Behaviorally-induced ultrastructural plasticity in the hippocampal region after cerebral ischemia

Environmental enrichment enhanced neurogenesis and behavioral recovery after stroke in aged rats

BACKGROUND AND PURPOSE

Age is identified as a significant prognostic factor for poorer outcome after stroke. However, environmental enrichment (EE) has been reported to promote functional recovery after ischemic stroke. The purpose of this study was to investigate whether environmental enrichment was beneficial to ischemic stroke in aged rats.

METHODS

Aged rats were randomly assigned as control rats, rats subjected to cerebral ischemia, and rats with cerebral ischemia treated with EE for 30 days. Focal cortical ischemia was induced by intracranial injection of endothelin-1 (ET-1). EE housing began one day after focal ischemia and was maintained for the whole experimental period. We used immunofluorescence staining to analyze the neurogenesis in the subventricular zone (SVZ) and TdT-mediated dUTP-biotin nick-end labeling (TUNEL) assay to evaluate apoptosis. The expression of neuronal nuclei, glial fibrillary acidic protein (GFAP) and Iba-1 around the infarcted area were also measured by double immunohistochemistry.

RESULTS

EE enhanced the proliferation of newborn neurons in the SVZ, as well as increased the long-term survival of newborn neurons. EE also exerted effects on inflammation after stroke. Furthermore, EE suppressed apoptosis and improved the motor functions after stroke in the aged rats.

CONCLUSIONS

EE improved post-stroke recovery on the basis of enhancing neurogenesis in aged rats.

Musical practice and BDNF plasma levels as a potential marker of synaptic plasticity: an instrument of rehabilitative processes

Background and objectives

The aim of the study was to investigate the influence of musical practice on brain plasticity. BDNF (brain-derived neurotrophic factor) is a neurotrophin involved in neuroplasticity and synaptic function.

Materials and methods

We recruited 48 healthy subjects of equal age and sex (21 musicians and 27 non-musicians). All subjects were administered the AQ (Autism-Spectrum Questionnaire) and plasma levels (PLs) of BDNF, oxytocin (OT), and vasopressin (VP) were measured in the blood sample of every participant.

Results.

The difference between BDNF PLs in the two groups was found to be statistically significant (t = − 2.214, p = 0.03). Furthermore, oxytocin (OT) PLs and musical practice were found to be independent positive predictors of BDNF PLs (p < 0.04). We also found a negative correlation between BDNF PLs and AD (attention to detail) sub-scale score of AQ throughout the whole sample. Assuming BDNF PLs to be a marker of synaptic plasticity, higher PLs could be associated with the activation of alternative neural pathways: a lower score in the “attention to detail” sub-scale could imply greater flexibility of higher cerebral functions among musicians.

Further researches should be conducted to assess the rehabilitative usefulness of these findings among patients affected by psychiatric disorders.

A Key Role for Prefrontocortical Small Conductance Calcium-Activated Potassium Channels in Stress Adaptation and Rapid Antidepressant Response

The muscarinic acetylcholine receptor antagonist scopolamine elicits rapid antidepressant activity, but its underlying mechanism is not fully understood. In a chronic stress model, a single low-dose administration of scopolamine reversed depressive-like reactivity. This antidepressant-like effect was mediated via a muscarinic M1 receptor–SKC pathway because it was mimicked by intra-medial prefrontal cortex (intra-mPFC) infusions of scopolamine, of the M1 antagonist pirenzepine or of the SKC antagonist apamin, but not by the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine. Extracellular and whole-cell recordings revealed that scopolamine and ketamine attenuate the SKC-mediated action potential hyperpolarization current and rapidly enhance mPFC neuronal excitability within the therapeutically relevant time window. The SKC agonist 1-EBIO abrogated scopolamine-induced antidepressant activity at a dose that completely suppressed burst firing activity. Scopolamine also induced a slow-onset activation of raphe serotonergic neurons, which in turn was dependent on mPFC-induced neuroplasticity or excitatory input, since mPFC transection abolished this effect. These early behavioral and mPFC activational effects of scopolamine did not appear to depend on prefrontocortical brain-derived neurotrophic factor and serotonin-1A activity, classically linked to SSRIs, and suggest a novel mechanism associated with antidepressant response onset through SKC-mediated regulation of activity-dependent plasticity.

