N-methyl-D-aspartate (NMDA) and the regulation of mitogen-activated protein kinase (MAPK) signaling pathways: a revolving neurochemical axis for therapeutic intervention?

Neuropharmacological Evidence Implicating Drug-Induced Glutamate Receptor Dysfunction in Affective and Cognitive Sequelae of Subchronic Methamphetamine Self-Administration in Mice

Methamphetamine (MA) is a highly addictive drug, and MA use disorder is often comorbid with anxiety and cognitive impairment. These comorbid conditions are theorized to reflect glutamate-related neurotoxicity within the frontal cortical regions. However, our prior studies of MA-sensitized mice indicate that subchronic, behaviorally non-contingent MA treatment is sufficient to dysregulate glutamate transmission in mouse brain. Here, we extend this prior work to a mouse model of high-dose oral MA self-administration (0.8, 1.6, or 3.2 g/L; 1 h sessions × 7 days) and show that while female C57BL/6J mice consumed more MA than males, MA-experienced mice of both sexes exhibited some signs of anxiety-like behavior in a behavioral test battery, although not all effects were concentration-dependent. No MA effects were detected for our measures of visually cued spatial navigation, spatial learning, or memory in the Morris water maze; however, females with a history of 3.2 g/L MA exhibited reversal-learning deficits in this task, and mice with a history of 1.6 g/L MA committed more working-memory incorrect errors and relied upon a non-spatial navigation strategy during the radial-arm maze testing. Relative to naïve controls, MA-experienced mice exhibited several changes in the expression of certain glutamate receptor-related proteins and their downstream effectors within the ventral and dorsal areas of the prefrontal cortex, the hippocampus, and the amygdala, many of which were sex-selective. Systemic pretreatment with the mGlu1-negative allosteric modulator JNJ 162596858 reversed the anxiety-like behavior expressed by MA-experienced mice in the marble-burying test, while systemic pretreatment with NMDA or the NMDA antagonist MK-801 bi-directionally affected the MA-induced reversal-learning deficit. Taken together, these data indicate that a relatively brief history of oral MA is sufficient to induce some signs of anxiety-like behavior and cognitive dysfunction during early withdrawal that reflect, at least in part, MA-induced changes in the corticolimbic expression of certain glutamate receptor subtypes of potential relevance to treating symptoms of MA use disorder.

Neuronal membrane proteasome-derived peptides modulate NMDAR-dependent neuronal signaling to promote changes in gene expression

The neuronal membrane proteasome (NMP) degrades intracellular proteins into peptides that are released directly into the extracellular space, whereby they stimulate neurons to promote signaling mechanisms that remain unknown. Here, we demonstrate that neuronal stimulation promotes NMP activity and, subsequently, enhanced production of NMP peptides. We show that these neuronal activity-dependent NMP peptides can rapidly promote N-methyl-D-aspartate receptor (NMDAR)-dependent calcium influx in neurons. This leads to sustained phosphorylation of the well-defined stimulus-induced transcription factor, cyclic AMP response element (CRE)-binding protein (CREB). Downstream of these events, we identified changes to neuronal target genes which included increased expression of immediate early genes (e.g., Fos, Npas4, Egr4) and other genes known to have critical neuroregulatory roles. Further observations led to the discovery that NMP peptide-induced changes in gene expression is dependent on NMDARs and independent of AMPA receptors or voltage-gated sodium channels. These data demonstrate that NMP peptides are endogenous and selective activators of NMDA receptors and act as sufficient and novel stimuli within the context of neuronal activity-dependent signaling. This novel pathway is parallel to classic neuronal activity-dependent programs and points to NMP and its resulting peptides as potential modulators of neuronal function.

Proteomic association with age-dependent sex differences in Wisconsin Card Sorting Test performance in healthy Thai subjects

Sex differences in cognitive function exist, but they are not stable and undergo dynamic change during the lifespan. However, our understanding of how sex-related neural information transmission evolves with age is still in its infancy. This study utilized the Wisconsin Card Sorting Test (WCST) and the label-free proteomics method with bioinformatic analysis to investigate the molecular mechanisms underlying age-related sex differences in cognitive performance in 199 healthy Thai subjects (aged 20-70 years), as well as explore the sex-dependent protein complexes for predicting cognitive aging. The results showed that males outperformed females in two of the five WCST sub-scores: %Corrects and %Errors. Sex differences in these scores were related to aging, becoming noticeable in those over 60. At the molecular level, differently expressed individual proteins and protein complexes between both sexes are associated with the potential N-methyl-D-aspartate type glutamate receptor (NMDAR)-mediated excitotoxicity, with the NMDAR complex being enriched exclusively in elderly female samples. These findings provided a preliminary indication that healthy Thai females might be more susceptible to such neurotoxicity, as evidenced by their cognitive performance. NMDAR protein complex enrichment in serum could be proposed as a potential indication for predicting cognitive aging in healthy Thai females.

LC-MS/MS-Based Serum Metabolomics and Transcriptome Analyses for the Mechanism of Augmented Renal Clearance

Augmented Renal Clearance (ARC) refers to the increased renal clearance of circulating solute in critically ill patients. In this study, the analytical research method of transcriptomics combined with metabolomics was used to study the pathogenesis of ARC at the transcriptional and metabolic levels. In transcriptomics, 534 samples from 5 datasets in the Gene Expression Omnibus database were analyzed and 834 differential genes associated with ARC were obtained. In metabolomics, we used Ultra-Performance Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometry to determine the non-targeted metabolites of 102 samples after matching propensity scores, and obtained 45 differential metabolites associated with ARC. The results of the combined analysis showed that purine metabolism, arginine biosynthesis, and arachidonic acid metabolism were changed in patients with ARC. We speculate that the occurrence of ARC may be related to the alteration of renal blood perfusion by LTB4R, ARG1, ALOX5, arginine and prostaglandins E2 through inflammatory response, as well as the effects of CA4, PFKFB2, PFKFB3, PRKACB, NMDAR, glutamate and cAMP on renal capillary wall permeability.

The Pathological Effects of Circulating Hydrophobic Bile Acids in Alzheimer's Disease

Recent clinical studies have revealed that the serum levels of toxic hydrophobic bile acids (deoxy cholic acid, lithocholic acid [LCA], and glycoursodeoxycholic acid) are significantly higher in patients with Alzheimer's disease (AD) and amnestic mild cognitive impairment (aMCI) when compared to control subjects. The elevated serum bile acids may be the result of hepatic peroxisomal dysfunction. Circulating hydrophobic bile acids are able to disrupt the blood-brain barrier and promote the formation of amyloid-β plaques through enhancing the oxidation of docosahexaenoic acid. Hydrophobic bile acid may find their ways into the neurons via the apical sodium-dependent bile acid transporter. It has been shown that hydrophobic bile acids impose their pathological effects by activating farnesoid X receptor and suppressing bile acid synthesis in the brain, blocking NMDA receptors, lowering brain oxysterol levels, and interfering with 17β-estradiol actions such as LCA by binding to E2 receptors (molecular modelling data exclusive to this paper). Hydrophobic bile acids may interfere with the sonic hedgehog signaling through alteration of cell membrane rafts and reducing brain 24(S)-hydroxycholesterol. This article will 1) analyze the pathological roles of circulating hydrophobic bile acids in the brain, 2) propose therapeutic approaches, and 3) conclude that consideration be given to reducing/monitoring toxic bile acid levels in patients with AD or aMCI, prior/in combination with other treatments.

Jing-an oral liquid alleviates Tourette syndrome via the NMDAR/MAPK/CREB pathway in vivo and in vitro

CONTEXT

Jing-an oral liquid (JA) is a Chinese herbal formula used in the treatment of Tourette syndrome (TS); however, its mechanism is unclear.

OBJECTIVE

To investigate the effects of JA on amino acid neurotransmitters and microglia activation in vivo and in vitro.

