CaMKII-dependent dendrite ramification and spine generation promote spatial training-induced memory improvement in a rat model of sporadic Alzheimer's disease

Homocysteine-potentiated Kelch-like ECH-associated protein 1 promotes senescence of neuroblastoma 2a cells via inhibiting ubiquitination of β-catenin

Elevated serum homocysteine (Hcy) level is a risk factor for Alzheimer's disease (AD) and accelerates cell aging. However, the mechanism by which Hcy induces neuronal senescence remains largely unknown. In this study, we observed that Hcy significantly promoted senescence in neuroblastoma 2a (N2a) cells with elevated β-catenin and Kelch-like ECH-associated protein 1 (KEAP1) levels. Intriguingly, Hcy promoted the interaction between KEAP1 and the Wilms tumor gene on the X chromosome (WTX) while hampering the β-catenin-WTX interaction. Mechanistically, Hcy attenuated the methylation level of the KEAP1 promoter CpG island and activated KEAP1 transcription. However, a slow degradation rate rather than transcriptional activation contributed to the high level of β-catenin. Hcy-upregulated KEAP1 competed with β-catenin to bind to WTX. Knockdown of both β-catenin and KEAP1 attenuated Hcy-induced senescence in N2a cells. Our data highlight a crucial role of the KEAP1-β-catenin pathway in Hcy-induced neuronal-like senescence and uncover a promising target for AD treatment.

Hyperhomocysteinemia: Metabolic Role and Animal Studies with a Focus on Cognitive Performance and Decline-A Review

Disturbances in the one-carbon metabolism are often indicated by altered levels of the endogenous amino acid homocysteine (HCys), which is additionally discussed to causally contribute to diverse pathologies. In the first part of the present review, we profoundly and critically discuss the metabolic role and pathomechanisms of HCys, as well as its potential impact on different human disorders. The use of adequate animal models can aid in unravelling the complex pathological processes underlying the role of hyperhomocysteinemia (HHCys). Therefore, in the second part, we systematically searched PubMed/Medline for animal studies regarding HHCys and focused on the potential impact on cognitive performance and decline. The majority of reviewed studies reported a significant effect of HHCys on the investigated behavioral outcomes. Despite of persistent controversial discussions about equivocal findings, especially in clinical studies, the present evaluation of preclinical evidence indicates a causal link between HHCys and cognition-related- especially dementia-like disorders, and points out the further urge for large-scale, well-designed clinical studies in order to elucidate the normalization of HCys levels as a potential preventative or therapeutic approach in human pathologies.

κ-Opioid Receptor Agonist Ameliorates Postoperative Neurocognitive Disorder by Activating the Ca2+/CaMKII/CREB Pathway

Objective

Cardiopulmonary bypass (CPB) is an important cardiac operation and also a high-risk procedure, leading to postoperative neurocognitive disorder. However, there are few effective drugs to treat the aftermath of CPB. Therefore, we observe the effect of kappa opioid receptor (KOR) agonist on cognitive disorders of rats after cardiopulmonary bypass (CPB) and investigate the mechanism of the Ca²⁺/calmodulin-dependent protein kinase (CaMKII)/cAMP responsive element-binding protein (CREB) pathway.

Methods

A total of 40 Sprague Dawley rats were randomly divided into the sham operation group (sham group, n = 10), CPB model group (CPB group, n = 10), CPB + KOR agonist U50488H group (UH group, n = 10), and CPB + specific CaMKII antagonist + U50488H group (CKU group, n = 10). The changes in the rats' cognitive function were evaluated using the Morris water maze, the hippocampal histopathological changes were observed via hematoxylin-eosin (H&E) staining, and the apoptosis rate of neuronal cells was detected through terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining. Moreover, enzyme-linked immunosorbent assay (ELISA) was applied to examine the changes in brain injury markers, inflammatory factors, and oxidative stress factors. The hippocampal variations in Ca²⁺ concentration and oxidative stress index (ROS) levels were measured by immunofluorescence staining, and western blotting was performed to determine the expression changes in the Ca²⁺/CaMKII/CREB pathway.

