Elevated levels of the NR2C subunit of the NMDA receptor in the locus coeruleus in depression.

Low levels of the intracellular mediator of glutamate receptor activation, neuronal nitric oxide synthase (nNOS) were previously observed in locus coeruleus (LC) from subjects diagnosed with major depression. This finding implicates abnormalities in glutamate signaling in depression. Receptors responding to glutamate in the LC include ionotropic N-methyl-D-aspartate receptors (NMDARs). The functional NMDAR is a hetero-oligomeric structure composed of NR1 and NR2 (A-D) subunits. Tissue containing the LC and a nonlimbic LC projection area (cerebellum) was obtained from 13 and 9 matched pairs, respectively, of depressed subjects and control subjects lacking major psychiatric diagnoses. NMDAR subunit composition in the LC was evaluated in a psychiatrically normal subject. NR1 and NR2C subunit immunoreactivities in LC homogenates showed prominent bands at 120 and 135 kDa, respectively. In contrast to NRI and NR2C, very weak immunoreactivity of NR2A and NR2B subunits was observed in the LC. Possible changes in concentrations of NR1 and NR2C that might occur in depression were assessed in the LC and cerebellum. The overall amount of NR1 immunoreactivity was normal in the LC and cerebellum in depressed subjects. Amounts of NR2C protein were significantly higher (+ 61%, p = 0.003) in the LC and modestly, but not significantly, elevated in the cerebellum (+ 35%) of depressives as compared to matched controls. Higher levels of NR2C subunit implicate altered glutamatergic input to the LC in depressive disorders.     

Disruption of the NMDA receptor-PSD-95 interaction in hippocampal neurons with no obvious physiological short-term effect

PSD-95 binds to and co-localizes with NMDA receptors at postsynaptic sites. Their co-expression in COS7 cells induces the formation of aggregates containing both proteins. These findings have lead to the hypothesis that PSD-95 helps to cluster NMDA receptors at postsynaptic sites. In addition, PSD-95 binds various regulatory proteins including Src, Pyk2, SynGAP, and nNOS and may recruit signaling proteins to NMDA receptors. We tested whether synaptic transmission or plasticity was affected by acute dissociation of the PSD-95-NMDA receptor interaction with various peptides that bound to the first two PDZ domains of PSD-95 and its homologs and with antibodies directed against the very C-terminus of the NR2A and NR2B subunits of the NMDA receptor. Membrane-impermeable peptides injected via whole cell patch electrodes distributed within minutes throughout dendritic branches into spines in acute hippocampal slices and membrane-permeable peptides containing 11 arginine residues effectively accumulated in neurites in slices and primary hippocampal cultures. Neither peptides nor antibodies showed any effect on basal synaptic transmission or induction of long-term potentiation (LTP) in hippocampal slices. Pharmacologically isolated NMDA receptor activity was also not affected. However, the membrane-permeable peptide disrupted the NMDA receptor-PSD-95 interaction in slices as tested by immunoprecipitation and subsequent immunoblotting. These findings suggest that acute dissociation of PSD-95 and its homologs from the NMDA receptor and likely from other protein complexes does not result in any easily detectable physiological effects in hippocampal slices. However, we cannot exclude a role of PSD-95 in early events that lead to clustering of NMDA receptors or of other proteins including stargazin and AMPA receptors at postsynaptic sites nor do these experiments address the possibility of long-term changes in the slices. In fact, incubation of primary hippocampal cultures with the membrane-permeable peptide lead to a moderate decrease in the number of dendritic clusters of PSD-95 and NMDA receptors and their colocalization by 20-30%, suggesting some role of PSD-95 and its homologs in NMDA receptor clustering.     

Regulation of NMDA receptor function by Fyn-mediated tyrosine phosphorylation]

The ionnotropic glutamate receptor, N-methyl-D-aspartate (NMDA) receptor, is a prominent ligand-gated and voltage-gated ion channel in excitatory synaptic transmission in the mammalian central nervous system. The NMDA channel is also regulated by its phosphorylation. We have shown that an Src family kinase Fyn phosphorylates NR2A and NR2B subunits of the NMDA receptor. The phosphorylation events are facilitated by the presence of PSD-95, which is quite likely due to the complex formation of Fyn, PSD-95, and the NMDA receptor: Fyn interacts with PSD-95 and PSD-95 interacts with the NMDA receptor. We have identified tyrosine phosphorylation sites on NR2A and NR2B. A phosphorylation of one of the sites on NR2B (Tyr1472) is largely dependent on Fyn and is elevated upon the LTP induction of hippocampal CA1 neurons. The data suggest that Tyr-1472 phosphorylation of NR2B is important for synaptic plasticity. A phosphorylation of the other tyrosine residues of NR2A and NR2B would also be involved in brain development and function.     