MATERIALS AND METHODS

Sixty male Sprague-Dawley rats were divided into a control group and 5 TS groups. TS was induced in rats with intraperitoneal injection of 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (1 mg/kg) and in BV2 cells with lipopolysaccharide. Control and model rats were administered saline, whereas treatment groups were administered JA (5.18, 10.36, or 20.72 g/kg) or tiapride (a benzamide, 23.5 mg/kg) by gavage once daily for 21 days. Stereotypic behaviour was tested. The levels of N-methyl-d-aspartate receptor (NMDAR)/mitogen-activated protein kinase/cAMP response element-binding protein (CREB)-related proteins in striatum and BV2 cells were measured via western blots. CD11b and IBa1 levels were also measured. Ultra-high-performance liquid-chromatography was used to determine γ-aminobutyric acid (GABA), glutamic acid (Glu), and aspartic acid (ASP) levels.

RESULTS

JA markedly alleviated the stereotype behaviour (25.92 ± 0.35 to 13.78 ± 0.47) in rats. It also increased NMDAR1 (0.48 ± 0.09 to 0.67 ± 0.08; 0.54 ± 0.07 to 1.19 ± 0.18) expression and down-regulated the expression of p-ERK, p-JNK, p-P38, and p-CREB in BV2 cells and rat striatum. Additionally, Glu, ASP, GABA, CD11b, and IBa1 levels were significantly decreased by JA.

DISCUSSION AND CONCLUSIONS

JA suppressed microglia activation and regulated the levels of amino acid neurotransmitters, indicating that it could be a promising therapeutic agent for TS.

Sevoflurane Induces Neurotoxicity in the Animal Model with Alzheimer's Disease Neuropathology via Modulating Glutamate Transporter and Neuronal Apoptosis

Perioperative neurocognitive disorders are frequently observed in postoperative patients and previous reports have shown that pre-existing mild cognitive impairment with accumulated neuropathology may be a risk factor. Sevoflurane is a general anesthetic agent which is commonly used in clinical practice. However, the effects of sevoflurane in postoperative subjects are still controversial, as both neurotoxic or neuroprotective effects were reported. The purpose of this study is to investigate the effects of sevoflurane in 3 × Tg mice, a specific animal model with pre-existing Alzheimer’s disease neuropathology. 3 × Tg mice and wild-type mice were exposed to 2 h of sevoflurane respectively. Cognitive function, glutamate transporter expression, MAPK kinase pathways, and neuronal apoptosis were accessed on day 7 post-exposure. Our findings indicate that sevoflurane-induced cognitive deterioration in 3 × Tg mice, which was accompanied with the modulation of glutamate transporter, MAPK signaling, and neuronal apoptosis in the cortical and hippocampal regions. Meanwhile, no significant impact was observed in wild-type mice. Our results demonstrated that prolonged inhaled sevoflurane results in the exacerbation of neuronal and cognitive dysfunction which depends on the neuropathology background.

SAM, a cystathionine beta-synthase activator, promotes hydrogen sulfide to promote neural repair resulting from massive cerebral infarction induced by middle cerebral artery occlusion

Neurologic deterioration after massive cerebral infarct should be identified at an early stage for medical and surgical treatments. We investigated the effect of hydrogen sulfide on the excitotoxity of PC12 cells exposed to oxygen-glucose deprivation (OGD) and its effect on the apoptosis of brain tissues in rats with middle cerebral artery occlusion (MCAO). Rats with MCAO were treated with SAM, a cystathionine beta-synthase (CBS) activator, or AOAA, a CBS inhibitor. Hydrogen sulfide content in the brain tissues of infarcted patients or rats with MCAO was decreased, whereas glutamate (GLU) content was increased. In addition, SAM reduced reactive oxygen species content, lactate dehydrogenase release, and apoptosis levels in the brain tissues of rats with MCAO. The PC12 cells that were exposed to OGD were also treated with 20 mM GLU and later treated with SAM or AOAA. In PC12 cells, SAM reduced the apoptosis caused by GLU after OGD. The protective effects of hydrogen sulfide was elicited through the sulfur-sulfhydrylation modification of NMDAR and the induction of ERK/MAPK signaling. Our results showed that hydrogen sulfide exerts a protective effect on the PC12 cells and the rats with MCAO, which might represent a possible therapeutic agent against massive cerebral infarct.

Ginsenoside Rg1 exerts neuroprotective effects in 3-nitropronpionic acid-induced mouse model of Huntington's disease via suppressing MAPKs and NF-κB pathways in the striatum

Huntington's disease (HD) is one of main neurodegenerative diseases, characterized by striatal atrophy, involuntary movements, and motor incoordination. Ginsenoside Rg1 (Rg1), an active ingredient in ginseng, possesses a variety of neuroprotective effects with low toxicity and side effects. In this study, we investigated the potential therapeutic effects of Rg1 in a mouse model of HD and explored the underlying mechanisms. HD was induced in mice by injection of 3-nitropropionic acid (3-NP, i.p.) for 4 days. From the first day of 3-NP injection, the mice were administered Rg1 (10, 20, 40 mg·kg^-1, p.o.) for 5 days. We showed that oral pretreatment with Rg1 alleviated 3-NP-induced body weight loss and behavioral defects. Furthermore, pretreatment with Rg1 ameliorated 3-NP-induced neuronal loss and ultrastructural morphological damage in the striatum. Moreover, pretreatment with Rg1 reduced 3-NP-induced apoptosis and inhibited the activation of microglia, inflammatory mediators in the striatum. We revealed that Rg1 exerted neuroprotective effects by suppressing 3-NP-induced activation of the MAPKs and NF-κΒ signaling pathways in the striatum. Thus, our results suggest that Rg1 exerts therapeutic effects on 3-NP-induced HD mouse model via suppressing MAPKs and NF-κΒ signaling pathways. Rg1 may be served as a novel therapeutic option for HD.

Reversible Changes in BDNF Expression in MK-801-Induced Hippocampal Astrocytes Through NMDAR/PI3K/ERK Signaling

Dizocilpine (MK-801), a non-competitive N-methyl-D-aspartic acid receptor (NMDA-R) antagonist, can induce schizophrenia-like symptoms in healthy individuals, implicating NMDA-R hypofunction in disease pathogenesis. Brain-derived neurotrophic factor (BDNF) is also implicated in schizophrenia, and expression is regulated by NMDA-R activity, suggesting a functional link. We previously found that BDNF signaling was upregulated by MK-801 in cultured hippocampal astrocytes, but the underlying mechanism is not clear. To address this issue, the levels of BDNF expression and secretion were evaluated in hippocampal astrocytes incubated with MK-801 by ELISA and qPCR, with and without NMDA co-incubation or pretreatment of either the ERK1/2 inhibitor, PD98059 or the PI3K inhibitor, LY294002. The apoptosis, viability, and proliferation of the astrocytes were also examined. In the current study, we demonstrate that MK-801 treatment (20 μM for 5 days) enhances the proliferation of rat cultured hippocampal astrocytes. Expression of BDNF mRNA was enhanced after 24 h in MK-801, but returned to near baseline over the next 24 h in the continued presence of MK-801. However, two successive 24-h treatments enhanced BDNF expression. These application regimens had no effect on apoptosis or proliferation rate. Co-addition of NMDA significantly inhibited MK-801-induced upregulation of BDNF. Similarly, MK-801-induced BDNF upregulation was blocked by pretreatment with inhibitors of PI3K and ERK1/2, but not by inhibitors of p38 and JNK. These findings suggested that astrocytes may contribute to the acute neurological and behavioral response to MK-801 treatment via a transient increase in BDNF expression involving NMDA-R–PI3K–ERK signaling.