Alterations in the corticotropin-releasing hormone (CRH) neurocircuitry: Insights into post stroke functional impairments

Although it is well accepted that changes in the regulation of the hypothalamic-pituitary adrenal (HPA) axis may increase susceptibility to affective disorders in the general population, this link has been less examined in stroke patients. Yet, the bidirectional association between depression and cardiovascular disease is strong, and stress increases vulnerability to stroke. Corticotropin-releasing hormone (CRH) is the central stress hormone of the HPA axis pathway and acts by binding to CRH receptors (CRHR) 1 and 2, which are located in several stress-related brain regions. Evidence from clinical and animal studies suggests a role for CRH in the neurobiological basis of depression and ischemic brain injury. Given its importance in the regulation of the neuroendocrine, autonomic, and behavioral correlates of adaptation and maladaptation to stress, CRH is likely associated in the pathophysiology of post stroke emotional impairments. The goals of this review article are to examine the clinical and experimental data describing (1) that CRH regulates the molecular signaling brain circuit underlying anxiety- and depression-like behaviors, (2) the influence of CRH and other stress markers in the pathophysiology of post stroke emotional and cognitive impairments, and (3) context and site specific interactions of CRH and BDNF as a basis for the development of novel therapeutic targets. This review addresses how the production and release of the neuropeptide CRH within the various regions of the mesocorticolimbic system influences emotional and cognitive behaviors with a look into its role in psychiatric disorders post stroke.

Critical Role of Endoplasmic Reticulum Stress in Chronic Intermittent Hypoxia-Induced Deficits in Synaptic Plasticity and Long-Term Memory

AIMS

This study examined the role of endoplasmic reticulum (ER) stress in mediating chronic intermittent hypoxia (IH)-induced neurocognitive deficits. We designed experiments to demonstrate that ER stress is initiated in the hippocampus under chronic IH and determined its role in apoptotic cell death, impaired synaptic structure and plasticity, and memory deficits.

RESULTS

Two weeks of IH disrupted ER fine structure and upregulated ER stress markers, glucose-regulated protein 78, caspase-12, and C/EBP homologous protein, in the hippocampus, which could be suppressed by ER stress inhibitors, tauroursodeoxycholic acid (TUDCA) and 4-phenylbutyric acid. Meanwhile, ER stress induced apoptosis via decreased Bcl-2, promoted reactive oxygen species production, and increased malondialdehyde formation and protein carbonyl, as well as suppressed mitochondrial function. These effects were largely prevented by ER stress inhibitors. On the other hand, suppression of oxidative stress could reduce ER stress. In addition, the length of the synaptic active zone and number of mature spines were reduced by IH. Long-term recognition memory and spatial memory were also impaired, which was accompanied by reduced long-term potentiation in the Schaffer collateral pathway. These effects were prevented by coadministration of the TUDCA.

INNOVATION AND CONCLUSION

These results show that ER stress plays a critical role in underlying memory deficits in obstructive sleep apnea (OSA)-associated IH. Attenuators of ER stress may serve as novel adjunct therapeutic agents for ameliorating OSA-induced neurocognitive impairment.

Neuroprotective effects of enriched environment housing after transient global cerebral ischaemia are associated with the upregulation of insulin-like growth factor-1 signalling

Aims

Use of enriched environment (EE) housing has been shown to promote recovery from cerebral ischaemic injury but the underlying mechanisms of their beneficial effects remains unclear. Here we examined whether the beneficial effects of EE housing on ischaemia‐induced neurodegeneration and cognitive impairment are associated with increased insulin‐like growth factor‐1 (IGF‐1) signalling in the hippocampus.

Methods

Forty‐two adult male Wistar rats were included in the study and received either ischaemia or sham surgery. Rats in each group were further randomized to either: EE or standard laboratory cage housing (control). Rats were placed in their assigned housing condition immediately after recovery from anaesthesia. Behavioural testing in the cued learning and discrimination learning tasks were conducted 2 weeks after ischaemia. Rats were euthanized after behavioural testing and the hippocampus was analysed for IGF‐1 level, IGF‐1 receptor (IGF‐1R) activation, protein kinase B (Akt) pathway activation, neurone loss and caspase 3 expression.

Results

Our data showed that EE housing: (1) mitigated ischaemia‐induced neuronal loss; (2) attenuated ischaemia‐induced increase in caspase 3 immunoreactivity in the hippocampus; (3) ameliorated ischaemia‐induced cognitive impairments; and (4) increased IGF‐1R activation and signalling through the Akt pathway after ischaemic injury.

Conclusion

Ultimately, these findings suggest the possibility that IGF‐1 signalling may be one of the underlying mechanisms involved in the beneficial effects of EE in optimizing recovery following cerebral ischaemic injury.

The effects of poststroke aerobic exercise on neuroplasticity: a systematic review of animal and clinical studies

Aerobic exercise may be a catalyst to promote neuroplasticity and recovery following stroke; however, the optimal methods to measure neuroplasticity and the effects of training parameters have not been fully elucidated. We conducted a systematic review and synthesis of clinical trials and studies in animal models to determine (1) the extent to which aerobic exercise influences poststroke markers of neuroplasticity, (2) the optimal parameters of exercise required to induce beneficial effects, and (3) consistent outcomes in animal models that could help inform the design of future trials. Synthesized findings show that forced exercise at moderate to high intensity increases brain-derived neurotrophic factor (BDNF), insulin-like growth factor-I (IGF-I), nerve growth factor (NGF), and synaptogenesis in multiple brain regions. Dendritic branching was most responsive to moderate rather than intense training. Disparity between clinical stroke and stroke models (timing of initiation of exercise, age, gender) and clinically viable methods to measure neuroplasticity are some of the areas that should be addressed in future research.

