STAT3 ameliorates truncated tau-induced cognitive deficits

Proteolytic cleavage of tau by asparagine endopeptidase (AEP) creates tau-N368 fragments, which may drive the pathophysiology associated with synaptic dysfunction and memory deterioration in the brain of Alzheimer's disease patients. Nonetheless, the molecular mechanisms of truncated tau-induced cognitive deficits remain unclear. Evidence suggests that signal transduction and activator of transcription-3 (STAT3) is associated with modulating synaptic plasticity, cell apoptosis, and cognitive function. Using luciferase reporter assays, electrophoretic mobility shift assays, western blotting, and immunofluorescence, we found that human tau-N368 accumulation inhibited STAT3 activity by suppressing STAT3 translocation into the nucleus. Overexpression of STAT3 improved tau-N368-induced synaptic deficits and reduced neuronal loss, thereby improving the cognitive deficits in tau-N368 mice. Moreover, in tau-N368 mice, activation of STAT3 increased N-methyl-D-aspartic acid receptor levels, decreased Bcl-2 levels, reversed synaptic damage and neuronal loss, and thereby alleviated cognitive deficits caused by tau-N368. Taken together, STAT3 plays a critical role in truncated tau-related neuropathological changes. This indicates a new mechanism behind the effect of tau-N368 on synapses and memory deficits. STAT3 can be used as a new molecular target to treat tau-N368-induced protein pathology.

[Effects of electroacupuncture on N-methyl-D-aspartate receptor and mitogen activated protein kinase in spinal cord of rats with primary dysmenorrhea]

OBJECTIVE

To observe the effects of electroacupuncture (EA) on the expression levels of N-methyl-D-aspartate receptor (NMDAR), extracellular signal-regulated kinase (ERK)1/2, p38 mitogen activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK) in the spinal cord of rats with primary dysmenoramia (PDM), so as to explore the underlying mechanism of EA treating PDM.

METHODS

Thirty female SD rats were randomly divided into normal group, model group and EA group, with 10 rats in each group. The PDM rat model was established by subcutaneous injection of estradiol benzoate and oxytocin into the thigh. At the same time of modeling, rats in the EA group were treated with EA (50 Hz) at "Sanyinjiao" (SP36) and "Guanyuan" (CV4) once daily, 20 min each time, for 10 consecutive days. The writhing times, writhing score and writhing latency were observed within 30 min after oxytocin injection. The uterine pathological morphology was observed by HE staining, and pathological score was calculated. Serum prostaglandin F2α (PGF2α) and prostaglandin E2 (PGE2) were determined by ELISA. The protein expression levels of NMDAR, ERK1/2, p38MAPK and JNK in spinal cord were detected by Western blot.

RESULTS

Compared with the normal group, the writhing times and writhing score were significantly increased (P<0.05); the endometrial epithelial cells showed vacuolar degeneration, death and hyperemia, the uterine pathological score was increased (P<0.05); the content of serum PGF2α and the ratio of PGF2α/PGE2 were significantly increased (P<0.01), while the content of serum PGE2 was significantly decreased (P<0.01); the expression levels of NMDAR, ERK1/2, p38MAPK and JNK in spinal cord were significantly increased (P<0.05, P<0.01) in the model group. Compared with the model group, the writhing times and writhing score were significantly decreased (P<0.05), the writhing latency was prolonged (P<0.05); the endometrial epithelial cells still showed vacuolar degeneration, death and hyperemia, and the uterine pathological score was decreased (P<0.01); the content of serum PGF2α and the ratio of PGF2α/PGE2 were significantly decreased (P<0.01), while the content of serum PGE2 was significantly increased (P<0.01); the protein expression levels of ERK1/2 and JNK in spinal cord were significantly decreased (P<0.01) in the EA group.

CONCLUSION

EA intervention at SP36 and GV4 has obvious analgesic effect on PDM rats, and its mechanisms may be related to reducing serum prostaglandin, alleviating uterine inflammation, and inhibiting the protein expressions of NMDAR, ERK1/2, p38 MAPK and JNK in spinal cord.

NMDA Receptor GluN2B Subunit Is Involved in Excitotoxicity Mediated by Death-Associated Protein Kinase 1 in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common form of neurodegenerative dementia among the elderly. Excitotoxicity has been implicated as playing a dominant role in AD, especially related to the hyperactivation of excitatory neurons. Death-associated protein kinase 1 (DAPK1) is a calcium/calmodulin-dependent kinase and involved in the pathogenesis of AD, but the roles and mechanisms of DAPK1 in excitotoxicity in AD are still uncertain.

OBJECTIVE

We mainly explored the underlying mechanisms of DAPK1 involved in the excitotoxicity of AD and its clinical relevance.

