NR2A Levels Research Articles

Altered emotionality, hippocampus-dependent performance and expression of NMDA receptor subunit mRNAs in chronically stressed mice

N-Methyl-d-aspartate receptor (NMDAR)-mediated neurotransmission in the hippocampus is implicated in cognitive and emotional disturbances during stress-related disorders. Here, using quantitative RT-PCR, we investigated the hippocampal expression of NR2A, NR2B and NR1 subunit mRNAs in a mouse stress paradigm that mimics clinically relevant conditions of simultaneously affected emotionality and hippocampus-dependent functions. A 2-week stress procedure, which comprised ethologically valid stressors, exposure to a rat and social defeat, was applied to male C57BL/6J mice. For predation stress, mice were introduced into transparent containers that were placed in a rat home cage during the night; social defeat was applied during the daytime using aggressive CD1 mice. This treatment impaired hippocampus-dependent performance during contextual fear conditioning. A correlation between this behavior and food displacement performance was demonstrated, suggesting that burrowing behavior is affected by the stress procedure and is hippocampus-dependent. Stressed mice (n = 22) showed behavioral invigoration and anomalous anxiolytic-like profiles in the O-maze and brightly illuminated open field, unaltered short-term memory in the step-down avoidance task and enhanced aggressive traits, as compared to non-stressed mice (n = 10). Stressed mice showed increased basal serum corticosterone concentrations, hippocampal mRNA expression for the NR2A subunit of the NMDAR and in the NR2A/NR2B ratio; mRNA expression of NR2B and NR1 was unchanged. Thus, stress-induced aberrations in both hippocampal-dependent performance and emotional abnormalities are associated with alterations in hippocampal mRNA NR2A levels and the NR2A/NR2B ratio and not with mRNA expression of NR2B or NR1.

Reduced Levels of NR1 and NR2A with Depression-Like Behavior in Different Brain Regions in Prenatally Stressed Juvenile Offspring

Adolescence is a time of continued brain maturation, particularly in limbic and cortical regions, which undoubtedly plays a role in the physiological and emotional changes. Juvenile rats repeatedly exposed to prenatal stress (PS) exhibit behavioral features often observed in neuropsychiatric disorders including depression. However, to date the underlying neurological mechanisms are still unclear. In the current study, juvenile offspring rats whose mothers were exposed to PS were evaluated for depression-related behaviors in open field and sucrose preference test. NMDA receptor subunits NR1 and NR2A in the hippocampus, frontal cortex and striatum were assayed by western blotting. The results indicated that PS resulted in several behavioral anomalies in the OFT and sucrose preference test. Moreover, reduced levels of NMDA receptor subunits NR1 and NR2A in the hippocampus, and NR1 in prefrontal cortex and striatum of prenatally stressed juvenile offspring were found. Treatment with MK-801 to pregnant dams could prevent all those changes in the juvenile offspring. Collectivity, these data support the argument that PS to pregnant dams could induce depression-like behavior, which may be involved with abnormal expression of NR1 and NR2A in specific brain regions, and MK-801 may have antidepressant-like effects on the juvenile offspring.

Downregulation of Src-Kinase and Glutamate-Receptor Phosphorylation after Traumatic Brain Injury

Phosphorylation of N-methyl-D-aspartate (NMDA) receptors is a major regulatory mechanism underlying synaptic plasticity. However, changes in NMDA receptors and phosphorylation after traumatic brain injury (TBI) remain incompletely understood. Using an animal TBI model, we observed that the protein level of NMDA receptor subunit NR2B was downregulated in synaptosomal fractions obtained from the ipsilateral neocortical injury region, whereas the levels of NR2A, NR1, and PSD93 were not significantly altered at 4 and 24 hours after TBI. Further investigation showed that tyrosine phosphorylations of NR2B Y1472 and PSD93 Y340 in synaptosomal fractions were significantly decreased relative to their total protein level after TBI. Correspondingly, phosphorylation of the Src-kinase-inhibitory site Y527 was increased, whereas phosphorylation of the activation site Y416 was decreased, indicating that the activity of Src kinase is significantly inhibited after TBI. In comparison, other Src family kinase substrates of NMDA receptor, NR2A Y1246, NR2A Y1325, and NR2B Y1070 were not obviously affected after TBI. The results suggest that TBI downregulates the Src-kinase-mediated phosphorylation of NR2 and PSD93 to destabilize the synaptic localization of NMDA receptors. Therefore, post-TBI loss of NMDA receptors may contribute to the depression of synaptic activity after TBI.

