively. Cortical lesion volume was quantified on day 19.

RESULTS

DON was ineffective when administered alone. In contrast, EE conferred significant motor and cognitive benefits, and reduced cortical lesion volume vs. STD (p < 0.05). Combining the therapies weakened the efficacy of rehabilitation as revealed by diminished motor and cognitive recovery in the TBI+EE+DON group vs. the TBI+EE+VEH group (p < 0.05).

CONCLUSION

These data replicate previous findings showing that EE is beneficial and DON is ineffective after CCI and add to the literature a novel and unpredicted finding that supports neither the hypothesis nor the use of DON for TBI. Investigation of other AChEIs after CCI injury is necessary to gain further insight into the value of this therapeutic strategy.

Longitudinal Microstructural Changes in Traumatic Brain Injury in Rats: A Diffusional Kurtosis Imaging, Histology, and Behavior Study

BACKGROUND AND PURPOSE

Traumatic brain injury is a major public health problem worldwide. Accurately evaluating the brain microstructural changes in traumatic brain injury is crucial for the treatment and prognosis assessment. This study aimed to assess the longitudinal brain microstructural changes in traumatic brain injury in the rat using diffusional kurtosis imaging.

MATERIALS AND METHODS

Diffusional kurtosis imaging was performed in a group of 5 rats at preinjury and 3, 14, and 28 days after traumatic brain injury. The diffusional kurtosis imaging parameters were measured in the bilateral cortex, hippocampus, and corpus callosum. Another 4 groups of 5 rats were used in brain immunohistochemistry analysis of neuron (neuron-specific nuclear protein [NeuN]), astroglia (glial fibrillary acidic protein [GFAP]), microglia (ionized calcium binding adaptor molecule 1 [Iba-1]), and myelin (myelin basic protein [MBP]) in the same area as the diffusional kurtosis imaging parameter measurements. Furthermore, 2 groups of 6 rats underwent a Morris water maze test at 28 days after traumatic brain injury. The diffusional kurtosis imaging parameters, immunohistochemistry results, and Morris water maze test results were compared longitudinally or between traumatic brain injury and control groups.

RESULTS

Compared with baseline, traumatic brain injury in the rat showed higher mean kurtosis and mean diffusivity values in the ipsilateral perilesional cortex and hippocampus and lower fractional anisotropy values in the corpus callosum (P < .05). The traumatic brain injury group showed higher staining of GFAP and Iba-1 and lower immunohistochemistry staining of NeuN and MBP in all ipsilateral ROIs (P < .05). There was no significant difference in the contralateral ROIs in diffusional kurtosis imaging parameters or immunohistochemistry results. The Morris water maze test revealed lower platform crossing times in the probe test (P < .05).

CONCLUSIONS

Our study indicated that there were longitudinal changes in diffusional kurtosis imaging parameters, accompanied by multiple pathologic changes at different time points following traumatic brain injury, and that mean kurtosis is more sensitive to detect microstructural changes, especially in gray matter, than mean diffusivity and fractional anisotropy.

Environmental enrichment, alone or in combination with various pharmacotherapies, confers marked benefits after traumatic brain injury

Traumatic brain injury (TBI) is a significant health care issue that affects over ten million people worldwide. Treatment options are limited with numerous failures resulting from single therapies. Fortunately, several preclinical studies have shown that combination treatment strategies may afford greater improvement and perhaps can lead to successful clinical translation, particularly if one of the therapies is neurorehabilitation. The aim of this review is to highlight TBI studies that combined environmental enrichment (EE), a preclinical model of neurorehabilitation, with pharmacotherapies. A series of PubMed search strategies yielded only nine papers that fit the criteria. The consensus is that EE provides robust neurobehavioral, cognitive, and histological improvement after experimental TBI and that the combination of EE with some pharmacotherapies can lead to benefits beyond those revealed by single therapies. However, it is noted that EE can be challenged by drugs such as the acetylcholinesterase inhibitor, donepezil, and the antipsychotic drug, haloperidol, which attenuate its efficacy. These findings may help shape clinical neurorehabilitation strategies to more effectively improve patient outcome. Potential mechanisms for the EE and pharmacotherapy-induced effects are also discussed. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