Aerobic exercise effects on neuroprotection and brain repair following stroke: a systematic review and perspective

Aerobic exercise (AE) enhances neuroplasticity and improves functional outcome in animal models of stroke, however the optimal parameters (days post-stroke, intensity, mode, and duration) to influence brain repair processes are not known. We searched PubMed, CINAHL, PsychInfo, the Cochrane Library, and the Central Register of Controlled Clinical Trials, using predefined criteria, including all years up to July 2013 (English language only). Clinical studies were included if participants had experienced an ischemic or hemorrhagic stroke. We included animal studies that utilized any method of global or focal ischemic stroke or intracerebral hemorrhage. Any intervention utilizing AE-based activity with the intention of improving cardiorespiratory fitness was included. Of the 4250 titles returned, 47 studies (all in animal models) met criteria and measured the effects of exercise on brain repair parameters (lesion volume, oxidative damage, inflammation and cell death, neurogenesis, angiogenesis and markers of stress). Our synthesized findings show that early-initiated (24-48h post-stroke) moderate forced exercise (10m/min, 5-7 days per week for about 30min) reduced lesion volume and protected perilesional tissue against oxidative damage and inflammation at least for the short term (4 weeks). The applicability and translation of experimental exercise paradigms to clinical trials are discussed.

Chronic neuroinflammation and cognitive impairment following transient global cerebral ischemia: role of fractalkine/CX3CR1 signaling

Although neuroinflammation has been studied extensively in animal models of cerebral ischemia, their contrasting functions are still not completely understood. A major participant in neuroinflammation is microglia and microglial activation usually regulated by the chemokine CX3CL1 (fractalkine) and its receptor, CX3CR1. Here, we examined the involvement of CX3CR1 on ischemia-induced chronic neuroinflammation and cognitive function using small interfering RNA (siRNA). Forty adult male Wistar rats were included in the study and received either ischemia or sham surgery then were randomized to receive either CX3CR1 siRNA or scrambled RNA as control starting at 7 days after reperfusion. Behavioral testing commenced 28 days after siRNA delivery and all rats were euthanized after behavioral testing. Our data showed that: (i) transient global cerebral ischemia significantly decreased fractalkine/CX3CR1 signaling in the hippocampus; (ii) inhibition of CX3CR1 function exacerbated the ischemia-induced chronic increase in microglial activation and pro-inflammatory cytokine levels; (iii) inhibition of CX3CR1 function worsened ischemia-induced chronic cognitive impairment; (iv) inhibition of CX3CR1 function in sham rats resulted in increased IL-1β expression and impaired behavioral performance. However, no significant effect of CX3CR1 on ischemia-induced neurodegeneration was seen. The present study provides important insight to understanding the involvement of CX3CR1 in chronic neuroinflammation and cognitive impairment.

Decreased neuroinflammation and increased brain energy homeostasis following environmental enrichment after mild traumatic brain injury is associated with improvement in cognitive function

Background

Persistent neuroinflammation and disruptions in brain energy metabolism is commonly seen in traumatic brain injury (TBI). Because of the lack of success of most TBI interventions and the documented benefits of environmental enrichment (EE) in enhancing brain plasticity, here we focused our study on use of EE in regulating injury-induced neuroinflammation and disruptions in energy metabolism in the prefrontal cortex and hippocampus. Adult male Wistar rats were used in the study and randomly assigned to receive either: mild TBI (mTBI) using the controlled cortical injury model or sham surgery. Following surgery, rats from each group were further randomized to either: EE housing or standard laboratory housing (CON). After 4 weeks of recovery, cognitive testing was performed using the non-matching-to-sample and delayed non-matching-to-sample tasks. After completion of behavioral testing, levels of the pro-inflammatory cytokines IL-1β and TNF-α and the anti-inflammatory cytokine IL-10 were measured. In addition, levels of AMPK (adenosine monophosphate-activated protein kinase), phosphorylated AMPK and uMtCK (ubiquitous mitochondrial creatine kinase) were assessed as measures of brain energy homeostasis.

Results

Our results showed that EE: (1) decreased the pro-inflammatory cytokines IL-1β and TNF-α and enhanced levels of the anti-inflammatory cytokine IL-10 after mTBI; (2) mitigated mTBI-induced cognitive impairment; and (3) attenuated mTBI-induced downregulation in pAMPK/AMPK ratio and uMtCK levels.

Conclusions

Our data demonstrated the potential of EE to modulate the persistent: (1) neuroinflammatory response seen following mTBI, and (2) persistent disturbance in brain energy homeostasis. It is possible that through the mechanism of modulating neuroinflammation, EE housing was able to restore the disruption in energy metabolism and enhanced functional recovery after mTBI.