Pain processing in a mouse model of Phelan-McDermid Syndrome, an autism spectrum disorder

Approximately 75% of patients with Phelan-McDermid Syndrome (PMS), an autism spectrum disorder, exhibit diminished responses to pain. Pain hyporesponsivity (PH) puts patients at risk for aggravated consequences from injuries and can conceal life-threatening painful conditions. The consequences of abnormal sensory responses, including PH, have a negative impact on the quality of life for autistic children and their caregivers. However, the neurologic basis for PH in PMS is unclear. PMS is caused by mutations or deletions in one copy of Shank3. The Shank family proteins (Shank 1-3) are postsynaptic scaffold proteins that regulate the function of glutamate receptors. We used mice with heterozygous (HET) C-terminal truncation of Shank3 to determine the impact of this mutation on pain processing. Shank3 immunoreactivity was present in anterior cingulate cortex (ACC) and lumbar spinal cord (LSC) dorsal horns. Baseline responses to noxious heat and innocuous touch were similar between wild-type (WT) and HET mice. After spared nerve injury (SNI), tactile response thresholds were significantly higher in HET than those in WT at post-SNI days 8, 13, and 20. Western blotting revealed significant SNI-induced upregulation of Shank3, mGluR1, and Homer1b/c in ACC of WT and HETs. In LSC, baseline expression levels of Shank3, NR2A, GKAP, and PSD95 were significantly lower in HET than in WT mice. SNI significantly reduced WT LSC expression of Shank3 and GKAP. Co-immunoprecipitation with an antibody to Shank3 revealed decreased association with scaffolding proteins after SNI in WT and HET mice. In conclusion, Shank3 mutation alters behavioral and biochemical responses to neuropathic pain. Differing patterns of SNI-induced synaptic protein expression between LSC and ACC suggest that Shank3 may serve region-specific roles. Abnormal synaptic function due to Shank3 mutations may play a role in PH in PMS patients.

Effects of lisinopril on NMDA receptor subunits 2A and 2B levels in the hippocampus of rats with l-NAME-induced hypertension

Hypertension is major risk factor leading to cerebrovascular pathologies. N-methyl d-aspartate receptors (NMDARs) and renin-angiotensin system are involved in neuronal plasticity, as well as cognitive functions in the hippocampus. In this study, we examined the effects of lisinopril, an ACE inhibitor, on the levels of hippocampal NMDAR subunits; NR2A and NR2B in l-NAME (Nϵ-nitro-l-arginine Methyl Ester)-induced hypertensive rats. In addition, malondialdehyde (MDA) levels were measured as a marker for lipid peroxidation. Compared with the control group, the MDA level was significantly increased after 8 weeks in the l-NAME-treated group. Rats treated with lisinopril and l-NAME plus lisinopril were found to have significantly decreased hippocampal MDA levels. Regarding the hippocampal concentrations of NR2A and NR2B, there were no statistically significant differences between groups. We demonstrated that lisinopril treatment has no direct regulatory effect on the levels of NR2A and NR2B in the rat hippocampus. Our results showed that Lisinopril could act as an antioxidant agent against hypertension-induced oxidative stress in rat hippocampus. The findings support that the use of lisinopril may offer a good alternative in the treatment of hypertension by reducing not only blood pressure but also prevent hypertensive complications in the brain.