METHODS

Differentiated SH-SY5Y human neuroblastoma cells, PS1 V97 L transgenic mice, and human plasma samples were used. Protein expression was assayed by immunoblotting, and intracellular calcium and neuronal damage were analyzed by flow cytometry. Plasma DAPK1 was measured by ELISA.

RESULTS

We found that DAPK1 was activated after amyloid-β oligomers (AβOs) exposure in differentiated SH-SY5Y cells. Besides, we found the phosphorylation of GluN2B subunit at Ser1303 was increased, which contributing to excitotoxicity and Ca2+ overload in SH-SY5Y cells. Inhibiting DAPK1 activity, knockdown of DAPK1 expression, and antagonizing GluN2B subunits could effectively prevent AβOs-induced activation of GluN2B subunit, Ca2+ overload, and neuronal apoptosis. Additionally, we found that DAPK1 was elevated in the brain of AD transgenic mouse and in the plasma of AD patients.

CONCLUSION

Our finding will help to understand the mechanism of DAPK1 in the excitotoxicity in AD and provide a reference for the diagnosis and therapy of AD.

Genetic variables of the glutamatergic system associated with treatment-resistant depression: A review of the literature

Depression is a common, recurrent mental disorder and one of the leading causes of disability and global burden of disease worldwide. Up to 15%-40% of cases do not respond to diverse pharmacological treatments and, thus, can be defined as treatment-resistant depression (TRD). The development of biomarkers predictive of drug response could guide us towards personalized and earlier treatment. Growing evidence points to the involvement of the glutamatergic system in the pathogenesis of TRD. Specifically, the N-methyl-D-aspartic acid receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), which are targeted by ketamine and esketamine, are proposed as promising pathways. A literature search was performed to identify studies on the genetics of the glutamatergic system in depression, focused on variables related to NMDARs and AMPARs. Our review highlights GRIN2B, which encodes the NR2B subunit of NMDAR, as a candidate gene in the pathogenesis of TRD. In addition, several studies have associated genes encoding AMPAR subunits with symptomatic severity and suicidal ideation. These genes encoding glutamatergic receptors could, therefore, be candidate genes for understanding the etiopathogenesis of TRD, as well as for understanding the pharmacodynamic mechanisms and response to ketamine and esketamine treatment.

Prostate-derived IL-1β upregulates expression of NMDA receptor in the paraventricular nucleus and shortens ejaculation latency in rats with experimental autoimmune prostatitis

Experimental autoimmune prostatitis (EAP)-induced persistent inflammatory immune response can significantly upregulate the expression of N-methyl-D-aspartic acid (NMDA) receptors in the paraventricular nucleus (PVN). However, the mechanism has not yet been elucidated. Herein, we screened out the target prostate-derived inflammation cytokines (PDICs) by comparing the inflammatory cytokine levels in peripheral blood and cerebrospinal fluid (CSF) between EAP rats and their controls. After identifying the target PDIC, qualified males in initial copulatory behavior testing (CBT) were subjected to implanting tubes onto bilateral PVN. Next, they were randomly divided into four subgroups (EAP-1, EAP-2, Control-1, and Control-2). After 1-week recovery, EAP-1 rats were microinjected with the target PDIC inhibitor, Control-1 rats were microinjected with the target PDIC, while the EAP-2 and Control-2 subgroups were only treated with the same amount of artificial CSF (aCSF). Results showed that only interleukin-1β (IL-1β) had significantly increased mRNA-expression in the prostate of EAP rats compared to the controls (P < 0.001) and significantly higher protein concentrations in both the serum (P = 0.001) and CSF (P < 0.001) of the EAP groups compared to the Control groups. Therefore, IL-1β was identified as the target PDIC which crosses the blood-brain barrier, thereby influencing the central nervous system. Moreover, the EAP-1 subgroup displayed a gradually prolonged ejaculation latency (EL) in the last three CBTs (all P < 0.01) and a significantly lower expression of NMDA NR1 subunit in the PVN (P = 0.043) compared to the respective control groups after a 10-day central administration of IL-1β inhibitors. However, the Control-1 subgroup showed a gradually shortened EL (P < 0.01) and a significantly higher NR1 expression (P = 0.004) after homochronous IL-1β administration. Therefore, we identified IL-1β as the primary PDIC which shortens EL in EAP rats. However, further studies should be conducted to elucidate the specific molecular mechanisms through which IL-1β upregulates NMDA expression.