MAGUK proteins: new targets for pharmacological intervention in the glutamatergic synapse

In the postsynaptic density of excitatory glutamatergic synapses, membrane associated guanylate kinase (MAGUK) proteins, such as Post-Synaptic Density 95 (PSD-95), organize ionotropic glutamate receptors and their associated signalling proteins regulating the strength of synaptic activity. Modifications of MAGUK proteins function in the glutamatergic synapse such as alterations of MAGUK proteins interaction with N-Methyl-D-Aspartate (NMDA) receptors regulatory subunits are common events in several neurodegenerative disorders. Thus, a better knowledge and understanding of MAGUK structure and function as well as of the molecular events regulating MAGUK-mediated interactions in the glutamatergic synapse could lead to the identification of new targets for pharmaceutical intervention for neurodegenerative diseases.     

Competitive binding of postsynaptic density 95 and Ca^2＋-calmodulin dependent protein kinase Ⅱ to N-methyl-D-aspartate receptor subunit 2B in rat brain

AIM: To investigate the interactions among postsynaptic density 95 (PSD-95), Ca^2 -calmodulin dependent protein kinase Ⅱα (CaMKⅡα), and N-methyl-D-aspartate receptor subunit 2B (NR2B) during ischemia and reperfusion in hippocampus of rats. METHODS: Brain ischemia was induced by four-vessel occlusion procedure in rats. Immunoprecipitation and immunoblotting were performed to study the interactions and phosphorylation of proteins. The association-dissociation of PSD-95 and CaMKⅡα to and from N-methyl-D-aspartate (NMDA) receptor induced by ischemia and reperfusion and the effects of 1-[N,O-bis-(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenyl-piperazine (KN-62, a selective inhibitor of CaMKⅡ) on these protein interactions were investigated. Coimmunoprecipitation and immunoblotting were performed for the studies of interactions among proteins. RESULTS: The alternations of the binding level of PSD-95 and CaMKⅡα to NR2B during ischemia and reperfusion demonstrated the negative correlation to each other. Pre-administration of KN62 through both cerebral ventricles inhibited the 10min ischemia-induced increase of the binding of PSD-95 to NR2B and, on the contrary, promoted the binding of CaMKⅡα to NR2B. CONCLUSION: PSD-95 competes with CaMKⅡ to bind to NR2B during ischemia and reperfusion in rat hippocampus.     

Protective effect of gan mai da zao decoction in unpredictable chronic mild stress-induced behavioral and biochemical alterations

Aim: Growing evidence indicates that the glutamatergic system, especially the abnormalities of glutamate and N-methyl-D-aspartate (NMDA) receptors contribute to the pathophysiology and possibly the pathogenesis of major depressive disorders. This study is to evaluate the effect of gan mai da zao (GMDZ) decoction on glutamate and NMDA receptor in unpredictable chronic mild stress (UCMS) rats.

Materials and methods: Sucrose preference test and open field test were used to estimate the depressive-like behaviors of UCMS rats. Glutamate levels and NMDA receptor subunits (NR1, NR2A and NR2B) in the frontal cortex and hippocampus were determined by HPLC-FLD and by western-blot respectively.

Results: 32 days UCMS induced depressive-like behaviors, increased glutamate concentration and decreased NMDA receptor subunits NR2A and NR2B in the frontal cortex and hippocampus of rats. However, NR1 expression remained constant in stressed rats compared with normal. The GMDZ decoction alleviated the depressive-like behavior, decreased glutamate level, and increased expression of NMDA receptor subunit NR2A and NR2B in the frontal cortex and hippocampus of stressed rats.

Conclusions: These results suggest that GMDZ treatment reversed chronic unpredictable stress-induced depressive-like behaviors in UCMS rats, possibly via reducing glutamate levels and increasing the NMDA receptor subunits NR2A and NR2B in frontal cortex and hippocampus.     

