Enriched environment influences brain-derived neurotrophic factor levels in rat forebrain after focal stroke

An enriched environment improves long-term functional outcomes in mice after intracerebral hemorrhage by mechanisms that involve the Nrf2/BDNF/glutaminase pathway

Post-stroke depression exacerbates neurologic deficits and quality of life. Depression after ischemic stroke is known to some extent. However, depression after intracerebral hemorrhage (ICH) is relatively unknown. Increasing evidence shows that exposure to an enriched environment (EE) after cerebral ischemia/reperfusion injury has neuroprotective effects in animal models, but its impact after ICH is unknown. In this study, we investigated the effect of EE on long-term functional outcomes in mice subjected to collagenase-induced striatal ICH. Mice were subjected to ICH with the standard environment (SE) or ICH with EE for 6 h/day (8:00 am-2:00 pm). Depressive, anxiety-like behaviors and cognitive tests were evaluated on day 28 with the sucrose preference test, tail suspension test, forced swim test, light-dark transition experiment, morris water maze, and novel object recognition test. Exposure to EE improved neurologic function, attenuated depressive and anxiety-like behaviors, and promoted spatial learning and memory. These changes were associated with increased expression of transcription factor Nrf2 and brain-derived neurotrophic factor (BDNF) and inhibited glutaminase activity in the perihematomal tissue. However, EE did not change the above behavioral outcomes in Nrf2-/- mice on day 28. Furthermore, exposure to EE did not increase BDNF expression compared to exposure to SE in Nrf2-/- mice on day 28 after ICH. These findings indicate that EE improves long-term outcomes in sensorimotor, emotional, and cognitive behavior after ICH and that the underlying mechanism involves the Nrf2/BDNF/glutaminase pathway.

Genetics in aphasia recovery

Considerable research efforts have been exerted toward understanding the mechanisms underlying recovery in aphasia. However, predictive models of spontaneous and treatment-induced recovery remain imprecise. Some of the hitherto unexplained variability in recovery may be accounted for with genetic data. A few studies have examined the effects of the BDNF val66met polymorphism on aphasia recovery, yielding mixed results. Advances in the study of stroke genetics and genetics of stroke recovery, including identification of several susceptibility genes through candidate-gene or genome-wide association studies, may have implications for the recovery of language function. The current chapter discusses both the direct and indirect evidence for a genetic basis of aphasia recovery, the implications of recent findings within the field, and potential future directions to advance understanding of the genetics-recovery associations.

Exposure of R6/2 mice in an enriched environment augments P42 therapy efficacy on Huntington's disease progression

Huntington's disease (HD) is due to a mutation in the gene encoding for Huntingtin protein generating polyQ domain extension. Mutant Htt (mHtt) leads to important dysfunction of the BDNF/TrkB signaling. We previously described the 23aa Htt fragment P42, that attenuated the pathological phenotypes induced by mHtt. We reported that, in the R6/2 mouse model of HD, P42 rescued striatal TrkB level but marginally increased cortical BDNF. In the present study, our aim was to address P42 neuroprotection in presence of an external input of BDNF. We combined P42 administration with environmental enrichment (EE), induced by training in the Hamlet test. We examined the consequences of P42 + EE combination on different phenotypes in R6/2 HD mice: motor and cognitive performances, recorded at early and late pathological stages, and analyzed aggregated mHtt and BDNF levels in forebrain structures. Hamlet exploration (i.e., entries in Run, Hide, Eat, Drink and Interact houses) was gradually impaired in R6/2 mice, but maintained by P42 treatment until week 8. Topographic memory alteration measured at week 7 was attenuated by P42. Motor performances (rotarod) were significantly ameliorated by the P42 + EE combination until late stage (week 12). The P42 + EE combination also significantly decreased aggregated Htt levels in the hippocampus, striatum and cortex, and increased BDNF levels in the cortex and striatum. We concluded that combination between P42 treatment, known to increase TrkB striatal expression, and a BDNF-enhancing therapy such as EE efficiently delayed HD pathology in R6/2 mice. Use of dual therapies might be a pertinent strategy to fight neurodegeneration in HD.

Neurotrophin-3 upregulation associated with intravenous transplantation of bone marrow mononuclear cells induces axonal sprouting and motor functional recovery in the long term after neocortical ischaemia

Bone marrow mononuclear cells (BMMCs) have been identified as a relevant therapeutic strategy for the treatment of several chronic diseases of the central nervous system. The aim of this work was to evaluate whether intravenous treatment with BMMCs facilitates the reconnection of lesioned cortico-cortical and cortico-striatal pathways, together with motor recovery, in injured adult Wistar rats using an experimental model of unilateral focal neocortical ischaemia. Animals with cerebral cortex ischaemia underwent neural tract tracing for axonal fibre analysis, differential expression analysis of genes involved in apoptosis and neuroplasticity by RT-qPCR, and motor performance assessment by the cylinder test. Quantitative and qualitative analyses of axonal fibres labelled by an anterograde neural tract tracer were performed. Ischaemic animals treated with BMMCs showed a significant increase in axonal sprouting in the ipsilateral neocortex and in the striatum contralateral to the injured cortical areas compared to untreated rodents. In BMMC-treated animals, there was a trend towards upregulation of the Neurotrophin-3 gene compared to the other genes, as well as modulation of apoptosis by BMMCs. On the 56th day after ischaemia, BMMC-treated animals showed significant improvement in motor performance compared to untreated rats. These results suggest that in the acute phase of ischaemia, Neurotrophin-3 is upregulated in response to the lesion itself. In the long run, therapy with BMMCs causes axonal sprouting, reconnection of damaged neuronal circuitry and a significant increase in motor performance.

Paired associated magnetic stimulation promotes neural repair in the rat middle cerebral artery occlusion model of stroke

Paired associative stimulation has been used in stroke patients as an innovative recovery treatment. However, the mechanisms underlying the therapeutic effectiveness of paired associative stimulation on neurological function remain unclear. In this study, rats were randomly divided into middle cerebral occlusion model (MCAO) and paired associated magnetic stimulation (PAMS) groups. The MCAO rat model was produced by middle cerebral artery embolization. The PAMS group received PAMS on days 3 to 20 post MCAO. The MCAO group received sham stimulation, three times every week. Within 18 days after ischemia, rats were subjected to behavioral experiments—the foot-fault test, the balance beam walking test, and the ladder walking test. Balance ability was improved on days 15 and 17, and the foot-fault rate was less in their affected limb on day 15 in the PAMS group compared with the MCAO group. Western blot assay showed that the expression levels of brain derived neurotrophic factor, glutamate receptor 2/3, postsynaptic density protein 95 and synapsin-1 were significantly increased in the PAMS group compared with the MCAO group in the ipsilateral sensorimotor cortex on day 21. Resting-state functional magnetic resonance imaging revealed that regional brain activities in the sensorimotor cortex were increased in the ipsilateral hemisphere, but decreased in the contralateral hemisphere on day 20. By finite element simulation, the electric field distribution showed a higher intensity, of approximately 0.4 A/m², in the ischemic cortex compared with the contralateral cortex in the template. Together, our findings show that PAMS upregulates neuroplasticity-related proteins, increases regional brain activity, and promotes functional recovery in the affected sensorimotor cortex in the rat MCAO model. The experiments were approved by the Institutional Animal Care and Use Committee of Fudan University, China (approval No. 201802173S) on March 3, 2018.