Glutamate-Gated NMDA Receptors: Insights into the Function and Signaling in the Kidney

N-Methyl-d-aspartate receptor (NMDAR) is a glutamate-gated ionotropic receptor that intervenes in most of the excitatory synaptic transmission within the central nervous system (CNS). Aside from being broadly distributed in the CNS and having indispensable functions in the brain, NMDAR has predominant roles in many physiological and pathological processes in a wide range of non-neuronal cells and tissues. The present review outlines current knowledge and understanding of the physiological and pathophysiological functions of NMDAR in the kidney, an essential excretory and endocrine organ responsible for the whole-body homeostasis. The review also explores the recent findings regarding signaling pathways involved in NMDAR-mediated responses in the kidney. As established from diverse lines of research reviewed here, basal levels of receptor activation within the kidney are essential for the maintenance of healthy tubular and glomerular function, while a disproportionate activation can lead to a disruption of NMDAR's downstream signaling pathways and a myriad of pathophysiological consequences.

Dopamine Receptor Activation Modulates the Integrity of the Perisynaptic Extracellular Matrix at Excitatory Synapses

In the brain, Hebbian-type and homeostatic forms of plasticity are affected by neuromodulators like dopamine (DA). Modifications of the perisynaptic extracellular matrix (ECM), which control the functions and mobility of synaptic receptors as well as the diffusion of transmitters and neuromodulators in the extracellular space, are crucial for the manifestation of plasticity. Mechanistic links between synaptic activation and ECM modifications are largely unknown. Here, we report that neuromodulation via D1-type DA receptors can induce targeted ECM proteolysis specifically at excitatory synapses of rat cortical neurons via proteases ADAMTS-4 and -5. We showed that receptor activation induces increased proteolysis of brevican (BC) and aggrecan, two major constituents of the adult ECM both in vivo and in vitro. ADAMTS immunoreactivity was detected near synapses, and shRNA-mediated knockdown reduced BC cleavage. We have outlined a molecular scenario of how synaptic activity and neuromodulation are linked to ECM rearrangements via increased cAMP levels, NMDA receptor activation, and intracellular calcium signaling.

EphrinB2/ephB2-mediated myenteric synaptic plasticity: mechanisms underlying the persistent muscle hypercontractility and pain in postinfectious IBS

Patients with irritable bowel syndrome (IBS) show pain hypersensitivity and smooth muscle hypercontractility in response to colorectal distension (CRD). Synaptic plasticity, a key process of memory formation, in the enteric nervous system may be a novel explanation. This study aimed to explore the regulatory role of ephrinB2/ephB2 in enteric synaptic plasticity and colonic hyperreactive motility in IBS. Postinfectious (PI)-IBS was induced by Trichinella spiralis infection in rats. Isometric contractions of colonic circular muscle strips, particularly neural-mediated contractions, were recorded ex vivo. Meanwhile, ephrinB2/ephB2-mediated enteric structural and functional synaptic plasticity were assessed in the colonic muscularis, indicating that ephrinB2 and ephB2 were located on enteric nerves and up-regulated in the colonic muscularis of PI-IBS rats. Colonic hypersensitivity to CRD and neural-mediated colonic hypercontractility were present in PI-IBS rats, which were correlated with increased levels of cellular homologous fos protein (c-fos) and activity-regulated cystoskeleton-associated protein (arc), the synaptic plasticity-related immediate early genes, and were ameliorated by ephB2Fc (an ephB2 receptor blocker) or MK801 (an NMDA receptor inhibitor) exposure. EphrinB2/ephB2 facilitated synaptic sprouting and NMDA receptor-mediated synaptic potentiation in the colonic muscularis of PI-IBS rats and in the longitudinal muscle-myenteric plexus cultures, involving the Erk-MAPK and PI3K-protein kinase B pathways. In conclusion, ephrinB2/ephB2 promoted the synaptic sprouting and potentiation of myenteric nerves involved in persistent muscle hypercontractility and pain in PI-IBS. Hence, ephrinB2/ephB2 may be an emerging target for the treatment of IBS.-Zhang, L., Wang, R., Bai, T., Xiang, X., Qian, W., Song, J., Hou, X. EphrinB2/ephB2-mediated myenteric synaptic plasticity: mechanisms underlying the persistent muscle hypercontractility and pain in postinfectious IBS.

Decreased expression of lncRNA Malat1 in rat spinal cord contributes to neuropathic pain by increasing neuron excitability after brachial plexus avulsion

Purpose: Neuropathic pain (NP) is a challenging clinical problem due to its complex pathogenesis. In our previous study using microarray, we found that the levels of lncRNA Malat1 were decreased in the spinal cord of NP rat after brachial plexus avulsion, but its contribution to NP remain unclear. The purpose of this study was to investigate its role in the pathogenesis of NP.

Methods: In the NP model of complete brachial plexus avulsion rat, spinal cords were harvested, and fluorescence in situ hybridization (FISH) was used to test the spatial expression of Malat1 and qRT-PCR was used to confirm the quantitative expression of Malat1. In primary cultured neurons, Malat1 expression interfered with adenovirus. Spontaneous electric activities of neurons were tested using multi-electrode arrays and apoptosis of neurons was tested using TUNEL method. The change of intracellular calcium concentration was analyzed using calcium imaging method.

Results: Decreased Malat1 expression was confirmed using qRT-PCR, and Malat1 was identified in the cytoplasm of neurons in spinal cord, but not in glia. In vitro, the decrease of Malat1 resulted in an increase in the frequency of spontaneous electric activity in neurons but had no effect on neuronal apoptosis. Further analysis indicated during glutamate stimulation, the change of intracellular calcium concentration in neurons with downregulated Malat1 expression was significantly greater than that in normal neurons.

Conclusion: Reduced Malat1 expression may induce NP by increasing neuronal excitability in the spinal cord via regulation of calcium flux.

Inactivation of NMDA Receptors in the Ventral Tegmental Area during Cocaine Self-Administration Prevents GluA1 Upregulation but with Paradoxical Increases in Cocaine-Seeking Behavior

Cocaine self-administration increases expression of GluA1 subunits in ventral tegmental area (VTA) dopamine neurons, which subsequently enhance the motivation for cocaine. This increase in GluA1 may be dependent on concomitant NMDA receptor (NMDAR) activation during self-administration, similar to cocaine-induced long-term potentiation in the VTA. In this study, we used viral-mediated expression of a dominant-negative GluN1 subunit (HSV-dnGluN1) in VTA neurons to study the effect of transient NMDAR inactivation on the GluA1 increases induced by chronic cocaine self-administration in male rats. We found that dnGluN1 expression in the VTA limited to the 3 weeks of cocaine self-administration prevents the subsequent increase in tissue GluA1 levels when compared with control infusions of HSV-LacZ. Surprisingly, dnGluN1 expression led to an enhancement in the motivation to self-administer cocaine as measured using a progressive ratio reinforcement schedule and to enhanced cocaine seeking measured in extinction/reinstatement tests following an extended 3 week withdrawal period. Despite blocking tissue GluA1 increases in cocaine self-administering animals, the HSV-dnGluN1 treatment resulted in increased membrane levels of GluA1 and GluN2B, along with markedly higher locomotor responses to intra-VTA infusions of AMPA, suggesting a paradoxical increase in VTA AMPA receptor responsiveness. Together, these data suggest that NMDARs mediate cocaine-induced increases in VTA GluA1 expression, but such transient NMDAR inactivation also leads to compensatory scaling of synaptic AMPA receptors that enhance the motivational for cocaine.SIGNIFICANCE STATEMENT Dopamine neurons in the ventral tegmental area (VTA) are critical substrates of drug rewards. Animal models indicate that chronic cocaine use enhances excitatory glutamatergic input to these neurons, making them more susceptible to environmental stimuli that trigger drug craving and relapse. We previously found that self-administration of cocaine increases AMPA glutamate receptors in the VTA, and this effect enhances motivation for cocaine. Here we report that the mechanism for this upregulation involves NMDA receptor activity during cocaine use. While interference with NMDA receptor function blocks AMPA receptor upregulation, it also produces a paradoxical enhancement in membrane AMPA receptor subunits, AMPA responsiveness, and the motivation for cocaine. Thus, pharmacotherapy targeting NMDA receptors may inadvertently produce substantial adverse consequences for cocaine addiction.