Impairment of long-term depression in the anterior cingulate cortex of mice with bone cancer pain

The anterior cingulate cortex (ACC) has been shown to play an important role in pain-related perception and chronic pain. However, little is known about the molecular mechanisms involved. To address this issue, we analyzed excitatory synaptic transmission and long-term synaptic plasticity in layer II/III pyramidal neurons within the rostral ACC (rACC) from mice with bone cancer pain induced by intra-tibia implantation of osteolytic fibrosarcoma cells. Ex vivo whole-cell patch-clamp recordings from rACC neurons showed no significant alterations in presynaptic glutamate release probability and postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated synaptic responses in mice with bone cancer pain. However, mechanical allodynia occurred in conjunction with decreased N-methyl-d-aspartate (NMDA)/AMPA ratio of synaptic currents elicited in bilateral rACC neurons. In addition, the induction of NMDA receptor-dependent long-term depression (LTD) at rACC synapses was impaired in rACC neurons of tumor-bearing mice. Western blot analysis revealed a significant decrease in the levels of NR1, NR2A, and NR2B subunits of NMDA receptors in the rACC under bone cancer pain condition. No significant changes in overall mRNA levels for any of the NMDA receptor subunits or calpain activity were observed in the rACC of tumor-bearing mice. These results indicate that tumor-induced injury or remodeling of primary afferent sensory nerve fibers that innervate the tumor-bearing bone may cause a persistent decrease in NMDA receptor expression in rACC neurons, resulting in a loss of LTD induction, thereby leading to long-term alterations of rACC activity and creating exaggerated pain behaviors.

Hypoxia associated NMDA receptor 2 subunit composition: developmental comparison between the hypoxia-tolerant subterranean mole-rat, Spalax, and the hypoxia-sensitive rat

Vertebrate brains are sensitive to oxygen depletion, which may lead to cell death. Hypoxia sensitivity originates from the high intrinsic rate of ATP consumption of brain tissue, accompanied by the release of glutamate, leading to the opening of ionotropic glutamate receptors, such as N-methyl-D-aspartate (NMDA) receptors (NMDARs). The relative expression levels of the four NMDAR-2 (NR2) subunits change during mammalian development with higher levels of units NR2B and NR2D observed during early development and correlated with hypoxic tolerance during embryonic and neonatal stages of development. Higher levels of NR2D are also abundant in brains of hypoxia tolerant species such as the crucian carp. The subterranean mole-rat, Spalax spends its life underground in sealed burrows and has developed a wide range of adaptations to this special niche including hypoxia-tolerance. In this study, we compared the in vivo mRNA expression of NR2 subunits in the brains of embryonic, neonatal and adult Spalax and rat. Our results demonstrate that under normoxic conditions, mRNA levels of NR2D are higher in Spalax than in rat at all developmental stages studied and are similar to levels in neonatal rat and in other hypoxia/anoxia tolerant species. Furthermore, under hypoxia Spalax NR2D mRNA levels increase while no response was observed in rat. Similarly, hypoxia induces an increase in mRNA levels of Spalax NR2A, claimed to promote neuronal survival. We suggest that indeed the proportional combinations of NMDAR-2 subunits contribute to the ability of the Spalax brain to cope with hypoxic environments.

Long-term behavioral and NMDA receptor effects of young-adult corticosterone treatment in BDNF heterozygous mice