Glutamate in CNS disorders as a target for drug development: an update

The authors provide an extensive review of new data related to the role of glutamate in CNS disorders, describing new aspects in glutamate and glutamatergic receptors-NMDA receptors, NR2B-selective antagonists, non-NMDA ionotropic glutamate receptors, N-acetylaspartylglutamate, and glutamate and glycine transporters. New findings in animal models and in human diseases-stroke, traumatic brain injury, Alzheimer's, Parkinson's and Huntington's diseases, tardive dyskinesia, ALS, olivopontcerebellar degeneration, AIDS, allergic encephalomyelitis, epilepsy, anxiety, depression, schizophrenia, liver disease, aminoglycoside antibiotic-induced hearing loss, hemiplegia, chronic pain and drug tolerance and abuse-are presented. Finally, the authors cite the progress achieved in the development of agents that interact with the glutamatergic system: NMDA channel blockers, competitive NMDA receptor antagonists, NR2B-selective antagonists, glutamate release inhibitors, glycineB antagonists, AMPA and kainate receptor antagonists, AMPA receptor-positive modulators and agents that act by modifying endogenous kynurenic acid metabolism.     

Requirement of PSD-95 for dopamine D1 receptor modulating glutamate NR1a/NR2B receptor function

Aim： To elucidate the role of scaffold protein postsynaptic density （PSD）-95 in the dopamine D1 receptor （D~R）-modulated NRla/NR2B receptor response. Methods： The human embryonic kidney 293 ceils expressing D1R （tagged with the enhanced yellow fluorescent protein） and NRla/NR2B with or without co-expres- sion of PSD-95 were used in the experiments. The Ca^2＋ influx measured by imaging technique was employed to monitor N-methyl-D-aspartic acid receptors （NMDAR） function. Results： The application of dopamine （DA, 100 μmol/L） did not alter glutamate/glycine （Glu/Gly）-induced NMDAR-mediated Ca^2＋ influx in cells only expressing the D1R/NRla/NR2B receptor. However, DA increased Glu/Glyinduced Ca^2＋ influx in a concentration-dependent manner while the cells were co-expressed with PSD-95. D1R-stimulated Ca^2＋ influx was inhibited by a selective D1R antagonist SCH23390. Moreover, pre-incubation with either the protein kinase A （PKA） inhibitor H89, or the protein kinase C （PKC） inhibitor chelerythrine attenuated D1R-enhanced Ca^2＋ influx induced by the N-methyl-D-aspartic acid （NMDA） agonist. The results clearly indicate that D1R-modulated NRla/NR2B receptor function depends on PSD-95 and is subjected to the regulation of PKA and PKC. Conclusion： The present study provides the first evidence that PSD-95 is essential in D1R-regulated NRla/NR2B receptor function.     

Protection from kainic acid neuropathological syndrome by NMDA receptor antagonists: effect of MK-801 and CGP 39551 on neurotransmitter and glial markers.

Systemic administration of kainic acid results in the development of a characteristic convulsive syndrome, accompanied by neuropathological alterations and loss of transmitter markers in some forebrain regions. Since some of these effects appear to involve the N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid receptors, the protection given by a non-competitive (MK-801) and a competitive (CGP 39551) NMDA receptor antagonist against the loss of glutamatergic and gamma-amino butyric acid (GABAergic) neurochemical markers was compared. Appropriate doses of both compounds (1 mg/kg MK-801 and 25 mg/kg CGP 39551) completely reversed the decrease of high affinity uptake of glutamate and activity of glutamate decarboxylase in the olfactory cortex, amygdala, hippocampus and lateral septum. In addition, they also essentially counteracted the increase of a glial marker, the enzyme glutamine synthetase, consequent to neuronal degeneration. The results confirmed that involvement of NMDA receptors is essential for the full expression of neuropathological effects of kainic acid. They also support the use of a competitive antagonist of the NMDA receptor, such as CGP 39551, to afford substantial protection against the excitotoxic damage, whilst giving fewer side effects and motor disturbances than MK-801.     

Functional Uncoupling NMDAR NR2A Subunit from PSD-95 in the Prefrontal Cortex: Effects on Behavioral Dysfunction and Parvalbumin Loss after Early-Life Stress