A preliminary study on the mechanism of the neurosteroid-mediated ionotropic receptor dysfunction in neurodevelopmental toxicity induced by decabromodiphenyl ether

The mechanism of neurodevelopmental toxicity of decabromodiphenyl ether (BDE209) remains unclear. Recent evidence suggests that neurosteroids disorders play a vital role in BDE209 induced-neurodevelopmental toxicity. To explore the mechanism of it, pregnant ICR mice were orally gavaged with 0, 225, and 900 mg kg^-1 BDE209 for about 42 days. Spatial learning and memory abilities of offspring were tested on postnatal day (PND) 21. Offspring were euthanized at PND26, the neuronal structure, neurosteroids level, and related proteins including neurosteroids synthase, ionotropic receptors and cAMP-response element binding protein (CREB) pathway were evaluated, as well as Ca²⁺ concentration and the mitochondrial membrane potential (Mmp). Our results showed that BDE209 impaired learning and memory abilities and disrupted neuronal structure. Meanwhile, BDE209 decreased the pregnenolone (PREG), dehydroepiandrosterone (DHEA), progesterone (PROG) and allopregnanolone (ALLO) levels in the serum and brain, as well as the mRNA and protein levels of cholesterol-side-chain cleavage enzyme (P450scc), steroid 17α-hy-droxylase (P450C17), 3β-hydroxysteroid dehydrogenase (3β-HSD) and steroid 5α-reductase of type I (5α-R) in the hippocampi. Also, BDE209 suppressed mRNA and protein levels of NR1, NR2A and NR2B subunits of the N-methyl-D-aspartic acid receptor (NMDAR) and α1 subunit of the Gamma-amino butyric acid A receptor (GABAAR), but increased the levels of β2 and γ2 subunits of the GABAAR in the hippocampi. Moreover, BDE209 increased the Ca²⁺ concentration and phosphorylation extracellular regulated protein kinases (P-ERK) 1/2 level, but decreased the P-CREB and Mmp level in the hippocampi. These results indicate that BDE209 exposure during pregnancy and lactation is possible to affect learning and memory formation of offspring by the neurosteroid-mediated ionotropic receptors dysfunction.

Regulation of mGluR1 on the Expression of PKC and NMDAR in Aluminum-Exposed PC12 Cells

Aluminum demonstrates clear neurotoxicity and can cause Alzheimer's disease (AD)-like symptoms, including cognitive impairment. One toxic effect of aluminum is a decrease in synaptic plasticity, but the specific mechanism remains unclear. In this study, PC12 cells were treated with Al(mal)₃ to construct a toxic cell model. (S)-3,5-Dihydroxyphenylglycine (DHPG), α-methyl-4-carboxyphenylglycine (MCPG), and mGluR1-siRNA were used to interfere with the expression of metabotropic glutamate receptor subtype 1 (mGluR1). Polymerase chain reaction and western blotting were used to investigate the expression of mGluR1, protein kinase C (PKC), and N-methyl-D-aspartate receptor (NMDAR) subunits. ELISA was used to detect PKC enzyme activity. In PC12 cells, mRNA and protein expressions of PKC and NMDAR subunits were inhibited by Al(mal)₃. Aluminum may further regulate the expression of NMDAR1 and NMDAR2B through mGluR1 to regulate PKC enzyme activity, thereby affecting learning and memory functions. Furthermore, the results implied that the mGluR1-PKC-NMDAR signaling pathway may predominately involve positive regulation. These findings provide new targets for studying the neurotoxic mechanism of aluminum.

Upregulated expression of NMDA receptor in the paraventricular nucleus shortens ejaculation latency in rats with experimental autoimmune prostatitis

BACKGROUND

Estimated 30%-40% of patients with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) suffer from premature ejaculation (PE), which is difficult to cure, but the mechanism is still unknown. Based on the results of our previous clinical studies and animal experiments, we propose that the glutamatergic system dysfunction in the paraventricular nucleus (PVN) may be involved.

METHODS

To test this hypothesis, we used experimental autoimmune prostatitis (EAP) rats to investigate the effects of CP/CPPS on ejaculation behavior through integrating copulatory behavior testing, neuroelectrophysiologic experiments, and molecular biology technologies.

RESULTS

Histological examination of prostate tissue in EAP rats exhibited consistent pathological findings with that in CP/CPPS patients. Behavior testing showed that ejaculation latency (EL) of EAP rats significantly shortened compared with the controls (5.1 ± 1.8 vs 9.1 ± 2.4 min, P < .001). Sympathetic nervous system (SNS) activity testing revealed that EAP rats displayed significantly higher plasma norepinephrine (NE) level (1780 ± 493 vs 1421 ± 453 pg/mL, P = .043) and SNS sensitivity (67.8 ± 9.6 vs 44.6 ± 8.7%, P < .001). Immunohistochemical detection and Western blot analysis both displayed that NR1 subunit expression of N-methyl-D-aspartic acid (NMDA) receptors in the PVN of EAP rats was significantly upregulated (P = .007 and P < .001). Furthermore, the expression of NMDA NR1 subunit positively correlated both with SNS sensitivity (r = .917, P < .001) and prostatic inflammation scores (r = .964, P < .001).

CONCLUSION

This study shows that EAP rats suffer from the same PE symptom as CP/CPPS patients. CP/CPPS-induced inflammatory-immune response can significantly upregulate the expression of NMDA receptors in the PVN, which shortening the EL by enhancing SNS sensitivity. However, the exact mechanism of chronic inflammation in the prostate causing the upregulated expression of NMDA receptors needs to be further studied.