Tenuigenin ameliorates learning and memory impairments induced by ovariectomy

Estrogen deficiency is associated with cognitive impairment. Hormone replacement therapy (HRT) has proven to be effective in preventing and reversing the memory and learning deficiencies. However, conventional estrogenic treatment could increase the risks of breast cancer and venous thromboembolism. Tenuigenin (TEN) is putatively believed as the active component extracted from a Chinese herb Polygala tenuifolia root. Although TEN has been shown to enhance learning and memory in healthy mice, it remains unknown whether or not TEN could ameliorate learning and memory impairments. In the present study, mice were divided into four groups: sham-operated (sham), ovariectomized (OVX), OVX+estradiol benzoate (EB) and OVX+TEN groups. Step-through passive avoidance and Y-maze tests were used to assess learning and memory abilities, and the number of nitric oxide synthase (NOS) positive neurons and the synaptic measurement of hippocampal CA1 area were examined. The results showed that TEN was given orally to OVX mice, leading to the improvement of learning and memory in step-through passive avoidance and Y-maze tests. TEN could reduce the loss of NOS positive neurons and prevent the synaptic morphological changes induced by ovariectomy. Our results suggest that TEN may exert a potential therapeutic value for menopause cognitive dysfunction.

Environmental enrichment prevents behavioral deficits and oxidative stress caused by chronic cerebral hypoperfusion in the rat

AIMS

The aim of the present study was to evaluate the neuroprotective effects of environmental enrichment (EE), assessed by cognitive activity in the Morris water maze, and on brain oxidative status, through measurement of macromolecules damage, lipid peroxidation levels, total cellular thiols and antioxidant enzymes in hippocampus, striatum and cerebral cortex.

MAIN METHODS

Adult male Wistar rats were submitted to the modified permanent bilateral occlusion of the common carotid arteries (2VO) method, with right common carotid artery being first occluded, and tested three months after the ischemic event. Cognitive and physical stimulation, named Environmental Enrichment, consisted of one-hour sessions run 3 times per week during 12weeks, following two different stimulation protocols: pre-ischemia and pre+post-ischemia. Rats were then tested for both reference and working spatial memory tasks in the water maze and later sacrificed for measurement of oxidative stress parameters.

KEY FINDINGS

A significant cognitive deficit was found in both spatial tasks after hypoperfusion; this effect was reversed in the 2VO enriched group. Moreover, hippocampal oxidative damage and antioxidant enzyme activity were decreased by environmental enrichment.

SIGNIFICANCE

These results suggest that both stimulation protocols exert a neuroprotective effect against the cognitive impairment and the reduction of biomarkers for oxidative damage caused by chronic cerebral hypoperfusion.

Delayed intensive acquisition training alleviates the lesion-induced place learning deficits after fimbria-fornix transection in the rat

This study evaluates the effects of two learning paradigms, intensive vs. baseline, on the posttraumatic acquisition of a water maze based place learning task. Rats were subjected either to a control operation (Sham) or to a fimbria-fornix (FF) transection, which renders the hippocampus dysfunctional and disrupts the acquisition of allocentric place learning. All animals were administered 30 post-lesion acquisition sessions, which spanned either 10 or 30days. The acquisition period was followed by a 7day pause after which a retention probe was administered. The lesioned animals were divided into 3 groups: i) Baseline Acquisition Paradigm (BAP) once daily for 30days starting 1week post-surgery; ii) Early Intensive Acquisition Paradigm (EIAP) 3 times daily for 10days starting 1week post-surgery; and iii) Late Intensive Acquisition Paradigm (LIAP) 3 times daily for 10days starting 3weeks post-surgery. Within the control animals, one group followed the schedule of BAP, and one group followed the schedule of Intensive Acquisition Paradigm (IAP). All lesioned animals showed an impaired task acquisition. LIAP was beneficial in FF animals, in that it led to a better acquisition of the place learning task than the two other acquisition paradigms. The FF/EIAP group did not show improved acquisition compared to the FF/BAP group. The control animals were not differentially affected by the two learning schedules. The findings have implications for cognitive rehabilitation after brain injury and support the assumption that intensive treatment can lead to an improved learning, even when the neural structures underlying such a process are compromised. However, the timing of intensive treatment needs to be considered further.

Modulation of ischemia-induced NMDAR1 activation by environmental enrichment decreases oxidative damage

In this study, we examined whether enriched environment (EE) housing has direct neuroprotective effects on oxidative damage following transient global cerebral ischemia. Fifty-two adult male Wistar rats were included in the study and received either ischemia or sham surgery. Once fully awake, rats in each group were randomly assigned to either: EE housing or socially paired housing (CON). Animals remained in their assigned environment for 7 days, and then were killed. Our data showed that glutamate receptor expression was significantly higher in the hippocampus of the ischemia CON group than in the ischemia EE group. Furthermore, the oxidative DNA damage, protein oxidation, and neurodegeneration in the hippocampus of the ischemia CON group were significantly increased compared to the ischemia EE group. These results suggest that EE housing possibly modulated the ischemia-induced glutamate excitotoxicity, which then attenuated the oxidative damage and neurodegeneration in the ischemia EE rats.