Brain-Derived Neurotrophic Factor Genotype-Specific Differences in Cortical Activation in Chronic Aphasia

Purpose The brain-derived neurotrophic factor (BDNF) gene has been shown to be important for synaptic plasticity in animal models. Human research has suggested that BDNF genotype may influence stroke recovery. Some studies have suggested a genotype-specific motor-related brain activation in stroke recovery. However, recovery from aphasia in relation to BDNF genotype and language-related brain activation has received limited attention. We aimed to explore functional brain activation by BDNF genotype in individuals with chronic aphasia. Consistent with findings in healthy individuals and individuals with poststroke motor impairment, we hypothesized that, among individuals with aphasia, the presence of the Met allele of the BDNF gene is associated with reduced functional brain activation compared to noncarriers of the Met allele. Method Eighty-seven individuals with chronic stroke-induced aphasia performed a naming task during functional magnetic resonance imaging scanning and submitted blood or saliva samples for BDNF genotyping. The mean number of activated voxels was compared between groups, and group-based activation maps were directly compared. Neuropsychological testing was conducted to compare language impairment between BDNF genotype groups. The Western Aphasia Battery Aphasia Quotient (Kertesz, 2007) was included as a covariate in all analyses. Results While lesion size was comparable between groups, the amount of activation, quantified as the number of activated voxels, was significantly greater in noncarriers of the Met allele (whole brain: 98,500 vs. 28,630, p < .001; left hemisphere only: 37,209 vs. 7,000, p < .001; right hemisphere only: 74,830 vs. 30,630, p < .001). This difference was most strongly expressed in the right hemisphere posterior temporal area, pre- and postcentral gyrus, and frontal lobe, extending into the white matter. Correspondingly, the atypical BDNF genotype group was found to have significantly less severe aphasia (Western Aphasia Battery Aphasia Quotient of 64.2 vs. 54.3, p = .033) and performed better on a naming task (Philadelphia Naming Test [Roach, Schwartz, Martin, Grewal, & Brecher, 1996] score of 74.7 vs. 52.8, p = .047). A region of interest analysis of intensity of activation revealed no group differences, and a direct comparison of average activation maps across groups similarly yielded null results. Conclusion BDNF genotype mediates cortical brain activation in individuals with chronic aphasia. Correspondingly, individuals carrying the Met allele present with more severe aphasia compared to noncarriers. These findings warrant further study into the effects of BDNF genotype in aphasia. Supplemental Material https://doi.org/10.23641/asha.10073147 Presentation Video https://doi.org/10.23641/asha.10257581.

Enhancing endogenous capacity to repair a stroke-damaged brain: An evolving field for stroke research

Stroke represents a severe medical condition that causes stroke survivors to suffer from long-term and even lifelong disability. Over the past several decades, a vast majority of stroke research targets neuroprotection in the acute phase, while little work has been done to enhance stroke recovery at the later stage. Through reviewing current understanding of brain plasticity, stroke pathology, and emerging preclinical and clinical restorative approaches, this review aims to provide new insights to advance the research field for stroke recovery. Lifelong brain plasticity offers the long-lasting possibility to repair a stroke-damaged brain. Stroke impairs the structural and functional integrity of entire brain networks; the restorative approaches containing multi-components have great potential to maximize stroke recovery by rebuilding and normalizing the stroke-disrupted entire brain networks and brain functioning. The restorative window for stroke recovery is much longer than previously thought. The optimal time for brain repair appears to be at later stage of stroke rather than the earlier stage. It is expected that these new insights will advance our understanding of stroke recovery and assist in developing the next generation of restorative approaches for enhancing brain repair after stroke.

Impact of social relationships on Alzheimer's memory impairment: mechanistic studies

Alzheimer's disease (AD) is characterized by progressive memory and neuronal loss culminating in cognitive impairment that not only affects a person's living ability but also becomes a society's as well as a family's economic burden. AD is the most common form of dementia in older persons. It is expected that the number of people with AD dementia will increase dramatically in the next 30 years, projecting to 75 million in 2030 and 131.5 million in 2050 worldwide. So far, no sufficient evidence is available to support that any medicine is able to prevent or reverse the progression of the disease. Early studies have shown that social environment, particularly social relationships, can affect one's behavior and mental health. A study analyzing the correlation between loneliness and risk of developing AD revealed that lonely persons had higher risk of AD compared with persons who were not lonely. On the other hand, it has been reported that we can prevent cognitive decline and delay the onset of AD if we keep mentally active and frequently participate in social activities. In this review, we focus on the impact of social behaviors on the progression of cognitive deficit in animal models of AD with a particular emphasis on a mechanistic scheme that explains how social isolation exacerbates cognitive impairment and how social interaction with conspecifics rescues AD patients' memory deficit.

BDNF Val66Met Polymorphism Is Related to Motor System Function After Stroke

BACKGROUND

The val(66)met polymorphism in brain-derived neurotrophic factor (BDNF) has been associated with poorer outcomes after stroke. The mechanism for this finding remains uncertain but might be related to the reduced motor system activation associated with this polymorphism in healthy people.

OBJECTIVE

The current study examined whether the presence of the BDNF val(66)met polymorphism is associated with reduced motor system activation after stroke.

DESIGN AND METHODS

Forty-two patients with stroke who were enrolled in 1 of 2 studies of robot-assisted arm motor therapy participated in the study. All participants were tested for the BDNF val(66)met polymorphism followed by functional magnetic resonance imaging during affected hand movement.

RESULTS

Participants averaged 12 months poststroke and had wide-ranging motor deficits (Fugl-Meyer scale scores=14-60). Brain activation in participants without the BDNF val(66)met polymorphism (n=26) spanned bilateral motor networks with a larger volume (total=334 cc) than that found in participants with this polymorphism (n=16) (97 cc). Regional analyses were consistent. Participants without this polymorphism showed larger ipsilesional primary sensorimotor cortex activation volume and magnitude compared with those in whom the polymorphism was present.

LIMITATIONS

The extent to which these findings generalize to other populations of people with stroke, such as those with stroke <7 days prior, remains uncertain.

CONCLUSIONS

Functional magnetic resonance imaging during affected hand movement showed decreased brain activation among participants with the BDNF val(66)met polymorphism compared with those lacking this polymorphism, especially in the ipsilesional primary sensorimotor cortex contralateral to movement. These results echo findings in healthy people and suggest that genetic factors affecting the normal brain continue to be operative after stroke. The findings suggest a potential imaging-based endophenotype for the BDNF val(66)met polymorphism's effect on the motor system that may be useful in a clinical trial setting.