A critical role of spinal Shank2 proteins in NMDA-induced pain hypersensitivity

Background

Self-injurious behaviors (SIBs) are devastating traits in autism spectrum disorder (ASD). Although deficits in pain sensation might be one of the contributing factors underlying the development of SIBs, the mechanisms have yet to be addressed. Recently, the Shank2 synaptic protein has been considered to be a key component in ASD, and mutations of SHANK2 gene induce the dysfunction of N-methyl-D-aspartate (NMDA) receptors, suggesting a link between Shank2 and NMDA receptors in ASD. Given that spinal NMDA receptors play a pivotal role in pain hypersensitivity, we investigated the possible role of Shank2 in nociceptive hypersensitivity by examining changes in spontaneous pain following intrathecal NMDA injection in Shank2−/− (Shank2 knock-out, KO) mice.

Results

Intrathecal NMDA injection evoked spontaneous nociceptive behaviors. These NMDA-induced nociceptive responses were significantly reduced in Shank2 KO mice. We also observed a significant decrease of NMDA currents in the spinal dorsal horn of Shank2 KO mice. Subsequently, we examined whether mitogen-activated protein kinase or AKT signaling is involved in this reduced pain behavior in Shank2 KO mice because the NMDA receptor is closely related to these signaling molecules. Western blotting and immunohistochemistry revealed that spinally administered NMDA increased the expression of a phosphorylated form of extracellular signal-regulated kinase (p-ERK) which was significantly reduced in Shank2 KO mice. However, p38, JNK, or AKT were not changed by NMDA administration. The ERK inhibitor, PD98059, decreased NMDA-induced spontaneous pain behaviors in a dose-dependent manner in wild-type mice. Moreover, it was found that the NMDA-induced increase in p-ERK was primarily colocalized with Shank2 proteins in the spinal cord dorsal horn.

Conclusion

Shank2 protein is involved in spinal NMDA receptor-mediated pain, and mutations of Shank2 may suppress NMDA-ERK signaling in spinal pain transmission. This study provides new clues into the mechanisms underlying pain deficits associated with SIB and deserves further study in patients with ASD.

The excitotoxity of NMDA receptor NR2D subtype mediates human fetal lung fibroblasts proliferation and collagen production

Studies have suggested that endogenous glutamate and N-methyl-d-aspartate (NMDA) receptor have an excitotoxity role during acute lung injury. Fibroblasts play a critical role in lung development and chronic lung disease after acute lung injury. This study aims to explore the immediate role of NMDAR activation in human lung fibroblasts. The expression of NMDAR 1 subtype (NR1) and four individual NMDAR 2 (NR2) subtypes (NR 2 A to D) was measured in human fetal lung fibroblasts (HFL-1 and MRC-5). Five NMDARs expression were all detectable in two cell lines. Although the expressions of NMDARs were different between MRC-5 and HFL-1, 1mM NMDA elicited the same trend in the downregulation of NR2A expression, the upregulation of NR2D, and the increase of cells proliferation and collagen production. Glutamate stimulation after 24-h of NMDA exposure resulted in weaker and more delayed but more prolonged iCa²⁺ elevation in HFL-1 than no NMDA exposed cells. NMDA increased the level of pERK_1/2, cells proliferation and collagen production, whereas nonspecific NMDAR antagonist MK-801, NR2D-preferring receptor antagonist UBP141 and ERK_1/2 phosphorylation inhibitor U0126 suppressed it, respectively. In conclusion, we found that NMDAR activation, NR2D in particular, is involved in human fetal lung fibroblast proliferation and collagen production through a potential ERK_1/2-mediated mechanism.

MEK/ERK- and calcineurin/NFAT-mediated mechanism of cerebral hyperemia and brain injury following NMDA receptor activation

N-methyl-d-aspartate (NMDA) receptor activation increases regional cerebral blood flow (rCBF) and induces neuronal injury, but similarities between these processes are poorly understood. In this study, by measuring rCBF in vivo, we identified a clear correlation between cerebral hyperemia and brain injury. NMDA receptor activation induced brain injury as a result of rCBF increase, which was attenuated by an inhibitor of mitogen-activated protein kinase or calcineurin. Moreover, NMDA induced phosphorylation of extracellular signal-regulated kinase (ERK) and nuclear translocation of nuclear factor of activated T-cell (NFAT) in neurons. Therefore, a MEK/ERK- and calcineurin/NFAT-mediated mechanism of neurovascular coupling underlies the pathophysiology of neurovascular disorders.

Effect of magnesium supplementation on depression status in depressed patients with magnesium deficiency: A randomized, double-blind, placebo-controlled trial

OBJECTIVES

The aim of this study was to determine the effect of magnesium supplementation on the depression status of depressed patients suffering from magnesium deficiency.

METHODS

Sixty depressed people suffering from hypomagnesemia participated in this trial. The individuals were randomly categorized into two groups of 30 members; one receiving two 250-mg tablets of magnesium oxide (MG) daily and the other receiving placebo (PG) for 8 wk. The Beck Depression Inventory-II was conducted and the concentration of serum magnesium was measured.

RESULTS

At the end of intervention, 88.5% of the MG and 48.1% of the PG (P = 0.002) had a normal level of magnesium. The mean changes of serum magnesium were significantly different across the two groups. After the intervention, the mean Beck score significantly declined. However, in the MG, this reduction was more significant than in the PG (P = 0.02), so that the mean changes in this group experienced 15.65 ± 8.9 reduction, but in the PG, it declined by 10.40 ± 7.9.

CONCLUSIONS

Daily consumption of 500 mg magnesium oxide tablets for ≥8 wk by depressed patients suffering from magnesium deficiency leads to improvements in depression status and magnesium levels. Therefore, assessment of the magnesium serum and resolving this deficiency positively influence the treatment of depressed patients.

Microwave-Induced Structural and Functional Injury of Hippocampal and PC12 Cells Is Accompanied by Abnormal Changes in the NMDAR-PSD95-CaMKII Pathway

Recent studies have highlighted the important role of the postsynaptic NMDAR-PSD95-CaMKII pathway for synaptic transmission and related neuronal injury. Here, we tested changes in the components of this pathway upon microwave-induced neuronal structure and function impairments. Ultrastructural and functional changes were induced in hippocampal neurons of rats and in PC12 cells exposed to microwave radiation. We detected abnormal protein and mRNA expression, as well as posttranslational modifications in the NMDAR-PSD95-CaMKII pathway and its associated components, such as synapsin I, following microwave radiation exposure of rats and PC12 cells. Thus, microwave radiation may induce neuronal injury via changes in the molecular organization of postsynaptic density and modulation of the biochemical cascade that potentiates synaptic transmission.

Tumor necrosis factor-α potentiates long-term potentiation in the rat dentate gyrus after acute hypoxia

An inadequate supply of oxygen in the brain may lead to an inflammatory response through neuronal and glial cells that can result in neuronal damage. Tumor necrosis factor-α (TNF-α) is a proinflammatory cytokine that is released during acute hypoxia and can have neurotoxic or neuroprotective effects in the brain. Both TNF-α and interleukin-1β (IL-1β) have been shown by a number of research groups to alter synaptic scaling and also to inhibit long-term potentiation (LTP) in the hippocampus when induced by specific high-frequency stimulation (HFS) protocols. This study examines the effects of TNF-α on synaptic transmission and plasticity in hippocampal slices after acute hypoxia using two HFS protocols. Field excitatory postsynaptic potentials were elicited in the medial perforant pathway of the dentate gyrus. Exogenous TNF-α (5 ng/ml) attenuated LTP induced by theta burst stimulation but had no effect on LTP induced by a more prolonged HFS. Pretreatment with lipopolysaccharide (100 ng/ml) or TNF-α but not IL-1β (4 ng/ml) prior to a 30-min hypoxic insult resulted in a significant enhancement of LTP post hypoxia when induced by the HFS. Anti-TNF, 3,6'-dithiothalidomide (a TNF-α synthesis inhibitor), and SB203580 (a p38 MAPK inhibitor) significantly reduced this effect. These results indicate an important modulatory role for elevated TNF-α levels on LTP in the hippocampus after an acute hypoxic event.

