Exposure to environmental complexity promotes recovery of cognitive function after traumatic brain injury

Social deficits mirror delayed cerebrovascular dysfunction after traumatic brain injury

Traumatic brain injury (TBI) survivors face debilitating long-term psychosocial consequences, including social isolation and depression. TBI modifies neurovascular physiology and behavior but the chronic physiological implications of altered brain perfusion on social interactions are unknown. Adult C57/BL6 male mice received a moderate cortical TBI, and social behaviors were assessed at baseline, 3-, 7-, 14-, 30-, and 60-days post injury (dpi). Magnetic resonance imaging (MRI, 9.4T) using dynamic susceptibility contrast perfusion weighted MRI were acquired. At 60dpi mice underwent histological angioarchitectural mapping. Analysis utilized standardized protocols followed by cross-correlation metrics. Social behavior deficits at 60dpi emerged as reduced interactions with a familiar cage-mate (partner) that mirrored significant reductions in cerebral blood flow (CBF) at 60dpi. CBF perturbations were dynamic temporally and across brain regions including regions known to regulate social behavior such as hippocampus, hypothalamus, and rhinal cortex. Social isolation in TBI-mice emerged with a significant decline in preference to spend time with a cage mate. Cortical vascular density was also reduced corroborating the decline in brain perfusion and social interactions. Thus, the late emergence of social interaction deficits mirrored the reduced vascular density and CBF in regions known to be involved in social behaviors. Vascular morphology and function improved prior to the late decrements in social function and our correlations strongly implicate a linkage between vascular density, cerebral perfusion, and social interactions. Our study provides a clinically relevant timeline of alterations in social deficits alongside functional vascular recovery that can guide future therapeutics.

A bridge to recovery: Acute amantadine prior to environmental enrichment after brain trauma augments cognitive benefit

Environmental enrichment (EE) facilitates motor and cognitive recovery after traumatic brain injury (TBI). Historically, EE has been provided immediately and continuously after TBI, but this paradigm does not model the clinic where rehabilitation is typically not initiated until after critical care. Yet, treating TBI early may facilitate recovery. Hence, we sought to provide amantadine (AMT) as a bridge therapy before commencing EE. It was hypothesized that bridging EE with AMT would augment motor and cognitive benefits. Anesthetized adult male rats received a cortical impact (2.8 mm deformation at 4 m/s) or sham surgery and then were housed in standard (STD) conditions where they received intraperitoneal AMT (10 mg/kg or 20 mg/kg) or saline vehicle (VEH; 1 mL/kg) beginning 24 h after surgery and once daily during the 6-day bridge phase or once daily for 19 days for the non-bridge groups (i.e., continuously STD-housed) to compare the effects of acute AMT plus EE vs. chronic AMT alone. Abbreviated EE, which was presented to closer emulate clinical rehabilitation (e.g., 6 h/day), began on day 7 for the AMT bridge and chronic EE groups. Motor (beam-walking) and cognition (acquisition of spatial learning and memory) were assessed on days 7-11 and 14-19, respectively. Cortical lesion volume and hippocampal cell survival were quantified on day 21. EE, whether provided in combination with VEH or AMT, and AMT (20 mg/kg) + STD, benefitted motor and cognition vs. the STD-housed VEH and AMT (10 mg/kg) groups (p < 0.05). The AMT (20 mg/kg) + EE group performed better than the VEH + EE, AMT (10 mg/kg) + EE, and AMT (20 mg/kg) + STD groups in the acquisition of spatial learning (p < 0.05) but did not differ in motor function (p > 0.05). All groups receiving EE exhibited decreased cortical lesion volumes and increased CA3 neuron survival relative to the STD-housed groups (p < 0.05) but did not differ from one another (p > 0.05). The added cognitive benefit achieved by bridging EE with AMT (20 mg/kg) supports the hypothesis that the temporal separation of combinational therapies is more effective after TBI.

Efficacy of a music-based intervention in a preclinical model of traumatic brain injury: An initial foray into a novel and non-pharmacological rehabilitative therapy

Traumatic brain injury (TBI) causes neurobehavioral and cognitive impairments that negatively impact life quality for millions of individuals. Because of its pernicious effects, numerous pharmacological interventions have been evaluated to attenuate the TBI-induced deficits or to reinstate function. While many such pharmacotherapies have conferred benefits in the laboratory, successful translation to the clinic has yet to be achieved. Given the individual, medical, and societal burden of TBI, there is an urgent need for alternative approaches to attenuate TBI sequelae and promote recovery. Music based interventions (MBIs) may hold untapped potential for improving neurobehavioral and cognitive recovery after TBI as data in normal, non-TBI, rats show plasticity and augmented cognition. Hence, the aim of this study was to test the hypothesis that providing a MBI to adult rats after TBI would improve cognition, neurobehavior, and histological endpoints. Adult male rats received a moderate-to-severe controlled cortical impact injury (2.8 mm impact at 4 m/s) or sham surgery (n = 10-12 per group) and 24 h later were randomized to classical Music or No Music (i.e., ambient room noise) for 3 h/day from 19:00 to 22:00 h for 30 days (last day of behavior). Motor (beam-walk), cognitive (acquisition of spatial learning and memory), anxiety-like behavior (open field), coping (shock probe defensive burying), as well as histopathology (lesion volume), neuroplasticity (BDNF), and neuroinflammation (Iba1, and CD163) were assessed. The data showed that the MBI improved motor, cognitive, and anxiety-like behavior vs. No Music (p's < 0.05). Music also reduced cortical lesion volume and activated microglia but increased resting microglia and hippocampal BDNF expression. These findings support the hypothesis and provide a compelling impetus for additional preclinical studies utilizing MBIs as a potential efficacious rehabilitative therapy for TBI.