The Effects of Antecedent Exercise on Motor Function Recovery and Brain-derived Neurotrophic Factor Expression after Focal Cerebral Ischemia in Rats

[Purpose] In the present study, we investigated the effect of antecedent exercise on functional recovery and brain-derived neurotrophic factor (BDNF) expression following focal cerebral ischemia injury. [Subjects] The rat middle cerebral artery occlusion (MCAO) model was employed. Adult male Sprague-Dawley rats were randomly divided into 4 groups. Group I included untreated normal rats (n=10); Group II included untreated rats with focal cerebral ischemia (n=10); Group III included rats that performed treadmill exercise (20 m/min) training after focal cerebral ischemia (n=10); and Group IV included rats that performed antecedent treadmill exercise (20 m/min) training before focal cerebral ischemia (n=10) as well as treadmill exercise after ischemia. At different time points (1, 7, 14, and 21 days) Garcia’s score, and the hippocampal expressions level of BDNF were examined. [Results] In the antecedent exercise group, improvements in the motor behavior index (Garcia’s score) were observed and hippocampal BDNF protein expression levels increased. [Conclusion] These results indicate that antecedent treadmill exercise, before permanent brain ischemia exerts a neuroprotective effect against ischemia brain injury by improving motor performance and increasing the level of BDNF expression. Furthermore, the antecedent treadmill exercise of appropriate intensity is critical for post-stroke rehabilitation.

Long-term results of enriched environment and erythropoietin after hypobaric hypoxia in rats

After global cerebral hypoxia, many patients are severely disabled even after intensive neurorehabilitation. Secondary mechanisms of brain injury as a result of biochemical and physiological events occur within a period of hours to months, and provide a window of opportunity for therapeutic intervention. Erythropoietin (EPO) has been shown to be neuroprotective in the brain subjected to a variety of injuries. Fifty-nine 3-month-old male Wistar rats were randomly distributed to experimental groups with respect to the housing (enriched environment - EE, standard housing - SH), to hypoxia exposure, and to EPO treatment. An acute mountain sickness model was used as a hypobaric hypoxia simulating an altitude of 8000 m. One half of the animals received erythropoietin injections, while the others were injected saline. Spatial memory was tested in a Morris water maze (MWM). The escape latency and the path length were measured. Better spatial learning in MWM was only seen in the group that received erythropoietin together with enriched environment. EPO administration itself had no influence on spatial memory. The results were very similar for both latencies and path lengths. These results support the idea that after brain injuries, the recovery can be potentiated by EPO administration combined with neurorehabilitation.

The combination of stem cell factor and granulocyte-colony stimulating factor for chronic stroke treatment in aged animals

Background

Stroke occurs more frequently in the elderly population and presents the number one leading cause of persistent disability worldwide. Lack of effective treatment to enhance brain repair and improve functional restoration in chronic stroke, the recovery phase of stroke, is a challenging medical problem to be solved in stroke research. Our early study has revealed the therapeutic effects of stem cell factor (SCF) in combination with granulocyte-colony stimulating factor (G-CSF) (SCF+G-CSF) on chronic stroke in young animals. However, whether this treatment is effective and safe to the aged population remains to be determined.

Methods

Cortical brain ischemia was produced in aged C57BL mice or aged spontaneously hypertensive rats. SCF+G-CSF or equal volume of vehicle solution was subcutaneously injected for 7 days beginning at 3–4 months after induction of cortical brain ischemia. Using the approaches of biochemistry assays, flow cytometry, pathology, and evaluation of functional outcome, several doses of SCF+G-CSF have been examined for their safety and efficiency on chronic stroke in aged animals.

Results

All tested doses did not show acute or chronic toxicity in the aged animals. Additionally, SCF+G-CSF treatment in chronic stroke of aged animals mobilized bone marrow stem cells and improved functional outcome in a dose-dependent manner.

Conclusions

SCF+G-CSF treatment is a safe and effective approach to chronic stroke in the aged condition. This study provides important information needed for developing a new therapeutic strategy to improve the health of older adults with chronic stroke.

The BDNF val(66)met polymorphism is not related to motor function or short-term cortical plasticity in elderly subjects

The brain derived neurotrophic factor (BDNF) val(66)met polymorphism affects function of the motor system in young subjects, but little is known about motor system effects in the elderly. The current study assessed motor system physiology and behavior, plus a measure of short-term motor cortex plasticity using transcranial magnetic stimulation, in 38 elderly subjects, then examined whether findings varied in relation to BDNF genotype. Baseline data were also collected from 14 young subjects. At baseline, elderly subjects had poorer motor performances, larger motor cortex maps, and smaller motor evoked potentials compared to young subjects. Degree of age-related differences in neurophysiology correlated inversely with motor performance, for example, larger map area correlated with weaker pinch grip force (r=-0.42, P=0.01). In elderly subjects, baseline behavior and neurophysiology did not differ in relation to BDNF genotype. In addition, although map area increased significantly (P=0.03) across 30 min of exercise, this change did not vary according to BDNF genotype. Aging is associated with changes in neurophysiology that might represent a compensatory response. The data do not support an association between BDNF genotype and behavior, neurophysiology, or short-term cortical plasticity in the motor system of healthy elderly subjects.

Ceruloplasmin deficiency reduces levels of iron and BDNF in the cortex and striatum of young mice and increases their vulnerability to stroke

Ceruloplasmin (Cp) is an essential ferroxidase that plays important roles in cellular iron trafficking. Previous findings suggest that the proper regulation and subcellular localization of iron are very important in brain cell function and viability. Brain iron dyshomeostasis is observed during normal aging, as well as in several neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases, coincident with areas more susceptible to insults. Because of their high metabolic demand and electrical excitability, neurons are particularly vulnerable to ischemic injury and death. We therefore set out to look for abnormalities in the brain of young adult mice that lack Cp. We found that iron levels in the striatum and cerebral cortex of these young animals are significantly lower than wild-type (WT) controls. Also mRNA levels of the neurotrophin brain derived neurotrophic factor (BDNF), known for its role in maintenance of cell viability, were decreased in these brain areas. Chelator-mediated depletion of iron in cultured neural cells resulted in reduced BDNF expression by a posttranscriptional mechanism, suggesting a causal link between low brain iron levels and reduced BDNF expression. When the mice were subjected to middle cerebral artery occlusion, a model of focal ischemic stroke, we found increased brain damage in Cp-deficient mice compared to WT controls. Our data indicate that lack of Cp increases neuronal susceptibility to ischemic injury by a mechanism that may involve reduced levels of iron and BDNF.

Genetic influences on neural plasticity

Neural plasticity refers to the capability of the brain to alter function or structure in response to a range of events and is a crucial component of both functional recovery after injury and skill learning in healthy individuals. A number of factors influence neural plasticity and recovery of function after brain injury. The current review considers the impact of genetic factors. Polymorphisms in the human genes coding for brain-derived neurotrophic factor and apolipoprotein E have been studied in the context of plasticity and stroke recovery and are discussed here in detail. Several processes involved in plasticity and stroke recovery, such as depression or pharmacotherapy effects, are modulated by other genetic polymorphisms and are also discussed. Finally, new genetic polymorphisms that have not been studied in the context of stroke are proposed as new directions for study. A better understanding of genetic influences on recovery and response to therapy might allow improved treatment after a number of forms of central nervous system injury.