Role of mGluR 1 in synaptic plasticity impairment induced by maltol aluminium in rats

The main symptoms of Alzheimer's disease (AD) is the loss of learning and memory ability, of which biological basis is synaptic plasticity. Aluminium has been found to cause changes in synaptic plasticity, but its molecular mechanism was unclear. In this study, Sprague-Dawley rats were injected with aluminium maltol (Al(mal)₃) through the lateral ventricle to establish an AD-like model. Y-maze, electrophysiological measurements, Golgi staining, scanning electron microscopy, quantitative real-time polymerase chain reaction, and western blot techniques were used to investigate regulation of the metabolic glutamate receptor 1 (mGluR1) in synaptic plasticity impairment induced by Al(mal)₃. The results showed that Al(mal)₃ inhibited the induction and maintenance of long-term potentiation in the hippocampal CA1 region. During this process, the expression of mGluR1 was up-regulated and it inhibited the expression and phosphorylation of the N-methyl-D-aspartic acid receptors (NMDARs). This mainly affected NMDAR1 and NMDAR2B but did not affect protein kinase C expression.

[Effects of N-methyl-D-aspartate Receptor in Keratinocyte on TypeⅠComplex Regional Pain Syndrome]

Objective To observe the cell origin of N-methyl-D-aspartic acid(NMDA)receptor expression in skin after chronic ischemic pain modeling in rats and explore the role of NMDA receptor in type Ⅰ complex regional pain syndrome. Methods Forty-two adult male Sprague-Dawley rats were randomly divided into five groups:sham operation group(n=12),chronic post ischemia pain(CPIP)group(n=12),CPIP+normal saline(NS)group(n=6),CPIP+NMDA group(n=6),and CPIP+MK801 group(n=6).Six rats in the sham operation group and CPIP group were sacrificed under deep anesthesia one day after modeling.The plantar skin and L3-L5 spinal cord tissue were used for NR1(NMDA receptor)subunit immunofluorescence detection and for Western blotting of NR1,interleukin(IL)-1β,and tumor necrosis factor(TNF)-α.For the remaining rats,the mechanical withdrawal threshold(MWT)values on the 2nd,6th,10th and 14th day after ischemia were recorded,and the corresponding drugs were injected subcutaneously from the 6th day after ischemia.The skin and L3-L5 spinal cords were collected on the 14th day,and the same detection methods were applied. Results Compared with the sham operation group,the CPIP group had significantly higher expressions of NR1(1.708±0.064;t=12.120, P<0.001),IL-1β(2.575±0.305;t=5.158, P=0.003),and TNF-α(2.691±0.217;t=7.786, P<0.001)in the skin on the first day after modeling.After intervention with NMDA and MK801,the MWT value was [(20.37±0.95)g] in the CPIP+NS group,which was significantly higher than that in CPIP+NMDA group [(15.85±1.09)g;q=10.920, P<0.001] but significantly lower than that in CPIP+MK801 group[(22.95±0.96)g;q=6.421, P<0.001] 10 days after modeling.On the 14th day,compared with the MWT of the CPIP+NS group [(21.57±0.96)g],the CPIP+NMDA group had significantly decreased MWT value [(16.53±1.63)g;q=12.190, P<0.001],and the CPIP+MK801 group had significantly increased MWT value [(23.27±1.28)g;q=4.094, P=0.025].Compared with the sham operation group,the CPIP group had significantly increased NR1 expression(1.708±0.064;t=10.910, P<0.001)and the CPIP+NS group had significantly increased expressions of IL-1β(2.518±0.147;q=11.010, P<0.001)and TNF-α(1.949±0.184;q=10.870, P<0.001).Compared with the CPIP+NS group,the CPIP+NMDA group had significantly increased expressions of IL-1β(4.816±0.607;q=16.670, P=0.003)and TNF-α(2.629±0.349;q=7.790, P<0.001)and the CPIP+MK801 group had significantly decreased expressions of IL-1β(1.048±0.257;q=10.660, P=0.003)and TNF-α(0.790±0.165;q=13.280, P<0.001). Conclusion NMDA receptor activation in skin keratinocytes after chronic ischemia in rats hinders the expression of inflammatory cytokines such as IL-1β and TNF-α,which may be involved in central sensitization and pain conduction of type Ⅰ complex regional pain syndrome.

Role of D-serine in the beneficial effects of repetitive transcranial magnetic stimulation in post-stroke patients

OBJECTIVE

Abnormalities in neurotransmission via N-methyl-D-aspartic acid receptor (NMDAR) play a role in the pathophysiology of neuropsychiatric disorders. The impact of repetitive transcranial magnetic stimulation (rTMS) on NMDAR-related amino acids remains unknown. We aim to investigate the effects of rTMS on NMDAR-related amino acids in serum of post-stroke patients.