Elucidating opportunities and pitfalls in the treatment of experimental traumatic brain injury to optimize and facilitate clinical translation

The aim of this review is to discuss the research presented in a symposium entitled "Current progress in characterizing therapeutic strategies and challenges in experimental CNS injury" which was presented at the 2016 International Behavioral Neuroscience Society annual meeting. Herein we discuss diffuse and focal traumatic brain injury (TBI) and ensuing chronic behavioral deficits as well as potential rehabilitative approaches. We also discuss the effects of stress on executive function after TBI as well as the response of the endocrine system and regulatory feedback mechanisms. The role of the endocannabinoids after CNS injury is also discussed. Finally, we conclude with a discussion of antipsychotic and antiepileptic drugs, which are provided to control TBI-induced agitation and seizures, respectively. The review consists predominantly of published data.

Rehabilitative Success After Brain Trauma by Augmenting a Subtherapeutic Dose of Environmental Enrichment With Galantamine

BACKGROUND

Environmental enrichment (EE) confers benefits after traumatic brain injury (TBI) when provided daily for > 6 hours, but not 2 or 4 hours, which more accurately reflects the daily amount of clinical rehabilitation. The lack of benefit with sub-therapeutic EE suggests that augmentation with galantamine (GAL), which enhances cognition after TBI, may be indicated to confer benefits.

OBJECTIVE

To test the hypothesis that 2 and 4 hours of EE paired with GAL will provide benefits comparable to 24 hours of EE alone. Moreover, all EE groups will perform better than the standard (STD)-housed GAL group.

METHODS

Anesthetized rats received a TBI or sham injury and then were randomized to receive intraperitoneal injections of GAL (2 mg/kg) or saline vehicle (VEH; 1 mL/kg) beginning 24 hours after surgery and once daily while receiving EE for 2, 4, or 24 hours. Motor and cognitive assessments were conducted on postoperative days 1-5 and 14-19, respectively.

RESULTS

Motor function was significantly improved in the TBI + 24-hour EE group versus the TBI + STD + VEH and TBI + STD + GAL groups ( P < .05). Cognitive performance was enhanced in all EE groups as well as in the TBI + STD + GAL versus TBI + STD + VEH ( P < .05). Moreover, the 2- and 4-hour EE groups receiving GAL did not differ from the 24-hour EE group ( P > .05) and performed better than GAL alone ( P < .05).

CONCLUSIONS

The findings support the hypothesis and have clinical relevance because, often, only brief rehabilitation may be available in the clinic and, thus, augmenting with a pharmacotherapy such as GAL may lead to outcomes that are significantly better than either therapy alone.

Comparable impediment of cognitive function in female and male rats subsequent to daily administration of haloperidol after traumatic brain injury

Antipsychotic drugs, such as haloperidol (HAL), are prescribed in the clinic to manage traumatic brain injury (TBI)-induced agitation. While preclinical studies have consistently shown that once-daily administration of HAL hinders functional recovery after TBI in male rats, its effects in females are unknown. Hence, the objective of this study was to directly compare neurobehavioral and histological outcomes in both sexes to determine whether the reported deleterious effects of HAL extend to females. Anesthetized adult female and male rats received either a controlled cortical impact (CCI) or sham injury and then were randomly assigned to a dosing regimen of HAL (0.5mg/kg, i.p.) or vehicle (VEH; 1mL/kg, i.p.) that was initiated 24h after injury and continued once daily for 19 consecutive days. Motor function was tested using established beam-balance/walk protocols on post-operative days 1-5 and acquisition of spatial learning was assessed with a well-validated Morris water maze task on days 14-19. Cortical lesion volume was quantified at 21days. No statistical differences were revealed between the HAL and VEH-treated sham groups and thus they were pooled for each sex. HAL only impaired motor recovery in males (p<0.05), but significantly diminished spatial learning in both sexes (p<0.05). Females, regardless of treatment, exhibited smaller cortical lesions vs VEH-treated males (p<0.05). Taken together, the data show that daily HAL does not prohibit motor recovery in females, but does negatively impact cognition. These task-dependent differential effects of HAL in female vs male rats may have clinical significance as they can direct therapy.