Psychiatric illnesses, such as schizophrenia, are most likely caused by an interaction between genetic predisposition and environmental factors, including stress during development. The neurotrophin, brain-derived neurotrophic factor (BDNF) has been implicated in this illness as BDNF levels are decreased in the brain of patients with schizophrenia. The aim of the present study was to assess the combined effect of reduced BDNF levels and postnatal stress, simulated by chronic young-adult treatment with the stress hormone, corticosterone. From 6weeks of age, female and male BDNF heterozygous mice and their wild-type controls were chronically treated with corticosterone in their drinking water for 3weeks. At 11weeks of age, male, but not female BDNF heterozygous mice treated with corticosterone exhibited a profound memory deficit in the Y-maze. There were no differences between the groups in baseline prepulse inhibition (PPI), a measure of sensorimotor gating, or its disruption by treatment with MK-801. However, an increase in startle caused by MK-801 treatment was absent in male, but not female BDNF heterozygous mice, irrespective of corticosterone treatment. Analysis of protein levels of the NMDA receptor subunits NR1, NR2A, NR2B and NR2C, showed a marked increase of NR2B levels in the dorsal hippocampus of male BDNF heterozygous mice treated with corticosterone. In the ventral hippocampus, significantly reduced levels of NR2A, NR2B and NR2C were observed in male BDNF heterozygous mice. The NMDA receptor effects in hippocampal sub-regions could be related to the spatial memory deficits and the loss of the effect of MK-801 on startle in these mice, respectively. No significant changes in NMDA receptor subunit levels were observed in any of the female groups. Similarly, no significant changes in levels of BDNF or its receptor, TrkB, were found other than the expected reduced levels of BDNF in heterozygous mice. In conclusion, the data show differential interactive effects of reduced levels of BDNF expression and corticosterone treatment on spatial memory and startle in male and female mice, accompanied by significant, but region-specific changes in NMDA receptor subunit levels in the dorsal and ventral hippocampus. These results could be important for our understanding of the interaction of neurodevelopmental stress and BDNF deficiency in cognitive and anxiety-related symptoms of psychiatric illnesses, such as schizophrenia.

Excessive activation of the loop between the NR2B subunit of the N-methyl-d-aspartate receptor and glycogen synthase kinase-3β in the hippocampi of patients with major depressive disorder.

Objective:We showed previously that glycogen synthase kinase-3β(GSK-3β) levels are significantly elevated in the hippocampi of patients with major depressive disorder (MDD). However, the exact cause of this elevation and its function are unknown. Recent animal studies have suggested a mechanism involving the N-methyl-d-aspartate (NMDA) NR2B–GSK-3βloop.Methods:To investigate the existence of an NR2B–GSK-3βloop in the hippocampi of patients with MDD, we examined the expression of NR2B. We also attempted to identify markers that correlate with NR2B levels in the hippocampus, using the Stanley Neuropathology Consortium Integrative Database (SNCID). The SNCID is a web-based tool used to integrate Stanley Medical Research Institute (SMRI) data sets.Results:We found that hippocampal levels of NR2B and DLGAP1 mRNA were higher in the MDD group (n= 8) than in unaffected controls (n= 12) (p< 0.05). NR2B expression levels were correlated with the expression levels of NR2A, NR1, DLGAP1, GSK-3βand nitric oxide synthase 1, as well as with the number of calretinin-immunoreactive neurons in the hippocampus in all subjects in the SNC (n= 42,p< 0.001).Conclusion:The results of our study show the possible involvement of excessive activation of the NR2B–GSK-3βloop in the overexpression of GSK-3βin the hippocampi of patients with MDD.

Heterozygous deletion of NR1 subunit of the NMDA receptor alters ethanol-related behaviors and regional expression of NR2 subunits in the brain