METHODS

Ninety-five consecutive post-stroke patients with upper limb hemiparesis were recruited. In 27 patients, the Beck Depression Inventory (BDI) score was 10 or higher. Twelve depressed patients underwent rehabilitation in combination with rTMS and 15 non-depressed patients underwent rehabilitation only without rTMS for 14 days. 1 Hz rTMS was applied to the primary motor area in the non-lesional hemisphere. BDI was conducted before and after treatment. Serum glutamine, glutamate, glycine, L-serine, and D-serine levels were measured before and after treatment.

RESULTS

There were no differences between depressed patients and non-depressed patients in clinical characteristics, levels of the five amino acids in serum, and the ratio of amino acids. However, in 27 depressed patients there was a significant correlation between levels of glutamate in serum and BDI (ρ=0.428、p=0.026). BDI decreased significantly in depressed patients after treatment with or without rTMS. D-serine decreased in the rehabilitation with rTMS group, but increased in the rehabilitation without rTMS group. L-serine increased in the rehabilitation with rTMS group, but decreased in the rehabilitation without rTMS group.

CONCLUSIONS

The results suggest that rTMS can modulate NMDAR-related amino acids in blood, producing beneficial effects.

Differences in sympathetic nervous system activity and NMDA receptor levels within the hypothalamic paraventricular nucleus in rats with differential ejaculatory behavior

Differences in intravaginal ejaculation latency reflect normal biological variation, but the causes are poorly understood. Here, we investigated whether variation in ejaculation latency in an experimental rat model is related to altered sympathetic nervous system (SNS) activity and expression of N-methyl-D-aspartic acid (NMDA) receptors in the paraventricular nucleus of the hypothalamus (PVN). Male rats were classified as “sluggish,” “normal,” and “rapid” ejaculators on the basis of ejaculation frequency during copulatory behavioral testing. The lumbar splanchnic nerve activity baselines in these groups were not significantly different at 1460 ± 480 mV, 1660 ± 600 mV, and 1680 ± 490 mV, respectively (P = 0.71). However, SNS sensitivity was remarkably different between the groups (P < 0.01), being 28.9% ± 8.1% in “sluggish,” 48.4% ± 7.5% in “normal,” and 88.7% ± 7.4% in “rapid” groups. Compared with “normal” ejaculators, the percentage of neurons expressing NMDA receptors in the PVN of “rapid” ejaculators was significantly higher, whereas it was significantly lower in “sluggish” ejaculators (P = 0.01). In addition, there was a positive correlation between the expression of NMDA receptors in the PVN and SNS sensitivity (r = 0.876, P = 0.02). This study shows that intravaginal ejaculatory latency is associated with SNS activity and is mediated by NMDA receptors in the PVN.

Paired associative stimulation improves synaptic plasticity and functional outcomes after cerebral ischemia

Paired associative stimulation is a relatively new non-invasive brain stimulation technique that combines transcranial magnetic stimulation and peripheral nerve stimulation. The effects of paired associative stimulation on the excitability of the cerebral cortex can vary according to the time interval between the transcranial magnetic stimulation and peripheral nerve stimulation. We established a model of cerebral ischemia in rats via transient middle cerebral artery occlusion. We administered paired associative stimulation with a frequency of 0.05 Hz 90 times over 4 weeks. We then evaluated spatial learning and memory using the Morris water maze. Changes in the cerebral ultra-structure and synaptic plasticity were assessed via transmission electron microscopy and a 64-channel multi-electrode array. We measured mRNA and protein expression levels of brain-derived neurotrophic factor and N-methyl-D-aspartate receptor 1 in the hippocampus using a real-time polymerase chain reaction and western blot assay. Paired associative stimulation treatment significantly improved learning and memory in rats subjected to cerebral ischemia. The ultra-structures of synapses in the CA1 area of the hippocampus in rats subjected to cerebral ischemia were restored by paired associative stimulation. Long-term potentiation at synapses in the CA3 and CA1 regions of the hippocampus was enhanced as well. The protein and mRNA expression of brain-derived neurotrophic factor and N-methyl-D-aspartate receptor 1 increased after paired associative stimulation treatment. These data indicate that paired associative stimulation can protect cognition after cerebral ischemia. The observed effect may be mediated by increases in the mRNA and protein expression of brain-derived neurotrophic factor and N-methyl-D-aspartate receptor 1, and by enhanced synaptic plasticity in the CA1 area of the hippocampus. The animal experiments were approved by the Animal Ethics Committee of Tongji Medical College, Huazhong University of Science & Technology, China (approval No. TJ-A20151102) on July 11, 2015.

