Sevoflurane-induced cognitive effect on α7-nicotine receptor and M1 acetylcholine receptor expression in the hippocampus of aged rats.

BACKGROUND: Sevoflurane treatment increases the incidence of postoperative cognitive dysfunction (POCD), and patients with POCD show a decline in cognitive abilities compared to preoperative levels. OBJECTIVES: This study aimed to investigate whether the activation of α7 nicotinic acetylcholine receptor (α7nAChR) and the expression of M1 acetylcholine receptor (mAChR M1) in the hippocampus affects the cognitive function of aged rats. METHODS: Forty-eight Sprague-Dawley (SD) rats of 1-week- and 12-months-old were divided into eight groups: four groups for α7nAChR and four groups for mAChR M1, respectively. All SD rats received 1.0-02% sevoflurane for α7nAChR and 1.0-02% sevoflurane for mAChR M1 for 2-6 h, respectively. The Y-maze test was used to assess the ability to learn and memory after receiving sevoflurane for 7 days at the same moment portion. RT-PCR was used to determine the expression of α7nAChR and mAChR M1 in the hippocampus of rats. RESULTS: The α7nAChR mitigated the formation of sevoflurane-induced memory impairment by modulating the translocation of NR2B from the intracellular reservoir to the cell surface reservoir within the hippocampus. Next, sevoflurane-induced decline of cognitive function and significantly decreased mAChR M1 expression at mRNA levels. CONCLUSION: α7nAChR regulates the trafficking of NR2B in the hippocampus of rats via the Src-family tyrosine kinase (SFK) pathway. This regulation is associated with cognitive deficits induced by sevoflurane in hippocampal development. Sevoflurane affects the cognitive function of rats by suppressing the mAChR M1 expression at mRNA levels in the hippocampus.

α7nAChR attenuates sevoflurane-induced memory deficits by regulating NR2B.α7nAChR controls NR2B via the SFK in the hippocampus of rats that contribute to sevoflurane-induced cognitive deficits.Sevoflurane may affect cognitive function in rats by suppressing the mAChR M1 expression at the mRNA levels in the hippocampus.Dysregulation of the α7nAChR and mAChR M1 receptors may contribute to cognitive deficits and neurodegenerative disorders.

APOE4 Affects Basal and NMDAR-Mediated Protein Synthesis in Neurons by Perturbing Calcium Homeostasis.

Apolipoprotein E (APOE), one of the primary lipoproteins in the brain has three isoforms in humans, APOE2, APOE3, and APOE4. APOE4 is the most well-established risk factor increasing the predisposition for Alzheimer's disease (AD). The presence of the APOE4 allele alone is shown to cause synaptic defects in neurons and recent studies have identified multiple pathways directly influenced by APOE4. However, the mechanisms underlying APOE4-induced synaptic dysfunction remain elusive. Here, we report that the acute exposure of primary cortical neurons or synaptoneurosomes to APOE4 leads to a significant decrease in global protein synthesis. Primary cortical neurons were derived from male and female embryos of Sprague Dawley (SD) rats or C57BL/6J mice. Synaptoneurosomes were prepared from P30 male SD rats. APOE4 treatment also abrogates the NMDA-mediated translation response indicating an alteration of synaptic signaling. Importantly, we demonstrate that both APOE3 and APOE4 generate a distinct translation response which is closely linked to their respective calcium signature. Acute exposure of neurons to APOE3 causes a short burst of calcium through NMDA receptors (NMDARs) leading to an initial decrease in protein synthesis which quickly recovers. Contrarily, APOE4 leads to a sustained increase in calcium levels by activating both NMDARs and L-type voltage-gated calcium channels (L-VGCCs), thereby causing sustained translation inhibition through eukaryotic translation elongation factor 2 (eEF2) phosphorylation, which in turn disrupts the NMDAR response. Thus, we show that APOE4 affects basal and activity-mediated protein synthesis responses in neurons by affecting calcium homeostasis.SIGNIFICANCE STATEMENT Defective protein synthesis has been shown as an early defect in familial Alzheimer's disease (AD). However, this has not been studied in the context of sporadic AD, which constitutes the majority of cases. In our study, we show that Apolipoprotein E4 (APOE4), the predominant risk factor for AD, inhibits global protein synthesis in neurons. APOE4 also affects NMDA activity-mediated protein synthesis response, thus inhibiting synaptic translation. We also show that the defective protein synthesis mediated by APOE4 is closely linked to the perturbation of calcium homeostasis caused by APOE4 in neurons. Thus, we propose the dysregulation of protein synthesis as one of the possible molecular mechanisms to explain APOE4-mediated synaptic and cognitive defects. Hence, the study not only suggests an explanation for the APOE4-mediated predisposition to AD, it also bridges the gap in understanding APOE4-mediated pathology.