Neuroprotective potential of intranasally delivered L-myc immortalized human neural stem cells in female rats after a controlled cortical impact injury

Efficacious stem cell-based therapies for traumatic brain injury (TBI) depend on successful delivery, migration, and engraftment of stem cells to induce neuroprotection. L-myc expressing human neural stem cells (LMNSC008) demonstrate an inherent tropism to injury sites after intranasal (IN) administration. We hypothesize that IN delivered LMNSC008 cells migrate to primary and secondary injury sites and modulate biomarkers associated with neuroprotection and tissue regeneration. To test this hypothesis, immunocompetent adult female rats received either controlled cortical impact injury or sham surgery. LMNSC008 cells or a vehicle were administered IN on postoperative days 7, 9, 11, 13, 15, and 17. The distribution and migration of eGFP-expressing LMNSC008 cells were quantified over 1 mm-thick optically cleared (CLARITY) coronal brain sections from TBI and SHAM controls. NSC migration was observed along white matter tracts projecting toward the hippocampus and regions of TBI. ELISA and Nanostring assays revealed a shift in tissue gene expression in LMNSC008 treated rats relative to controls. LMNSC008 treatment reduced expression of genes and pathways involved in inflammatory response, microglial function, and various cytokines and receptors. Our proof-of-concept studies, although preliminary, support the rationale of using intranasal delivery of LMNSC008 cells for functional studies in preclinical models of TBI and provide support for potential translatability in TBI patients.

Neuroprotective potential of intranasally delivered L-myc immortalized human neural stem cells in female rats after a controlled cortical impact injury

Efficacious stem cell-based therapies for traumatic brain injury (TBI) depend on successful delivery, migration, and engraftment of stem cells to induce neuroprotection. L-myc expressing human neural stem cells (LMNSC008) demonstrate an inherent tropism to injury sites after intranasal (IN) administration. We hypothesize that IN delivered LMNSC008 cells migrate to primary and secondary injury sites and modulate biomarkers associated with neuroprotection and tissue regeneration. To test this, immunocompetent adult female rats received a controlled cortical impact injury (CCI) or sham surgery. LMNSC008 cells or a vehicle (VEH) were administered IN on postoperative days 7, 9, 11, 13, 15, and 17. The distribution and migration of eGFP-expressing LMNSC008 cells were quantified over 1 mm-thick optically cleared (CLARITY) coronal brain sections from TBI and SHAM controls. NSC migration was observed along white matter tracts projecting toward the hippocampus and regions of TBI. ELISA and Nanostring assays revealed a shift in tissue gene expression in LMNSC008 treated rats relative to controls. LMNSC008 treatment reduced expression of genes and pathways involved in inflammatory response, microglial function, and various cytokines and receptors. The data demonstrate a robust proof-of-concept for LMNSC008 therapy for TBI and provides a strong rationale for IN delivery for translation in TBI patients.

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.

Duration of Environmental Enrichment Determines Astrocyte Number and Cervical Lymph Node T Lymphocyte Proportions but Not the Microglial Number in Middle-Aged C57BL/6 Mice

Environmental enrichment (EE) has been shown to modulate behavior and immunity. We recently reported that both short and long-term EE enhance baseline locomotion and alleviate depressive-like behavior, but only long-term EE affects locomotion adversely in a threatening environment and enhances anxiety-like behavior in middle-age mice. We have now investigated whether the observed changes in behavior after short- and long-term EE were associated with underlying immune changes. Hence, at the end of behavioral testing, mice were sacrificed, and brains and cervical lymph nodes were collected to investigate the differential effects of the duration of EE (short- and long-term) on the number of immunopositive glial cells in the dentate gyrus, CA1, CA2, and CA3 regions of the hippocampus and proportions of T cell subsets in the cervical lymph nodes using immunohistochemistry and flow cytometry, respectively. EE, regardless of duration, caused an increase in microglia number within the dentate gyrus, CA1 and CA3 hippocampal regions, but only long-term EE increased astrocytes number within the dentate gyrus and CA3 hippocampal regions. A significantly higher proportion of CD8⁺ naive T cells was observed after long-term EE vs. short-term EE. No significant differences were observed in the proportion of central memory and effector memory T cells or early activated CD25⁺ cells between any of the test groups. Our results suggest that EE, irrespective of duration, enhances the numbers of microglia, but long-term EE is required to modify astrocyte number and peripheral T cell proportions in middle-aged mice. Our findings provide new insights into the therapeutic effects of EE on various brain disorders, which may be at least partly mediated by glial and neuroimmune modulation.

Beneficial effects of Spirulina platensis, voluntary exercise and environmental enrichment against adolescent stress induced deficits in cognitive functions, hippocampal BDNF and morphological remolding in adult female rats

Chronic exposure to stress during adolescent period has been demonstrated to impair cognitive functions and the dendritic morphology of pyramidal neurons in the rat hippocampal CA3 area. The present study investigated the combined protective effects of Spirulina platensis (SP), a supplement made from blue-green algae with neuroprotective properties, voluntary exercise (EX) and environmental enrichment (EE) against cognitive deficits, alternations in hippocampal BDNF levels, and abnormal neuronal remodeling in adult female rats (PND 60) induced by exposure to chronic restraint stress during adolescent period (PND 30-40). Rats were exposed to restraint stress (2 h/day for 10 days, PND 30-40). Then, the animals were subjected to treatment with SP (200 mg/kg/day), EX, EE and the combined treatments (SP + EX, and SP + EE) between PND 41 and 55 of age. Following the interventions, spatial learning and memory, passive avoidance performance, hippocampal dendritic morphology and BDNF levels were assessed. Results showed that plasma corticosterone levels increased at PND 40 and remained elevated at PND 55 and 70 in the stressed rats. Stressed rats showed deficits in spatial learning and memory and passive avoidance performance, decreased BDNF levels in the hippocampus, and reduced apical dendritic length and branch points of the CA3 pyramidal neurons. These deficits were alleviated by the SP, EX and EE, and the combined treatments, which accompanied with a decline in serum corticosterone in stressed animals. Some treatments even enhanced cognitive functions, and BDNF levels and neuroanatomical remodeling in the hippocampus of non-stressed animals. Our findings provide important evidences that physical activity, exposure to EE, and the SP treatment during adolescent period can protect against adolescent stress induced behavioral, biochemical and neuroanatomical impairments in adulthood.