General anesthesia causes long-lasting disturbances in the ultrastructural properties of developing synapses in young rats

Common general anesthetics administered to young rats at the peak of brain development cause widespread apoptotic neurodegeneration in their immature brain. Behavioral studies have shown that this leads to learning and memory deficiencies later in life. The subiculum, a part of the hippocampus proper and Papez's circuit, is involved in cognitive development and is vulnerable to anesthesia-induced developmental neurodegeneration. This degeneration is manifested by acute substantial neuroapoptotic damage and permanent neuronal loss in later stages of synaptogenesis. Since synapse formation is a critical component of brain development, we examined the effects of highly neurotoxic anesthesia combination (isoflurane, nitrous oxide, and midazolam) on ultrastructural development of synapses in the rat subiculum. We found that this anesthesia, when administered at the peak of synaptogenesis, causes long-lasting injury to the subicular neuropil. This is manifested as neuropil scarcity and disarray, morphological changes indicative of mitochondria degeneration, a decrease in the number of neuronal profiles with multiple synaptic boutons and significant decreases in synapse volumetric densities. We believe that observed morphological disturbances of developing synapses may, at least in part, contribute to the learning and memory deficits that occur later in life after exposure of the immature brain to general anesthesia.

Environmental experience modulates ischemia-induced amyloidogenesis and enhances functional recovery

In this study, we examined whether ischemia-induced amyloidogenesis could be modulated by environmental "experience," and whether this modulation is associated with improved cognitive functioning. Rats were subjected to either global ischemia or sham surgery and then were randomly assigned to either enriched environment housing (EE) or socially paired housing (controls). After 14 days of differential environmental housing, the rats were tested in the water maze. Our results show decreased C-terminal fragments of the beta-amyloid precursor protein (betaAPP) and decreased amyloid beta (Abeta) load in the ischemic EE rats compared to the ischemic control animals. In addition, Abeta oligomerization was significantly decreased in the ischemic EE animals compared to the ischemic control rats. Further, significantly increased levels of neprilysin, but not insulin-degrading enzyme, amyloid-degrading enzymes, were seen in the ischemic EE rats compared to the ischemic control animals. Behavioral analyses showed that ischemic EE rats performed significantly better on the memory task compared to the ischemic control group. These results suggest that use of multi-sensory environmental enrichment following cerebral ischemia may reduce the accumulation of Abeta peptide in the more pathologic oligomeric form, and consequently may enhance functional recovery.

Environmental Enrichment Induces Synaptic Structural Modification After Transient Focal Cerebral Ischemia in Rats

Environmental enrichment (EE), where animals are exposed to a complex novel environment, has been shown to induce synaptic plasticity in both intact and injured animals. The purpose of this study was to investigate the effects of EE on spatial memory and structural modifications of synaptic junctions in rats following transient focal cerebral ischemia. Adult male Sprague-Dawley rats underwent right middle cerebral artery occlusion (MCAO) for 40 min and reperfusion. On day 3 after MCAO or sham surgery, rats were randomly assigned for 14 days to enriched or standard environmental housing. Spatial memory was then tested by the Morris water maze. Parietal cortex and the CA1 region of hippocampus were processed for electron microscopy and stereological techniques were used to evaluate plasticity of synaptic junctions. EE after MCAO improved spatial memory, with shortened escape length, increased frequency of crossings at the location of the platform, and increased percentage of time spent in the quadrant where the platform was previously located. Synaptic ultrastructural analysis showed that EE after MCAO increased numeric synaptic density in parietal cortex, and induced structural changes in synaptic junctions, with a decreased width of synaptic clefts and increased thickness of postsynaptic densities (PSD) in parietal cortex and hippocampus, accompanying improved performance on the spatial memory task. Using Western blot analysis, we determined the expression of glutamate receptor NMDAR1, and PSD-95, the best characterized protein member of the PSD-95 family, that was abundantly expressed in the PSD of excitatory synapses. The results showed that the content of NMDAR1 was not altered in MCAO rats of EE; however, the phosphorylated NMDAR1 increased significantly when compared with the standard environment housing MCAO rats. In addition, EE inhibited the impaired expression of PSD-95 induced by MCAO in parietal cortex and hippocampus. These data suggest that improved spatial memory of cerebral ischemic rats by EE is associated with structural modifications of synaptic junctions in several brain regions.