The Memory-Enhancing Effects of Liquiritigenin by Activation of NMDA Receptors and the CREB Signaling Pathway in Mice

Liquiritigenin (LQ) is a flavonoid that can be isolated from Glycyrrhiza radix. It is frequently used as a tranditional oriental medicine herbal treatment for swelling and injury and for detoxification. However, the effects of LQ on cognitive function have not been fully explored. In this study, we evaluated the memory-enhancing effects of LQ and the underlying mechanisms with a focus on the N-methyl-D-aspartic acid receptor (NMDAR) in mice. Learning and memory ability were evaluated with the Y-maze and passive avoidance tests following administration of LQ. In addition, the expression of NMDAR subunits 1, 2A, and 2B; postsynaptic density-95 (PSD-95); phosphorylation of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII); phosphorylation of extracellular signal-regulated kinase 1/2 (ERK 1/2); and phosphorylation of cAMP response element binding (CREB) proteins were examined by Western blot. In vivo, we found that treatment with LQ significantly improved memory performance in both behavioral tests. In vitro, LQ significantly increased NMDARs in the hippocampus. Furthermore, LQ significantly increased PSD-95 expression as well as CaMKII, ERK, and CREB phosphorylation in the hippocampus. Taken together, our results suggest that LQ has cognition enhancing activities and that these effects are mediated, in part, by activation of the NMDAR and CREB signaling pathways.

Chronic ethanol exposure induces SK-N-SH cell apoptosis by increasing N-methyl-D-aspartic acid receptor expression and intracellular calcium

It has been identified that chronic ethanol exposure damages the nervous system, particularly neurons. There is scientific evidence suggesting that neuronal loss caused by chronic ethanol exposure has an association with neuron apoptosis and intracellular calcium oscillation is one of the primary inducers of apoptosis. Therefore, the present study aimed to investigate the inductive effects of intracellular calcium oscillation on apoptosis in SK-N-SH human neuroblastoma cells and the protective effects of the N-methyl-D-aspartic acid receptor (NMDAR) antagonist, memantine, on SK-N-SH cell apoptosis caused by chronic ethanol exposure. SK-N-SH cells were treated with 100 mM ethanol and memantine (4 µM) for 2 days. Protein expression of NR1 was downregulated by RNA interference (RNAi). Apoptosis was detected by Annexin V/propidium iodide (PI) double-staining and flow cytometry and cell viability was detected using an MTS kit. Fluorescence dual wavelength spectrophotometry was used to determine the intracellular calcium concentration and the levels of NR1 and caspase-3 were detected using western blotting. NR1 mRNA levels were also detected using qPCR. It was found that chronic ethanol exposure reduced neuronal cell viability and caused apoptosis of SK-N-SH cells, and the extent of damage in SK-N-SH cells was associated with ethanol exposure concentration and time. In addition, chronic ethanol exposure increased the concentration of intracellular calcium in SK-N-SH cells by inducing the expression of NMDAR, resulting in apoptosis, and memantine treatment reduced ethanol-induced cell apoptosis. The results of the present study indicate that the application of memantine may provide a novel strategy for the treatment of alcoholic dementia.

MicroRNA-217 suppresses homocysteine-induced proliferation and migration of vascular smooth muscle cells via N-methyl-D-aspartic acid receptor inhibition

Hyperhomocysteine has become a critical risk for atherosclerosis and can stimulate proliferation and migration of vascular smooth muscle cells (VSMCs). N-methyl-D-aspartic acid receptor (NMDAR) is a receptor of homocysteine and mediates the effects of homocysteine on VSMCs. Bioinformatics analysis has shown NMDAR is a potential target of microRNA-217 (miR-217), which exerts multiple functions in cancer tumorigenesis and carotid plaque progression. In this study, we sought to investigate the role of miR-217 in VSMCs phenotype transition under homocysteine exposure and elucidate its effect on atherosclerotic plaque formation. After treating with several doses of homocysteine (0-8 × 10(-4)  mol/L) for 24 hours, the expression of miR-217 in HA-VSMCs and rat aortic VSMCs was not altered. Intriguingly, the expression of NMDAR mRNA and protein was reduced by homocysteine in a dose-dependent manner. Transfection of miR-217 mimic significantly inhibited the proliferation and migration of VSMCs with homocysteine treatment, while transfection of miR-217 inhibitor promoted VSMCs migration. Moreover, miR-217 mimic down-regulated while miR-217 inhibitor up-regulated NMDAR protein expression but not NMDAR mRNA expression. Through luciferase reporter assay, we showed that miR-217 could directly bind to the 3'-UTR of NMDAR. MiR-217 mimic transfection also released the inhibition of cAMP-response element-binding protein (CREB)-PGC-1α signalling induced by homocysteine. Additionally, restoration of PGC-1α expression via AdPGC-1α infection markedly suppressed VSMCs proliferation through the degradation of NADPH oxidase (NOX1) and reduction of reactive oxygen species (ROS). Collectively, our study identified the role of miR-217 in regulating VSMCs proliferation and migration, which might serve as a target for atherosclerosis therapy.