NMDA receptors have been hypothesized to play a role in various aspects of ethanol-related phenotypes, notably in ethanol withdrawal. However, the role of each of the specific subunits remains unclear. To address this issue, mice that are heterozygous for the NR1 deletion, and thus have a reduction in functional NMDA receptors, were examined for ethanol consumption and acute ethanol withdrawal. Additionally, mice were examined for the level of vocalization following footshock, and behavior in an elevated plus maze, to determine their responses to stress. In these behavioral tests, NR1 heterozygous mice were shown to consume significantly higher levels of ethanol in the two bottle-choice test showing a possible role for this receptor in ethanol consumption. Analysis of acute withdrawal found that the heterozygous mice exhibit lower levels of handling-induced convulsions consistent with a role in ethanol sensitivity or withdrawal. In contrast, no effects on stress-related phenotypes were detected. Levels of NR2A–NR2D subunits of the NMDA receptor in specific brain regions were compared between NR1+/− mice and wild-type controls to assess whether the behavioral responses were specific to the diminution in NR1 expression or whether these changes could be due to secondary changes in expression of other NMDA subunits. Real-time quantitative PCR, Western blot and immunohistochemistry were used to examine expression levels in the hippocampus, neocortex, striatum and cerebellum. For the majority of the subunits, no differences were found between the wild-type and heterozygous mice in any of the brain regions. However, the NR2B subunit exhibited differences in expression of RNA in the hippocampus and protein levels in multiple brain regions, between wild-type and NR1+/− mice. These results show that NR1 plays a role, through mechanisms as yet unknown, in the expression of NR2 subunits in a region and subtype specific manner. This provides evidence of the effects of altered levels of NR1 expression on ethanol withdrawal and consumption, and suggests that concomitant changes in the levels of NR2B may contribute to that effect.

Molecular motor KIF17 is fundamental for memory and learning via differential support of synaptic NR2A/2B levels

Summary Kinesin superfamily motor protein 17 (KIF17) is a candidate transporter of N-methyl-D-aspartate (NMDA) receptor subunit 2B (NR2B). Disruption of the murine kif17 gene inhibits NR2B transport, accompanied by decreased transcription of nr2b , resulting in a loss of synaptic NR2B. In kif17 −/− hippocampal neurons, the NR2A level is also decreased because of accelerated ubiquitin-proteasome system-dependent degradation. Accordingly, NMDA receptor-mediated synaptic currents, early and late long-term potentiation, long-term depression, and CREB responses are attenuated in kif17 −/− neurons, concomitant with a hippocampus-dependent memory impairment in knockout mice. In wild-type neurons, CREB is activated by synaptic inputs, which increase the levels of KIF17 and NR2B. Thus, KIF17 differentially maintains the levels of NR2A and NR2B, and, when synapses are stimulated, the NR2B/KIF17 complex is upregulated on demand through CREB activity. These KIF17-based mechanisms for maintaining NR2A/2B levels could underlie multiple phases of memory processes in vivo.

Involvement of NMDA receptors in ryanodine receptor expression in dopaminergic neurons in the ventral tegmental area of mice with intermittent methamphetamine treatment

Excitatory synapses on dopaminergic neurons of the ventral tegmental area (VTA) represent an important role in psychostimulant-induced rewarding effect. This study investigated the regulation of ryanodine receptor (RyR) and N-methyl-D-aspartate (NMDA) receptor expression in mice under intermittent methamphetamine (METH) treatment using a place preference procedure. RyR-1 and -2 significantly increased in the VTA of mice with METH-induced place preference, whereas RyR-3 showed no changes. In addition, the levels of NR1, NR2A, and NR2B subunits were increased in the VTA. The METH-induced place preference was inhibited by intracerebroventricular pretreatment with MK-801, a noncompetitive NMDA receptor antagonist, and ifenprodil, a selective NR2B subunit-containing NMDA receptor antagonist, in a dose-dependent manner. Under these conditions, the increase of RyR-1 and -2 in the VTA was significantly blocked by ifenprodil. The immunohistochemical analysis revealed the colocalization of RyR-1 and -2 with NR2B subunits in dopaminergic neurons in the mouse VTA. These findings suggest that RyRs could be involved in the development of METH-induced place preference and that NR2B subunit-containing NMDA receptors in mice showing METH-induced place preference play an important role in expression of RyRs.