Glial elements contribute to stress-induced torsinA expression in the CNS and peripheral nervous system

DYT1 dystonia is caused by a single GAG deletion in exon 5 of TOR1A, the gene encoding torsinA, a putative chaperone protein. In this study, central and peripheral nervous system perturbations (transient forebrain ischemia and sciatic nerve transection, respectively) were used to examine the systems biology of torsinA in rats. After forebrain ischemia, quantitative real-time reverse transcriptase-polymerase chain reaction identified increased torsinA transcript levels in hippocampus, cerebral cortex, thalamus, striatum, and cerebellum at 24 h and 7 days. Expression declined toward sham values by 14 days in striatum, thalamus and cortex, and by 21 days in cerebellum and hippocampus. TorsinA transcripts were localized to dentate granule cells and pyramidal neurons in control hippocampus and were moderately elevated in these cell populations at 24 h after ischemia, after which CA1 expression was reduced, consistent with the loss of this vulnerable neuronal population. Increased in situ hybridization signal in CA1 stratum radiatum, stratum lacunosum-moleculare, and stratum oriens at 7 days after ischemia was correlated with the detection of torsinA immunoreactivity in interneurons and reactive astrocytes at 7 and 14 days. Sciatic nerve transection increased torsinA transcript levels between 24 h and 7 days in both ipsilateral and contralateral dorsal root ganglia (DRG). However, increased torsinA immunoreactivity was localized to both ganglion cells and satellite cells in ipsilateral DRG but was restricted to satellite cells contralaterally. These results suggest that torsinA participates in the response of neural tissue to central and peripheral insults and its sustained up-regulation indicates that torsinA may contribute to remodeling of neuronal circuitry. The striking induction of torsinA in astrocytes and satellite cells points to the potential involvement of glial elements in the pathobiology of DYT1 dystonia.

An ultrastructural study of cell death in the CA1 pyramidal field of the hippocapmus in rats submitted to transient global ischemia followed by reperfusion

In the course of ischemia and reperfusion a disruption of release and uptake of excitatory neurotransmitters occurs. This excitotoxicity triggers delayed cell death, a process closely related to mitochondrial physiology and one that shows both apoptotic and necrotic features. The aim of the present study was to use electron microscopy to characterize the cell death of pyramidal cells from the CA1 field of the hippocampus after 10 min of transient global ischemia followed by short reperfusion periods. For this study 25 adult male Wistar rats were used, divided into six groups: 10 min of ischemia, 3, 6, 12 and 24 h of reperfusion and an untouched group. Transient forebrain ischemia was produced using the 4-vessel occlusion method. The pyramidal cells of the CA1 field from rat hippocampus submitted to ischemia exhibited intracellular alterations consistent with a process of degeneration, with varied intensities according to the reperfusion period and bearing both apoptotic and necrotic features. Gradual neuronal and glial modifications allowed for the classification of the degenerative process into three stages: initial, intermediate and final were found. With 3 and 6 h of reperfusion, slight and moderate morphological alterations were seen, such as organelle and cytoplasm edema. Within 12 h of reperfusion, there was an apparent recovery and more 'intact' cells could be identified, while 24 h after the event neuronal damage was more severe and cells with disrupted membranes and cell debris were identified. Necrotic-like neurons were found together with some apoptotic bodies with 24 h of reperfusion. Present results support the view that cell death in the CA1 field of rat hippocampus submitted to 10 min of global transient ischemia and early reperfusion times includes both apoptotic and necrotic features, a process referred to as parapoptosis.

Temporal profiles of axon terminals, synapses and spines in the ischemic penumbra of the cerebral cortex: ultrastructure of neuronal remodeling

BACKGROUND AND PURPOSE

Because the recovery process of axon terminals, synapses, and spine-dendrites in the ischemic penumbra of the cerebral cortex is obscure, we studied the temporal profile of these structures up to 12 weeks after the ischemic insult, using a gerbil model.

METHODS

Stroke-positive animals were selected according to their stroke index score during the first 10-minute left carotid occlusion done twice with 5-hour interval. The animals were euthanized at various times after the second ischemic insult. Ultra-thin sections including the 2nd to 4th cortical layers were obtained from the neocortex coronally sectioned at the infundibular level, in which the penumbra appeared. We counted the number of synapses, spines and multiple synapse boutons, measured neurite thickness, and determined the percent volume of the axon terminals and spines by Weibel point counting method.

RESULTS

The number of synapses, synaptic vesicles and spines and the total percent volume of the axon terminals and spines decreased until the 4th day. From 1 to 12 weeks after the ischemic insult, these values increased to or exceeded the control ones, and neuritic thickening and increase in number of multiple synapse boutons occurred.

CONCLUSIONS

In the ischemic penumbra, the above structures degenerated, with a reduction in their number and size, until 4 days and then recovered from 1 to 12 weeks after the ischemic insult.