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.

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.

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.

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".

Negative Impact of Female Sex on Outcomes from Repetitive Mild Traumatic Brain Injury in hTau Mice Is Age Dependent: A Chronic Effects of Neurotrauma Consortium Study

Traumatic brain injury (TBI) is a serious public health concern which strikes someone every 15 s on average in the US. Even mild TBI, which comprise as many as 75% of all TBI cases, carries long term consequences. The effects of age and sex on long term outcome from TBI is not fully understood, but due to the increased risk for neurodegenerative diseases after TBI it is important to understand how these factors influence the outcome from TBI. This study examined the neurobehavioral and neuropathological effects of age and sex on the outcome 15 days following repetitive mild traumatic brain injury (r-mTBI) in mice transgenic for human tau (hTau). These mice express the six human isoforms of tau but do not express endogenous murine tau and they develop tau pathology and memory impairment in an age-dependent manner. After 5 mild impacts, aged female mice showed motor impairments that were absent in aged male mice, as well as younger animals. Conversely, aged female sham mice outperformed all other groups of aged mice in a Barnes maze spatial memory test. Pathologically, increases in IBA-1 and GFAP staining typically seen in this model of r-mTBI showed the expected increases with both injury and age, but phosphorylated tau stained with CP13 in the hippocampus (reduced in female sham mice compared to males) and PHF1 in the cortex (reduced in female TBI mice compared to male TBI mice) showed the only histological signs of sex-dependent differences in these mice.

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.

Pathophysiology and Treatment of Memory Dysfunction After Traumatic Brain Injury

Memory is fundamental to everyday life, and cognitive impairments resulting from traumatic brain injury (TBI) have devastating effects on TBI survivors. A contributing component to memory impairments caused by TBI is alteration in the neural circuits associated with memory function. In this review, we aim to bring together experimental findings that characterize behavioral memory deficits and the underlying pathophysiology of memory-involved circuits after TBI. While there is little doubt that TBI causes memory and cognitive dysfunction, it is difficult to conclude which memory phase, i.e., encoding, maintenance, or retrieval, is specifically altered by TBI. This is most likely due to variation in behavioral protocols and experimental models. Additionally, we review a selection of experimental treatments that hold translational potential to mitigate memory dysfunction following injury.

Traumatic Brain Injury: Current Treatment Strategies and Future Endeavors

Traumatic brain injury (TBI) presents in various forms ranging from mild alterations of consciousness to an unrelenting comatose state and death. In the most severe form of TBI, the entirety of the brain is affected by a diffuse type of injury and swelling. Treatment modalities vary extensively based on the severity of the injury and range from daily cognitive therapy sessions to radical surgery such as bilateral decompressive craniectomies. Guidelines have been set forth regarding the optimal management of TBI, but they must be taken in context of the situation and cannot be used in every individual circumstance. In this review article, we have summarized the current status of treatment for TBI in both clinical practice and basic research. We have put forth a brief overview of the various subtypes of traumatic injuries, optimal medical management, and both the noninvasive and invasive monitoring modalities, in addition to the surgical interventions necessary in particular instances. We have overviewed the main achievements in searching for therapeutic strategies of TBI in basic science. We have also discussed the future direction for developing TBI treatment from an experimental perspective.

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.

Galantamine and Environmental Enrichment Enhance Cognitive Recovery after Experimental Traumatic Brain Injury But Do Not Confer Additional Benefits When Combined

Environmental enrichment (EE) enhances cognition after traumatic brain injury (TBI). Galantamine (GAL) is an acetylcholinesterase inhibitor that also may promote benefits. Hence, the aims of this study were to assess the efficacy of GAL alone (standard [STD] housing) and in combination with EE in adult male rats after TBI. The hypothesis was that both therapies would confer motor, cognitive, and histological benefits when provided singly, but that their combination would be more efficacious. Anesthetized rats received a controlled cortical impact or sham injury, then were randomly assigned to receive GAL (1, 2, or 3 mg/kg; intraperitoneally [i.p.]) or saline vehicle (VEH; 1 mL/kg; i.p.) beginning 24 h after surgery and once daily for 21 days (experiment 1). Motor (beam-balance/walk) and cognitive (Morris water maze [MWM]) assessments were conducted on post-operative Days 1-5 and 14-19, respectively. Cortical lesion volumes were quantified on Day 21. Sham controls were better versus all TBI groups. No differences in motor function or lesion volumes were observed among the TBI groups (p > 0.05). In contrast, GAL (2 mg/kg) enhanced MWM performance versus VEH and GAL (1 and 3 mg/kg; p < 0.05). In experiment 2, GAL (2 mg/kg) or VEH was combined with EE and the data were compared with the STD-housed groups from experiment 1. EE alone enhanced motor performance over the VEH-treated and GAL-treated (2 mg/kg) STD-housed groups (p < 0.05). Moreover, both EE groups (VEH or GAL) facilitated spatial learning and reduced lesion size versus STD + VEH controls (p < 0.05). No additional benefits were observed with the combination paradigm, which does not support the hypothesis. Overall, the data demonstrate that EE and once daily GAL (2 mg/kg) promote cognitive recovery after TBI. Importantly, the combined therapies did not negatively affect outcome and thus this therapeutic protocol may have clinical utility.