A novel role for the ADHD risk gene latrophilin-3 in learning and memory in Lphn3 knockout rats.

Latrophilins (LPHNs) are adhesion G protein-coupled receptors with three isoforms but only LPHN3 is brain specific (caudate, prefrontal cortex, dentate, amygdala, and cerebellum). Variants of LPHN3 are associated with ADHD. Null mutations of Lphn3 in rat, mouse, zebrafish, and Drosophila result in hyperactivity, but its role in learning and memory (L&M) is largely unknown. Using our Lphn3 knockout (KO) rats we examined the cognitive abilities, long-term potentiation (LTP) in CA1, NMDA receptor expression, and neurohistology from heterozygous breeding pairs. KO rats were impaired in egocentric L&M in the Cincinnati water maze, spatial L&M and cognitive flexibility in the Morris water maze (MWM), with no effects on conditioned freezing, novel object recognition, or temporal order recognition. KO-associated locomotor hyperactivity had no effect on swim speed. KO rats had reduced early-LTP but not late-LTP and had reduced hippocampal NMDA-NR1 expression. In a second experiment, KO rats responded to a light prepulse prior to an acoustic startle pulse, reflecting visual signal detection. In a third experiment, KO rats given extra MWM pretraining and hidden platform overtraining showed no evidence of reaching WT rats' levels of learning. Nissl histology revealed no structural abnormalities in KO rats. LPHN3 has a selective effect on egocentric and allocentric L&M without effects on conditioned freezing or recognition memory.

Differential effects of memory enhancing and impairing doses of methylphenidate on serotonin metabolism and 5-HT1A, GABA, glutamate receptor expression in the rat prefrontal cortex.

Methylphenidate (MPD), a psychostimulant, is a prescription medicine for treating attention deficit hyperactivity disorder (ADHD). Previously we have shown that moderate doses of MPD enhanced learning and memory while higher doses impaired it. To understand neurochemical mechanisms and receptors involved in memory enhancing and impairing effects of MPD, the present study concerns the effects of these doses of MPD on serotonin, 5-HT1A, GABA, and NMDA receptor mRNA expression in the prefrontal cortex (PFC). We found that low doses (2.5 mg/kg) of MPD improved performance in the water-maze test but higher doses (5 mg/kg) impaired memory retention. Animals showing improved performance had high 5-HT metabolism in the PFC while these levels were not affected in the group treated with higher MPD doses and exhibiting impaired memory. There was downregulation of 5-HT1A receptors in the PFC of rats treated with higher dose MPD, which didn't occur in low dose of MPD treated animals. Further, a decrease in GABAAreceptor mRNA expression occurred in low doses of MPD treated animals and GluN2A expression was reduced in higher doses of MPD treated animals. The findings suggest that memory enhancing doses of MPD increase 5-HT and reduce GABAA receptor mRNA expression in the PFC to release excitatory glutamate neurons from the inhibitory influence of GABA. Conversely, higher dose of MPD downregulates 5-HT1A receptor mRNA expression to enhance inhibitory GABA influence on glutamate neurons and impair cognitive performance. The findings show an important role of 5-HT1A heteroreceptors in the PFC for improving therapeutic use of MPD and developing novel cognitive enhancers.

Attenuated NMDAR signaling on fast-spiking interneurons in prefrontal cortex contributes to age-related decline of cognitive flexibility.