On neural plasticity, new neurons and the postischemic milieu: An integrated view on experimental rehabilitation

This review discusses actual and potential contributors to functional improvement after stroke injuries. Topics that will be covered are neuronal re-organization and sprouting, neural stem/progenitor cell activation and neuronal replacement, as well as the neuronal milieu defined by glia, inflammatory cells and blood vessel supply. It is well established that different types of neuronal plasticity ultimately lead to post-stroke recovery. However, an untapped potential which only recently has started to be extensively explored is neuronal replacement through endogenous or exogenous resources. Major experimental efforts are needed to achieve progress in this burgeoning area. The review stresses the importance of applying neurodevelopmental principles as well as performing a characterization of the role of the postischemic milieu when studying adult brain neural stem/progenitor cells. Integrated and multifaceted experimentation, incorporating actual and possible poststroke function modulators, will be necessary in order to determine future strategies that will ultimately enable considerable progress in the field of neurorehabilitation.

Astrocytic changes in the hippocampus and functional recovery after cerebral ischemia are facilitated by rehabilitation training

In this study we examined whether astrocytic and basic fibroblast growth factor changes after cerebral ischemia can be influenced by rehabilitation training and if these changes are associated with functional improvement. After receiving either ischemia or sham surgery, male adult Wistar rats were assigned to one of two rehabilitation training group: complex environment housing (EC) or paired housing as controls (CON). Rats were tested in the water maze after 14 days of rehabilitation training. Results showed increased expression of reactive astrocytes (GFAP) in all ischemic animals and in the sham EC rats with a significant overall increased seen in the ischemia EC housed animals. The pattern of basic fibroblast growth factor (FGF-2) expression seen was somewhat similar to that of GFAP. Behavioral data showed that even though all animals learned to perform the water maze task over time, the ischemia CON rats took longer to learn the task while all the ischemia EC animals performed as well as the sham groups. Regression analysis showed that increased GFAP was able to explain some of the variances in the behavioral parameters in the water maze of the ischemia EC rats suggesting that the activation of astrocytes in this group probably mediated enhanced functional recovery. Lastly, it is possible that the favorable effect of astrocyte activation after cerebral ischemia was mediated by FGF-2.

Behaviorally induced synaptogenesis and dendritic growth in the hippocampal region following transient global cerebral ischemia are accompanied by improvement in spatial learning

Reports have shown that damage to the adult brain can result in adaptive changes in regions adjacent or surrounding the site of the principal injury and that these changes may be modulated by rehabilitation training. In this study, we examined the influence of complex environment housing as a rehabilitation strategy on ischemia-induced synaptic and dendritic changes in the hippocampus. Thirty-six adult male Wistar rats were included in the study and assigned to either transient global cerebral ischemia or sham group. Following ischemic or sham surgery, rats were randomized to either complex environment housing (EC) or social condition (SC, paired housing) group during the rehabilitation period. Following 14 days of rehabilitation, rats were tested in the water maze. Our results showed that: (1) ischemic injury and EC housing were able to independently influence synaptogenesis and dendritic growth in the hippocampal area adjacent to the site of injury, and (2) EC housing-induced synaptic and dendritic changes were accompanied by enhanced functional recovery after transient global cerebral ischemia. These data suggest that behavioral experience during the rehabilitation period may be able to alter the neuronal circuitry in the surrounding region where primary neuronal damage was seen and that such modification may have contributed to functional improvement.

Amelioration of cognitive impairment and changes in microtubule-associated protein 2 after transient global cerebral ischemia are influenced by complex environment experience

In this study we examined whether expression of microtubule-associated protein 2 (MAP2) after transient global cerebral ischemia can be influenced by behavioral experience and if the changes are associated with functional improvement. Rats received either ischemia or sham surgery then assigned to: complex environment housing (EC) or social housing (SC) as controls for 14 days followed by water maze testing. Upregulation of MAP2 was seen in all ischemic animals with a significant overall increase evident in the EC housed rats. Behaviorally, all animals learned to perform the water maze task over time but the ischemia SC rats had the worst performance overall while all the EC housed animals demonstrated the best performance in general. Regression analysis showed that increase MAP2 expression was able to explain some of the variance in the behavioral parameters in the water maze suggesting that this cytoskeletal protein probably played a role in mediating enhanced functional outcomes.

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.

Electrophysiological correlates of neural plasticity compensating for ischemia-induced damage in the hippocampus

Injury to the brain often results in loss of synapses or cell death in the damaged area. Subsequent to the injury, the areas that are not directly affected often exhibit enhanced neuronal plasticity. Although there are many reports of morphological changes resulting from such plasticity, their functional consequences are poorly understood. In this study we examined electrophysiological changes associated with ischemia-induced neurogenesis in the hippocampus, a brain region that is particularly vulnerable but also exceptionally plastic. Transient global ischemia was induced in Sprague-Dawley rats by occlusion of both carotid arteries and a reduction in blood pressure for 12 min. The procedure resulted in delayed cell death in the CA1 field of the hippocampus while the dentate gyrus (DG) was spared. To assess neurogenesis and synaptic changes in parallel we used both hemispheres from each animal. One side was used for immunohistochemistry and the other for in vitro electrophysiological experiments in brain slices. Synaptic field responses and synaptic plasticity (LTP) in perforant path within the DG were reduced by 50% at 10 days after the ischemic injury but recovered at 35 days. Synaptic responses in non-neurogenic CA1 were abolished in parallel with cell death and did not recover. Gamma irradiation applied focally to the head selectively prevented neurogenesis and the synaptic recovery in the DG. These experiments reveal electrophysiological changes associated with reactive neural plasticity in the hippocampus.