Rehabilitation intervention in animal model can improve neuromotor and cognitive functions after traumatic brain injury: pilot study

The aim of the present study was to quantify the effect of multisensory rehabilitation on rats' cognition after an experimental brain trauma and to assess its possible clinical implications. The complex intermittent multisensory rehabilitation consisted of currently used major therapeutic procedures targeted at the improvement of cognitive functions; including multisensory and motor stimulation and enriched environment. We have confirmed this positive effect of early multisensory rehabilitation on the recovery of motor functions after traumatic brain injury. However, we have been able to prove a positive effect on the recovery of cognitive functions only with respect to the frequency of efficient search strategies in a Barnes maze test, while results for search time and travelled distance were not significantly different between study groups. We have concluded that the positive effects of an early treatment of functional deficits are comparable with the clinical results in early neurorehabilitation in human patients after brain trauma. It might therefore be reasonable to apply these experimental results to human medical neurorehabilitation care.

Early motor balance and coordination training increased synaptophysin in subcortical regions of the ischemic rat brain

The aim of this study was to evaluate the effect of early motor balance and coordination training on functional recovery and brain plasticity in an ischemic rat stroke model, compared with simple locomotor exercise. Adult male Sprague-Dawley rats with cortical infarcts were trained under one of four conditions: nontrained control, treadmill training, motor training on the Rota-rod, or both Rota-rod and treadmill training. All types of training were performed from post-operation day 1 to 14. Neurological and behavioral performance was evaluated by Menzies' scale, the prehensile test, and the limb placement test, at post-operation day 1, 7, and 14. Both Rota-rod and treadmill training increased the expression of synaptophysin in subcortical regions of the ischemic hemisphere including the hippocampus, dentate gyrus, and thalamus, but did not affect levels of brain-derived neurotrophic factor or tyrosin kinase receptor B. The Rota-rod training also improved Menzies' scale and limb placement test scores, whereas the simple treadmill training did neither. The control group showed significant change only in Menzies' scale score. This study suggests that early motor balance and coordination training may induce plastic changes in subcortical regions of the ischemic hemisphere after stroke accompanied with the recovery of sensorimotor performance.

Empirical comparison of typical and atypical environmental enrichment paradigms on functional and histological outcome after experimental traumatic brain injury

Several studies have shown that housing rats in an enriched environment (EE) after traumatic brain injury (TBI) improves functional and histological outcome. The typical EE includes exploratory, sensory, and social components in cages that are often vastly larger than standard (STD) housing. It is uncertain, however, whether a single or specific component is sufficient to confer these benefits after TBI, or if all, perhaps in an additive or synergistic manner, are necessary. To clarify this ambiguity, anesthetized adult male rats were subjected to either a controlled cortical impact or sham injury, and then were randomly assigned to five different housing paradigms: (1) EE (typical), (2) EE (-social), (3) EE (-stimuli), (4) STD (typical), and (5) STD (+stimuli). Motor and cognitive function were assessed using conventional motor (beam-balance/traversal) and cognitive (spatial learning in a Morris water maze) tests on postoperative days 1-5 and 14-19, respectively, and cortical lesion volume and CA1/CA3 cell loss were quantified at 3 weeks. No significant differences were observed among the sham groups in any comparison and thus their data were pooled (i.e., SHAM). In the TBI groups, typical EE improved beam-balance versus both STD (+stimuli) and EE (-social), it facilitated the acquisition of spatial learning and memory retention versus all other housing conditions (p < 0.003), and it reduced lesion volume and CA3 cell loss versus STD (typical) housing. While rats in the three atypical EE conditions exhibited slightly better cognitive performance and histological protection versus the typical STD group, the overall effects were not significant. These data suggest that exposing TBI rats to any of the three components individually may be more advantageous than no enrichment, but only exposure to typical EE yields optimal benefits.

Wheel running and environmental enrichment differentially modify exon-specific BDNF expression in the hippocampus of wild-type and pre-motor symptomatic male and female Huntington's disease mice

Brain-derived neurotrophic factor (BDNF) is an essential neurotrophin and regulation of its expression is complex due to multiple 5' untranslated exons which are separately spliced to a common coding exon to form unique mRNA transcripts. Disruption of BDNF gene expression is a key to the development of symptoms in Huntington's disease (HD), a fatal neurodegenerative condition. Abnormal epigenetic modifications are associated with reduced gene expression in late-stage HD but such regulation of BDNF gene expression has yet to be investigated. We hypothesized that BDNF gene expression is altered in the HD hippocampus of pre-motor symptomatic R6/1 transgenic HD mice, correlating with a change in the DNA methylation profile. The effects of wheel-running and environmental enrichment on wild-type mice, in association with a proposed environment-mediated correction of BDNF gene expression deficits in HD mice, were also investigated. Using real-time PCR, levels of total BDNF mRNA were found to be reduced in the hippocampus of both male and female HD mice. Wheel-running significantly increased total BDNF gene expression in all groups of mice except male HD mice. In contrast, environmental enrichment significantly increased expression only in male wild-type animals. Further quantification of BDNF exon-specific transcripts revealed sex-specific changes in relation to the effect of the HD mutation and differential effects on gene expression by wheel-running and environmental enrichment. The HD-associated reduction of BDNF gene expression was not due to increased methylation of the gene sequence. Furthermore, environment-induced changes in BDNF gene expression in the wild-type hippocampus were independent of the extent of DNA methylation. Overall, the results of this study provide new insight into the role of BDNF in HD pathogenesis in addition to the mechanisms regulating normal BDNF gene expression.

Brain plasticity and genetic factors

Brain plasticity refers to changes in brain function and structure that arise in a number of contexts. One area in which brain plasticity is of considerable interest is recovery from stroke, both spontaneous and treatment-induced. A number of factors influence these poststroke brain events. The current review considers the impact of genetic factors. Polymorphisms in the human genes coding for brain-derived neurotrophic factor (BDNF) and apolipoprotein E (ApoE) have been studied in the context of plasticity and/or stroke recovery and are discussed here in detail. Several other genetic polymorphisms are indirectly involved in stroke recovery through their modulating influences on processes such as depression and pharmacotherapy effects. Finally, new genetic polymorphisms that have not been studied in the context of stroke are proposed as new directions for study. A better understanding of genetic influences on recovery and response to therapy might allow improved treatment after stroke.

Enriched environment promotes efficiency of compensatory movements after cerebral ischemia in rats

Rehabilitation therapy is known to drive motor improvement in stroke patients. However, the interplay of functional recovery and compensation in postischemic motor behavior is poorly understood. This study focused on the time course of functional recovery versus motor compensation in skilled forelimb movements after cerebral ischemia in rats. Young adult male rats underwent a focal cerebral ischemia by unilateral photothrombotic lesion of the motor cortex related to the preferred forelimb. In a first set of experiments animals were exposed to small cortical lesions comprising the forelimb motor cortex (n=8) or to larger lesions additionally extending into the hind limb motor area (n=8). In a second set of experiments animals with large lesion were either housed in standard (n=10) or enriched environment (n=14). Skilled reaching was assessed for 25 to 28 days postischemia. This task allows the distinction between recovery and compensation by parallel quantitative (reaching success) and qualitative (movement pattern) analysis. The results reveal that lesion size determines the initial magnitude of motor deficits, but not the degree of chronic impairments in movement pattern in all experimental groups. Compensatory movements represent the major mechanism of functional improvement and were accompanied by a partial functional restitution. Enriched environment facilitates effective compensation in skilled reaching, while it does not promote restitution of function. In particular, rotating movements of the forelimb during reaching were permanently impaired and required functional compensation through intensified use of the upper body. We conclude an activity dependent postischemic restoration of movement success. Enriched environment provides benefit by increased motor activity mainly due to compensation. Furthermore, these findings emphasize the power of comprehensive movement analysis to gain insight into recovery processes after stroke.

