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1.
NMDA receptors (NMDARs) are glutamate-gated ion channels involved in excitatory synaptic transmission and in others physiological processes such as synaptic plasticity and development. The overload of Ca 2+ ions through NMDARs, caused by an excessive activation of receptors, leads to excitotoxic neuronal cell death. For this reason, the reduction of Ca 2+ flux through NMDARs has been a central focus in finding therapeutic strategies to prevent neuronal cell damage.Extracellular H + are allosteric modulators of NMDARs. Starting from previous studies showing that extracellular mild acidosis reduces NMDA-evoked whole cell currents, we analyzed the effects of this condition on the NMDARs Ca 2+ permeability, measured as “fractional calcium current” (P f, i.e. the percentage of the total current carried by Ca 2+ ions), of human NMDARs NR1/NR2A and NR1/NR2B transiently transfected in HeLa cells. Extracellular mild acidosis significantly reduces P f of both human NR1/NR2A and NR1/NR2B NMDARs, also decreasing single channel conductance in outside out patches for NR1/NR2A receptor. Reduction of Ca 2+ flux through NMDARs was also confirmed in cortical neurons in culture. A comparative analysis of both NMDA evoked Ca 2+ transients and whole cell currents showed that extracellular H + differentially modulate the permeation of Na + and Ca 2+ through NMDARs.Our data highlight the synergy of two distinct neuroprotective mechanisms during acidosis: Ca 2+ entry through NMDARs is lowered due to the modulation of both open probability and Ca 2+ permeability. Furthermore, this study provides the proof of concept that it is possible to reduce Ca 2+ overload in neurons modulating the NMDAR Ca 2+ permeability. 相似文献
2.
In the presence of glutamate and co-agonists, e.g., glycine, the N-methyl-D-aspartate receptor (NMDAR) plays an important role in physiological and pathophysiological brain processes. Previous studies indicate glycine could inhibit NMDAR responses induced by high concentration of NMDA in hippocampal neurons. The mechanism underlying this inhibitory impact, however, has been unclear. In this study, the whole-cell patch-clamp recording and Ca 2+ imaging with Fluo-3/AM under laser scanning confocal microscope were used to analyze the possible involvement of NMDAR subunits in this effect. We found that the peak current of NMDARs and Ca 2+ influx induced by high concentration of NMDA were reduced by treatment of glycine (0.03?C10 ??mol L ?1) in a dose-dependent manner, and that the glycine-dependent inhibition of NMDAR responses, which were induced at 300 ??mol L ?1 NMDA, was reversed by ZnCl 2 through the blocking of the NR2A subunit of NMDARs, but was less influenced by ifenprodil, a NR2B inhibitor. Our results suggest that the glycine-dependent inactivation of NMDARs is potentially modulated by the regulatory subunit NR2A. 相似文献
3.
Methylmercury (MeHg) is an extremely dangerous environmental pollutant that induces severe toxic effects in the central nervous system. Neuronal damage plays critical roles mediating MeHg-induced loss of brain function and neurotoxicity. The molecular mechanisms of MeHg neurotoxicity are incompletely understood. The objective of the study is to explore mechanisms that contribute to MeHg-induced neurocyte injuries focusing on neuronal Ca 2+ dyshomeostasis and alteration of N-methyl-D-aspartate receptors (NMDARs) expression, as well as oxidative stress in primary cultured cortical neurons. In addition, the neuroprotective effects of memantine against MeHg cytotoxicity were also investigated. The cortical neurons were exposed to 0, 0.01, 0.1, 1, or 2 μM methylmercury chloride (MeHgCl) for 0.5–12 h, or pre-treated with 2.5, 5, 10, or 20 μM memantine for 0.5–6 h, respectively; cell viability and LDH release were then quantified. For further experiments, 2.5, 5, and 10 μM of memantine pre-treatment for 3 h followed by 1 μM MeHgCl for 6 h were performed for evaluation of neuronal injuries, specifically addressing apoptosis; intracellular free Ca 2+ concentrations; ATPase activities; calpain activities; expressions of NMDAR subunits (NR1, NR2A, NR2B); NPSH levels; and ROS formation. Exposure of MeHgCl resulted in toxicity of cortical neurons, which were shown as a loss of cell viability, high levels of LDH release, morphological changes, and cell apoptosis. Moreover, intracellular Ca 2+ dyshomeostasis, ATPase activities inhibition, calpain activities, and NMDARs expression alteration were observed with 1 μM MeHgCl administration. Last but not least, NPSH depletion and reactive oxygen species (ROS) overproduction showed an obvious oxidative stress in neurons. However, memantine pre-treatment dose-dependently antagonized MeHg-induced neuronal toxic effects, apoptosis, Ca 2+ dyshomeostasis, NMDARs expression alteration, and oxidative stress. In conclusion, the cytoprotective effects of memantine against MeHg appeared to be mediated not only via its NMDAR binding properties and Ca 2+ homeostasis maintenance but also by indirect antioxidation effects. 相似文献
4.