Results

The KOR agonist could shorten latency, increase the swimming distance and residence time in the target quadrant, and ameliorate postoperative neurocognitive disorder (PND). Meanwhile, the KOR agonist relieved CPB-induced hippocampal and oxidative stress injuries, reduced NSE and S-100β expression, decreased the apoptosis rate, and repressed the inflammatory response, which alleviated the brain injury. In addition, U50488H was able to decrease Ca²⁺ influx and glutamate (Glu) level, inhibit N-methyl-D-aspartate receptor (NMDAR) expression, upregulate CaMKII expression, promote CREB phosphorylation, and increase the brain-derived neurotrophic factor (BDNF) level in CPB rats. However, the protective effects of KORs against PND were suppressed following the application of the CaMKII-specific antagonist.

Conclusion

The KOR agonist activates the Ca²⁺/CaMKII/CREB pathway, which improves the brain injury and relieves PND in CPB rats.

Co-Expression of Three Wild-Type 3R-Tau Isoforms Induces Memory Deficit via Oxidation-Related DNA Damage and Cell Death: A Promising Model for Tauopathies

The three isoforms of 3R-tau are predominantly deposited in neurons bearing neurofibrillary tangles in Alzheimer's disease (AD), while only 3R-tau accumulation has been detected in Pick's disease (PiD), suggesting the involvement of 3R-tau in neurodegeneration. However, both the role and the molecular mechanism of 3R-tau in neurodegeneration are elusive. Here, we co-expressed three isoforms of human wild-type 3R-tau in adult mouse hippocampal to mimic the pathologic tau accumulating observed in PiD patients. We found that co-expressing three 3R-tau isoforms induced hyperphosphorylation and accumulation of tau proteins; simultaneously, the mice showed remarkable neuron death with synapse and memory deficits. Further in vitro and in vivo studies demonstrated that co-expressing 3R-tau isoforms caused oxidative stress evidenced by an increased malondialdehyde, and the decreased superoxide dismutase and glutathione peroxidase; the 3R-tau accumulation also induced significant glial activation and DNA double-strand breaks (DSBs). Notably, the toxic effects of 3R-tau accumulation were efficiently reversed by administration of antioxidants Vitamin E (VitE) and Vitamin C (VitC), respectively. These data reveal that intracellular accumulation of 3R-tau isoforms in adult brain induces significant neuron death and memory deficits with the mechanism involving oxidation-mediated DSBs; and the antioxidants VitE and VitC can efficiently attenuate the toxicities of 3R-tau. Given that no significant cell death has been detected in the currently available wild-type tau-accumulating models, co-expressing 3R-tau isoforms could be a promising model for drug development of tauopathies, such as PiD.

Administering crocin ameliorates anxiety-like behaviours and reduces the inflammatory response in amyloid-beta induced neurotoxicity in rat

Anxiety, hippocampus synaptic plasticity deficit, as well as pro-inflammatory cytokines, are involved in Alzheimer's disease (AD). The present study is designed to evaluate the possible therapeutic effect of crocin on anxiety-like behaviours, hippocampal synaptic plasticity and neuronal shape, as well as pro-inflammatory cytokines in the hippocampus using in vivo amyloid-beta (Aβ) models of AD. The Aβ peptide (1-42) was bilaterally injected into the frontal-cortex. Five hours after the surgery, the rats were given intraperitoneal (IP) crocin (30 mg/kg) daily up to 12 days. Elevated plus maze results showed that crocin treatment after bilateral Aβ injection significantly increased the percentage of spent time into open arms, frequency of entries, and percentage of entries into open arms as compared with the Aβ group. In the open field test, the Aβ+crocin group showed a higher percentage of spent time in the centre and frequency of entries into central zone as compare with the Aβ treated animals. Administering crocin increased the number of soma, dendrites and axonal arbores in the CA1 neurons among the rats with Aβ neurotoxicity. Cresyl violet (CV) staining showed that crocin increased the number of CV-positive cells in the CA1 region of the hippocampus compared with the Aβ group. Silver-nitrate staining indicated that crocin reduced neurofibrillary tangle formation induced by Aβ. Crocin treatment attenuated the expression of TNF-α and IL-1β mRNA in the hippocampus compared with the Aβ group. Our results suggest that crocin attenuated Aβ-induced anxiety-like behaviours and neuronal damage, and synaptic plasticity loss in hippocampal CA1 neurons may via its anti-inflammatory effects.