IQGAP1 Regulates NR2A Signaling, Spine Density, and Cognitive Processes

General or brain-region-specific decreases in spine number or morphology accompany major neuropsychiatric disorders. It is unclear, however, whether changes in spine density are specific for an individual mental process or disorder and, if so, which molecules confer such specificity. Here we identify the scaffolding protein IQGAP1 as a key regulator of dendritic spine number with a specific role in cognitive but not emotional or motivational processes. We show that IQGAP1 is an important component of NMDAR multiprotein complexes and functionally interacts with the NR2A subunits and the extracellular signal-regulated kinase 1 (ERK1) and ERK2 signaling pathway. Mice lacking the IQGAP1 gene exhibited significantly lower levels of surface NR2A and impaired ERK activity compared to their wild-type littermates. Accordingly, primary hippocampal cultures of IQGAP1(-/-) neurons exhibited reduced surface expression of NR2A and disrupted ERK signaling in response to NR2A-dependent NMDAR stimulation. These molecular changes were accompanied by region-specific reductions of dendritic spine density in key brain areas involved in cognition, emotion, and motivation. IQGAP1 knock-outs exhibited marked long-term memory deficits accompanied by impaired hippocampal long-term potentiation (LTP) in a weak cellular learning model; in contrast, LTP was unaffected when induced with stronger stimulation paradigms. Anxiety- and depression-like behavior remained intact. On the basis of these findings, we propose that a dysfunctional IQGAP1 gene contributes to the cognitive deficits in brain disorders characterized by fewer dendritic spines.

Reelin deficiency causes specific defects in the molecular composition of the synapses in the adult brain

The extracellular protein Reelin regulates radial neuronal migration in the embryonic brain, promotes dendrite outgrowth in the developing postnatal forebrain, and strengthens synaptic transmission in the adult brain. Heterozygous reeler mice expressing reduced levels of Reelin are grossly normal but exhibit behavioral and physiological abnormalities. We previously demonstrated that dendritic spine density is reduced in the developing hippocampus of these mice. In this study, we investigated the consequence of Reelin deficiency on synapse formation in adult heterozygous reeler mice using imaging and biochemical approaches. Using a reeler colony that expresses yellow fluorescent protein in selected neurons, we analyzed spine density in hippocampal area CA1 by confocal microscopy and found modest abnormalities in heterozygous reeler mice. However, biochemical analysis of synaptic composition revealed specific postsynaptic defects in scaffolding proteins, neurotransmitter receptors, and signaling proteins. Using whole brain homogenates and purified pre- and postsynaptic fractions, we found that the defects were localized to the postsynaptic compartment of heterozygous reeler synapses. Decreased levels of postsynaptic density-95 (PSD-95), the N-methyl d-aspartate (NMDA) receptor subunits NR2A and NR2B, and the phosphatase PTEN were found specifically in the postsynaptic density fraction obtained from these mice. Furthermore, we found that PSD-95, NR2A, and PTEN interact with each other at the synapse. Finally, we show that levels of NR2A are reduced in conditional Pten knock out mice, demonstrating that the PTEN phosphatase regulates NMDA receptor expression at the synapse in vivo. These studies may provide insights into the etiology of cognitive disorders associated with deficiencies in Reelin signaling and PTEN dysfunction.

Gestational nicotine exposure regulates expression of AMPA and NMDA receptors and their signaling apparatus in developing and adult rat hippocampus