Increased extrasynaptic GluN2B expression is involved in cognitive impairment after isoflurane anesthesia

There is increasing concern regarding the postoperative cognitive dysfunction (POCD) in the aging population, and general anesthetics are believed to be involved. Isoflurane exposure induced increased N-methyl-D-aspartic acid receptor (NMDAR) GluN2B subunit expression following anesthesia, which was accompanied by alteration of the cognitive function. However, whether isoflurane affects this expression in different subcellular compartments, and is involved in the development of POCD remains to be elucidated. The aims of the study were to investigate the effects of isoflurane on the expression of the synaptic and extrasynaptic NMDAR subunits, GluN2A and GluN2B, as well as the associated alteration of cognitive function in aged rats. The GluN2B antagonist, Ro25–6981, was given to rats exposed to isoflurane to determine the role of GluN2B in the isoflurane-induced alteration of cognitive function. The results showed that spatial learning and memory tested in the Morris water maze (MWM) was impaired at least 7 days after isoflurane exposure, and was returned to control levels 30 days thereafter. Ro25-6981 treatment can alleviate this impairment. Extrasynaptic GluN2B protein expression, but not synaptic GluN2B or GluN2A, increased significantly after isoflurane exposure compared to non-isoflurane exposure, and returned to control levels approximately 30 days thereafter. The results of the present study indicated that isoflurane induced the prolonged upregulation of extrasynaptic GluN2B expression after anesthesia and is involved in reversible cognitive impairment.

High dosage of agmatine alleviates pentylenetetrazole-induced chronic seizures in rats possibly by exerting an anticonvulsive effect

The aim of the present study was to investigate the mechanism underlying the effects of different doses of agmatine in rats with chronic epilepsy. To generate chronic epilepsy models, rats pretreated with different doses of agmatine (20, 40 and 80 mg/kg) were intraperitoneally injected with pentylenetetrazole (35 mg/kg) for 28 consecutive days. Epileptic behavior was observed using behavioral measurements of convulsion for 1 h after each treatment with pentylenetetrazole. Morphological alterations of the hippocampal neurons were also observed using hematoxylin and eosin staining. In addition, the expression levels of glial fibrillary acidic protein and inducible nitric oxide synthase (iNOS) in the hippocampus were detected by immunohistochemistry. Furthermore, reverse transcription polymerase chain reaction was performed to detect the mRNA expression of two subunits (NR1 and NR2B) of the N-methyl-D-aspartic acid (NMDA) receptor in the rat hippocampus. The results demonstrated that administration of agmatine (80 mg/kg) significantly decreased the daily average grade of epileptic seizures and also reduced neuronal loss and astrocyte hyperplasia in the hippocampal area. Furthermore, agmatine (80 mg/kg) affected the mRNA expression levels of the NR1 subunit of the NMDA receptor, however, agmatine had no effect on the expression of iNOS in the hippocampus. Higher doses of agmatine inhibited the effect of pentylenetetrazole in rats, reduced astrocytic hyperplasia and neuronal damage in the hippocampus caused by seizures and selectively reduced the expression of the NR1 subunit of NMDA. Our results suggest that agmatine has an anticonvulsive effect in chronic epilepsy.

A novel role of spinal astrocytic connexin 43: mediating morphine antinociceptive tolerance by activation of NMDA receptors and inhibition of glutamate transporter-1 in rats

AIMS

Connexin 43 (Cx43) has been reported to be involved in neuropathic pain, but whether it contributes to morphine antinociceptive tolerance remains unknown. The present study investigated the role of spinal Cx43 in the development of morphine tolerance and its mechanisms in rats.

METHODS

Morphine tolerance was induced by intrathecal (i.t.) administration of morphine (15 μg) daily for seven consecutive days. The analgesia effect was assessed by hot-water tail-flick test. Expression of proteins was detected by Western blot and immunohistochemistry assay.

RESULTS

Chronic morphine markedly increased the expression of spinal Cx43. Gap26, a specific Cx43 mimic peptide, attenuated not only morphine antinociceptive tolerance, but also the up-regulation of spinal Cx43 expression, the activation of astrocytes, and N-methyl-D-aspartic acid (NMDA) receptors (NR1 and NR2B subunits), as well as the decreased GLT-1 expression induced by chronic morphine. MK-801, a noncompetitive NMDA receptors antagonist, suppressed the chronic morphine-induced spinal Cx43 up-regulation, astrocytes activation and decline of GLT-1 expression.

CONCLUSIONS

The spinal astrocytic Cx43 contributes to the development of morphine antinociceptive tolerance by activating astrocytes and NMDA receptors, and inhibiting GLT-1 expression. We also demonstrate that the role of interaction between the spinal astrocytic Cx43 and neuronal NMDA receptors is important in morphine tolerant rats.