Physical Exercise and Alzheimer's Disease: Effects on Pathophysiological Molecular Pathways of the Disease

Alzheimer’s disease (AD), the most common form of neurodegenerative dementia in adults worldwide, is a multifactorial and heterogeneous disorder characterized by the interaction of genetic and epigenetic factors and the dysregulation of numerous intracellular signaling and cellular/molecular pathways. The introduction of the systems biology framework is revolutionizing the study of complex diseases by allowing the identification and integration of cellular/molecular pathways and networks of interaction. Here, we reviewed the relationship between physical activity and the next pathophysiological processes involved in the risk of developing AD, based on some crucial molecular pathways and biological process dysregulated in AD: (1) Immune system and inflammation; (2) Endothelial function and cerebrovascular insufficiency; (3) Apoptosis and cell death; (4) Intercellular communication; (5) Metabolism, oxidative stress and neurotoxicity; (6) DNA damage and repair; (7) Cytoskeleton and membrane proteins; (8) Synaptic plasticity. Moreover, we highlighted the increasingly relevant role played by advanced neuroimaging technologies, including structural/functional magnetic resonance imaging, diffusion tensor imaging, and arterial spin labelling, in exploring the link between AD and physical exercise. Regular physical exercise seems to have a protective effect against AD by inhibiting different pathophysiological molecular pathways implicated in AD.

The involvement of NLRP3 inflammasome in the treatment of Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases, and it is characterised by progressive deterioration in cognitive and memory abilities, which can severely influence the elderly population's daily living abilities. Although researchers have made great efforts in the field of AD, there are still no well-established strategies to prevent and treat this disease. Therefore, better clarification of the molecular mechanisms associated with the onset and progression of AD is critical to provide a theoretical basis for the establishment of novel preventive and therapeutic strategies. Currently, it is generally believed that neuroinflammation plays a key role in the pathogenesis of AD. Inflammasome, a multiprotein complex, is involved in the innate immune system, and it can mediate inflammatory responses and pyroptosis, which lead to neurodegeneration. Among the various types of inflammasomes, the NLRP3 inflammasome is the most characterised in neurodegenerative diseases, especially in AD. The activation of the NLRP3 inflammasome causes the generation of caspase-1-mediated interleukin (IL)-1β and IL-18 in microglia cells, where neuroinflammation is involved in the development and progression of AD. Thus, the NLRP3 inflammasome is likely to be a crucial therapeutic molecular target for AD via regulating neuroinflammation. In this review, we summarise the current knowledge on the role and regulatory mechanisms of the NLRP3 inflammasome in the pathogenic mechanisms of AD. We also focus on a series of potential therapeutic treatments targeting NLRP3 inflammasome for AD. Further clarification of the regulatory mechanisms of the NLRP3 inflammasome in AD may provide more useful clues to develop novel AD treatment strategies.

Metoprolol prevents neuronal dendrite remodeling in a canine model of chronic obstructive sleep apnea

Obstructive sleep apnea (OSA) is closely associated with central nervous system diseases and could lead to autonomic nerve dysfunction, which is often seen in neurodegenerative diseases. Previous studies have shown that metoprolol prevents several chronic OSA-induced cardiovascular diseases through inhibiting autonomic nerve hyperactivity. It remains unclear whether chronic OSA can lead to dendritic remodeling in the brain, and whether metoprolol affects the dendritic remodeling. In this study we investigated the effect of metoprolol on dendrite morphology in a canine model of chronic OSA, which was established in beagles through clamping and reopening the endotracheal tube for 4 h every other day for 12 weeks. OSA beagles were administered metoprolol (5 mg· kg⁻¹· d⁻¹). The dendritic number, length, crossings and spine density of neurons in hippocampi and prefrontal cortices were assessed by Golgi staining. And the protein levels of hypoxia-inducible factor-1α (HIF-1α) and brain-derived neurotrophic factor (BDNF) were measured by Western blotting. We showed that chronic OSA successfully induced significant brain hypoxia evidenced by increased HIF-1α levels in CA1 region and dentate gyrus of hippocampi, as well as in prefrontal cortex. Furthermore, OSA led to markedly decreased dendrite number, length and intersections, spine loss as well as reduced BDNF levels. Administration of metoprolol effectively prevented the dendritic remodeling and spine loss induced by chronic OSA. In addition, administration of metoprolol reversed the decreased BDNF, which might be associated with the metoprolol-induced neuronal protection. In conclusion, metoprolol protects against neuronal dendritic remodeling in hippocampi and prefrontal cortices induced by chronic OSA in canine.