Untimely activation of nicotinic acetylcholine receptors (nAChRs) by nicotine results in short- and long-term consequences on learning and behavior. In this study, the aim was to determine how prenatal nicotine exposure affects components of glutamatergic signaling in the hippocampus during postnatal development. We investigated regulation of both nAChRs and glutamate receptors for AMPA and N-methyl-D-aspartate (NMDA), from postnatal day 1 (P1) to P63 after a temporally restricted exposure to saline or nicotine for 14 days in utero. We analyzed postsynaptic density components associated with AMPA receptor (AMPAR) and NMDA receptor (NMDAR) signaling: calmodulin (CaM), CaM Kinase II alpha (CaMKIIα), and postsynaptic density-95 (PSD95), as well as presynaptically localized synaptosomal-associated protein 25 (SNAP25). At P1, there was significantly heightened expression of AMPAR subunit GluR1 but not GluR2, and of NMDAR subunits NR1, NR2a, and NR2d but not NR2b. NR2c was not detectable. CaM, CaMKIIα, and PSD95 were also significantly upregulated at P1, together with presynaptic SNAP25. This enhanced expression of glutamate receptors and signaling proteins was concomitant with elevated levels of [³H]epibatidine (³H]EB) binding in prenatal nicotine-exposed hippocampus, indicating that α4β2 nAChR may influence glutamatergic function in the hippocampus at P1. By P14, neither [³H]EB binding nor the expression levels of subunits GluR1, GluR2, NR1, NR2a, NR2b, NR2c, or NR2d seemed changed with prenatal nicotine. However, CaMKIIα was significantly upregulated with nicotine treatment while CaM showed downregulation at P14. The effects of nicotine persisted in P63 young adult brains which exhibited significantly downregulated GluR2, NR1, and NR2c expression levels in hippocampal homogenates and a considerably muted overall distribution of [³H]AMPA binding in areas CA1, CA2 and CA3, and the dentate gyrus. Our results suggest that prenatal nicotine exposure can regulate the glutamatergic signaling system throughout postnatal development by enhancing or inhibiting availability of AMPAR and NMDAR or their signaling components. The persistent depression, in adults, of the requisite NR1 subunit for NMDAR assembly, and of GluR2, important for assembly, trafficking, and biophysical properties of AMPAR, indicates that nicotine may alter ionotropic glutamate receptor stoichiometry and functional properties in adults after prenatally restricted nicotine exposure.

Effects of chronic oral treatment with aripiprazole on the expression of NMDA receptor subunits and binding sites in rat brain

The glutamatergic theory of schizophrenia proposes a dysfunction of ionotropic N-methyl-D: -aspartate receptors (NMDA-R). Several therapeutic strategies address NMDA-R function and the effects of antipsychotic agents on NMDA-R expression have been described. Within the second-generation antipsychotics, the partial dopaminergic and serotonergic agonist aripiprazole (APZ) was able to counteract the behavioral effects of NMDA-R antagonists. This study aims to investigate the effects of APZ on NMDA-R subunit expression and binding. We treated Sprague-Dawley rats for 4 weeks or 4 months with APZ in daily oral doses of 10 and 40 mg per kilogram of body weight. Gene expression of the NMDA-R subunits NR1, NR2A, NR2B, NR2C, and NR2D, respectively, was assessed by semiquantitative radioactive in situ hybridization and in parallel receptor binding using (3)H-MK-801 receptor autoradiography. Increased expression levels of NR1 (4 weeks), NR2A (4 weeks), NR2C (4 weeks and 4 months), and NR2D (4 months) were observed in several hippocampal and cortical brain regions. The parallel reduced expression of NR2B mRNAs (4 months) resulted in a relative increase of the NR2A/NR2B ratio. Marked differences between specific brain regions, the doses of APZ, and the time points of assessment became obvious. On the receptor level, increased MK-801-binding was found after 4 weeks in the 40-mg group and after 4 months in the 10-mg group. The effects of APZ converge in enhanced NMDA receptor expression and a shift of subunit composition towards adult-type receptors. Our results confirm the regulatory connections between dopaminergic, serotonergic, and glutamatergic neurotransmissions with relevance for cognitive and negative symptoms of schizophrenia.

Calorie restriction modulates hippocampal NMDA receptors in diet-induced obese rats