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

Environmental enrichment (EE) promotes behavioral recovery after experimental traumatic brain injury (TBI). However, the chronic rehabilitation provided in the laboratory is not analogous to the clinic where physiotherapy is typically limited. Moreover, females make up approximately 40% of the clinical TBI population, yet they are seldom studied in brain trauma. Hence, the goal of this study was to test the hypothesis that abbreviated EE would confer neurobehavioral, cognitive, and histological benefits in brain injured female rats. Anesthetized rats received a cortical impact of moderate-to-severe injury (2.8mm tissue deformation at 4m/s) or sham surgery and then were randomly assigned to groups receiving standard (STD) housing or 4h, 6h, or 24h of EE daily. Motor function (beam-balance/walk and rotarod) was assessed on post-operative days 1-5 and every other day from 1 to 19, respectively. Spatial learning/memory (Morris water maze) was evaluated on days 14-19, and cortical lesion volume was quantified on day 21. No statistical differences were appreciated among the sham controls in any assessment and thus the data were pooled. All EE conditions improved motor function and memory retention, but only 6h and 24h enhanced spatial learning relative to STD (p<0.05). Moreover, EE, regardless of duration reduced cortical lesion volume (p<0.05). These data confirm that abbreviated EE confers robust neurobehavioral, cognitive, and histological benefits in TBI female rats, which supports the hypothesis and strengthens the utility of EE as a pre-clinical model of neurorehabilitation.

Traumatic brain injury decreases AMP-activated protein kinase activity and pharmacological enhancement of its activity improves cognitive outcome

Prolonged metabolic suppression in the brain is a well-characterized secondary pathology of both experimental and clinical traumatic brain injury (TBI). AMP-activated kinase (AMPK) acts as a cellular energy sensor that, when activated, regulates various metabolic and catabolic pathways to decrease ATP consumption and increase ATP synthesis. As energy availability after TBI is suppressed, we questioned if increasing AMPK activity after TBI would improve cognitive outcome. TBI was delivered using the electromagnetic controlled cortical impact model on male Sprague-Dawley rats (275-300 g) and C57BL/6 mice (20-25 g). AMPK activity within the injured parietal cortex and ipsilateral hippocampus was inferred by western blots using phospho-specific antibodies. The consequences of acute manipulation of AMPK signaling on cognitive function were assessed using the Morris water maze task. We found that AMPK activity is decreased as a result of injury, as indicated by reduced AMPK phosphorylation and corresponding changes in the phosphorylation of its downstream targets: ribosomal protein S6 and Akt Substrate of 160 kDa (AS160). Increasing AMPK activity after injury using the drugs 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide or metformin did not affect spatial learning, but significantly improved spatial memory. Taken together, our results suggest that decreased AMPK activity after TBI may contribute to the cellular energy crisis in the injured brain, and that AMPK activators may have therapeutic utility. Increased phosphorylation of Thr172 activates AMP-activated protein kinase (AMPK) under conditions of low cellular energy availability. This leads to inhibition of energy consuming, while activating energy generating, processes. Hill et al., present data to indicate that TBI decreases Thr172 phosphorylation and that its stimulation by pharmacological agents offers neuroprotection and improves memory. These results suggest that decreased AMPK phosphorylation after TBI incorrectly signals the injured brain that excess energy is available, thereby contributing to the cellular energy crisis and memory impairments.

Feasibility of online self-administered cognitive training in moderate-severe brain injury

PURPOSE

Cognitive environmental enrichment (C-EE) offers promise for offsetting neural decline that is observed in chronic moderate-severe traumatic brain injury (TBI). Brain games are a delivery modality for C-EE that can be self-administered over the Internet without therapist oversight. To date, only one study has examined the feasibility of self-administered brain games in TBI, and the study focused predominantly on mild TBI. Therefore, the primary purpose of the current study was to examine the feasibility of self-administered brain games in moderate-severe TBI. A secondary and related purpose was to examine the feasibility of remote monitoring of any C-EE-induced adverse symptoms with a self-administered evaluation tool.

METHOD

Ten patients with moderate-severe TBI were asked to complete 12 weeks (60 min/day, five days/week) of online brain games with bi-weekly self-evaluation, intended to measure any adverse consequences of cognitive training (e.g., fatigue, eye strain).

RESULTS

There was modest weekly adherence (42.6% ± 4.4%, averaged across patients and weeks) and 70% patient retention; of the seven retained patients, six completed the self-evaluation questionnaire at least once/week for each week of the study.

CONCLUSIONS

Even patients with moderate-severe TBI can complete a demanding, online C-EE intervention and a self-administered symptom evaluation tool with limited therapist oversight, though at daily rate closer to 30 than 60 min per day. Further self-administered C-EE research is underway in our lab, with more extensive environmental support. Implications for Rehabilitation Online brain games (which may serve as a rehabilitation paradigm that can help offset the neurodegeneration observed in chronic TBI) can be feasibly self-administered by moderate-to-severe TBI patients. Brain games are a promising therapy modality, as they can be accessed by all moderate-to-severe TBI patients irrespective of geographic location, clinic and/or therapist availability, or impairments that limit mobility and access to rehabilitation services. Future efficacy trials that examine the effect of brain games for offsetting neurodegeneration in moderate-to-severe TBI patients are warranted.

Degeneration, Trophic Interactions, and Repair of Severed Axons: A Reconsideration of Some Common Assumptions

We suggest that several interrelated properties of severed axons (degeneration, trophic dependencies, initial repair, and eventual repair) differ in important ways from commonly held assumptions about those properties. Specifically, (1) axotomy does not necessarily produce rapid degeneration of distal axonal segments because (2) the trophic maintenance of nerve axons does not necessarily depend entirely on proteins transported from the perikaryon—but instead axonal proteins can be trophically maintained by slowing their degradation and/or by acquiring new proteins via axonal synthesis or transfer from adjacent cells (e.g., glia). (3) The initial repair of severed distal or proximal segments occurs by barriers (seals) formed amid accumulations of vesicles and/or myelin delaminations induced by calcium influx at cut axonal ends—rather than by collapse and fusion of cut axolemmal leaflets. (4) The eventual repair of severed mammalian CNS axons does not necessarily have to occur by neuritic outgrowths, which slowly extend from cut proximal ends to possibly reestablish lost functions weeks to years after axotomy—but instead complete repair can be induced within minutes by polyethylene glycol to rejoin (fuse) the cut ends of surviving proximal and distal stumps. Strategies to repair CNS lesions based on fusion techniques combined with rehabilitative training and induced axonal outgrowth may soon provide therapies that can at least partially restore lost CNS functions.