Establishment of an ideal time window model in hypothermic-targeted temperature management after traumatic brain injury in rats

Although hypothermic-targeted temperature management (HTTM) holds great potential for the treatment of traumatic brain injury (TBI), translation of the efficacy of hypothermia from animal models to TBI patientshas no entire consistency. This study aimed to find an ideal time window model in experimental rats which was more in accordance with clinical practice through the delayed HTTM intervention. Sprague-Dawley rats were subjected to unilateral cortical contusion injury and received therapeutic hypothermia at 15mins, 2 h, 4 h respectively after TBI. The neurological function was evaluated with the modified neurological severity score and Morris water maze test. The brain edema and morphological changes were measured with the water content and H&E staining. Brain sections were immunostained with antibodies against DCX (a neuroblast marker) and GFAP (an astrocyte marker). The apoptosis levels in the ipsilateral hippocampi and cortex were examined with antibodies against the apoptotic proteins Bcl-2, Bax, and cleaved caspase-3 by the immunofluorescence and western blotting. The results indicated that each hypothermia therapy group could improve neurobehavioral and cognitive function, alleviate brain edema and reduce inflammation. Furthermore, we observed that therapeutic hypothermia increased DCX expression, decreased GFAP expression, upregulated Bcl-2 expression and downregulated Bax and cleaved Caspase-3 expression. The above results suggested that HTTM at 2h or even at 4h post-injury revealed beneficial brain protection similarly, despite the best effect at 15min post-injury. These findings may provide relatively ideal time window models, further making the following experimental results more credible and persuasive.

Refining environmental enrichment to advance rehabilitation based research after experimental traumatic brain injury

The typical environmental enrichment (EE) paradigm, which consists of continuous exposure after experimental traumatic brain injury (TBI), promotes behavioral and histological benefits. However, rehabilitation is often abbreviated in the clinic and administered in multiple daily sessions. While recent studies have demonstrated that a once daily 6-hr bout of EE confers benefits comparable to continuous EE, breaking the therapy into two shorter sessions may increase novelty and ultimately enhance recovery. Hence, the aim of the study was to test the hypothesis that functional and histological outcomes will be significantly improved by daily preclinical neurorehabilitation consisting of two 3-hr periods of EE vs. a single 6-hr session. Anesthetized adult male rats received a controlled cortical impact of moderate-to-severe injury (2.8mm tissue deformation at 4m/s) or sham surgery and were then randomly assigned to groups receiving standard (STD) housing, a single 6-hr session of EE, or two 3-hr sessions of EE daily for 3weeks. Motor function (beam-balance/traversal) and acquisition of spatial learning/memory retention (Morris water maze) were assessed on post-operative days 1-5 and 14-19, respectively. Cortical lesion volume was quantified on day 21. Both EE conditions improved motor function and acquisition of spatial learning, and reduced cortical lesion volume relative to STD housing (p<0.05), but did not differ from one another in any endpoint (p>0.05). The findings replicate previous work showing that 6-hr of EE daily is sufficient to confer behavioral and histological benefits after TBI and extend the findings by demonstrating that the benefits are comparable regardless of how the 6-hrs of EE are accrued. The relevance of the finding is that it can be extrapolated to the clinic and may benefit patients who cannot endure a single extended period of neurorehabilitation.