The potential of targeting NMDA receptors outside the CNS

INTRODUCTION

NMDA receptor (NMDAR) is an ionotropic glutamate receptor with a high permeability to calcium and a unique feature of controlling numerous calcium-dependent processes. Apart from being widely distributed in the CNS, the presence of NMDAR and its potential significance in a variety of non-neuronal cells and tissues has become an interesting research topic.

AREAS COVERED

The current review summarizes prevailing knowledge on the role of NMDARs in the kidney, bone and parathyroid gland, three main organs responsible for calcium homeostasis, as well as in the heart, an organ whose function is highly dependable on balanced intracellular calcium concentrations. The review also examines studies that have advanced our understanding of the therapeutic potential of NMDAR agonists and antagonists in renal, cardiovascular and bone pathologies.

EXPERT OPINION

NMDARs have a preeminent role in many physiological and pathological processes outside the CNS. In certain organs and/or disease conditions, activating the NMDAR leads to beneficial effects for the target organ, whereas in other diseases cell signaling downstream of NMDAR activation can exacerbate their pathology. Therefore, targeting NMDARs therapeutically is rather intricate work, and surely requires more extensive investigation in order to properly tune up the diverse NMDAR's actions translating them into beneficial cellular responses.

Dietary magnesium restriction reduces amygdala-hypothalamic GluN1 receptor complex levels in mice

Reduced daily intake of magnesium (Mg(2+)) is suggested to contribute to depression. Indeed, preclinical studies show dietary magnesium restriction (MgR) elicits enhanced depression-like behaviour establishing a causal relationship. Amongst other mechanisms, Mg(2+) gates the activity of N-methyl-D-asparte (NMDA) receptors; however, it is not known whether reduced dietary Mg(2+) intake can indeed affect brain NMDA receptor complexes. Thus, the aim of the current study was to reveal whether MgR induces changes in brain NMDA receptor subunit composition that would indicate altered NMDA receptor regulation. The results revealed that enhanced depression-like behaviour elicited by MgR was associated with reduced amygdala-hypothalamic protein levels of GluN1-containing NMDA complexes. No change in GluN1 mRNA levels was observed indicating posttranslational changes were induced by dietary Mg(2+) restriction. To reveal possible protein interaction partners, GluN1 immunoprecipitation and proximity ligation assays were carried out revealing the expected GluN1 subunit association with GluN2A, GluN2B, but also novel interactions with GluA1, GluA2 in addition to known downstream signalling proteins. Chronic paroxetine treatment in MgR mice normalized enhanced depression-like behaviour, but did not alter protein levels of GluN1-containing NMDA receptors, indicating targets downstream of the NMDA receptor. Collectively, present data demonstrate that dietary MgR alters brain levels of GluN1-containing NMDA receptor complexes, containing GluN2A, GluN2B, AMPA receptors GluA1, GluA2 and several protein kinases. These data indicate that the modulation of dietary Mg(2+) intake may alter the function and signalling of this receptor complex indicating its involvement in the enhanced depression-like behaviour elicited by MgR.

Ethyl pyruvate ameliorates 3-nitropropionic acid-induced striatal toxicity through anti-neuronal cell death and anti-inflammatory mechanisms

The potential neuroprotective value of ethyl pyruvate (EP) for the treatment of the striatal toxicity is largely unknown. We investigated whether EP promotes the survival of striatal neurons in a 3-nitropropionic acid (3-NP)-induced mouse model of Huntington's disease (HD). EP (5, 10, 20, and 40mg/kg/day, i.p.) was daily injected from 30min before 3-NP intoxication (pretreatment) and from onset/progression/peak point of neurological impairment by 3-NP intoxication. EP produced a neuroprotective effect in dose- and time-dependant manners. EP pretreatment of 40mg/kg/day produced the best neuroprotective effect among other conditions. Pretreatment of EP significantly attenuated neurological impairment and lethality and prevented formation of lesion area and neuronal loss in the striatum after 3-NP intoxication. This neuroprotection afforded by EP was associated with the suppression of succinate dehydrogenase activity, apoptosis, and microglial activation. The suppressive effect of EP corresponded to the down-regulation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) signal pathways, and mRNA expression of inflammatory mediators including tumor necrosis factor-alpha, interleukin (IL)-1β, IL-6, inducible nitric oxide synthase, and cyclooxygenase-2 in the striatum after 3-NP intoxication. Interestingly, the intrathecal introduction of inhibitors MAPKs and NF-κB into control mice decreased the lethality after 3-NP intoxication. Our findings indicate that EP may effectively alleviate 3-NP-induced striatal toxicity by inhibition of the MAPKs and NF-κB pathways in the striatum, and that EP has a wide therapeutic window, suggesting that EP may have therapeutic value in the treatment of aspects of HD's disease related to inflammation.

Glutamate signalling in roots

As a signalling molecule, glutamate is best known for its role as a fast excitatory neurotransmitter in the mammalian nervous system, a role that requires the activity of a family of ionotropic glutamate receptors (iGluRs). The unexpected discovery in 1998 that Arabidopsis thaliana L. possesses a family of iGluR-related (GLR) genes laid the foundations for an assessment of glutamate's potential role as a signalling molecule in plants that is still in progress. Recent advances in elucidating the function of Arabidopsis GLR receptors has revealed similarities with iGluRs in their channel properties, but marked differences in their ligand specificities. The ability of plant GLR receptors to act as amino-acid-gated Ca(2+) channels with a broad agonist profile, combined with their expression throughout the plant, makes them strong candidates for a multiplicity of amino acid signalling roles. Although root growth is inhibited in the presence of a number of amino acids, only glutamate elicits a specific sequence of changes in growth, root tip morphology, and root branching. The recent finding that the MEKK1 gene is a positive regulator of glutamate sensitivity at the root tip has provided genetic evidence for the existence in plants of a glutamate signalling pathway analogous to those found in animals. This short review will discuss the most recent advances in understanding glutamate signalling in roots, considering them in the context of previous work in plants and animals.

Antiepileptic Effect of Uncaria rhynchophylla and Rhynchophylline Involved in the Initiation of c-Jun N-Terminal Kinase Phosphorylation of MAPK Signal Pathways in Acute Seizures of Kainic Acid-Treated Rats

Seizures cause inflammation of the central nervous system. The extent of the inflammation is related to the severity and recurrence of the seizures. Cell surface receptors are stimulated by stimulators such as kainic acid (KA), which causes intracellular mitogen-activated protein kinase (MAPK) signal pathway transmission to coordinate a response. It is known that Uncaria rhynchophylla (UR) and rhynchophylline (RP) have anticonvulsive effects, although the mechanisms remain unclear. Therefore, the purpose of this study is to develop a novel strategy for treating epilepsy by investigating how UR and RP initiate their anticonvulsive mechanisms. Sprague-Dawley rats were administered KA (12 mg/kg, i.p.) to induce seizure before being sacrificed. The brain was removed 3 h after KA administration. The results indicate that pretreatment with UR (1.0 g/kg), RP (0.25 mg/kg), and valproic acid (VA, 250 mg/kg) for 3 d could reduce epileptic seizures and could also reduce the expression of c-Jun aminoterminal kinase phosphorylation (JNKp) of MAPK signal pathways in the cerebral cortex and hippocampus brain tissues. Proinflammatory cytokines interleukin (IL)-1β, IL-6, and tumor necrosis factor-α remain unchanged, indicating that the anticonvulsive effect of UR and RP is initially involved in the JNKp MAPK signal pathway during the KA-induced acute seizure period.