2-Guanidine-4-methylquinazoline acts as a novel competitive antagonist of A type γ-aminobutyric acid receptors

The pentameric A type γ-aminobutyric acid receptors (GABAARs) are the major inhibitory neurotransmitter receptors in the nervous system and have long been considered as important pharmaceutical targets for the treatment of multiple neurological or psychological disorders. Here, we show that 2-guanidine-4-methylquinazoline (GMQ), a recently identified acid-sensing ion channel (ASIC) modulator, strongly and preferentially inhibits GABAAR among the major neurotransmitter-gated ion channels in cultured rat hippocampal neurons. GMQ inhibited GABA (1 μM)-induced currents in a competitive manner, with an IC50 (0.39±0.05 μM) comparable to that of bicuculline. Schild analysis revealed a slope of 1.04±0.06 for GMQ on α1β2 GABAARs expressed in HEK293T cells. Single-channel analysis showed that GMQ decreased open probability of GABAARs without affecting conductance. Moreover, GMQ inhibited GABAergic neurotransmission in hippocampal neurons, while having no significant effect on the basal field excitatory postsynaptic potentials (fEPSPs) and the intrinsic excitability of neurons. Using site-directed mutagenesis, we further demonstrated that mutations at Glu155 of β2 subunit and Phe64 of α1 subunit, both located inside the GABA binding pocket, profoundly decreased the sensitivity of the receptor to both GABA and GMQ. Interestingly, these mutations did not significantly affect the inhibition by amiloride, a diuretic structurally similar to GMQ and a known GABAAR inhibitor. We conclude that GMQ represents a novel chemical structure that acts, possibly, by competing with GABA binding to GABAARs. It is anticipated that GMQ and its analogs will facilitate the development of new chemical probes for GABAARs.

Decoding Alzheimer's disease from perturbed cerebral glucose metabolism: implications for diagnostic and therapeutic strategies

Alzheimer's disease (AD) is an age-related devastating neurodegenerative disorder, which severely impacts on the global economic development and healthcare system. Though AD has been studied for more than 100 years since 1906, the exact cause(s) and pathogenic mechanism(s) remain to be clarified. Also, the efficient disease-modifying treatment and ideal diagnostic method for AD are unavailable. Perturbed cerebral glucose metabolism, an invariant pathophysiological feature of AD, may be a critical contributor to the pathogenesis of this disease. In this review, we firstly discussed the features of cerebral glucose metabolism in physiological and pathological conditions. Then, we further reviewed the contribution of glucose transportation abnormality and intracellular glucose catabolism dysfunction in AD pathophysiology, and proposed a hypothesis that multiple pathogenic cascades induced by impaired cerebral glucose metabolism could result in neuronal degeneration and consequently cognitive deficits in AD patients. Among these pathogenic processes, altered functional status of thiamine metabolism and brain insulin resistance are highly emphasized and characterized as major pathogenic mechanisms. Finally, considering the fact that AD patients exhibit cerebral glucose hypometabolism possibly due to impairments of insulin signaling and altered thiamine metabolism, we also discuss some potential possibilities to uncover diagnostic biomarkers for AD from abnormal glucose metabolism and to develop drugs targeting at repairing insulin signaling impairment and correcting thiamine metabolism abnormality. We conclude that glucose metabolism abnormality plays a critical role in AD pathophysiological alterations through the induction of multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, and so forth. To clarify the causes, pathogeneses and consequences of cerebral hypometabolism in AD will help break the bottleneck of current AD study in finding ideal diagnostic biomarker and disease-modifying therapy.

Effects of protopanaxatriol-ginsenoside metabolites on rat N-methyl-d-aspartic Acid receptor-mediated ion currents

Ginsenosides are low molecular weight glycosides found in ginseng that exhibit neuroprotective effects through inhibition of N-methyl-D-aspartic acid (NMDA) receptor channel activity. Ginsenosides, like other natural compounds, are metabolized by gastric juices and intestinal microorganisms to produce ginsenoside metabolites. However, little is known about how ginsenoside metabolites regulate NMDA receptor channel activity. In the present study, we investigated the effects of ginsenoside metabolites, such as compound K (CK), protopanaxadiol (PPD), and protopanaxatriol (PPT), on oocytes that heterologously express the rat NMDA receptor. NMDA receptor-mediated ion current (I_NMDA) was measured using the 2-electrode voltage clamp technique. In oocytes injected with cRNAs encoding NMDA receptor subunits, PPT, but not CK or PPD, reversibly inhibited I_NMDA in a concentration-dependent manner. The IC₅₀ for PPT on I_NMDA was 48.1±4.6 µM, was non-competitive with NMDA, and was independent of the membrane holding potential. These results demonstrate the possibility that PPT interacts with the NMDA receptor, although not at the NMDA binding site, and that the inhibitory effects of PPT on I_NMDA could be related to ginseng-mediated neuroprotection.