Prenatal auditory stimulation alters the levels of CREB mRNA, p-CREB and BDNF expression in chick hippocampus

Prenatal auditory stimulation influences the development of the chick auditory pathway and the hippocampus showing an increase in various morphological parameters as well as expression of calcium-binding proteins. Calcium regulates the activity of cyclic adenosine monophosphate-response element binding (CREB) protein. CREB is known to play a role in development, undergo phosphorylation with neural activity as well as regulate transcription of BDNF. BDNF is important for the survival of neurons and regulates synaptic strength. Hence in the present study, we have evaluated the levels of CREB mRNA and protein along with p-CREB protein as well as BDNF mRNA and protein levels in the chick hippocampus at embryonic days (E) 12, E16, E20 and post-hatch day (PH) 1 following activation by prenatal auditory stimulation. Fertilized eggs were exposed to species-specific sound or sitar music (frequency range: 100-6300Hz) at 65dB levels for 15min/h over 24h from E10 till hatching. The control chick hippocampus showed higher CREB mRNA and p-CREB protein in the early embryonic stages, which later decline whereas BDNF mRNA and BDNF protein levels increase until PH1. The CREB mRNA and p-CREB protein were significantly increased at E12, E16 and PH1 in the auditory stimulated groups as compared to control group. A significant increase in the level of BDNF mRNA was observed from E12 and the protein expression from E16 onwards in both auditory stimulated groups. Therefore, enhanced phosphorylation of CREB during development following prenatal sound stimulation may be responsible for cell survival. Increased levels of p-CREB again at PH1 may trigger synthesis of proteins necessary for synaptic plasticity. Further, the increased levels of BDNF may also help in regulating synaptic plasticity.

Brain-derived neurotrophic factor contributes to recovery of skilled reaching after focal ischemia in rats

BACKGROUND AND PURPOSE

Brain-derived neurotrophic factor (BDNF) is involved in neuronal survival, synaptic plasticity, learning and memory, and neuroplasticity. Further, exogenous treatment with BDNF or exposing animals to enrichment and exercise regimens, which also increase BDNF, enhances behavioral recovery after brain injury. Thus, the beneficial effects of rehabilitation in promoting recovery after stroke may also depend on BDNF. We tested this hypothesis by evaluating the contribution of BDNF to motor skill relearning after endothelin-1-induced middle cerebral artery occlusion in rats.

METHODS

Antisense BDNF oligonucleotide, which blocks the expression of BDNF (or saline vehicle) was infused into the contralateral lateral ventricle for 28 days after ischemia. Animals received either a graduated rehabilitation program, including running exercise and skilled reaching training, which simulates clinical practice, or no rehabilitation. Functional recovery was assessed with a battery of tests that measured skilled reaching, forelimb use asymmetry, and foraging ability.

RESULTS

Rehabilitation significantly improved skilled reaching ability in the staircase task. Antisense BDNF oligonucleotide effectively blocked BDNF mRNA, and negated the beneficial effects of rehabilitation on recovery of skilled reaching. Importantly, antisense BDNF oligonucleotide did not affect reaching with the unaffected limb, body weight, infarct size, or foraging ability, indicating the treatment was specific to relearning of motor skill after ischemia.

CONCLUSIONS

This study is the first to identify a critical role for BDNF in rehabilitation-induced recovery after stroke, and our results suggest that new treatments to enhance BDNF would constitute a promising therapy for promoting recovery of function after stroke.

Panax Notoginseng Burk attenuates impairment of learning and memory functions and increases ED1, BDNF and beta-secretase immunoreactive cells in chronic stage ischemia-reperfusion injured rats

Panax Notoginseng Burk (PN) has been reported to improve blood circulation, as well as learning and memory functions. The purpose of the present study was to investigate the effect of PN on learning and memory functions in chronic cerebral infarct rats. A cerebral infarct animal model was established by blocking the blood flow of both common carotid arteries and right middle cerebral artery for 90 min followed by reperfusion for 4 weeks. PN (0.5 g/kg) was administered orally 3 days per week for 4 weeks, whereas the control group provided bait and water only. The learning and memory functions were estimated by measuring how successful rats were able to negotiate an 8-arm radial maze test; the test was performed after operation once a week for 4 weeks. Finally, the rats were sacrificed and their brains were removed. The brains were sectioned and analyzed for ED1, glial fibrillary acid protein (GFAP), nuclear factor-kappaB, and brain derivative neurotrophin factor (BDNF) and beta-secretase by immunostaining. Cerebral infarct rats given PN were able to successfully navigate the 8-arm radial maze test four weeks after cerebral infarction. PN also increased ED1, BDNF and beta-secretase immunoreactive cells, but did not increase GFAP and NF-kappaB immunoreactive cells. PN attenuated the reduction in learning and memory functions induced by cerebral infarction in cerebral ischemia-reperfusion injured rats; it also increased the amount of activated microglia and BDNF. These data suggest that the effect of PN, at least in part, is closely related to the increase in BDNF that was generated by activated microglia. The effect that PN has on astrocytes, NF-kappaB and beta-secreatase immunoreactive cells requires further study.

Repairing the human brain after stroke: I. Mechanisms of spontaneous recovery

Stroke remains a leading cause of adult disability. Some degree of spontaneous behavioral recovery is usually seen in the weeks after stroke onset. Variability in recovery is substantial across human patients. Some principles have emerged; for example, recovery occurs slowest in those destined to have less successful outcomes. Animal studies have extended these observations, providing insight into a broad range of underlying molecular and physiological events. Brain mapping studies in human patients have provided observations at the systems level that often parallel findings in animals. In general, the best outcomes are associated with the greatest return toward the normal state of brain functional organization. Reorganization of surviving central nervous system elements supports behavioral recovery, for example, through changes in interhemispheric lateralization, activity of association cortices linked to injured zones, and organization of cortical representational maps. A number of factors influence events supporting stroke recovery, such as demographics, behavioral experience, and perhaps genetics. Such measures gain importance when viewed as covariates in therapeutic trials of restorative agents that target stroke recovery.