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.

Combination therapies for neurobehavioral and cognitive recovery after experimental traumatic brain injury: Is more better?

Traumatic brain injury (TBI) is a significant health care crisis that affects two million individuals in the United Sates alone and over ten million worldwide each year. While numerous monotherapies have been evaluated and shown to be beneficial at the bench, similar results have not translated to the clinic. One reason for the lack of successful translation may be due to the fact that TBI is a heterogeneous disease that affects multiple mechanisms, thus requiring a therapeutic approach that can act on complementary, rather than single, targets. Hence, the use of combination therapies (i.e., polytherapy) has emerged as a viable approach. Stringent criteria, such as verification of each individual treatment plus the combination, a focus on behavioral outcome, and post-injury vs. pre-injury treatments, were employed to determine which studies were appropriate for review. The selection process resulted in 37 papers that fit the specifications. The review, which is the first to comprehensively assess the effects of combination therapies on behavioral outcomes after TBI, encompasses five broad categories (inflammation, oxidative stress, neurotransmitter dysregulation, neurotrophins, and stem cells, with and without rehabilitative therapies). Overall, the findings suggest that combination therapies can be more beneficial than monotherapies as indicated by 46% of the studies exhibiting an additive or synergistic positive effect versus on 19% reporting a negative interaction. These encouraging findings serve as an impetus for continued combination studies after TBI and ultimately for the development of successful clinically relevant therapies.

Combining the Antipsychotic Drug Haloperidol and Environmental Enrichment after Traumatic Brain Injury Is a Double-Edged Sword

Environmental enrichment (EE) confers significant benefits after experimental traumatic brain injury (TBI). In contrast, the antipsychotic drug (APD) haloperidol (HAL) exerts deleterious effects on neurobehavioral and cognitive recovery. Neurorehabilitation and management of agitation, however, are integral components of the treatment strategy for patients with TBI. Hence, the goal of this study was to determine how the two therapeutic approaches interact and influence motor and cognitive recovery. Anesthetized adult male rats received a controlled cortical impact (2.8 mm tissue deformation at 4 m/sec) or sham injury and then were provided HAL (0.5 mg/kg; intraperitoneally [IP]) or vehicle (VEH; 1 mL/kg; IP) commencing 24 h after surgery and once daily for 19 days while housed in EE or standard (STD) conditions. Beam balance/walk and Morris water maze performance were assessed on post-injury days 1-5 and 14-19, respectively, followed immediately by quantification of cortical lesion volumes. The data revealed both expected and unexpected findings. It was not surprising that the TBI groups receiving EE performed significantly better than those in STD housing and that the TBI + STD + HAL group performed worse than the TBI + STD + VEH group (p < 0.05). What was surprising was that the therapeutic effects of EE were greatly reduced by concomitant administration of HAL. No differences in cortical lesion volumes were observed among the groups (p > 0.05). The potential clinical implications of these findings suggest that administering HAL to patients undergoing neurorehabilitation may be a double-edged sword because agitation must be controlled before rehabilitation can be safely initiated and executed, but its use may compromise therapeutic efficacy.

Closed-Head TBI Model of Multiple Morbidity

Successful therapy for TBI disabilities awaits refinement in the understanding of TBI neurobiology, quantitative measurement of treatment-induced incremental changes in recovery trajectories, and effective translation to human TBI using quantitative methods and protocols that were effective to monitor recovery in preclinical models. Details of the specific neurobiology that underlies these injuries and effective quantitation of treatment-induced changes are beginning to emerge utilizing a variety of preclinical and clinical models (for reviews see (Morales et al., Neuroscience 136:971-989, 2005; Fujimoto et al., Neurosci Biobehav Rev 28:365-378, 2004; Cernak, NeuroRx 2:410-422, 2005; Smith et al., J Neurotrauma 22:1485-1502, 2005; Bose et al., J Neurotrauma 30:1177-1191, 2013; Xiong et al., Nat Rev Neurosci 14:128-142, 2013; Xiong et al., Expert Opin Emerg Drugs 14:67-84, 2009; Johnson et al., Handb Clin Neurol 127:115-128, 2015; Bose et al., Brain neurotrauma: molecular, neuropsychological, and rehabilitation aspects, CRC Press/Taylor & Francis, Boca Raton, 2015)). Preclinical models of TBI, essential for the efficient study of TBI neurobiology, benefit from the setting of controlled injury and optimal opportunities for biometric quantitation of injury and treatment-induced changes in the trajectories of disability. Several preclinical models are currently used, and each offer opportunities for study of different aspects of TBI primary and secondary injuries (for review see (Morales et al., Neuroscience 136:971-989, 2005; Xiong et al., Nat Rev Neurosci 14:128-142, 2013; Xiong et al., Expert Opin Emerg Drugs 14:67-84, 2009; Johnson et al., Handb Clin Neurol 127:115-128, 2015; Dixon et al., J Neurotrauma 5:91-104, 1988)). The closed-head, impact-acceleration model of TBI designed by Marmarou et al., 1994 (J Neurosurg 80:291-300, 1994), when used to produce mild to moderate TBI, produces diffuse axonal injuries without significant additional focal injuries of the brain (Morales et al., Neuroscience 136:971-989, 2005; Foda and Marmarou, J Neurosurg 80:301-313, 1994; Kallakuri et al., Exp Brain Res 148:419-424, 2003). Accordingly, use of this preclinical model offers an opportunity for (a) gaining a greater understanding of the relationships of TBI induced diffuse axonal injuries and associated long term disabilities, and (b) to provide a platform for quantitative assessment of treatment interactions upon the trajectories of TBI-induced disabilities. Using the impact acceleration closed head TBI model to induce mild/moderate injuries in the rat, we have observed and quantitated multiple morbidities commonly observed following TBI in humans (Bose et al., J Neurotrauma 30:1177-1191, 2013). This chapter describes methods and protocols used for TBI-induced multiple morbidity involving cognitive dysfunction, balance instability, spasticity and gait, and anxiety-like disorder.