Ionotropic glutamate receptors of the NMDA and AMPA subtypes transduce excitatory signaling on neurons in the prefrontal cortex (PFC) in support of cognitive flexibility. Cognitive flexibility is reliably observed to decline at advanced ages, coinciding with changes in PFC glutamate receptor expression and neuronal physiology. However, the relationship between age-related impairment of cognitive flexibility and changes to excitatory signaling on distinct classes of PFC neurons is not known. In this study, one cohort of young adult (4 months) and aged (20 months) male F344 rats were characterized for cognitive flexibility on an operant set-shifting task. Expression of the essential NMDAR subunit, NR1, was correlated with individual differences in set-shifting abilities such that lower NR1 in the aged PFC was associated with worse set-shifting. In contrast, lower expression of two AMPAR subunits, GluR1 and GluR2, was not associated with set-shift abilities in aging. As NMDARs are expressed by both pyramidal cells and fast-spiking interneurons (FSI) in PFC, whole-cell patch clamp recordings were performed in a second cohort of age-matched rats to compare age-associated changes on these neuronal subtypes. Evoked excitatory postsynaptic currents were generated using a bipolar stimulator while AMPAR vs. NMDAR-mediated components were isolated using pharmacological tools. The results revealed a clear increase in AMPA/NMDA ratio in FSIs that was not present in pyramidal neurons. Together, these data indicate that loss of NMDARs on interneurons in PFC contributes to age-related impairment of cognitive flexibility.

Angiotensin II induces cognitive decline and anxiety-like behavior via disturbing pattern of theta-gamma oscillations.

Hypertension is the most common chronic disease accompanied by cognitive decline and anxiety-like behavior. Angiotensin II (Ang II) induces hypertension by activating angiotensin II receptor subtype 1 (AT1R). The purpose of the study was to examine the potential underlying mechanism of alterations in cognition and anxiety-like behavior induced by Ang II. Adult C57 mice were intraperitoneal injected with either 1 mg/kg/d Ang II or saline individually for 14 consecutive days. Ang II resulted in cognitive decline and anxious like behavior in C57 mice. Moreover, Ang II disturbed bidirectional synaptic plasticity and neural oscillation coupling between high theta and gamma on PP (perforant pathway)-DG (dentate gyrus) pathway. In addition, Ang II decreased the expression of N-methyl-d-aspartate receptor (NR) 2A and NR 2B and increased the expression of GABAAR α1. The data suggest that Ang II disturb neural oscillations via altering excitatory and inhibitory (E/I) balance and eventually damage cognition and anxiety-like behavior in mice.

Protective effect of alpha-linoleic acid on Aß-induced oxidative stress, neuroinflammation, and memory impairment by alteration of α7 nAChR and NMDAR gene expression in the hippocampus of rats.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that affects many older people around the world. Numerous studies are underway to evaluate the protective effects of natural products in AD. Alpha-linoleic acid (ALA) is an essential unsaturated fatty acid that exhibits neuroprotective outcomes in rat models of ischemic stroke and Parkinson's disease. This research aimed to investigate the effect of ALA on oxidative stress, neuroinflammation, neuronal death, and memory deficit induced by amyloid-beta (Aß) peptide. After intrahippocampal injection of Aß1-42, rats received ALA (150 µg/kg, subcutaneously) for 14 consecutive days. ALA decreased the levels of malondialdehyde and nitric oxide, enhanced glutathione content, and increased the activity of catalase in the hippocampus of the rat model of AD. It also reduced the expression of tumor necrosis factor-α, interleukin-1ß, interleukin-6, nuclear factor-kappa B, and N-methyl-d-aspartate receptor subunits NR2A and NR2B mRNAs in the hippocampus, prevented the neuronal loss in the CA1 region, and enhanced the expression of α7 nicotinic acetylcholine receptor. In addition, ALA allowed Aß1-42-injected rats to spend less time and distance to reach the hidden platform in the Morris water maze test and to swim longer in the target quadrant. We concluded that ALA reduces the biochemical, molecular, histological, and behavioral changes caused by Aß1-42 and it may be an effective option for treating AD.

Forebrain GluN2A overexpression impairs fear extinction and NMDAR-dependent long-term depression in the lateral amygdala.

N-methyl-d-aspartic acid receptor (NMDAR)-dependent synaptic plasticity at the thalamus-lateral amygdala (T-LA) synapses is related to acquisition and extinction of auditory fear memory. However, the roles of the NMDAR GluN2A subunit in acquisition and extinction of auditory fear memory as well as synaptic plasticity at T-LA synapses remain unclear. Here, using electrophysiologic, molecular biological techniques and behavioral methods, we found that the forebrain specific GluN2A overexpression transgenic (TG) mice exhibited normal acquisition but impaired extinction of auditory fear memory. In addition, in vitro electrophysiological data showed normal basal synaptic transmission and NMDAR-dependent long-term potentiation (LTP) at T-LA synapses, but deficit in NMDAR-dependent long-term depression (LTD) at T-LA synapses in GluN2A TG mice. Consistent with the reduced NMDAR-dependent LTD, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) internalization was also weakened during NMDAR-dependent LTD in GluN2A TG mice. Taken together, our findings for the first time indicate that GluN2A overexpression impairs extinction of auditory fear memory and NMDAR-dependent LTD at T-LA synapses, which further confirms the close relationship between NMDAR-dependent LTD and fear extinction.