Glutamate drugs and pharmacogenetics of OCD: a pathway-based exploratory approach

INTRODUCTION

Neuropharmacology research in glutamate-modulating drugs supports their development and use in the management of neuropsychiatric disorders, including major depression, Alzheimer's disorder and schizophrenia. Concomitantly, there is a growing use of these agents used in the treatment of obsessive-compulsive disorder (OCD).

AREAS COVERED

This article provides a review of glutamate-modulating drugs used in the treatment of OCD. Specifically, the authors examine riluzole, N-acetylcysteine, d-cycloserine, glycine, ketamine, memantine and acamprosate as treatments. Furthermore, recent genetic epidemiology research findings are presented with a focus on the positional candidate genes SLC1A1 (a glutamate transporter), ADAR3 (an RNA-editing enzyme), RYR3 (a Ca(2+) channel), PBX1 (a homeobox transcription factor) and a GWAS candidate gene, DLGAP1 (a protein interacting with post-synaptic density). These genetic findings are submitted to a curated bioinformatics database to conform a biological network for discerning potential pharmacological targets.

EXPERT OPINION

In the genetically informed network, known genes and identified key connecting components, including DLG4 (a developmental gene), PSD-95 (a synaptic scaffolding protein) and PSEN1 (presenilin, a regulator of secretase), conform a group of potential pharmacological targets. These potential targets can be explored, in the future, to deliver new therapeutic approaches to OCD. There is also the need to develop a better understanding of neuroprotective mechanisms as a foundation for future OCD drug discovery.

Gene expression profiling in treatment-naive schizophrenia patients identifies abnormalities in biological pathways involving AKT1 that are corrected by antipsychotic medication

Distinct gene expression profiles can be detected in peripheral blood mononuclear cells (PBMCs) in patients with schizophrenia; however, little is known about the effects of antipsychotic medication. This study compared gene expression profiles in PMBCs from treatment-naive patients with schizophrenia before and after antipsychotic drug treatment. PBMCs were obtained from 10 treatment-naive schizophrenia patients before and 6 wk after initiating antipsychotic drug treatment and compared to PMBCs collected from 11 healthy community volunteers. Genome-wide expression profiling was conducted using Illumina HumanHT-12 expression bead arrays and analysed using significance analysis of microarrays. This analysis identified 624 genes with altered expression (208 up-regulated, 416 down-regulated) prior to antipsychotic treatment (p < 0.05) including schizophrenia-associated genes AKT1, DISC1 and DGCR6. After 6-8 wk treatment of patients with risperidone or risperidone in combination with haloperidol, only 106 genes were altered, suggesting that the treatment corrected the expression of a large proportion of genes back to control levels. However, 67 genes continued to show the same directional change in expression after treatment. Ingenuity® pathway analysis and gene set enrichment analysis implicated dysregulation of biological functions and pathways related to inflammation and immunity in patients with schizophrenia. A number of the top canonical pathways dysregulated in treatment-naive patients signal through AKT1 that was up-regulated. After treatment, AKT1 returned to control levels and less dysregulation of these canonical pathways was observed. This study supports immune dysfunction and pathways involving AKT1 in the aetiopathophysiology of schizophrenia and their response to antipsychotic medication.

Glutamate signalling via a MEKK1 kinase-dependent pathway induces changes in Arabidopsis root architecture

A chemical genetic approach has been used to investigate the mechanism by which external glutamate (l-Glu) is able to trigger major changes in root architecture in Arabidopsis thaliana L. An initial screen of 80 agonists and antagonists of mammalian glutamate and GABA receptors, using a specially developed 96-well microphenotyping system, found none that replicated the response of the root to l-Glu or antagonized it. However, a larger screen using >1500 molecules bioactive in Saccharomyces cerevisiae (yeast) identified two groups that interfered with the l-Glu response. One of the antagonists, 2-(4-chloro-3-methylphenyl)-2-oxoethyl thiocyanate (CMOT), has been reported to target Ste11, an evolutionarily conserved MAP kinase kinase kinase (MAP3K) in yeast. This led to the discovery that root growth in a triple mekk1 mekk2 mekk3 mutant (mekk1/2/3), defective in a set of three tandemly arranged MAP3Ks, was almost insensitive to l-Glu. However, the sensitivity of mekk1/2/3 roots to inhibition by other amino acids reported to act as agonists of glutamate receptor-like (GLR) channels in Arabidopsis roots (Asn, Cys, Gly and Ser) was unaffected. The l-Glu sensitivity of the mekk1/2/3 mutant was restored by transformation with a construct carrying the intact MEKK1 gene. These results demonstrate that MEKK1 plays a key role in transducing the l-Glu signal that elicits large-scale changes in root architecture, and provide genetic evidence for the existence in plants of an l-Glu signalling pathway analogous to that found in animals.

Korean Red Ginseng Extract Attenuates 3-Nitropropionic Acid-Induced Huntington's-Like Symptoms

Korean red ginseng (KRG) possesses neuroprotective activity. However, the potential neuroprotective value of KRG for the striatal toxicity is largely unknown. We investigated whether KRG extract (KRGE) could have a neuroprotective effect in a 3-nitropropionic acid- (3-NP) induced (i.p.) Huntington's disease (HD) model. KRGE (50, 100, and 250 mg/kg/day, p.o.) was administrated 10 days before 3-NP injection (pre-administration), from the same time with 3-NP injection (co-administration), or from the peak point of neurological impairment by 3-NP injection (post-administration). Pre-administration of KRGE produced the greatest neuroprotective effect in this model. Pre-administration of KRGE significantly decreased 3-NP-induced neurological impairment, lethality, lesion area, and neuronal loss in the 3-NP-injected striatum. KRGE attenuated microglial activation and phosphorylation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) signal pathway. KRGE also reduced the level of mRNA expression of tumor necrosis factor-alpha, interleukin- (IL-) 1β, IL-6, inducible nitric oxide synthase, and OX-42. Interestingly, the intrathecal administration of SB203580 (a p38 inhibitor) or PD98059 (an inhibitor of MAPK Kinase, MEK) increased the survival rate in the 3-NP-induced HD model. Pre-administration of KRGE may effectively inhibit 3-NP-induced striatal toxicity via the inhibition of the phosphorylation of MAPKs and NF-κB pathways, indicating its therapeutic potential for suppressing Huntington's-like symptoms.

Brain-derived neurotrophic factor, acting at the spinal cord level, participates in bladder hyperactivity and referred pain during chronic bladder inflammation

Brain-derived neurotrophic factor (BDNF) is a neurotrophin (NT) known to participate in chronic somatic pain. A recent study has indicated that BDNF may participate in chronic cystitis at the peripheral level. However, the principal site of action for this NT is the central nervous system, most notably the spinal cord. The effects of centrally-acting BDNF on bladder function in normal animals and its central role during chronic cystitis are presently unknown. The present study was undertaken to clarify this issue. For that purpose, control non-inflamed animals were intrathecally injected with BDNF, after which bladder function was evaluated. This treatment caused short-lasting bladder hyperactivity; whereas chronic intrathecal administration of BDNF did not elicit this effect. Cutaneous sensitivity was assessed by mechanical allodynia as an internal control of BDNF action. To ascertain the role of BDNF in bladder inflammation, animals with cyclophosphamide-induced cystitis received intrathecal injections of either a general Trk receptor antagonist or a BDNF scavenger. Blockade of Trk receptors or BDNF sequestration notably improved bladder function. In addition, these treatments also reduced referred pain, typically observed in rats with chronic cystitis. Reduction of referred pain was accompanied by a decrease in the spinal levels of extracellular signal-regulated kinase (ERK) phosphorylation, a marker of increased sensory barrage in the lumbosacral spinal cord, and spinal BDNF expression. Results obtained here indicate that BDNF, acting at the spinal cord level, contributes to bladder hyperactivity and referred pain, important hallmarks of chronic cystitis. In addition, these data also support the development of BDNF modulators as putative therapeutic options for the treatment of chronic bladder inflammation.

