Enriched environment alleviates post-stroke cognitive impairment through enhancing α7-nAChR expression in rats

Enriched environment treatment promotes neural functional recovery together with microglia polarization and remyelination after cerebral ischemia in rats

BACKGROUND

Microglia activation and oligodendrocyte maturation are critical for remyelination after cerebral ischemia. Studies have shown that enriched environment (EE) can effectively alleviate stroke-induced neurological deficits. However, little is known about the mechanism associated with glial cells underlying the neuroprotection of EE. Therefore, this study focuses on investigating the effect of EE on activated microglia polarization as well as oligodendrogenesis in the progress of remyelination following cerebral ischemia.

METHODS

The ischemia/reperfusion (I/R) injury model was established by middle cerebral artery occlusion (MCAO) in rats. Animals executed 4 weeks of environmental intervention after performing MCAO or sham surgery and were divided into sham, MCAO, and MCAO+EE groups. Cognitive function, myelin damage, microglia activation and polarization, inflammation, oligodendrogenesis, remyelination, and protein expression of the PI3K/AKT/GSK3β signaling pathway were determined.

RESULTS

The staining of NeuN indicated that the infarct size of MCAO rats was decreased under EE. EE intervention improved animal performance in the Morris water maze test and novel object recognition test, promoting the recovery of cognitive function after I/R injury. EE treatment alleviated myelin damage in MCAO rats, as evidenced by the lower fluorescence intensity ratio of SMI-32/MBP in MCAO+EE group. EE increased the fluorescence intensity ratio of NG2+/Ki67+/Olig2+, MBP, and MOG, enhancing the proliferation and differentiation of OPCs and oligodendrogenesis after MCAO. In terms of remyelination, more myelinated axons and lower G/ratio were detected in MCAO+EE rats compared with MCAO group. Moreover, EE treatment decreased the number of Iba1+/CD86+ M1 microglia, increased the number of Iba1+/CD206+ M2 microglia, and suppressed the inflammation response after I/R injury, which could be attributed to the augmented expression of PI3K/AKT/GSK3β axis.

CONCLUSION

EE improved long‑term recovery of cognitive function after cerebral I/R injury, at least in part by promoting M2 microglia transformation through activation of the PI3K/AKT/GSK3β signaling pathway, inhibiting inflammation to provide a favorable microenvironment for oligodendrocyte maturation and remyelination. The effect of the EE on myelin and inflammation could account for the neuroprotection provided by EE.

Environmental Enrichment in Stroke Research: an Update

Environmental enrichment (EE) refers to different forms of stimulation, where the environment is designed to improve the levels of sensory, cognitive, and motor stimuli, inducing stroke recovery in animal models. Stroke is a leading cause of mortality and neurological disability among older adults, hence the importance of developing strategies to improve recovery for such patients. This review provides an update on recent findings, compiling information regarding the parameters affected by EE exposure in both preclinical and clinical studies. During stroke recovery, EE exposure has been shown to improve both the cognitive and locomotor aspects, inducing important neuroplastic alterations, increased angiogenesis and neurogenesis, and modified gene expression, among other effects. There is a need for further research in this field, particularly in those aspects where the evidence is inconclusive. Moreover, it is necessary refine and adapt the EE paradigms for application in human patients.

Acupuncture treatment vs. cognitive rehabilitation for post-stroke cognitive impairment: A systematic review and meta-analysis of randomized controlled trials

Background

Cognitive impairment is one of the common sequelae after stroke, which not only hinders the recovery of patients but also increases the financial burden on families. In the absence of effective therapeutic measures, acupuncture treatment has been widely used in China to treat post-stroke cognitive impairment (PSCI), but the specific efficacy is unclear. Therefore, this review aimed to evaluate the true efficacy of acupuncture treatment in patients with PSCI.