The α2δ-1/NMDA receptor complex is involved in brain injury after intracerebral hemorrhage in mice.

BACKGROUND: Intracerebral hemorrhage (ICH), a common cerebrovascular disease, seriously threatens human health and has severe secondary injuries, while existing treatment methods have many limitations. α2δ-1 is a subunit of voltage-gated Ca2+ channels (VGCCs) and can act on glutamate receptor N-methyl-D-aspartate receptors (NMDARs) to relieve neuropathic pain. METHODS: We first performed ICH modeling on WT mice and Cacna2d1 knockout (KO) mice. The expression levels of GluN1 and α2δ-1 were measured by Western blot and q-PCR, and the interaction between the two proteins was evaluated by co-precipitation. The neuronal apoptosis was detected by the TUNEL assay, and the expression levels of inflammatory factors were assessed by ELISA. The nerve functions of mice were evaluated using behavioral experiments including corner turn test and forelimb use asymmetry. Cerebral hematoma was indicated by brain water content and lesion volume. RESULTS: ICH up-regulated the expression levels of α2δ-1 and GluN1. KO of Cacna2d1 significantly reduced the ICH-induced apoptosis. The treatment of gabapentin on α2δ-1 also significantly reduced the occurrence of apoptosis. KO of Cacna2d1 also reduced the ICH-induced levels of inflammatory factors. Furthermore, neural functions were also significantly improved. CONCLUSION: Cacna2d1 KO alleviates cerebral hematoma in ICH mice, exhibits a significant regulating effect on its secondary injuries such as neuronal apoptosis and inflammation, and restores the nerve functions of ICH mice. Loss of Cacna2d1 can provide useful therapeutic clues for ICH treatment.

Modulation of prefrontal cortex function by basal forebrain cholinergic and GABAergic neurons at the behavioral and molecular level.

The present research aimed to study the effects of selective immunolesions of cholinergic or gamma-aminobutyric acid (GABA)ergic neurons in the nucleus basalis magnocellularis (NBM) on memory function as well as cholinergic activity and the level of expression of glutamatergic [NR2B subunit of N-methyl-D-aspartate(NMDA)] receptors in the medial prefrontal cortex (mPFC) and hippocampus of behaviorally characterized rats. In behavioral experiments, working memory was assessed by a spatial alternation testing procedure in a plus-maze, and acquisition and retention of spatial memory was evaluated in a Morris water maze. The rats were divided into three groups: the NBM cholinergic, GABAergic immunolesioned groups and the normal control group. Cholin acetyltransferase or parvalbumin staining of the NBM and acetylcholinesterase staining of the mPFC and hippocampal sections were performed to visualize the effects of immunotoxins. The electrophoresis and immunoblotting were run to evaluate the effect of NBM lesions on the amount of the NR2B subunit of NMDA receptors. The results indicate that the immunolesion of cholinergic NBM neurons impair spatial working memory, as well as long-term spatial memory which is accompanied by significant changes in glutamatergic (the NR2B subunit of NMDA receptor) and cholinergic markers in the mPFC, whereas immunolesion of GABAergic NBM neurons does not affect long-term spatial memory, it does though cause the impairment of working memory with a reduction of the NMDA NR2B receptor signaling in the mPFC. The present results demonstrate that the cholinergic and GABAergic NBM cell groups play diverse and complementary roles and are integrated in distinct NBM-mPFC networks that may play different roles in mPFC memory function.

Changes in concentrations of NMDA receptor subunit GluN2B, Arc and syntaxin-1 in dorsal hippocampus Schaffer collateral synapses in a rat learned helplessness model of depression.