Melatonin alleviates cognition impairment by antagonizing brain insulin resistance in aged rats fed a high-fat diet

Brain insulin resistance, induced by neuroinflammation and oxidative stress, contributes to neurodegeneration, that is, processes that are associated with Aβ accumulation and TAU hyperphosphorylation. Here, we tested the effect of chronic administration of melatonin (MLT) on brain insulin resistance and cognition deficits caused by a high-fat diet (HFD) in aged rats. Results showed that MLT supplementation attenuated peripheral insulin resistance and lowered hippocampal oxidative stress levels. Activated microglia and astrocytes and hippocampal levels of TNF-α in HFD-fed rats were reduced by MLT treatment. Melatonin also prevented HFD-induced increases in beta-amyloid (Aβ) accumulation and TAU phosphorylation in the hippocampus. In addition, impairments of brain insulin signaling elicited by long-term HFD were restored by MLT treatment, as confirmed by ex vivo insulin stimulation. Importantly, MLT reversed HFD-induced cognitive decline as measured by a water maze test, normalized hippocampal LTP and restored CREB activity and BDNF levels as well as cholinergic neuronal activity in the hippocampus. Collectively, these findings indicate that MLT may exhibit substantial protective effects on cognition, via restoration of brain insulin signaling.

ALWPs Improve Cognitive Function and Regulate Aβ Plaque and Tau Hyperphosphorylation in a Mouse Model of Alzheimer's Disease

Recently, we reported that ALWPs, which we developed by combining Liuwei Dihuang pills (LWPs) with antler, regulate the LPS-induced neuroinflammatory response and rescue LPS-induced short- and long-term memory impairment in wild-type (WT) mice. In the present study, we examined the effects of ALWPs on Alzheimer’s disease (AD) pathology and cognitive function in WT mice as well as 5x FAD mice (a mouse model of AD). We found that administration of ALWPs significantly reduced amyloid plaque levels in 5x FAD mice and significantly decreased amyloid β (Aβ) levels in amyloid precursor protein (APP)-overexpressing H4 cells. In addition, ALWPs administration significantly suppressed tau hyperphosphorylation in 5x FAD mice. Oral administration of ALWPs significantly improved long-term memory in scopolamine (SCO)-injected WT mice and 5x FAD mice by altering dendritic spine density. Importantly, ALWPs promoted spinogenesis in primary hippocampal neurons and WT mice and modulated the dendritic spine number in an extracellular signal-regulated kinase (ERK)-dependent manner. Taken together, our results suggest that ALWPs are a candidate therapeutic drug for AD that can modulate amyloid plaque load, tau phosphorylation, and synaptic/cognitive function.

Exercise, spinogenesis and cognitive functions

Exercise training improves mental and cognitive functions by enhancing neurogenesis and neuroprotection. Recent studies suggest the facilitation of spinogenesis across different brain regions including hippocampus and cerebral cortex by physical activity. In this article we will summarize major findings for exercise effects on synaptogenesis and spinogenesis, in order to provide mechanisms for exercise intervention of both psychiatric diseases and neurodegenerative disorders. We will also revisit major findings for molecular mechanism governing exercise-related spinogenesis, and will discuss the screening for novel factors, or exerkines, whose levels are correlated with endurance training and affect neural plasticity. We believe that further studies focusing on the molecular mechanism of exercise-mediate spinogenesis should benefit the optimization of exercise therapy in clinics and the evaluation of treatment efficiency using specific biomarkers.

Nature of Tau-Associated Neurodegeneration and the Molecular Mechanisms

Neurodegeneration is defined as the progressive loss of structure or function of the neurons. As the nature of degenerative cell loss is currently not clear, there is no specific molecular marker to measure neurodegeneration. Therefore, researchers have been using apoptotic markers to measure neurodegeneration. However, neurodegeneration is completely different from apoptosis by morphology and time course. Lacking specific molecular marker has been the major hindrance in research of neurodegenerative disorders. Alzheimer's disease (AD) is the most common neurodegenerative disorder, and tau accumulation forming neurofibrillary tangles is a hallmark pathology in the AD brains, suggesting that tau must play a critical role in AD neurodegeneration. Here we review part of our published papers on tau-related studies, and share our thoughts on the nature of tau-associated neurodegeneration in AD.