Learning decreases A beta*56 and tau pathology and ameliorates behavioral decline in 3xTg-AD mice

Transgenic mouse models of Alzheimer's disease (AD), such as the 3xTg-AD mice, are instrumental for elucidating genetic, pharmacologic, environmental, and behavioral factors that affect the cognitive phenotype. Here we present the novel findings that longitudinal water-maze spatial training produces a significant, albeit transient, improvement in subsequent learning performance and reduces amyloid beta (Abeta) and tau neuropathology. The 3xTg-AD mice were trained and tested at 3 month intervals from 2 to 18 months. Separate groups of naive mice were also tested at each age. The improvement in performance seen at 6 and 12 months is dependent on spatial training, because animals that were similarly handled and exposed to swimming without a learning contingency failed to show improved performance. Training before the development of overt neuropathology is required for full expression of the training effect because we found it delays Abeta redistribution to extracellular plaques and reduces Abeta oligomers associated with cognitive decline. In addition, learning leads to decreased glycogen synthase kinase-3beta activity, which likely underlies the reduced tau pathology. The previous training effects on both maze performance and neuropathology are attenuated at 15 and 18 months. These findings indicate that, in young and middle-aged 3xTg-AD mice, repeated spatial training can significantly delay the development of neuropathology and decline in spatial memory.

Functional recovery in rats with chronic spinal cord injuries after exposure to an enriched environment

BACKGROUND/OBJECTIVE

The objective of this study was to determine the effect of environmental enrichment on the sensorimotor function of rats with chronic spinal cord injuries.

DESIGN

Adult Sprague-Dawley rats received a contusive injury of moderate severity at vertebral level T8 using a weight-drop device. Three months after injury, 1 randomized group (n = 16) of rats was placed in an enriched environment, whereas the control group (n = 16) remained housed in standard laboratory cages (2/cage).

METHODS

Animals were placed in an enriched environment for 4 weeks beginning at 3 months after injury. The enriched environment consisted of a large cage (5-6 rats/cage) with access to items such as tubes, ramps, and running wheel, with items changed daily.

MAIN OUTCOME MEASURES

Functional evaluation consisted of the open field Basso, Beattie and Bresnahan (BBB) locomotor test and the tests that form the combined behavioral score (CBS). The CBS includes motor score, toe spread, placing, withdrawal, righting, inclined plane, hot plate, and swim tests. Behavioral testing was repeated 7 times before and after the period of intervention.

RESULTS

The group placed in the enriched environment scored significantly better on the BBB (ANOVA repeated-measures, P < 0.01) test and CBS (ANOVA repeated-measures, P < 0.01).

CONCLUSIONS

Environmental enrichment results in significant functional improvement in animals with spinal cord injury even with a substantial delay in initiating treatment after injury. The features of an enriched environment that may be responsible for the improvement include social interactions, exercise, and novel items in an interesting environment. These findings suggest a continued plasticity of the chronically injured rat spinal cord and a possible therapeutic intervention for people with spinal cord injury.

Decreased expression of brain-derived neurotrophic factor in BDNF+/− mice is associated with enhanced recovery of motor performance and increased neuroblast number following experimental stroke

Brain-derived neurotrophic factor (BDNF) is involved in brain plasticity and neuronal survival. Generally, BDNF enhances synaptic activity and neurite growth, although the effect of BDNF on neuronal survival and brain plasticity following injury is equivocal. Housing rats in an enriched environment after experimental stroke enhances recovery of sensory-motor function, which is associated with a decrease in the BDNF mRNA and protein levels. We used BDNF(+/-) mice and wild-type littermate mice to investigate whether the decrease in the brain levels of BDNF affected motor function or infarct volume following transient occlusion of the middle cerebral artery (tMCAO) for 40 min. We found that the BDNF(+/-) mice had a significantly improved motor function on the rotating pole test 2 weeks after tMCAO compared with wild-type mice. When intermittently exposed to an enriched environment following tMCAO, the wild-type mice improved motor function to the same degree as BDNF(+/-) mice. There was no effect of BDNF reduction on infarct volume. Neurogenesis is induced following experimental stroke, and in the striatum of BDNF(+/-) mice significantly increased numbers of neuroblasts compared with wild-type mice were seen, both in standard and in enriched conditions. We conclude that decreasing brain levels of BDNF enhances the recovery of function following experimental stroke.

Enriched environment and spatial learning enhance hippocampal neurogenesis and salvages ischemic penumbra after focal cerebral ischemia

Enriched environment (EE) has been shown to increase neurogenesis in the adult brain. The aim of this study is to determine the effect of EE and spatial learning on neurogenesis following ischemic stroke. Male adult SD rats were subjected to sham surgery or distal middle cerebral artery occlusion (MCAO). MCAO induced a transient increase followed by a sustained depression of progenitor cell proliferation and neuroblast production below baseline level in both ipsilateral and contralateral DG compared to sham. Increased neuronal differentiation and neurogenesis in the DG were observed in both sham and MCAO rats following 8 weeks in the EE combined with spatial learning, compared to rats housed in the standard environment. EE/Learning also restored the total number of neuroblasts in the DG after MCAO compared to sham. Furthermore, EE/learning enhanced the density of NeuN positive cells in the ischemic penumbra, though no new neurons were detected in this region.

Exercise increased BDNF and trkB in the contralateral hemisphere of the ischemic rat brain

Previous studies have suggested that brain-derived neurotrophic factor (BDNF) and trkB both have a role in plasticity following brain insults and exercise increases BDNF and trkB mRNA levels in the normal brain. We attempted to determine whether treadmill exercise improves motor function following experimental cerebral ischemia, and whether motor outcome is associated with BDNF and trkB expression. We subjected adult male Sprague-Dawley rats to a permanent ischemia, followed by either 12 days of treadmill exercise or non-exercise. In the exercise group, improvements in the motor behavior index were found and BDNF and trkB proteins in contralateral hemisphere were increased. This study suggests that after permanent brain ischemia, exercise improves motor performance and elevates BDNF and trkB proteins in the contralateral hemisphere.

Endurance exercise regimens induce differential effects on brain-derived neurotrophic factor, synapsin-I and insulin-like growth factor I after focal ischemia

The optimal amount of endurance exercise required to elevate proteins involved in neuroplasticity during stroke rehabilitation is not known. This study compared the effects of varying intensities and durations of endurance exercise using both motorized and voluntary running wheels after endothelin-I-induced focal ischemia in rats. Hippocampal levels of brain-derived neurotrophic factor, insulin-like growth factor I and synapsin-I were elevated in the ischemic hemisphere even in sedentary animals suggesting an intrinsic restorative response 2 weeks after ischemia. In the sensorimotor cortex and the hippocampus of the intact hemisphere, one episode of moderate walking exercise, but not more intense running, resulted in the greatest increases in levels of brain-derived neurotrophic factor and synapsin-I. Exercise did not increase brain-derived neurotrophic factor, insulin-like growth factor I or synapsin-I in the ischemic hemisphere. In voluntary running animals, both brain and serum insulin-like growth factor I appeared to be intensity dependent and were associated with decreasing serum levels of insulin-like growth factor I and increasing hippocampal levels of insulin-like growth factor I in the ischemic hemisphere. This supports the notion that exercise facilitates the movement of insulin-like growth factor I across the blood-brain barrier. Serum corticosterone levels were elevated by all exercise regimens and were highest in rats exposed to motorized running of greater speed or duration. The elevation of corticosterone did not seem to alter the expression of the proteins measured, however, graduated exercise protocols may be indicated early after stroke. These findings suggest that relatively modest exercise intervention can increase proteins involved in synaptic plasticity in areas of the brain that likely subserve motor relearning after stroke.