5-hydroxytryptamine1A (5-HT1A) receptor agonists: A decade of empirical evidence supports their use as an efficacious therapeutic strategy for brain trauma

Traumatic brain injury (TBI) is a significant and enduring health care issue with limited treatment options. While several pre-clinical therapeutic approaches have led to enhanced motor and/or cognitive performance, the benefits of these treatments have not translated to the clinic. One plausible explanation is that the therapies may not have been rigorously evaluated, thus rendering the bench-to-bedside leap premature and subsequently unsuccessful. An approach that has undergone considerable empirical research after TBI is pharmacological targeting of 5-HT1A receptors with agonists such as repinotan HCl, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), and buspirone. The goal of this review is to integrate and interpret the findings from a series of studies that evaluated the efficacy of 5-HT1A receptor agonists on functional, histological, and molecular outcome after acquired brain injury. The overwhelming consensus of this exhaustive review is that a decade of empirical evidence supports their use as an efficacious therapeutic strategy for brain trauma. 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.

Equal effects of typical environmental and specific social enrichment on posttraumatic cognitive functioning after fimbria-fornix transection in rats

Enriched environment (EE) has been shown to have beneficial effects on cognitive recovery after brain injury. Typical EE comprises three components: (i) enlarged living area providing physical activation, (ii) sensory stimulation, and (iii) social stimulation. The present study assessed the specific contribution of the social stimulation. Animals were randomly divided into groups of (1) a typical EE, (2) pure social enrichment (SE), or (3) standard housing (SH) and subjected to either a sham operation or transection of the fimbria-fornix (FF). The effect of these conditions on acquisition of a delayed alternation task in a T-maze was assessed. The sham control groups were not affected by housing conditions. In the lesioned groups, both typical EE and SE improved the task acquisition, compared to SH. A baseline one-hour activity measurement confirmed an equal level of physical activity in the EE and SE groups. After delayed alternation testing, pharmacological challenges (muscarinergic antagonist scopolamine and dopaminergic antagonist SKF-83566) were used to assess cholinergic and dopaminergic contributions to task solution. Scopolamine led to a marked impairment in all groups. SKF-83566 significantly enhanced the performance of the lesioned group subjected to SE. The results demonstrate that housing in a typical as well as atypical EE can enhance cognitive recovery after mechanical injury to the hippocampus. The scopolamine challenge revealed a cholinergic dependency during task performance in all groups, regardless of lesion and housing conditions. The dopaminergic challenge revealed a difference in the neural substrates mediating recovery in the lesioned groups exposed to different types of housing.

Effects of environmental enrichment during induction of methamphetamine dependence on the behavioral withdrawal symptoms in rats

This study was designed to examine the effect of environmental enrichment during METH administration on the behavioral withdrawal symptoms after drug abstinence in rats. Rats reared in standard (SE) or enriched environment (EE) during induction of METH dependence with bi-daily injections of METH (2mg/kg, at 12-h. intervals) for 14 days. Then, rats were evaluated for behavioral withdrawal symptoms, and also for anxiety (elevated plus maze-EPM) and depression (Forced swim test-FST) over a ten day period of abstinence. The results showed that stereotypic behaviors score and the number of rearing were significantly lower in METH/EE rats compared to the SE group during 1-4 days. Also, The METH/EE group exhibited more weight gain during 6-10 days of abstinence. The METH/EE rats exhibited lower levels of immobility after METH abstinence than control group in the FST. EE had no effect on anxiety-like behavior. This study showed that exposure to EE diminished the severity of withdrawal symptoms and depressive-like behavior during spontaneous withdrawal from METH.

Long-Term Effects of Enriched Environment on Neurofunctional Outcome and CNS Lesion Volume After Traumatic Brain Injury in Rats

To determine whether the exposure to long term enriched environment (EE) would result in a continuous improvement of neurological recovery and ameliorate the loss of brain tissue after traumatic brain injury (TBI) vs. standard housing (SH). Male Sprague-Dawley rats (300-350 g, n=28) underwent lateral fluid percussion brain injury or SHAM operation. One TBI group was held under complex EE for 90 days, the other under SH. Neuromotor and sensorimotor dysfunction and recovery were assessed after injury and at days 7, 15, and 90 via Composite Neuroscore (NS), RotaRod test, and Barnes Circular Maze (BCM). Cortical tissue loss was assessed using serial brain sections. After day 7 EE animals showed similar latencies and errors as SHAM in the BCM. SH animals performed notably worse with differences still significant on day 90 (p<0.001). RotaRod test and NS revealed superior results for EE animals after day 7. The mean cortical volume was significantly higher in EE vs. SH animals (p=0.003). In summary, EE animals after lateral fluid percussion (LFP) brain injury performed significantly better than SH animals after 90 days of recovery. The window of opportunity may be wide and also lends further credibility to the importance of long term interventions in patients suffering from TBI.

Training and Stimulation in Post Stroke Recovery Brain Reorganization

In both animal and clinical studies, training or rehabilitation increases cortical representation with subsequent functional recovery, whereas a lack of rehabilitation or training decreases cortical representation and delays recovery. Animals exposed to enriched environments post stroke have improved functional outcomes compared with animals exposed to nonenriched environments. In humans, stroke units may be the closest approximation there is to an enriched environment. However, studies indicate that patients spend the majority of time being inactive and alone while on a stroke unit. Given the animal evidence (which emphasizes increased stimulation and increased activity), there is clearly an opportunity for improving the stroke rehabilitation experience to maximize post stroke recovery.