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.

Dentate gyrus neurogenesis after cerebral ischemia and behavioral training

Neurogenesis in the mammalian brain continues throughout adulthood. Several factors have been shown to influence neurogenesis, including experience in a complex environment (EC), exercise (EX), and ischemic insult. The authors investigated the effects of behavioral rehabilitation training following transient global cerebral ischemia on the number of new cells in the dentate gyrus that incorporated bromodeoxyuridine (BrdU), a thymidine analog that labels cells undergoing DNA replication. Seventy-two animals were included in the study, and 4-vessel occlusion was used to induce cerebral ischemia while control animals were subjected to anesthesia and sham surgery alone. Within 3 days of surgery, rats were randomly assigned to either EC, EX, or control (paired housing in standard laboratory conditions) groups. All animals were sacrificed 2 weeks after behavioral training. Immunohistochemistry results showed an increased number of BrdU-labeled cells in the subgranular zone of the dentate gyrus in all ischemic groups and in the EC and EX sham groups, although no significant group differences were seen. Examination of cell phenotype showed that almost all BrdU-positive cells colabeled with TuJ1, an immature neuron marker, in all animals whereas only a few BrdU-positive cells colabeled with NeuN, a mature neuron marker. BrdU/NeuN-labeled cells were seen only in the sham and ischemia EC groups. No new cells showed glial fibrillary acidic protein, astrocyte marker, colabeling. These results suggest that the adult brain has an inherent regenerative capacity after insult and that behavioral training following injury does not have an additive effect on neurogenesis. Finally, the enhanced maturation of BrdU-positive cells seen in the EC rats is probably modulated by environmental cues.

Changes in number of synapses and mitochondria in presynaptic terminals in the dentate gyrus following cerebral ischemia and rehabilitation training

Damage to the adult brain can result in adaptive plasticity in regions adjacent to the site of the principal insult and that the plastic changes may be modulated by post-injury rehabilitation training. In this study, we examined the effects of rehabilitation training on synaptic morphology in the dentate gyrus following transient global cerebral ischemia and the metabolic correlates of the ultrastructural changes. Forty adult male Wistar rats were included in the study and assigned to either ischemia or sham group. Following ischemic or sham surgery, rats were randomized to either complex environment housing (EC), exercise (EX), or social condition (SC, paired housing) group. Electron microscopy and unbiased stereological methods were used to evaluate synaptic plasticity and the number and size of mitochondria in synaptic axon terminals. Increased number of granule neurons was seen in all ischemic groups and in the sham EC rats. Changes in the number of synapses per neuron in the outer and inner molecular layers of the dentate gyrus parallel those seen in granule neurons. Similarly, ischemia and behavioral experience in EC independently increased the number of synaptic mitochondria in presynaptic terminals in both the outer and inner molecular layers; however, no significant changes were seen in mitochondrial size. These data suggest a link between behavioral training and synaptic plasticity in the region adjacent to the injury and that the likely metabolic correlate of this synaptic plasticity is increased number of mitochondria at synaptic axon terminals.

Unilateral ischemic sensorimotor cortical damage induces contralesional synaptogenesis and enhances skilled reaching with the ipsilateral forelimb in adult male rats

Unilateral damage to the forelimb representation area of the sensorimotor cortex (SMC) results in a compensatory reliance on the unimpaired (ipsilateral to the lesion) forelimb as well as reorganization of neuronal structure and connectivity in the contralateral motor cortex. Recently, male rats with unilateral electrolytic SMC lesions were found to have enhanced skilled reaching performance with the ipsilesional forelimb compared with sham-operated controls. The present study was performed to determine whether these behavioral findings are replicable using an ischemic lesion and whether there is a link between the enhanced learning and synaptogenesis in motor cortical layer V opposite the trained limb and lesion, as assessed using stereological methods for light and electron microscopy. Rats were given a sham operation or an endothelin-1 (ET-1) induced ischemic SMC lesion. They were then trained for 20 days on a skilled reaching task with the unimpaired limb or received control procedures. As with previous findings using electrolytic lesions, rats with unilateral ischemic SMC lesions performed significantly better using the unimpaired forelimb than did sham-operates. Lesions, but not training, significantly increased the total number of motor cortical layer V synapses per neuron as well as the number of perforated and multisynaptic bouton (MSB) synapses per neuron compared with shams. Thus, in addition to a net increase in synapses, the improved reaching ability was coupled with an increase in synapse subtypes that have previously been linked to enhanced synaptic efficacy. The failure to induce synaptogenesis in layer V with reach training alone is in contrast to previous findings and may be related to training intensity.