Prophylactic activation of neuroprotective stress response pathways by dietary and behavioral manipulations

It is well established that when most types of cells, including neurons, are exposed to a mild stress they increase their ability to resist more severe stress. This "preconditioning" phenomenon involves up-regulation of genes that encode cytoprotective proteins such as heat-shock proteins and growth factors. We found that a similar beneficial cellular stress response can be induced in neurons throughout the brain by a "meal-skipping" dietary restriction (DR) regimen in rats and mice. DR is effective in protecting neurons and improving functional outcome in models of stroke, Alzheimer's, Parkinson's and Huntington's diseases. DR induces an increase in the levels of brain-derived neurotrophic factor (BDNF) and heat-shock proteins in neurons. DR also stimulates neurogenesis in the hippocampus, and BDNF plays a role in this effect of DR. Physical exercise and environmental enrichment are two other manipulations that have been shown to induce BDNF expression in the brain, presumably because it is a mild cellular stress. When taken together with epidemiological and clinical studies in humans, the data from animal studies suggest that it may be possible to reduce the risk for age-related neurodegenerative disorders through dietary and behavioral modifications that act by promoting neuronal plasticity and survival.

Social interaction improves experimental stroke outcome

BACKGROUND AND PURPOSE

Social interaction can have a profound effect on health. The purpose of the present study was to determine whether affiliative social interactions before and after stroke improve ischemic outcomes as assessed through histological analysis and behavioral assays.

METHODS

Male and female C57BL/6 mice were housed individually or with an ovariectomized female. Behavioral assessments were made 24 hours before 60 or 90 minutes of transient intraluminal middle cerebral artery occlusion (MCAO) or SHAM surgery and after 7 days of reperfusion. Two hours after behavioral testing on day 7, infarct size was determined by 2,3,5-triphenyltetrazolium histology, and blood samples were collected for assessment of corticosterone and C-reactive protein (CRP) concentrations.

RESULTS

Pair housing significantly decreased infarct size and improved contralateral paw use in 60-minute MCAO males and 90-minute MCAO females compared with socially isolated cohorts. Housing condition had no significant effect on infarct size in females that underwent 60 minutes of MCAO, but pair housing was associated with improved contralateral paw use relative to socially isolated mice. In a separate cohort of males, intraischemic CRP concentration was significantly reduced in pair-housed males relative to isolated males.

CONCLUSIONS

Affiliative interaction during the peri-ischemic period reduces intraischemic CRP concentration, decreases ischemic damage in male and female mice, and improves behavioral outcome.

Nature, nurture and neurology: gene-environment interactions in neurodegenerative disease. FEBS Anniversary Prize Lecture delivered on 27 June 2004 at the 29th FEBS Congress in Warsaw

Neurodegenerative disorders, such as Huntington's, Alzheimer's, and Parkinson's diseases, affect millions of people worldwide and currently there are few effective treatments and no cures for these diseases. Transgenic mice expressing human transgenes for huntingtin, amyloid precursor protein, and other genes associated with familial forms of neurodegenerative disease in humans provide remarkable tools for studying neurodegeneration because they mimic many of the pathological and behavioural features of the human conditions. One of the recurring themes revealed by these various transgenic models is that different diseases may share similar molecular and cellular mechanisms of pathogenesis. Cellular mechanisms known to be disrupted at early stages in multiple neurodegenerative disorders include gene expression, protein interactions (manifesting as pathological protein aggregation and disrupted signaling), synaptic function and plasticity. Recent work in mouse models of Huntington's disease has shown that enriching the environment of transgenic animals delays the onset and slows the progression of Huntington's disease-associated motor and cognitive symptoms. Environmental enrichment is known to induce various molecular and cellular changes in specific brain regions of wild-type animals, including altered gene expression profiles, enhanced neurogenesis and synaptic plasticity. The promising effects of environmental stimulation, demonstrated recently in models of neurodegenerative disease, suggest that therapy based on the principles of environmental enrichment might benefit disease sufferers and provide insight into possible mechanisms of neurodegeneration and subsequent identification of novel therapeutic targets. Here, we review the studies of environmental enrichment relevant to some major neurodegenerative diseases and discuss their research and clinical implications.

Postischemic exercise attenuates whereas enriched environment has certain enhancing effects on lesion-induced subventricular zone activation in the adult rat

Experimental stroke increases cell proliferation and neurogenesis in the subventricular zone (SVZ) and in the dentate gyrus subgranular zone (SGZ) in the adult mammalian brain. This study examined the effects of postischemic voluntary exercise (running wheel) and environmental enrichment on the SVZ and SGZ 1 week after focal cortical ischemia in adult spontaneously hypertensive rats. Immunohistochemical labeling was performed for incorporation of specific cell markers such as Ki67 and 5-bromodeoxyuridine (proliferating and newborn cells), terminal deoxynucleotidyl transferase-mediated dUTP in situ nick-end labeling (apoptotic cells), Sox-2 and glial fibrillary acidic protein (neural stem and progenitor cells), polysialylated neural cell adhesion molecule and doublecortin (neuroblasts). Postischemic exercise and environmental enrichment differentially modulated SVZ cell genesis but lacked effects on the SGZ. Lesion-induced proliferation of neural stem/progenitor cells and neuronal precursors was attenuated in stroke runners without any effects on apoptosis or neuronal migration in the forebrain. Running activity did not affect the SVZ in intact rats. In contrast to postischemic wheel running, postischemic environmental enrichment did not have attenuating effects on the ipsilateral SVZ and increased proliferating putative neural stem cells and neuronal precursors contralaterally. A significant functional improvement, assessed using a rotating pole, was observed only in the postischemically enriched group and was likely due to other types of plasticity than neuronal replacement at this early time point. It may be concluded that in contrast to enriched environment, exercise during the first postischemic week might be detrimental for regenerative processes initiated in the SVZ after stroke.

Motor response to amphetamine treatment, task-specific training, and limited motor experience in a postacute animal stroke model

Despite advances in acute treatment of ischemic cerebrovascular events, the most common clinical outcome is disabling neurological impairment. Despite experimental evidence that psychostimulant treatment can positively affect recovery rate after focal brain lesions, beyond rehabilitation therapies there are no currently accepted medical treatments indicated for diminishing neurological impairment after clinically established stroke. To test the effect of amphetamine, task-specific training, limiting motor experience, and their interaction on motor recovery in a postacute animal model of stroke, animals were nonaversively trained in beam walking before a unilateral photochemical sensorimotor cortex lesion and tested for 10 days after lesion. Animals were randomized to groups receiving: a single session of motor training 24 h after lesion; a single injection of amphetamine 2 mg/kg 24 h after lesion; beam-walking experience limited to testing on days 1 and 10 after lesion; and groups that received amphetamine treatment combined with training or combined with limited experience. Motor recovery was maximally enhanced by training, delayed by amphetamine treatment, and most negatively affected by limiting beam-walking experience during the recovery period. These findings support physical training after stroke, indicating that limiting physical activity negatively affects motor recovery and raises questions about the role of stimulant treatment to enhance motor recovery in the postacute phase after stroke.