Tau accumulation triggers STAT1-dependent memory deficits by suppressing NMDA receptor expression

Intracellular tau accumulation forming neurofibrillary tangles is hallmark pathology of Alzheimer's disease (AD), but how tau accumulation induces synapse impairment is elusive. By overexpressing human full-length wild-type tau (termed hTau) to mimic tau abnormality as seen in the brain of sporadic AD patients, we find that hTau accumulation activates JAK2 to phosphorylate STAT1 (signal transducer and activator of transcription 1) at Tyr701 leading to STAT1 dimerization, nuclear translocation, and its activation. STAT1 activation suppresses expression of N-methyl-D-aspartate receptors (NMDARs) through direct binding to the specific GAS element of GluN1, GluN2A, and GluN2B promoters, while knockdown of STAT1 by AAV-Cre in STAT1^flox/flox mice or expressing dominant negative Y701F-STAT1 efficiently rescues hTau-induced suppression of NMDAR expression with amelioration of synaptic functions and memory performance. These findings indicate that hTau accumulation impairs synaptic plasticity through JAK2/STAT1-induced suppression of NMDAR expression, revealing a novel mechanism for hTau-associated synapse and memory deficits.

Transcranial Low-Intensity Pulsed Ultrasound Modulates Structural and Functional Synaptic Plasticity in Rat Hippocampus

Plasticity of synaptic structure and function play an essential role in neuronal development, cognitive functions, and degenerative diseases. Recently, low-intensity pulsed ultrasound (LIPUS) stimulation has been reported as a promising technology for neuromodulation. However, the effect of LIPUS stimulation on the structural and functional synaptic plasticity in rat hippocampus has not yet been addressed. The aim of this study was to investigate whether LIPUS stimulation could affect the dendritic structure, electrophysiological properties, and expression level of glutamate receptors GluN2A, GluN2B, and GluR1 subunits in rat hippocampus. Transcranial LIPUS was delivered to CA1 of the intact hippocampus of rats ( n = 40 ) for 10 days (10 min/day) with the following parameters: fundamental frequency of 0.5 MHz, pulse repetition frequency (PRF) of 500 Hz, peak negative pressure of 0.42 MPa, and I_spta of 360 mW/cm². The effect of LIPUS on dendritic structure, electrophysiological properties, and the expression of neurotransmitter receptors was measured using Golgi staining, electrophysiological recording, and western blotting, respectively. Golgi staining and electrophysiological recordings showed that LIPUS stimulation significantly increased the density of dendritic spines (0.72 ± 0.17 versus 0.94 ± 0.19 spines/ [Formula: see text], ) and the frequency of spontaneous excitatory postsynaptic current (0.37 ± 0.14 versus 1.77 ± 0.37 Hz, ) of CA1 hippocampal neurons. Furthermore, the western blotting analysis demonstrated a significant increase in the expression level of GluN2A ( ). The results illustrated the effect of LIPUS on the dendritic structure, function, and neurotransmitter receptors, which may provide a powerful tool for treating neurodegenerative diseases.

Moderate- and Low-Dose of Atorvastatin Alleviate Cognition Impairment Induced by High-Fat Diet via Sirt1 Activation