Exposure to early-life stress increases vulnerability to psychiatric disorders, including depression, schizophrenia, and anxiety. Growing evidence implicates aberrant development of the prefrontal cortex (PFC) in the effects of early-life stress, which often emerge in adolescence or young adulthood. Specifically, early-life stress in the form of maternal separation (MS) in rodents has been shown to decrease parvalbumin (PVB)-positive interneurons in the adolescent PFC; however, the mechanism underpinning behavioral dysfunction and PVB loss is not yet known. We recently reported that MS causes overexpression of the NMDA subunit NR2A in the PFC of adolescent rats. Elevated PFC NR2A is also found in developmental models of schizophrenia and is correlated with behavioral deficits, acting largely through its association with the postsynaptic protein PSD-95. In addition, adolescent maturation of PVB-positive interneurons relies on NR2A-driven NMDA activity. Therefore, it is possible that the NR2A/PSD-95 signaling complex has a role in adolescent MS effects. Here, we aimed to determine whether a discrete manipulation of PFC NR2A could prevent MS effects on PFC-controlled behaviors, including cognition, anxiety, and novelty-induced hyperlocomotion, as well as PVB loss in adolescence. We intracranially infused the NR2A-specific blocking peptide TAT2A in order to uncouple NR2A from PSD-95 in the early-adolescent PFC, without antagonizing the NMDA receptor. We demonstrated that MS rats treated with TAT2A during early adolescence were protected from MS-induced PVB loss and exhibited less anxious behavior than those infused with control peptide. These data implicate NR2A-related N-methyl-D-aspartate receptor development in adolescent behavioral and neural consequences of early-life stress.     

Dynamic regulation of glutamatergic postsynaptic activity in rat prefrontal cortex by repeated administration of antipsychotic drugs

Antipsychotics are the mainstay for the treatment of schizophrenia. Although these drugs act at several neurotransmitter receptors, they are expected to elicit different neuroadaptive changes at structures relevant for schizophrenia. Because glutamatergic dysfunction plays a role in the pathophysiology of schizophrenia, we focused our analysis on glutamatergic neurotransmission after repeated treatment with antipsychotic drugs. Rats were exposed to a 2-week pharmacological treatment with the first generation antipsychotic haloperidol and the second generation antipsychotic olanzapine. By using Western blot and immunoprecipitation techniques, we investigated the expression, trafficking, and interaction of essential components of glutamatergic synapse in rat prefrontal cortex. Prolonged treatment with haloperidol, but not olanzapine, dynamically affects glutamatergic synapse by selectively reducing the synaptic level of the obligatory N-methyl-d-aspartate (NMDA) subunit NR1, the regulatory NMDA subunit NR2A, and its scaffolding protein postsynaptic density 95 as well as the trafficking of subunit 1 of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor to the membrane. In addition, haloperidol alters total as well as phosphorylated levels of calcium calmodulin kinase type II at synaptic sites and its interaction with the regulatory NMDA subunit NR2B. Our data suggest that the glutamatergic synapse is a vulnerable target for prolonged haloperidol treatment. The global attenuation of glutamatergic function in prefrontal cortex might explain, at least in part, the cognitive deterioration observed in patients treated with haloperidol.     

Pathophysiological implications of the structural organization of the excitatory synapse.

The glutamatergic synapse is the key structure in the development of activity-dependent synaptic plasticity in the central nervous system. The analysis of the complex biochemical mechanisms at the basis of the long-term changes in synaptic efficacy have received a tremendous impulse by the observation that the post-synaptic constituents of the synapse can be separated and purified through a simple procedure involving detergent treatment of synaptosomes and differential centrifugation. In this fraction, called post-synaptic density (PSD), the functional interactions of its constituents are preserved. The various subunits of ionotropic glutamate receptors are held in register with the presynaptic active zone through their interaction with linker proteins. N-methyl-D-aspartate (NMDA) subunits NR2A and NR2B, bind to the PSD protein called PSD-95, which in turn binds neuroligins, providing a handle for interacting with neurexin, located in the plasma membrane at the presynaptic active zone. Additional clustering of NMDA receptors is provided through the binding of NRI subunits to the cytoskeletal protein alpha-actinin-2. AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and kainate receptors are other important constituents of PSDs and bind to different anchoring proteins. Phosphorylation processes have long been known to modulate NMDA receptor functional activity: the finding that several protein kinases, particularly Ca2+/Calmodulin-dependent protein kinase II and protein tyrosine kinases of the src family, are major constituents of PSDs has allowed to demonstrate that these enzymes are localized in a strategic position of the glutamatergic synapse, so that their activation provides a means for NMDA receptor function regulation upon its activation. The relevance of these mechanisms has been demonstrated in experimental models of pathologies involving deficits in synaptic plasticity, such as in streptozotocin-induced diabetes and in an animal model of prenatal induced ablation of hippocampal neurons. Both animal models display disturbances in long-term potentiation and cognitive deficits, thus providing in vivo models to study pathology related changes in both the structure and the function of the excitatory synapse.     