Gene Expression Profiling in the Intact and Injured Brain Following Environmental Enrichment

An enriched environment promotes structural changes in both injured and intact brain and improves behavioral performance. In 2 different experimental approaches, the effects of enriched surroundings were analyzed utilizing DNA microarrays. First, gene expression patterns of the sensorimotor cortex and the hippocampus of noninjured adult rats with enriched housing were compared with analogous regions of rats kept in standard cages. Second, circumscribed infarcts affecting the forelimb area of the sensorimotor cortex were induced, and gene expression patterns of the non-necrotic ipsilesional as well as the contralesional homotopic cortex of rats (postlesionally enriched housing versus standard) were analyzed. In the intact brain, the hippocampus, which had 43 upregulations and 15 downregulations showed more changes than the sensorimotor cortex, which had 13 upregulations and 4 downregulations, indicating a greater responsiveness of the hippocampus to environmental stimuli. In the injured brain, enrichment led ipsilesionally to 28 downregulations and 14 upregulations, while in the contralesional cortex, upregulations prevailed with 46 upregulations and 13 downregulations. The larger number of genes responsive to enrichment in the contralesional cortex (59 gene regulations) as compared to the analogous area (i.e. sensorimotor cortex) of the intact brain (17 gene regulations) likely reflects increased susceptibility for plastic changes due to injury. With the exception of the perilesional cortex, similar functional groups of genes were differentially regulated in different brain regions/paradigms, suggesting basically similar molecular cascades being involved in reorganizing the brain following external stimuli. Many of the genes detected here correspond to molecular pathways known to be involved in neuroplasticity, whereas others provide new and hitherto unrecognized entry points.

Environmental enrichment rescues protein deficits in a mouse model of Huntington's disease, indicating a possible disease mechanism

Huntington's disease (HD) is a devastating neurodegenerative disorder caused by a CAG repeat expansion encoding an extended polyglutamine tract in the huntingtin protein. Transgenic mice expressing a human huntingtin transgene containing an expanded CAG repeat (R6/1 model) develop a neurodegenerative disorder closely resembling human HD. Previous work demonstrated that environmental enrichment delays the onset of motor symptoms in this mouse model. We confirmed that at 5 months of age, enrichment ameliorates motor symptoms (assessed using the rotarod test) and prevents loss of body weight induced by the HD transgene. We further examined molecular consequences of enrichment by determining changes in protein levels in the neostriatum, hippocampus, and anterior cortex using quantitative Western blot analysis. Non-enriched HD mice have severe reductions in BDNF in the hippocampus and striatum at 5 months, which are entirely rescued by enrichment. BDNF levels are unaltered by HD in the anterior cortex, suggesting that enrichment might prevent HD-induced impairment of anterograde transport of this neurotrophin to the striatum. NGF is unaffected by HD. Non-enriched HD mice also exhibit deficits in dopamine and cAMP-regulated phosphoprotein (32 kDa) in striatum and anterior cortex. Environmental enrichment rescues the cortical but not the striatal deficit at 5 months. These results suggest that environmental enrichment benefits animals at early stages of the disease by rescuing protein deficits, possibly through rescuing transcription or protein transport problems.

Motor enrichment and the induction of plasticity before or after brain injury

Voluntary exercise, treadmill activity, skills training, and forced limb use have been utilized in animal studies to promote brain plasticity and functional change. Motor enrichment may prime the brain to respond more adaptively to injury, in part by upregulating trophic factors such as GDNF, FGF-2, or BDNF. Discontinuation of exercise in advance of brain injury may cause levels of trophic factor expression to plummet below baseline, which may leave the brain more vulnerable to degeneration. Underfeeding and motor enrichment induce remarkably similar molecular and cellular changes that could underlie their beneficial effects in the aged or injured brain. Exercise begun before focal ischemic injury increases BDNF and other defenses against cell death and can maintain or expand motor representations defined by cortical microstimulation. Interfering with BDNF synthesis causes the motor representations to recede or disappear. Injury to the brain, even in sedentary rats, causes a small, gradual increase in astrocytic expression of neurotrophic factors in both local and remote brain regions. The neurotrophic factors may inoculate those areas against further damage and enable brain repair and use-dependent synaptogenesis associated with recovery of function or compensatory motor learning. Plasticity mechanisms are particularly active during time-windows early after focal cortical damage or exposure to dopamine neurotoxins. Motor and cognitive impairments may contribute to self-imposed behavioral impoverishment, leading to a reduced plasticity. For slow degenerative models, early forced forelimb use or exercise has been shown to halt cell loss, whereas delayed rehabilitation training is ineffective and disuse is prodegenerative. However, it is possible that, in the chronic stages after brain injury, a regimen of exercise would reactivate mechanisms of plasticity and thus enhance rehabilitation targeting residual functional deficits.

BDNF and activity-dependent synaptic modulation

It is widely accepted that neuronal activity plays a pivotal role in synaptic plasticity. Neurotrophins have emerged recently as potent factors for synaptic modulation. The relationship between the activity and neurotrophic regulation of synapse development and plasticity, however, remains unclear. A prevailing hypothesis is that activity-dependent synaptic modulation is mediated by neurotrophins. An important but unresolved issue is how diffusible molecules such as neurotrophins achieve local and synapse-specific modulation. In this review, I discuss several potential mechanisms with which neuronal activity could control the synapse-specificity of neurotrophin regulation, with particular emphasis on BDNF. Data accumulated in recent years suggest that neuronal activity regulates the transcription of BDNF gene, the transport of BDNF mRNA and protein into dendrites, and the secretion of BDNF protein. There is also evidence for activity-dependent regulation of the trafficking of the BDNF receptor, TrkB, including its cell surface expression and ligand-induced endocytosis. Further study of these mechanisms will help us better understand how neurotrophins could mediate activity-dependent plasticity in a local and synapse-specific manner.

Effects of cortical ischemia and postischemic environmental enrichment on hippocampal cell genesis and differentiation in the adult rat

The study aimed to elucidate the effects of cortical ischemia and postischemic environmental enrichment on hippocampal cell genesis. A cortical infarct was induced by a permanent ligation of the middle cerebral artery distal to the striatal branches in 6-month-old spontaneously hypertensive rats. Bromodeoxyuridine (BrdU) was administered as 7 consecutive daily injections starting 24 hours after surgery and animals were housed in standard or enriched environment. Four weeks after completed BrdU administration, BrdU incorporation and its co-localization with the neuronal markers NeuN and calbindin D28k, and the astrocytic marker glial fibrillary acidic protein in the granular cell layer and subgranular zone of the hippocampal dentate gyrus were determined with immunohistochemistry and were quantified stereologically. Compared with sham-operated rats, rats with cortical infarcts had a five-to sixfold ipsilateral increase in BrdU-labeled cells. About 80% of the new cells were neurons. Differential postischemic housing did not influence significantly the total number of surviving BrdU-labeled cells or newborn neurons. However, postischemic environmental enrichment increased the ipsilateral generation of astrocytes normalizing the astrocyte-to-neuron ratio, which was significantly reduced in rats housed in standard environment postischemically.