Mounting evidences have demonstrated that diet-induced obesity is associated with cognition impairment via increasing oxidative stress and inflammation in the brain. Atorvastatin (Ator, a HMG-CoA reductase inhibitor) is a cholesterol lowering drug. Studies have reported that Ator can ameliorate the development and progression of cognition impairment. Additionally, silent information regulator 1 (SIRT1) has been demonstrated to be beneficial in cognition impairment. However, the interaction between Ator and SIRT1 activation for cognition impairment remains unclear. This study aimed to identify a relationship between the use of Ator and cognition impairment induced by high-fat diet via Sirt1 activation. A total of 60 healthy male C57BL/6J mice were purchased and then divided into 6 groups, including normal diet group (control), a high-fat diet group (40%HFD, 40% energy from fat), a model group (60%HFD, 60% energy from fat), and model group treated with different doses of Ator (high-dose (80 mg), moderate-dose (40 mg), and low-dose (20 mg) groups). All interventions took place for 7 months. Metabolic phenotypes were characterized for body weight and analysis of serum lipid level. The level of cognition development was examined by Morris water maze (MWM) approach and novel object recognition test (NORT); besides, the expression of Creb1, Gap-43, BDNF, CaMKII, and ERKs of frontal cortex and hippocampus was determined by reverse transcription polymerase chain reaction (RT-PCR). Then, the levels of factors related to inflammation (TNF-a, IL-1β, HMGB1 and IL-6) and oxidation stress (SOD, MDA, CAT and GSH-Px) were assessed using commercially available kits. Finally, SIRT1 and its downstream molecules (Ac-FoxO1, Ac-p53, Ac-NF-κB, Bcl-2 and Bax) were evaluated by Western blot analysis. Compared with the 60% HFD group, body weight and serum lipid levels were significantly decreased in the Ator treated groups. The results of MWM and NORT, as well as the levels of Creb1, Gap-43, BDNF, CaMKII, and ERKs were markedly reversed in the moderate- and low-dose of Ator treated groups. Meanwhile, the expression of IL-1β, TNF-a, IL-6, HMGB1, and MDA was notably decreased, whereas the activity of SOD, CAT, and GSH-Px was increased. It was also revealed that the expression of SIRT1 was remarkably unregulated, the level of Bcl-2 was upregulated, and the content of Ac-FoxO1, Ac-p53, Ac-NF-κB, and Bax was downregulated in the moderate- and low-dose of Ator. Furthermore, results showed that the effect of moderate-dose of Ator was significantly greater than the low-dose of Ator. However, these effects were not observed in the high-dose of Ator. Our results showed that moderate- and low-dose of Ator can significantly attenuate cognition impairment induced by HFD through its antioxidant and anti-inflammatory functions related to SIRT1 activation.

Monosodium glutamate exposure during the neonatal period leads to cognitive deficits in adult Sprague-Dawley rats

Epidemiological surveys show that 70-80% of patients with Alzheimer's disease (AD) have type 2 diabetes mellitus (T2DM) or show an abnormality of blood glucose levels. Therefore, an increasing number of evidence has suggested that diabetic hyperglycemia is tightly linked with the pathogenesis and progression of AD. In the present study, we replicated T2DM animal model via subcutaneous injection of newborn Sprague-Dawley (SD) rats with monosodium glutamate (MSG) during the neonatal period to investigate the effects and underlying mechanisms of hyperglycemia on cognitive ability. We found that neonatal MSG exposure induced hyperglycemia as well as Alzheimer-like learning and memory deficits with decreased dendritic spine density and hippocampal synaptic-related protein expression and increased phosphorylated tau levels in ∼3-month-old SD rats. Our results suggested that hyperglycemia probably causes cognitive impairment and Alzheimer-like neuropathological changes, which provide the experimental data connecting T2DM and AD.

Role of the endogenous cannabinoid receptor 1 in brain injury induced by chronic intermittent hypoxia in rats

PURPOSE

This study investigated the effect of rimonabant, a cannabinoid receptor type 1 antagonist, on calcium/calmodulin- dependent protein kinase II and cannabinoid receptor type 1 in chronic intermittent hypoxia.

MATERIALS AND METHODS

Healthy male rats were divided into control group, intermittent hypoxia group for 4 or 6 weeks, hypoxic intervention group that received rimonabant (1 mg/kg/d) before exposure to hypoxia for 4 or 6 weeks (n = 10/group). Morphological changes and expressions of the two indexes in the cerebral hippocampus cells were determined by haematoxylin-eosin staining and immunohistochemistry, respectively.

RESULTS

In the intermittent hypoxia group at 4 weeks, the hippocampal cells were damaged with sparse cytoplasm and unclear boundaries, which are even worse at 6 weeks. In contrast, the hippocampal cells of the hypoxic intervention group were neatly arranged at 4 weeks. At 6 weeks, cells were larger with scarce cytoplasm and nuclear changes indicative of cell death. Calcium/calmodulin-dependent protein kinase II and cannabinoid receptor type 1 expression in the cerebral hippocampus was elevated in the intermittent hypoxia group at 4 weeks with even greater at 6 weeks. Cannabinoid receptor type 1 expression was reduced in the hypoxic intervention group compared to the intermittent hypoxia group. Correlation analysis revealed significant positive correlation of them in the intermittent hypoxia group.