Calorie restriction (CR) has attracted increased interest since CR enhances lifespan and alters age-related decline in hippocampal-dependent cognitive functions. Obesity is associated with poor neurocognitive outcome including impaired hippocampal synaptic plasticity and cognitive abilities such as learning and memory. N-Methyl-d-aspartate receptors (NMDARs) are linked to hippocampal-dependent learning and memory, which may be stabilized by CR. In the present study, we aimed to establish the effects of CR on NMDARs in CA1 region of hippocampus in obese and non-obese rats. In addition, malondialdehyde (MDA) levels were determined as a marker for lipid peroxidation (LPO) in hippocampus. Four groups were constituted as control group (C, n = 9), obese group (OB, n = 10), obese calorie-restricted group (OCR, n = 9), and non-obese calorie-restricted group (NCR, n = 10). OCR and NCR were fed with a 60% CR diet for 10 weeks. After 10 weeks of CR, the MDA levels significantly decreased in the calorie-restricted groups. Obesity caused significant decreases in NR2A and NR2B subunit expressions in the hippocampus. The hippocampal NR2A and NR2B levels significantly increased in the OCR group compared with the OB group (P < 0.05). In contrast, the hippocampal NR2A and NR2B levels significantly decreased in the NCR group compared with the C group (P < 0.05). Oxidative stress can be prevented by CR, and these data may provide a molecular and cellular mechanism by which CR may regulate NMDAR-mediated response against obesity-induced changes in the hippocampus.

Molecular Motor KIF17 Is Fundamental for Memory and Learning via Differential Support of Synaptic NR2A/2B Levels

Kinesin superfamily motor protein 17 (KIF17) is a candidate transporter of N-methyl-D-aspartate (NMDA) receptor subunit 2B (NR2B). Disruption of the murine kif17 gene inhibits NR2B transport, accompanied by decreased transcription of nr2b, resulting in a loss of synaptic NR2B. In kif17(-/-) hippocampal neurons, the NR2A level is also decreased because of accelerated ubiquitin-proteasome system-dependent degradation. Accordingly, NMDA receptor-mediated synaptic currents, early and late long-term potentiation, long-term depression, and CREB responses are attenuated in kif17(-/-) neurons, concomitant with a hippocampus-dependent memory impairment in knockout mice. In wild-type neurons, CREB is activated by synaptic inputs, which increase the levels of KIF17 and NR2B. Thus, KIF17 differentially maintains the levels of NR2A and NR2B, and, when synapses are stimulated, the NR2B/KIF17 complex is upregulated on demand through CREB activity. These KIF17-based mechanisms for maintaining NR2A/2B levels could underlie multiple phases of memory processes invivo.

FC29-03 - Effects of chronic oral treatment with aripiprazole on expression of nmda receptor subunits and binding sites in rat brain

IntroductionThe glutamatergic theory of schizophrenia proposes a dysfunction of ionotropic N-Methyl-D-aspartate (NMDA)-receptors (NR). Several therapeutic strategies address NR function and effects of antipsychotic agents on NR expression have been described.ObjectivesThe partial dopaminergic and serotonergic agonist aripiprazole (APZ) was able to counteract behavioural effects of NR antagonists, but effects of APZ on NR expression have not been investigated.AimsTo evaluate effects of APZ on NR mRNA and protein expressionMethodsWe treated Sprague-Dawley rats for 4 weeks or 4 months with APZ in daily oral doses of 10 and 40 mg per kg body weight. Expression of the NR subunits NR1, NR2A, NR2B, NR2C and NR2D was assessed by semiquantitative radioactive in situ-hybridization, and in parallel receptor binding using 3H-MK-801 receptor autoradiography.ResultsIncreased expression levels of NR1 (4 weeks), NR2A (4 weeks), NR2C (4 weeks and 4 months) and NR2D (4 months) were observed in several hippocampal and cortical brain regions. The parallel reduced expression of NR2B mRNAs (4 months) resulted in a relative increase of the NR2A/NR2B ratio. Marked differences between specific brain regions, the doses and time points of assessment became obvious. On the receptor level, increased MK-801-binding was found after 4 weeks in the 40 mg-group and after 4 months in the 10 mg-group.ConclusionsThe effects of APZ converge in enhanced NMDA-receptor expression and a shift of subunit-composition towards adult-type receptors. Our results confirm regulatory connections between dopaminergic, serotonergic and glutamatergic neurotransmission with relevance for cognitive and negative symptoms of schizophrenia.

Dysbindin and Schizophrenia: It's Dopamine and Glutamate All Over Again

Dysbindin and Schizophrenia: It's Dopamine and Glutamate All Over Again