Neurotrophins and synaptic plasticity

It has been suggested that long-term modifications of synaptic transmission constitute the foundation of the processes by which information is stored in the central nervous system. A group of proteins called neurotrophins are considered powerful molecular mediators in central synaptic plasticity. Among these, brain-derived neurotrophic factor (BDNF) as well as neurotrophin-3 (NT-3) have emerged as having key roles in the neurobiological mechanisms related to learning and memory. In this chapter, we review the studies that have represented a significant step forward in understanding the role played by BDNF and NT-3 in long-term synaptic plasticity. The effects of BDNF and NT-3 on synaptic plasticity can be of a permissive nature, establishing the conditions under which plastic changes can take place, or it may be instructive, directly modifying the communication and morphology of synapses. The actions carried out by BDNF include its capacity to contribute to the stabilization and maturation of already-existing synapses, as well as to generate new synaptic contacts. One important finding that highlights the participation of these neurotrophins in synaptic plasticity is the observation that adding BDNF or NT-3 gives rise to drastic long-term increases in synaptic transmission, similar to the long-term potentiation in the hippocampus and neocortex of mammals. Because neurotrophins modulate both the electrical properties and the structural organization of the synapse, these proteins have been considered important biological markers of learning and memory processes.

Acute antidepressant treatment differently modulates ERK/MAPK activation in neurons and astrocytes of the adult mouse prefrontal cortex

The onset of action of antidepressants (ADs) usually takes several weeks, but first molecular responses to these drugs may appear already after acute administration. The Extracellular Signal-regulated Kinase/Mitogen-Activated Protein Kinase (ERK/MAPK) signaling pathway is a target of ADs and an important pathway involved in cellular plasticity. In major depressive disorder (MDD), especially the prefrontal cortex (PFC) and hippocampus (Hip) are most likely affected in depressive patients and recent work revealed a hyperactivated ERK signaling in the rat PFC after chronic stress, a precipitating factor for MDD. Strong evidences support that not only neurons but also astrocytes participate in neuronal activity and may therefore additionally be a substrate of AD action. In this study, we show by Western blot that neither fluoxetine (FLX) nor desipramine (DMI) preferentially affects the activation of one of the two ERK isoforms, ERK1 and ERK2, with respect to the other. Further immunohistochemical analysis in the PFC revealed that basal levels of phospho-activated ERK (pERK) are mostly found in neurons in contrast to very few astrocytes. Both ADs can inhibit neuronal pERK as early as 15 min after drug administration with peculiar regional and layer specificities. Contrarily, at this time point none of the two ADs shows a clear modulation of astrocytic pERK. We propose that this mechanism of action of ADs may be protective against an exacerbated cortical ERK activity that may exert detrimental effects on susceptible neuronal populations. Our findings on acute effects of AD treatment in the adult mouse PFC encourage to examine further how this treatment might influence pERK in animal models of depression to identify early targets of AD action.

Elevated homocysteine by levodopa is detrimental to neurogenesis in parkinsonian model

BACKGROUND

Modulation of neurogenesis that acts as an endogenous repair mechanism would have a significant impact on future therapeutic strategies for Parkinson's disease (PD). Several studies demonstrated dopaminergic modulation of neurogenesis in the subventricular zone (SVZ) of the adult brain. Levodopa, the gold standard therapy for PD, causes an increase in homocysteine levels that induces neuronal death via N-methyl-D-aspartate (NMDA) receptor. The present study investigated whether elevated homocysteine by levodopa treatment in a parkinsonian model would modulate neurogenesis via NMDA receptor signal cascade and compared the effect of levodopa and pramipexol (PPX) on neurogenic activity.

METHODOLOGY/PRINCIPAL FINDINGS

Neurogenesis was assessed in vitro using neural progenitor cells (NPCs) isolated from the SVZ and in vivo with the BrdU-injected animal model of PD using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Modulation of homocysteine levels was evaluated using co-cultures of NPCs and astrocytes and PD animals. Immunochemical and Western blot analyses were used to measure neurogenesis and determine the cell death signaling. Levodopa treatment increased release of homocysteine on astrocytes culture media as well as in plasma and brain of PD animals. Increased homocysteine by levodopa led to increased apoptosis of NPCs through the NMDA receptor-dependent the extracellular signal-regulated kinase (ERK) signaling pathways. The administration of a NMDA antagonist significantly attenuated apoptotic cell death in levodopa-treated NPCs and markedly increased the number of BrdU-positive cells in the SVZ of levodopa-treated PD animals. Comparative analysis revealed that PPX treatment significantly increased the number of NPCs and BrdU-positive cells in the SVZ of PD animals compared to levodopa treatment. Our present study demonstrated that increased homocysteine by levodopa has a detrimental effect on neurogenesis through NMDA receptor-mediated ERK signaling pathway.

CONCLUSIONS/SIGNIFICANCE

Modulation of levodopa-induced elevated homocysteine by NMDA antagonist or dopamine agonist has a clinical relevance for PD treatment in terms of adult neurogenesis.

PTEN, a widely known negative regulator of insulin/PI3K signaling, positively regulates neuronal insulin resistance

Lipid and protein tyrosine phosphatase, phosphatase and tension homologue (PTEN), is a widely known negative regulator of insulin/phosphoinositide 3-kinase signaling. Down-regulation of PTEN is thus widely documented to ameliorate insulin resistance in peripheral tissues such as skeletal muscle and adipose. However, not much is known about its exact role in neuronal insulin signaling and insulin resistance. Moreover, alterations of PTEN in neuronal systems have led to discovery of several unexpected outcomes, including in the neurodegenerative disorder Alzheimer's disease (AD), which is increasingly being recognized as a brain-specific form of diabetes. In addition, contrary to expectations, its neuron-specific deletion in mice resulted in development of diet-sensitive obesity. The present study shows that PTEN, paradoxically, positively regulates neuronal insulin signaling and glucose uptake. Its down-regulation exacerbates neuronal insulin resistance. The positive role of PTEN in neuronal insulin signaling is likely due to its protein phosphatase actions, which prevents the activation of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK), the kinases critically involved in neuronal energy impairment and neurodegeneration. Results suggest that PTEN acting through FAK, the direct protein substrate of PTEN, prevents ERK activation. Our findings provide an explanation for unexpected outcomes reported earlier with PTEN alterations in neuronal systems and also suggest a novel molecular pathway linking neuronal insulin resistance and AD, the two pathophysiological states demonstrated to be closely linked.

In vivo investigation on the potential of galangin, kaempferol and myricetin for protection of D-galactose-induced cognitive impairment

The potential of three natural flavonols (galangin, kaempferol and myricetin) to protect against D-galactose-induced cognitive impairment in mice was investigated. After 8 weeks treatment, the mice were assessed by behavioural tests. The levels of oxidative stress, the amount of Na(+),K(+)-ATPase and extracellular signal-regulated kinases (ERK)-cyclic AMP response element binding protein (CREB) signaling pathway in hippocampus were also analysed. It was found that all the three dietary flavonols could ameliorate the oxidative stress, enhance the activity of Na(+),K(+)-ATPase and regulate the expression of ERK-CREB pathway in mice. However, only kaempferol and myricetin could significantly improve the learning and memory capability when compared with D-galactose model. Our results suggest that the presence of hydroxyl groups in the B ring of flavonols may have contribution to the neuroprotective activity.