GHB-Induced Cognitive Deficits During Adolescence and the Role of NMDA Receptor

We have earlier reported that γ-hydroxybutyric acid (GHB) disrupts the acquisition of spatial learning and memory in adolescent rats. GHB is known to interact with several neurotransmitter systems that have been implicated in cognitive functioning. The N-methyl-D-aspartate receptor (NR) -type of glutamate receptor is considered to be an important target for spatial learning and memory. Molecular mechanisms governing the neuroadptations following repeated GHB treatment in adolecent rats remain unknown. We examined the role of NMDA receptor in adolescent GHB-induced cognitive deficit. Adolescent rats were administered with GHB on 6 consecutive days, and surface-expressed NMDA receptor subunits levels were measured. GHB significantly decreased NR1 levels in the frontal cortex. Adolescent GHB also significantly reduced cortical NR2A subunit levels. Our findings support the hypothesis that adolescent GHB-induced cogntive deficits are associated with neuroadaptations in glutamatergic transmission, particulaly NR functioning in the frontal cortex.     

Opiate physical dependence and N-methyl-d-aspartate receptors

The present review focused the involvement of N-methyl-d-aspartate (NMDA) receptors in morphine physical dependence. The increased levels of extracellular glutamate, NMDA receptor ζ subunit (NR1) mRNA, NMDA receptor 1 subunit (NR2A) protein, phosphorylated Ca²⁺/calmodulin kinase II (p-CaMKII) protein, c-fos mRNA, c-Fos protein, are observed in the specific brain areas of mice and/or rats showing signs of naloxone-precipitated withdrawal. In preclinical and clinical studies, a variety of NMDA receptor antagonists and pretreatment with an antisense oligonucleotide of the NR1 have been reported to inhibit the development, expression and/or maintenance of opiate physical dependence. In contrast to data obtained in adult animals, NMDA receptor antagonists are neither effective in blocking the development of opiate dependence nor the expression of opiate withdrawal in neonatal rats. In the NMDA receptor-deficient mice, the NR2A knockout mice show the marked loss of typical withdrawal abstinence behaviors precipitated by naloxone. The rescue of NR2A protein by electroporation into the nucleus accumbens of NR2A knockout mice reverses the loss of abstinence behaviors. The activation of CaMKII and increased expression of c-Fos protein in the brain of animals with naloxone-precipitated withdrawal syndrome are prevented by NMDA receptor antagonists, whereas the increased levels of extracellular glutamate are not prevented by them. These findings indicate that glutamatergic neurotransmission at the NMDA receptor site contributes to the development, expression and maintenance of opiate dependence, and suggest that NMDA receptor antagonists may be a useful adjunct in the treatment of opiate dependence.     

Glutamate receptor subunits are altered in forebrain and cerebellum in rats chronically exposed to the NMDA receptor antagonist phencyclidine.

Phencyclidine (PCP) is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) glutamate receptor subtype. It produces transient psychoses in normal individuals and exacerbates psychoses in schizophrenics. When administered to rodents, PCP elicits stereotypic behaviors including unrelenting head swaying, hyperlocomotion, and social withdrawal. In this study, we examined the relative distribution of the NMDA receptor subunits, as well as the subunits of its modulating receptor, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) in the forebrain, hippocampus, and cerebellum of rats chronically exposed to PCP. Rats were injected for 30 days with PCP (10 mg/kg) and age/sex-matched controls were injected for 30 days with saline vehicle. Brain NMDA and AMPA receptor subunit distribution patterns and protein levels were then analyzed by immunocytochemistry and Western blot analysis. Chronic PCP-treated animals showed significant alterations in glutamate receptor subunits, particularly for the NR1, NR2B, NR2C, and NR2D components of the NMDA receptor. AMPA receptor subunits demonstrated few significant changes in subunit availabilities. Western blot analysis largely confirmed the immunocytochemical findings. These results support the conclusion that subunits of the NMDA receptor are selectively altered by chronic PCP antagonism, with minimal to no changes observed in AMPA receptor subunits. Our findings are consistent with the interpretation that a dysfunctional NMDA receptor complex may mediate abnormal glutamatergic neurotransmission and potentially contribute to the complex etiology of cognitive disorders.     