Major depressive disorder involves changes in synaptic structure and function, but the molecular underpinnings of these changes are still not established. In an initial pilot experiment, whole-brain synaptosome screening with quantitative western blotting was performed to identify synaptic proteins that may show concentration changes in a congenital rat learned helplessness model of depression. We found that the N-methyl-d-aspartate receptor (NMDAR) subunits GluN2A/GluN2B, activity-regulated cytoskeleton-associated protein (Arc) and syntaxin-1 showed significant concentration differences between congenitally learned helpless (LH) and nonlearned helpless (NLH) rats. Having identified these three proteins, we then performed more elaborate quantitative immunogold electron microscopic analyses of the proteins in a specific synapse type in the dorsal hippocampus: the Schaffer collateral synapse in the CA1 region. We expanded the setup to include also unstressed wild-type (WT) rats. The concentrations of the proteins in the LH and NLH groups were compared to WT animals. In this specific synapse, we found that the concentration of NMDARs was increased in postsynaptic spines in both LH and NLH rats. The concentration of Arc was significantly increased in postsynaptic densities in LH animals as well as in presynaptic cytoplasm of NLH rats. The concentration of syntaxin-1 was significantly increased in both presynaptic terminals and postsynaptic spines in LH animals, while pre- and postsynaptic syntaxin-1 concentrations were significantly decreased in NLH animals. These protein changes suggest pathways by which synaptic plasticity may be increased in dorsal hippocampal Schaffer collateral synapses during depression, corresponding to decreased synaptic stability.

A new insight into mechanisms of interferon alpha neurotoxicity: Expression of GRIN3A subunit of NMDA receptors and NMDA-evoked exocytosis.

Neurological and psychiatric side effects accompany the high-dose interferon-alpha (IFNA) therapy. The primary genes responsible for these complications are mostly unknown. Our genome-wide search in mouse and rat genomes for the conservative genes containing IFN-stimulated response elements (ISRE) in their promoters revealed a new potential target gene of IFNA, Grin3α, which encodes the 3A subunit of NMDA receptor. This study aimed to explore the impact of IFNA on the expression of Grin3α and Ifnα genes and neurotransmitters endo/exocytosis in the mouse brain. We administered recombinant human IFN-alpha 2b (rhIFN-α2b) intracranially, and 24 h later, we isolated six brain regions and used the samples for RT-qPCR and western blot analysis. Synaptosomes were isolated from the cortex to analyze endo/exocytosis with acridine orange and L-[14C]glutamate. IFNA induced an increase in Grin3α mRNA and GRIN3A protein, but a decrease in Ifnα mRNA and protein. IFNA did not affect the accumulation and distribution of L-[14C]glutamate and acridine orange between synaptosomes and the extra-synaptosomal space. It caused the more significant acridine orange release activated by NMDA or glutamate than from control mice's synaptosomes. In response to IFNA, the newly discovered association between elevated Grin3α expression and NMDA- and glutamate-evoked neurotransmitters release from synaptosomes implies a new molecular mechanism of IFNA neurotoxicity.

The NMDA Receptor Subunit (GluN1 and GluN2A) Modulation Following Different Conditions of Cocaine Abstinence in Rat Brain Structures.

Different neuronal alterations within glutamatergic system seem to be crucial for developing of cocaine-seeking behavior. Cocaine exposure provokes a modulation of the NMDA receptor subunit expression in rodents, which probably contributes to cocaine-induced behavioral alterations. The aim of this study was to examine the composition of the NMDA receptor subunits in the brain structures in rats with the history of cocaine self-administration after cocaine abstinence (i) in an enriched environment, (ii) in an isolated condition, (iii) with extinction training, or (iv) without instrumental task, as well as the Grin1 (encoding GluN1) and Grin2A (encoding GluN2A) gene expression were evaluated after 10-day extinction training in rat brain structures. In the present study, we observed changes only following cocaine abstinence with extinction training, when the increased GluN2A subunit levels were seen in the postsynaptic density fraction but not in the whole homogenate of the prelimbic cortex (PLC) and dorsal hippocampus (dHIP) in rats previously self-administered cocaine. At the same time, extinction training did not change the Grin1 and Grin2A gene expression in these structures. In conclusion, NMDA receptor subunit modulation observed following cocaine abstinence with extinction training may represent a potential target in cocaine-seeking behavior.

NMDA GluN2C/2D receptors contribute to synaptic regulation and plasticity in the anterior cingulate cortex of adult mice.