Methods

We searched eight databases [PubMed, Embase, Web of Science, Cochrane Central Register of Controlled Trials, China Biomedical Literature Database (CBM), China Science and Technology Journal (VIP) database, the China National Knowledge Infrastructure (CNKI) database, and Wan fang database] from the inception to May 2022 for randomized controlled trials (RCTs) related to acupuncture treatment combined with cognitive rehabilitation (CR) for PSCI. Two investigators independently used a pre-designed form to extract valid data from eligible RCTs. The risk of bias was assessed through tools provided by the Cochrane Collaboration. The meta-analysis was implemented through Rev Man software (version 5.4). The strength of the evidence obtained was evaluated using GRADE profiler software. Adverse events (AEs) were collected by reading the full text and used to evaluate the safety of acupuncture treatment.

Results

Thirty-eight studies involving a total of 2,971 participants were included in this meta-analysis. Overall, the RCTs included in this meta-analysis were poor in methodological quality. The combined results showed that acupuncture treatment combined with CR showed significant superiority compared to CR alone in terms of improving cognitive function [Mean Difference (MD) = 3.94, 95% confidence intervals (CI): 3.16-4.72, P < 0.00001 (MMSE); MD = 3.30, 95%CI: 2.53-4.07, P < 0.00001 (MoCA); MD = 9.53, 95%CI: 5.61-13.45, P < 0.00001 (LOTCA)]. Furthermore, the combination of acupuncture treatment and CR significantly improved patients' self-care ability compared to CR alone [MD = 8.66, 95%CI: 5.85-11.47, P < 0.00001 (MBI); MD = 5.24, 95%CI: 3.90-6.57, P < 0.00001 (FIM)]. Meanwhile, subgroup analysis showed that MMSE scores were not sufficiently improved in the comparison of electro-acupuncture combined with CR versus CR alone (MD = 4.07, 95%CI: -0.45-8.60, P = 0.08). However, we also observed that electro-acupuncture combined with CR was superior to the use of CR alone in improving MoCA and MBI scores in patients with PSCI [MD = 2.17, 95%CI: 0.65-3.70, P = 0.005 (MoCA); MD = 1.74, 95%CI: 0.13-3.35, P = 0.03 (MBI)]. There was no significant difference in the occurrence of adverse events (AE) between acupuncture treatment combined with CR and CR alone (P > 0.05). The certainty of the evidence was rated low level because of flaws in the study design and considerable heterogeneity among the included studies.

Conclusion

This review found that acupuncture treatment combined with CR may have a positive effect on improving cognitive function and self-care ability in PSCI patients. However, our findings should be treated with caution owing to the existence of methodological quality issues. High-quality studies are urgently required to validate our results in the future.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022338905, identifier: CRD42022338905.

The role of enriched environment in neural development and repair

In addition to genetic information, environmental factors play an important role in the structure and function of nervous system and the occurrence and development of some nervous system diseases. Enriched environment (EE) can not only promote normal neural development through enhancing neuroplasticity but also play a nerve repair role in restoring functional activities during CNS injury by morphological and cellular and molecular adaptations in the brain. Different stages of development after birth respond to the environment to varying degrees. Therefore, we systematically review the pro-developmental and anti-stress value of EE during pregnancy, pre-weaning, and “adolescence” and analyze the difference in the effects of EE and its sub-components, especially with physical exercise. In our exploration of potential mechanisms that promote neurodevelopment, we have found that not all sub-components exert maximum value throughout the developmental phase, such as animals that do not respond to physical activity before weaning, and that EE is not superior to its sub-components in all respects. EE affects the developing and adult brain, resulting in some neuroplastic changes in the microscopic and macroscopic anatomy, finally contributing to enhanced learning and memory capacity. These positive promoting influences are particularly prominent regarding neural repair after neurobiological disorders. Taking cerebral ischemia as an example, we analyzed the molecular mediators of EE promoting repair from various dimensions. We found that EE does not always lead to positive effects on nerve repair, such as infarct size. In view of the classic issues such as standardization and relativity of EE have been thoroughly discussed, we finally focus on analyzing the essentiality of the time window of EE action and clinical translation in order to devote to the future research direction of EE and rapid and reasonable clinical application.