Negative neuroplasticity in chronic traumatic brain injury and implications for neurorehabilitation

Based on growing findings of brain volume loss and deleterious white matter alterations during the chronic stages of injury, researchers posit that moderate-severe traumatic brain injury (TBI) may act to “age” the brain by reducing reserve capacity and inducing neurodegeneration. Evidence that these changes correlate with poorer cognitive and functional outcomes corroborates this progressive characterization of chronic TBI. Borrowing from a framework developed to explain cognitive aging (Mahncke et al., Progress in Brain Research, 157, 81–109, 2006a; Mahncke et al., Proceedings of the National Academy of Sciences of the United States of America, 103(33), 12523–12528, 2006b), we suggest here that environmental factors (specifically environmental impoverishment and cognitive disuse) contribute to a downward spiral of negative neuroplastic change that may modulate the brain changes described above. In this context, we review new literature supporting the original aging framework, and its extrapolation to chronic TBI. We conclude that negative neuroplasticity may be one of the mechanisms underlying cognitive and neural decline in chronic TBI, but that there are a number of points of intervention that would permit mitigation of this decline and better long-term clinical outcomes.

A combined therapeutic regimen of buspirone and environmental enrichment is more efficacious than either alone in enhancing spatial learning in brain-injured pediatric rats

Buspirone, a 5-HT1A receptor agonist, and environmental enrichment (EE) enhance cognition and reduce histopathology after traumatic brain injury (TBI) in adult rats, but have not been fully evaluated after pediatric TBI, which is the leading cause of death in children. Hence, the aims of this study were to assess the efficacy of buspirone alone (Experiment 1) and in combination with EE (Experiment 2) in TBI postnatal day-17 male rats. The hypothesis was that both therapies would confer cognitive and histological benefits when provided singly, but their combination would be more efficacious. Anesthetized rats received a cortical impact or sham injury and then were randomly assigned to receive intraperitoneal injections of buspirone (0.08 mg/kg, 0.1 mg/kg, and 0.3 mg/kg) or saline vehicle (1.0 mL/kg) 24 h after surgery and once daily for 16 days (Experiment 1). Spatial learning and memory were assessed using the Morris water maze (MWM) on post-operative days 11-16, and cortical lesion volume was quantified on day 17. Sham controls for each condition were significantly better than all TBI groups. In the TBI groups, buspirone (0.1 mg/kg) enhanced MWM performance versus vehicle and buspirone (0.08 mg/kg and 0.3 mg/kg) (p<0.05) and reduced lesion volume relative to vehicle (p=0.038). In Experiment 2, buspirone (0.1 mg/kg) or vehicle was combined with EE after TBI, and the data were compared to the standard (STD)-housed groups from Experiment 1. EE lead to a significant enhancement of spatial learning and a reduction in lesion size versus STD. Moreover, the combined treatment group (buspirone+EE) performed markedly better than the buspirone+STD and vehicle+EE groups, which suggests an additive effect and supports the hypothesis. The data replicate previous studies assessing these therapies in adult rats. These novel findings may have important rehabilitation-relevant implications for clinical pediatric TBI.

Environmental enrichment and the sensory brain: the role of enrichment in remediating brain injury

The brain's life-long capacity for experience-dependent plasticity allows adaptation to new environments or to changes in the environment, and to changes in internal brain states such as occurs in brain damage. Since the initial discovery by Hebb (1947) that environmental enrichment (EE) was able to confer improvements in cognitive behavior, EE has been investigated as a powerful form of experience-dependent plasticity. Animal studies have shown that exposure to EE results in a number of molecular and morphological alterations, which are thought to underpin changes in neuronal function and ultimately, behavior. These consequences of EE make it ideally suited for investigation into its use as a potential therapy after neurological disorders, such as traumatic brain injury (TBI). In this review, we aim to first briefly discuss the effects of EE on behavior and neuronal function, followed by a review of the underlying molecular and structural changes that account for EE-dependent plasticity in the normal (uninjured) adult brain. We then extend this review to specifically address the role of EE in the treatment of experimental TBI, where we will discuss the demonstrated sensorimotor and cognitive benefits associated with exposure to EE, and their possible mechanisms. Finally, we will explore the use of EE-based rehabilitation in the treatment of human TBI patients, highlighting the remaining questions regarding the effects of EE.

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.

Old dog, new tricks: the attentional set-shifting test as a novel cognitive behavioral task after controlled cortical impact injury

Cognitive impairment associated with prefrontal cortical dysfunction is a major component of disability in traumatic brain injury (TBI) survivors. Specifically, deficits of cognitive flexibility and attentional set-shifting are present across all levels of injury severity. Though alterations in spatial learning have been extensively described in experimental models of TBI, studies investigating more complex cognitive deficits are relatively scarce. Hence, the aim of this preclinical study was to expand on this important issue by evaluating the effect of three injury levels on executive function and behavioral flexibility performance as assessed using an attentional set-shifting test (AST). Isoflurane-anesthetized male rats received a controlled cortical impact (CCI) injury (2.6, 2.8, and 3.0 mm cortical depth at 4 m/sec) or sham injury, whereas an additional group had no surgical manipulation (naïve). Four weeks postsurgery, rats were tested on the AST, which involved a series of discriminative tasks of increasing difficulty, such as simple and compound discriminations, stimulus reversals, and intra- and extradimensional (ED) shifts. TBI produced accompanying impact depth-dependent increases in cortical lesion volumes, with the 3.0-mm cortical depth group displaying significantly larger injury volumes than the 2.6-mm group (p=0.05). Further, injury severity-induced deficits in ED set-shifting and stimulus reversals, as well as increases in total response error rates and total set loss errors, were observed. These novel findings demonstrate executive function and behavioral flexibility deficits in our animal model of CCI injury and provide the impetus to integrate the AST in the standard neurotrauma behavioral battery to further evaluate cognitive dysfunction after TBI. Ongoing experiments in our laboratory are assessing AST performance after pharmacological and rehabilitative therapies post-TBI, as well as elucidating possible mechanisms underlying the observed neuropsychological deficits.