INTRODUCTION: N-Methyl-D-aspartate receptors (NMDARs) play a critical role in different forms of plasticity in the central nervous system. NMDARs are always assembled in tetrameric form, in which two GluN1 subunits and two GluN2 and/or GluN3 subunits combine together. Previous studies focused mainly on the hippocampus. The anterior cingulate cortex (ACC) is a key cortical region for sensory and emotional functions. NMDAR GluN2A and GluN2B subunits have been previously investigated, however much less is known about the GluN2C/2D subunits. RESULTS: In the present study, we found that the GluN2C/2D subunits are expressed in the pyramidal cells of ACC of adult mice. Application of a selective antagonist of GluN2C/2D, (2R*,3S*)-1-(9-bromophenanthrene-3-carbonyl) piperazine-2,3-dicarboxylic acid (UBP145), significantly reduced NMDAR-mediated currents, while synaptically evoked EPSCs were not affected. UBP145 affected neither the postsynaptic long-term potentiation (post-LTP) nor the presynaptic LTP (pre-LTP). Furthermore, the long-term depression (LTD) was also not affected by UBP145. Finally, both UBP145 decreased the frequency of the miniature EPSCs (mEPSCs) while the amplitude remained intact, suggesting that the GluN2C/2D may be involved in presynaptic regulation of spontaneous glutamate release. CONCLUSIONS: Our results provide direct evidence that the GluN2C/2D contributes to evoked NMDAR mediated currents and mEPSCs in the ACC, which may have significant physiological implications.

Psychosocial Crowding Stress-Induced Changes in Synaptic Transmission and Glutamate Receptor Expression in the Rat Frontal Cortex.

This study demonstrates how exposure to psychosocial crowding stress (CS) for 3, 7, and 14 days affects glutamate synapse functioning and signal transduction in the frontal cortex (FC) of rats. CS effects on synaptic activity were evaluated in FC slices of the primary motor cortex (M1) by measuring field potential (FP) amplitude, paired-pulse ratio (PPR), and long-term potentiation (LTP). Protein expression of GluA1, GluN2B mGluR1a/5, VGLUT1, and VGLUT2 was assessed in FC by western blot. The body's response to CS was evaluated by measuring body weight and the plasma level of plasma corticosterone (CORT), adrenocorticotropic hormone (ACTH), and interleukin 1 beta (IL1B). CS 3 14d increased FP and attenuated LTP in M1, while PPR was augmented in CS 14d. The expression of GluA1, GluN2B, and mGluR1a/5 was up-regulated in CS 3d and downregulated in CS 14d. VGLUTs expression tended to increase in CS 7d. The failure to blunt the effects of chronic CS on FP and LTP in M1 suggests the impairment of habituation mechanisms by psychosocial stressors. PPR augmented by chronic CS with increased VGLUTs level in the CS 7d indicates that prolonged CS exposure changed presynaptic signaling within the FC. The CS bidirectional profile of changes in glutamate receptors' expression seems to be a common mechanism evoked by stress in the FC.

Intermittent Hypoxia Activates N-Methyl-D-Aspartate Receptors to Induce Anxiety Behaviors in a Mouse Model of Sleep-Associated Apnea.

Sleep apnea disrupts physiologic homeostasis and causes neuronal dysfunction. In addition to signs of mental disorders and cognitive dysfunction, patients with sleep apnea have a higher anxiety rate. Here, we examined the mechanisms underlying this critical health issue. We used a mouse model with sleep-associated chronic intermittent hypoxia (IH) to verify the effects of sleep apnea on neuronal dysfunction. To evaluate how IH alters neuronal function to yield anxiety-like behavior and cognitive dysfunction, we examined synaptic plasticity and neuronal inflammation in related brain areas, including the medial prefrontal cortex (mPFC), striatum, and hippocampus. Mice subjected to chronic IH for 10 days exhibited significant anxiety-like behaviors in the elevated plus maze test. IH mice spent less travel time in open arms and more travel time in enclosed arms compared to control mice. However, cognitive impairment was minimal in IH mice. Increased glutamate N-methyl-D-aspartate (NMDA) receptor subunits 2B (GluN2B) and phosphorylated-ERK1/2 were seen in the mPFC, striatum, and hippocampus of IH mice, but no significant microglial and astrocyte activation was found in these brain areas. Chronic IH in mice induced compensatory increases in GluN2B to disturb neuronal synaptic plasticity, without neuronal inflammation. The altered synaptic plasticity subsequently led to anxiety-like behavior in mice. Treatment with the NMDA receptor antagonist dextromethorphan attenuated chronic IH-induced anxiety-like behavior and GluN2B expression. Our findings provide mechanistic evidence of how IH may provoke anxiety and support for the importance of early intervention to alleviate anxiety-associated complications in patients with chronic sleep apnea.