Opiate physical dependence and N-methyl-D-aspartate receptors

The present review focused the involvement of N-methyl-D-aspartate (NMDA) receptors in morphine physical dependence. The increased levels of extracellular glutamate, NMDA receptor zeta subunit (NR1) mRNA, NMDA receptor epsilon 1 subunit (NR2A) protein, phosphorylated Ca(2+)/calmodulin kinase II (p-CaMKII) protein, c-fos mRNA, c-Fos protein, are observed in the specific brain areas of mice and/or rats showing signs of naloxone-precipitated withdrawal. In preclinical and clinical studies, a variety of NMDA receptor antagonists and pretreatment with an antisense oligonucleotide of the NR1 have been reported to inhibit the development, expression and/or maintenance of opiate physical dependence. In contrast to data obtained in adult animals, NMDA receptor antagonists are neither effective in blocking the development of opiate dependence nor the expression of opiate withdrawal in neonatal rats. In the NMDA receptor-deficient mice, the NR2A knockout mice show the marked loss of typical withdrawal abstinence behaviors precipitated by naloxone. The rescue of NR2A protein by electroporation into the nucleus accumbens of NR2A knockout mice reverses the loss of abstinence behaviors. The activation of CaMKII and increased expression of c-Fos protein in the brain of animals with naloxone-precipitated withdrawal syndrome are prevented by NMDA receptor antagonists, whereas the increased levels of extracellular glutamate are not prevented by them. These findings indicate that glutamatergic neurotransmission at the NMDA receptor site contributes to the development, expression and maintenance of opiate dependence, and suggest that NMDA receptor antagonists may be a useful adjunct in the treatment of opiate dependence.     

Uncompetitive antagonists of the N-methyl-D-aspartate (NMDA) receptors alter the mRNA expression of proteins associated with the NMDA receptor complex

N-methyl-D-aspartate (NMDA) receptor function appears to be under complex control during physiological and pharmacological states. We have investigated the effects of acute administration of uncompetitive NMDA receptor antagonists on mRNA levels of NMDA receptor subunits and on molecules known to cluster or phosphorylate the receptor utilizing in situ hybridization on rat brain sections. A high dose (5 mg/kg; 4 hr) of dizocilpine (MK-801) decreased mRNA levels of NMDA receptor subunits NR2C and NR2B in the entorhinal and parietal cortices, respectively. MK-801 increased mRNA levels of synapse-associated protein-90/postsynaptic density-95 (SAP90/PSD-95) and a gamma-isoform of protein kinase C (PKCgamma) in cortical regions. Synapse-associated protein-97 (SAP97) mRNA levels were increased in the entorhinal cortex layer III after MK-801 or after relatively high doses of other uncompetitive NMDA receptor antagonists: phencyclidine (15 mg/kg; 6 hr) and memantine (50 mg/kg; 6 hr). Memantine also increased SAP97 mRNA expression in other cortical regions, but this effect was not observed with MK-801 or phencyclidine. NMDA receptor uncompetitive antagonists alter the expression of multiple receptor components and such events may ultimately play a role in adaptation or toxic responses.     

Acute and chronic effects of MDMA on molecular mechanisms implicated in memory formation in rat hippocampus: surface expression of CaMKII and NMDA receptor subunits

Acute 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") treatment induces learning deficits in different animal models. In a passive avoidance learning task in rats, previous studies suggested a role for Ca2+/calmodulin-dependent protein kinase II (CaMKII) and N-methyl-D-aspartate (NMDA) receptors in the acute learning impairment. As cognitive deficits by "ecstasy" in humans have been only reported in frequent recreational users, we examined whether a repeated MDMA treatment could induce in rats lasting molecular changes related to memory consolidation of passive avoidance. In rats with a pronounced 5-HT depletion by MDMA, the effect of another drug challenge was also examined. The surface expression in the hippocampus of NMDA receptor subunits, the scaffolding postsynaptic density protein PSD-95, phosphorylated CaMKII and protein phosphatase 1 (PP1) was measured. In rats repeatedly treated with MDMA (10 mg/kg) twice daily for 4 consecutive days, hippocampal 5-HT levels were markedly reduced 1 week later. At this time, neither learning performance was affected nor changes in membrane levels of NMDA receptor subunits, PSD-95, CaMKII and PP1 were found. In these rats, however, another drug challenge produced a rapid reduction in PSD-95 immunoreactivity and prevented the learning-specific increase in the NMDA receptor NR1 subunit and phosphorylated CaMKII. The results show no lasting change in learning-associated molecular events after a neurotoxic MDMA treatment. This drug only produces transient effects on early molecular events involved in memory consolidation, which do not appear to depend on endogenous 5-HT levels.