CONCLUSIONS

Chronic intermittent hypoxia induced structural damage in the hippocampus and increased cannabinoid receptor type 1 and calcium/calmodulin-dependent protein kinase II expression, which may mediate cognitive impairment associated with chronic intermittent hypoxia. Rimonabant had a protective effect against chronic intermittent hypoxia.

Fluoxetine administration during adolescence attenuates cognitive and synaptic deficits in adult 3×TgAD mice

Fluoxetine (FLX) has broad neurobiological functions and neuroprotective effects; however, the preventive effects of FLX on cognitive impairments in Alzheimer's disease (AD) have not been reported. Here, we studied whether adolescent administration of fluoxetine can prevent memory deficits in AD transgenic mice that harbour PS1_m146v, APP_swe and TauP_301L mutations (3 × TgAD). FLX was applied through peritoneal injection to the mice at postnatal day 35 (p35) for 15 consecutive days, and the effects of FLX were observed at 6-month. We found that adolescent administration of FLX improved learning and memory abilities in 6-month-old 3 × TgAD mice. FLX exposure also increased the sizes of the hippocampal CA1, dentate gyrus (DG) and extensive cortex regions, with increased numbers of neurons and higher dendritic spine density. Meanwhile, the synaptic plasticity of neurons in the hippocampus was remodelled, and the expression levels of synaptic-related proteins were increased along with activation of the cyclic AMP response element-binding (CREB) protein/brain-derived neurotrophic factor (BDNF) signalling pathway. Finally, we found that FLX effectively prevented the increase of beta-amyloid (Aβ) levels. These data suggest that adolescent administration of the antidepressant drug FLX can efficiently preserve cognitive functions and improve pathologies in 3×Tg AD mice.

GSK-3β deletion in dentate gyrus excitatory neuron impairs synaptic plasticity and memory

Increasing evidence suggests that glycogen synthase kinase-3β (GSK-3β) plays a crucial role in neurodegenerative/psychiatric disorders, while pan-neural knockout of GSK-3β also shows detrimental effects. Currently, the function of GSK-3β in specific type of neurons is elusive. Here, we infused AAV-CaMKII-Cre-2A-eGFP into GSK-3β^lox/lox mice to selectively delete the kinase in excitatory neurons of hippocampal dentate gyrus (DG), and studied the effects on cognitive/psychiatric behaviors and the molecular mechanisms. We found that mice with GSK-3β deletion in DG excitatory neurons displayed spatial and fear memory defects with an anti-anxiety behavior. Further studies demonstrated that GSK-3β deletion in DG subset inhibited hippocampal synaptic transmission and reduced levels of GluN1, GluN2A and GluN2B (NMDAR subunits), GluA1 (AMPAR subunit), PSD93 and drebrin (postsynaptic structural proteins), and synaptophysin (presynaptic protein). GSK-3β deletion also suppressed the activity-dependent neural activation and calcium/calmodulin-dependent protein kinase II (CaMKII)/CaMKIV-cAMP response element binding protein (CREB) signaling. Our data suggest that GSK-3β in hippocampal DG excitatory neurons is essential for maintaining synaptic plasticity and memory.

MicroRNA-195 prevents dendritic degeneration and neuron death in rats following chronic brain hypoperfusion

Impaired synaptic plasticity and neuron loss are hallmarks of Alzheimer’s disease and vascular dementia. Here, we found that chronic brain hypoperfusion (CBH) by bilateral common carotid artery occlusion (2VO) decreased the total length, numbers and crossings of dendrites and caused neuron death in rat hippocampi and cortices. It also led to increase in N-terminalβ-amyloid precursor protein (N-APP) and death receptor-6 (DR6) protein levels and in the activation of caspase-3 and caspase-6. Further study showed that DR6 protein was downregulated bymiR-195overexpression, upregulated bymiR-195inhibition, and unchanged by binding-site mutation and miR-masks. Knockdown of endogenousmiR-195by lentiviral vector-mediated overexpression of its antisense molecule (lenti-pre-AMO-miR-195) decreased the total length, numbers and crossings of dendrites and neuron death, upregulated N-APP and DR6 levels, and elevated cleaved caspase-3 and caspase-6 levels. Overexpression ofmiR-195using lenti-pre-miR-195prevented these changes triggered by 2VO. We conclude thatmiR-195is involved in CBH-induced dendritic degeneration and neuron death through activation of the N-APP/DR6/caspase pathway.