Transient forebrain ischemia under hyperthermic condition accelerates memory impairment and neuronal death in the gerbil hippocampus by increasing NMDAR1 expression.

Altered expression levels of N­methyl­D­aspartate receptor (NMDAR), a ligand­gated ion channel, have a harmful effect on cellular survival. Hyperthermia is a proven risk factor of transient forebrain ischemia (tFI) and can cause extensive and severe brain damage associated with mortality. The objective of the present study was to investigate whether hyperthermic preconditioning affected NMDAR1 immunoreactivity associated with deterioration of neuronal function in the gerbil hippocampal CA1 region following tFI via histological and western blot analyses. Hyperthermic preconditioning was performed for 1 h before tFI, which was developed by ligating common carotid arteries for 5 min. tFI­induced cognitive impairment under hyperthermia was worse compared with that under normothermia. Loss (death) of pyramidal neurons in the CA1 region occurred fast and was more severe under hyperthermia compared with that under normothermia. NMDAR1 immunoreactivity was not observed in the somata of pyramidal neurons of sham gerbils with normothermia. However, its immunoreactivity was strong in the somata and processes at 12 h post­tFI. Thereafter, NMDAR1 immunoreactivity decreased with time after tFI. On the other hand, NMDAR1 immunoreactivity under hyperthermia was significantly increased in the somata and processes at 6 h post­tFI. The change pattern of NMDAR1 immunoreactivity under hyperthermia was different from that under normothermia. Overall, accelerated tFI­induced neuronal death under hyperthermia may be closely associated with altered NMDAR1 expression compared with that under normothermia.

Forebrain expression of serine racemase during postnatal development.

N-methyl-D-aspartate receptors (NMDARs) are important for synaptogenesis, synaptic maturation and refinement during the early postnatal weeks after birth. Defective synapse formation or refinement underlie cognitive and emotional abnormalities in various neurodevelopmental disorders (NDDs), including schizophrenia (Sz) and autism spectrum disorder (ASD). Serine racemase (SR) is a neuronal enzyme that produces D-serine, a co-agonist required for full NMDAR activation. NMDAR hypofunction as a result of genetic SR elimination and reduced synaptic availability of D-serine reduces neuronal dendritic arborization and spine density. In adult mouse brain, the expression of SR parallels that of NMDARs across forebrain regions including the striatum, amygdala, hippocampus, and medial prefrontal cortex (mPFC). However, there have yet to be studies providing a detailed characterization of the spatial and temporal expression of SR during early periods of synaptogenesis. Here, we examined the postnatal expression of SR in cortical and subcortical brain regions important for learning, memory and emotional regulation, during the first four weeks after birth. Using dual-antigen immunofluorescence, we demonstrate that the number of SR+ neurons steadily increases with postnatal age across the mPFC, amygdala, hippocampus and striatum. We also identified differences in the rate of SR protein induction both across and within brain regions. Analyzing existing human post-mortem brain in situ data, there was a similar developmental mRNA expression profile of SRR and GRIN1 (GluN1 subunit) from infancy through the first decade of life. Our findings further support a developmental role for D-serine mediated NMDAR activation regulating synaptogenesis and neural circuit refinement, which has important implications for the pathophysiology of Sz and other NDDs.

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.

Abnormal expression of post-synaptic proteins in prefrontal cortex of patients with schizophrenia.

There is converging evidence of dendritic spine dysfunction in schizophrenia. In the present study we hypothesized that the expression of key proteins involved in dendritic spine development and stability may be affected in schizophrenia. Postmortem frontal cortex (BA6) from patients with schizophrenia, major depressive disorder, bipolar disorder and healthy controls was processed for glutamate post-synaptic fraction extraction and post-synaptic density purification. Protein expression of the post-synaptic fraction and the post-synaptic density was assessed using immunoprecipitation and Western blotting respectively. The expression of the N-methyl-d-aspartate glutamate receptor (NMDAR) subunit NR2A, post-synaptic density 95 (PSD-95), Ca2+/calmodulin-dependent protein kinase II subunits α and ß (CaMKIIα and ß) were significantly reduced in schizophrenia. A significant decrease in the expression of NR2A was also observed in patients with major depressive disorder relative to controls, but not in patients with bipolar disorder. These results add to existing evidence for disturbed post-synaptic glutamate function and synaptic plasticity in schizophrenia. There may also be subtle disturbances in the post-synaptic glutamatergic function in major depressive disorder.