Neuroprotective effects of sodium valproate on hippocampal cell and volume, and cognitive function in a rat model of focal cerebral ischemia

Valproate (VPA) as a histone deacetylase (HDAC) inhibitor has shown neuroprotective effects in neurodegenerative diseases. This study evaluated whether VPA treatment ameliorated the synaptic plasticity dysfunction, hippocampal neuronal loss, and spatial memory deficits induced by cerebral ischemia in the middle cerebral artery occlusion (MCAO) model. Thirty-two male Sprague-Dawley rats were randomly divided into 4 groups control, sham, cerebral ischemia+vehicle (MCAO+V), and MCAO+VPA. The right common carotid artery was occluded for 1 hour. VPA (300 mg/kg) or vehicles were injected intraperitoneally on days 0,1,2 and 3 of the reperfusion. After 7 days of reperfusion the Morris water maze, passive avoidance, and open field tests were performed. Hippocampal synaptic plasticity in the CA1 area was recorded by field potential recording. We used the term neuronal Input-Output (I/O) function and paired-pulse ratio (PPR) to refer to basal synaptic transmission and presynaptic neurotransmitter release probability respectively. After that, the brains were removed for assaying stereological parameters of the CA1 neurons. Our results showed the VPA administration significantly reduced the total infarct volume, improved MCAO-induced spatial learning -memory, fear memory, and anxiety compared to the MCAO+V group. In addition, the field potential recording showed that VPA significantly ameliorated the impaired the long- term potentiation (LTP) induced by MCAO, without any effects on basal synaptic transmission and neurotransmitter release probability. Therefore, it seems that a decrease in total infarct volume and induction of long-term potentiation via postsynaptic mechanisms is responsible for improving MCAO-induced cognitive impairment.

Possible Engagement of Nicotinic Acetylcholine Receptors in Pathophysiology of Brain Ischemia-Induced Cognitive Impairment

Post-stroke disabilities like cognitive impairment impose are complex conditions with great economic burdens on health care systems. For these comorbidities, no effective therapies have been identified yet. Nicotinic acetylcholine receptors (nAChRs) are multifunctional receptors participating in various behavioral and neurobiological functions. During brain ischemia, the increased glutamate accumulation leads to neuronal excitotoxicity as well as mitochondrial dysfunction. These abnormalities then cause the increased levels of oxidants, which play key roles in neuronal death and apoptosis in the infarct zone. Additionally, recall of cytokines and inflammatory factors play a prominent role in the exacerbation of ischemic injury. As well, neurotrophic factors' insufficiency results in synaptic dysfunction and cognitive impairments in ischemic brain. Of note, nAChRs through various signaling pathways can participate in therapeutic approaches such as cholinergic system's stimulation, and reduction of excitotoxicity, inflammation, apoptosis, oxidative stress, mitochondrial dysfunction, and autophagy. Moreover, the possible roles of nAChRs in neurogenesis, synaptogenesis, and stimulation of neurotrophic factors expression have been reported previously. On the other hand, the majority of the above-mentioned mechanisms were found to be common in both brain ischemia pathogenesis and cognitive function tuning. Therefore, it seems that nAChRs might be known as key regulators in the control of ischemia pathology, and their modulation could be considered as a new avenue in the multi-target treatment of post-stroke cognitive impairment.

Effectiveness and mechanisms of enriched environment in post-stroke cognitive impairment

Post-stroke cognitive impairment (PSCI) is one of the most common complications of stroke, it is also an important reason for the poor prognosis in stroke patients with motor and speech dysfunction. Enriched Environment (EE), a novel and easy-to-implement rehabilitation treatment strategy, is thought to be a potential intervention for PSCI recently. In this paper, we review the therapeutic effects and related mechanisms of EE in PSCI from the level of animal research and clinical application. Besides, we further discuss the application prospects and limitations of EE in PSCI patients.