Cellular and molecular mechanisms of immunomodulation in the brain through environmental enrichment

Recent studies on environmental enrichment (EE) have shown cytokines, cellular immune components [e.g., T lymphocytes, natural killer (NK) cells], and glial cells in causal relationship to EE in bringing out changes to neurobiology and behavior. The purpose of this review is to evaluate these neuroimmune mechanisms associated with neurobiological and behavioral changes in response to different EE methods. We systematically reviewed common research databases. After applying all inclusion and exclusion criteria, 328 articles remained for this review. Physical exercise (PE), a form of EE, elicits anti-inflammatory and neuromodulatory effects through interaction with several immune pathways including interleukin (IL)-6 secretion from muscle fibers, reduced expression of Toll-like receptors on monocytes and macrophages, reduced secretion of adipokines, modulation of hippocampal T cells, priming of microglia, and upregulation of mitogen-activated protein kinase phosphatase-1 in central nervous system. In contrast, immunomodulatory roles of other enrichment methods are not studied extensively. Nonetheless, studies showing reduction in the expression of IL-1β and tumor necrosis factor-α in response to enrichment with novel objects and accessories suggest anti-inflammatory effects of novel environment. Likewise, social enrichment, though considered a necessity for healthy behavior, results in immunosuppression in socially defeated animals. This has been attributed to reduction in T lymphocytes, NK cells and IL-10 in subordinate animals. EE through sensory stimuli has been investigated to a lesser extent and the effect on immune factors has not been evaluated yet. Discovery of this multidimensional relationship between immune system, brain functioning, and EE has paved a way toward formulating environ-immuno therapies for treating psychiatric illnesses with minimal use of pharmacotherapy. While the immunomodulatory role of PE has been evaluated extensively, more research is required to investigate neuroimmune changes associated with other enrichment methods.

Decoding hippocampal signaling deficits after traumatic brain injury

There are more than 3.17 million people coping with long-term disabilities due to traumatic brain injury (TBI) in the United States. The majority of TBI research is focused on developing acute neuroprotective treatments to prevent or minimize these long-term disabilities. Therefore, chronic TBI survivors represent a large, underserved population that could significantly benefit from a therapy that capitalizes on the endogenous recovery mechanisms occurring during the weeks to months following brain trauma. Previous studies have found that the hippocampus is highly vulnerable to brain injury, in both experimental models of TBI and during human TBI. Although often not directly mechanically injured by the head injury, in the weeks to months following TBI, the hippocampus undergoes atrophy and exhibits deficits in long-term potentiation (LTP), a persistent increase in synaptic strength that is considered to be a model of learning and memory. Decoding the chronic hippocampal LTP and cell signaling deficits after brain trauma will provide new insights into the molecular mechanisms of hippocampal-dependent learning impairments caused by TBI and facilitate the development of effective therapeutic strategies to improve hippocampal-dependent learning for chronic survivors of TBI.

Non-spatial pre-training in the water maze as a clinically relevant model for evaluating learning and memory in experimental TBI

Explicit and implicit learning and memory networks exist where each network can facilitate or inhibit cognition. Clinical evidence suggests that implicit networks are relatively preserved after traumatic brain injury (TBI). Non-spatial pre-training (NSPT) in the Morris Water Maze (MWM) provides the necessary behavioral components to complete the task, while limiting the formation of spatial maps. Our study utilized NSPT in the MWM to assess implicit and explicit learning and memory system deficits in the controlled cortical impact (CCI) model of TBI. 76 adult male Sprague-Dawley rats were divided: CCI vs. sham surgery, NSPT vs. No-NSPT, and cued vs. non-cued groups. NSPT occurred for 4d prior to surgery (dynamic hidden platform location, extra-maze cues covered, static pool entry point). Acquisition (d14-18), Probe/Visible Platform (d19), and Reversal (d20-21) trials were conducted with or without extra-maze cues. Novel time allocation and search strategy selection metrics were utilized. Results indicated implicit and explicit learning/memory networks are distinguishable in the MWM. In the cued condition, NSPT reduced thigmotaxis, improved place learning, and largely eliminated the apparent injury-induced deficits typically observed between untrained CCI and sham rats. However, among NSPT groups, incorporation of cues into search strategy selection for CCI rats was relatively impaired compared to shams. Non-cued condition performance showed sham/NSPT and CCI/NSPT rats perform similarly, suggesting implicit memory networks are largely intact 2weeks after CCI. Place learning differences between CCI/NSPT and sham/NSPT rats more accurately reflect spatial deficits in our CCI model compared to untrained controls. These data suggest NSPT as a clinically relevant construct for evaluating potential neurorestorative and neuroprotective therapies. These findings also support development of non-spatial cognitive training paradigms for evaluating rehabilitation relevant combination therapies.

Environmental enrichment protects against functional deficits caused by traumatic brain injury

Environmental enrichment (EE) increases cortical weight, neuronal density, dendritic branching, and angiogenesis, all of which may be critical for functional recovery following insult. Our study was designed to determine possible benefits of pre-exposure to EE in preventing functional deficits following traumatic brain injury (TBI) to the prefrontal cortex. To examine the benefit of EE, adult male rats were placed in an enriched environment for 15 days. Enrichment was provided through social interaction, exercise, olfactory stimulation, and new objects/toys to explore. Following enrichment, experimental and age-matched controls were subjected to a moderate medial prefrontal cortex injury via controlled cortical impact (CCI). After 1 week recovery, animals were behaviorally tested to assess memory, anxiety, and sensory neglect. Lesion-induced deficits in spatial memory [Morris water maze (MWM)] were significantly attenuated in EE pre-exposed rats 18–21 days following injury. In addition, TBI-induced sensory neglect was significantly reduced in EE rats relative to non-enriched animals. No differences in anxiety-like behavior on the elevated plus maze (EPM) were detected. The behavioral data suggest that EE is neuroprotective when applied prior to TBI, resulting in improved recovery following injury.