Exercise as a Positive Modulator of Brain Function

Various forms of exercise have been shown to prevent, restore, or ameliorate a variety of brain disorders including dementias, Parkinson's disease, chronic stress, thyroid disorders, and sleep deprivation, some of which are discussed here. In this review, the effects on brain function of various forms of exercise and exercise mimetics in humans and animal experiments are compared and discussed. Possible mechanisms of the beneficial effects of exercise including the role of neurotrophic factors and others are also discussed.

Late running is not too late against Alzheimer's pathology

In the last decade a vast number of animal studies have produced overwhelming evidence that exercise not only compensates for memory loss by increasing brain plasticity and cognitive reserve but also directly counteracts Alzheimer-like pathology when provided before disease onset or in early disease stages. But so far, there is little knowledge about therapeutic effects of training when started in advanced disease stages. In the present study we show that following seven months of sedentary life style five months of wheel running, started four months after disease onset was still able to mitigate at least some aspects of the full-blown Alzheimer's pathology in TgCRND8 mice. Late running had mild but significant effects on structural plasticity by increasing the dendritic complexity. It further reduced beta-amyloid (Aβ) plaque burden and enhanced Aβ clearance across the blood-brain barrier, along with attenuating microgliosis, inflammation, oxidative stress, and autophagy deficits, resulting in better memory performance and less agitation. However, unlike early exercise, late running did not affect abnormal amyloid precursor protein metabolism, tau pathology, or angiogenesis. These results allow concluding that it is never too late to counteract Alzheimer's disease with physical training but the earlier the intervention starts, the more pronounced is the therapeutic potential.

Spatial training promotes short-term survival and neuron-like differentiation of newborn cells in Aβ1-42-injected rats

Neurogenesis plays a role in hippocampus-dependent learning and impaired neurogenesis may correlate with cognitive deficits in Alzheimer's disease. Spatial training influences the production and fate of newborn cells in hippocampus of normal animals, whereas the effects on neurogenesis in Alzheimer-like animal are not reported until now. Here, for the first time, we investigated the effect of Morris water maze training on proliferation, survival, apoptosis, migration, and differentiation of newborn cells in β-amyloid-treated Alzheimer-like rats. We found that spatial training could preserve a short-term survival of newborn cells generated before training, during the early phase, and the late phase of training. However, the training had no effect on the long-term survival of mature newborn cells generated at previously mentioned 3 different phases. We also demonstrated that spatial training promoted newborn cell differentiation preferentially to the neuron direction. These findings suggest a time-independent neurogenesis induced by spatial training, which may be indicative for the cognitive stimulation in Alzheimer's disease therapy.

Modulation of Synaptic Plasticity by Exercise Training as a Basis for Ischemic Stroke Rehabilitation

In recent years, rehabilitation of ischemic stroke draws more and more attention in the world, and has been linked to changes of synaptic plasticity. Exercise training improves motor function of ischemia as well as cognition which is associated with formation of learning and memory. The molecular basis of learning and memory might be synaptic plasticity. Research has therefore been conducted in an attempt to relate effects of exercise training to neuroprotection and neurogenesis adjacent to the ischemic injury brain. The present paper reviews the current literature addressing this question and discusses the possible mechanisms involved in modulation of synaptic plasticity by exercise training. This review shows the pathological process of synaptic dysfunction in ischemic roughly and then discusses the effects of exercise training on scaffold proteins and regulatory protein expression. The expression of scaffold proteins generally increased after training, but the effects on regulatory proteins were mixed. Moreover, the compositions of postsynaptic receptors were changed and the strength of synaptic transmission was enhanced after training. Finally, the recovery of cognition is critically associated with synaptic remodeling in an injured brain, and the remodeling occurs through a number of local regulations including mRNA translation, remodeling of cytoskeleton, and receptor trafficking into and out of the synapse. We do provide a comprehensive knowledge of synaptic plasticity enhancement obtained by exercise training in this review.