Magnesium intake is not related to depression risk in Spanish university graduates

Magnesium is the second most predominant intracellular cation and it is an important cofactor in over 300 enzymatic reactions. It is a calcium antagonist and a voltage-dependent blocker of the N-methyl-D-aspartate channel, which plays a role in the entrance of calcium into the neuron. Other mechanisms also add biological plausibility to neuro-protective properties for magnesium, including an inverse association with major depression. A higher magnesium intake has been related to lower depressive symptoms. However, epidemiological evidence on this issue is scarce. Our aim was to prospectively evaluate the association between dietary magnesium intake and depression incidence in a cohort of 12,939 Spanish university graduates initially free of depression (Seguimiento Universidad de Navarra Cohort Study). Total magnesium intake was assessed with a validated, semiquantitative FFQ and incident depression was ascertained through self-reports of a new clinical diagnosis of depression done by a medical doctor and/or the habitual use of antidepressive drugs. The self-report was validated against the Diagnostic and Statistical Manual of Mental Disorders (4th edition) criteria in a subsample of the cohort. Cox regression models were used to obtain HR of incident depression during follow-up according to baseline quintiles of magnesium intake using the lowest quintile as the reference category. After a median follow-up of 6.3 y, 737 new cases of depression were identified. No association between magnesium intake and depression was found, with multivariate-adjusted HR = 1 (reference), 1.00 (95% CI: 0.78-1.27), 1.00 (0.76-1.31), 0.95 (0.70-1.30), and 1.11 (0.77-1.59) for increasing categories (quintiles 1-5) of total magnesium intake. No dose-response relationship was found (P-trend = 0.59). Results were robust through different sensitivity analyses, including nutrient density or residual models. In conclusion, our findings do not suggest an inverse association between magnesium intake and depressive disorder.

Insulin in central nervous system: more than just a peripheral hormone

Insulin signaling in central nervous system (CNS) has emerged as a novel field of research since decreased brain insulin levels and/or signaling were associated to impaired learning, memory, and age-related neurodegenerative diseases. Thus, besides its well-known role in longevity, insulin may constitute a promising therapy against diabetes- and age-related neurodegenerative disorders. More interestingly, insulin has been also faced as the potential missing link between diabetes and aging in CNS, with Alzheimer's disease (AD) considered as the "brain-type diabetes." In fact, brain insulin has been shown to regulate both peripheral and central glucose metabolism, neurotransmission, learning, and memory and to be neuroprotective. And a future challenge will be to unravel the complex interactions between aging and diabetes, which, we believe, will allow the development of efficient preventive and therapeutic strategies to overcome age-related diseases and to prolong human "healthy" longevity. Herewith, we aim to integrate the metabolic, neuromodulatory, and neuroprotective roles of insulin in two age-related pathologies: diabetes and AD, both in terms of intracellular signaling and potential therapeutic approach.

Calcium signaling in renal tubular cells

The kidney handles calcium by filtration and reabsorption. About 60% of the plasma calcium is filterable, and 99% is reabsorbed in the tubule. In the proximal tubule, the reabsorption is passive and paracellular, but in the distal tubule is active and transcellular. Thus, renal tubular cells are exposed to very high concentrations of calcium in both, the extracellular and the intracellular compartments. Extracellular calcium signaling is transmitted by the calcium sensing receptor, located both in the luminal and basolateral sides of tubular cells. This receptor is able to control levels of extracellular calcium and acts in consequence to maintain calcium homeostasis. Furthermore, renal tubular cells possess several calcium channels that regulate some of the cell functions. Among those, voltage gated calcium channels, transient receptor potential channels and N-methyl-D-aspartate receptor channels have been reported to control several functions. Those functions include survival, apoptosis, differentiation, epithelial-mesenchymal transition, and active vitamin D and renin synthesis.

L-Carnitine rescues ketamine-induced attenuated heart rate and MAPK (ERK) activity in zebrafish embryos

Ketamine, an antagonist of the N-methyl-D-aspartate (NMDA)-type glutamate receptors, is a pediatric anesthetic. Ketamine has been shown to be neurotoxic and cardiotoxic in mammals. Here, we show that after 2 h of exposure, 5 mM ketamine significantly reduced heart rate in 26 h old zebrafish embryos. In 52 h old embryos, 1 mM ketamine was effective after 2 h and 0.5 mM ketamine at 20 h of exposure. Ketamine also induced significant reductions in activated MAPK (ERK) levels. Treatment of the embryos with the ERK inhibitor, PD 98059, also significantly reduced heart rate whereas the p38/SAPK inhibitor, SB203580, was ineffective. Ketamine is known to inhibit lipolysis and a decrease of ATP content in the heart. Co-treatment with l-carnitine that enhances fatty acid metabolism effectively rescued ketamine-induced attenuated heart rate and ERK activity. These findings demonstrate that l-carnitine counteracts ketamine's negative effects on heart rate and ERK activity in zebrafish embryos.

Magnesium deficiency induces anxiety and HPA axis dysregulation: modulation by therapeutic drug treatment

Preclinical and some clinical studies suggest a relationship between perturbation in magnesium (Mg²⁺) homeostasis and pathological anxiety, although the underlying mechanisms remain largely unknown. Since there is evidence that Mg²⁺ modulates the hypothalamic-pituitary adrenal (HPA) axis, we tested whether enhanced anxiety-like behaviour can be reliably elicited by dietary Mg²⁺ deficiency and whether Mg²⁺ deficiency is associated with altered HPA axis function. Compared with controls, Mg²⁺ deficient mice did indeed display enhanced anxiety-related behaviour in a battery of established anxiety tests. The enhanced anxiety-related behaviour of Mg²⁺ deficient mice was sensitive to chronic desipramine treatment in the hyponeophagia test and to acute diazepam treatment in the open arm exposure test. Mg²⁺ deficiency caused an increase in the transcription of the corticotropin releasing hormone in the paraventricular hypothalamic nucleus (PVN), and elevated ACTH plasma levels, pointing to an enhanced set-point of the HPA axis. Chronic treatment with desipramine reversed the identified abnormalities of the stress axis. Functional mapping of neuronal activity using c-Fos revealed hyper-excitability in the PVN of anxious Mg²⁺ deficient mice and its normalisation through diazepam treatment. Overall, the present findings demonstrate the robustness and validity of the Mg²⁺ deficiency model as a mouse model of enhanced anxiety, showing sensitivity to treatment with anxiolytics and antidepressants. It is further suggested that dysregulations in the HPA axis may contribute to the hyper-emotionality in response to dietary induced hypomagnesaemia.

This article is part of a Special Issue entitled ‘Anxiety and Depression’.

Glutamatergic signaling maintains the epithelial phenotype of proximal tubular cells

Epithelial-mesenchymal transition (EMT) contributes to the progression of renal tubulointerstitial fibrosis. The N-methyl-d-aspartate receptor (NMDAR), which is present in proximal tubular epithelium, is a glutamate receptor that acts as a calcium channel. Activation of NMDAR induces actin rearrangement in cells of the central nervous system, but whether it helps maintain the epithelial phenotype of the proximal tubule is unknown. Here, knockdown of NMDAR1 in a proximal tubule cell line (HK-2) induced changes in cell morphology, reduced E-cadherin expression, and increased α-SMA expression. Induction of EMT with TGF-β1 led to downregulation of both E-cadherin and membrane-associated β-catenin, reorganization of F-actin, expression of mesenchymal markers de novo, upregulation of Snail1, and increased cell migration; co-treatment with NMDA attenuated all of these changes. Furthermore, NMDA reduced TGF-β1-induced phosphorylation of Erk1/2 and Akt and the activation of Ras, suggesting that NMDA antagonizes TGF-β1-induced EMT by inhibiting the Ras-MEK pathway. In the unilateral ureteral obstruction model, treatment with NMDA blunted obstruction-induced upregulation of α-SMA, FSP1, and collagen I and downregulation of E-cadherin. Taken together, these results suggest that NMDAR plays a critical role in preserving the normal epithelial phenotype and modulating tubular EMT.