Abstract: P19 embryonic carcinoma (EC) stem cells are pluripotent and are efficiently induced to differentiate into neurons and glia with retinoic acid (RA) treatment. Within 5 days, a substantial number of differentiating P19 cells express gene products that are characteristic of a neuronal phenotype. P19 neurons were used as a model to explore the relationship between neuronal “differentiation” in vitro and the acquisition of γ-aminobutyric acid (GABA A) receptors and functional GABA responses. Pulse-labeling experiments using bromodeoxyuridine indicated that all neurons had become postmitotic within 3–4 days after treatment with RA. This was confirmed by a reduction in the immunocytochemical detection of the undifferentiated stem cell antigen SSEA-1. Subsequently, a transient expression of nestin was observed during the first 5 days in vitro (DIV) after exposure to RA. By 5–10 DIV after RA, a significant number of neurons (~80–90%) expressed immunocytochemically detectable glutamate decarboxylase and GABA coincident with the acquisition of membrane binding sites for tetanus toxin. These phenotypic markers were maintained for >30 DIV after RA. Under current-clamp conditions, random, low-amplitude, spontaneous electrical activity appeared in neurons within the first few days after RA treatment and this was blocked by the specific GABA A receptor antagonist bicuculline. Thereafter, the appearance and progressive increases in the frequency of spontaneous action potentials in P19 neurons were observed that were similarly attenuated by bicuculline. In neurons > 5 DIV after RA, exogenous application of GABA elicited similar action potentials. The onset of excitatory responses to GABA or muscimol in voltage-clamped neurons appeared immediately after the cessation of neuronal mitosis and before the previously reported acquisition of responses to glutamate. In fura-2 imaging studies, the exogenous application of GABA resulted in neuron-specific increases in intracellular Ca 2+. Thus, P19 neurons provide an in vitro model for the study of the early acquisition and properties of electrical excitability to GABA and the expression of functional GABA A receptors. 相似文献
5.
Primary lens epithelial cell (LEC) cultures derived from newborn (P0) and one-month-old (P30) mouse lenses were used to study GABA (gamma-aminobutyric acid) signaling expression and its effect on the intracellular Ca 2+ ([Ca 2+] i) level. We have found that these cultures express specific cellular markers for lens epithelial and fiber cells, all components of the functional GABA signaling pathway and GABA, thus recapitulating the developmental program of the ocular lens. Activation of both GABA-A and GABA-B receptors (GABA AR and GABA BR) with the specific agonists muscimol and baclofen, respectively induces [Ca 2+] i transients that could be blocked by the specific antagonists bicuculline and CGP55845 and were dependent on extracellular Ca 2+. Bicuculline did not change the GABA-evoked Ca 2+ responses in Ca 2-containing buffers, but suppressed them significantly in Ca 2+-free buffers suggesting the two receptors couple to convergent Ca 2+ mobilization mechanisms with different extracellular Ca 2+ sensitivity. Prolonged activation of GABA BR induced wave propagation of the Ca 2+ signal and persistent oscillations. The number of cells reacting to GABA or GABA + bicuculline in P30 mouse LEC cultures expressing predominantly the synaptic type GABA AR did not differ significantly from the number of reacting cells in P0 mouse LEC cultures. The GABA-induced Ca 2+ transients in P30 (but not P0) mouse LEC could be entirely suppressed by co-application of bicuculline and CGP55845. The GABA-mediated Ca 2+ signaling may be involved in a variety of Ca 2+-dependent cellular processes during lens growth and epithelial cell differentiation. 相似文献
6.
Cell adhesion molecules (CAMs) play indispensable roles in the developing and mature brain by regulating neuronal migration and differentiation, neurite outgrowth, axonal fasciculation, synapse formation and synaptic plasticity. CAM-mediated changes in neuronal behavior depend on a number of intracellular signaling cascades including changes in various second messengers, among which CAM-dependent changes in intracellular Ca 2+ levels play a prominent role. Ca 2+ is an essential secondary intracellular signaling molecule that regulates fundamental cellular functions in various cell types, including neurons. We present a systematic review of the studies reporting changes in intracellular Ca 2+ levels in response to activation of the immunoglobulin superfamily CAMs, cadherins and integrins in neurons. We also analyze current experimental evidence on the Ca 2+ sources and channels involved in intracellular Ca 2+ increases mediated by CAMs of these families, and systematically review the role of the voltage-dependent Ca 2+ channels (VDCCs) in neurite outgrowth induced by activation of these CAMs. Molecular mechanisms linking CAMs to VDCCs and intracellular Ca 2+ stores in neurons are discussed. 相似文献
7.
Inhibitory GABA B receptors (GABA BRs) can down-regulate most excitatory synapses in the CNS by reducing postsynaptic excitability. Functional GABA BRs are heterodimers of GABA B1 and GABA B2 subunits and here we show that the trafficking and surface expression of GABA BRs is differentially regulated by synaptic or pathophysiological activation of NMDA receptors (NMDARs). Activation of synaptic NMDARs using a chemLTP protocol increases GABA BR recycling and surface expression. In contrast, excitotoxic global activation of synaptic and extrasynaptic NMDARs by bath application of NMDA causes the loss of surface GABA BRs. Intriguingly, exposing neurons to extreme metabolic stress using oxygen/glucose deprivation (OGD) increases GABA B1 but decreases GABA B2 surface expression. The increase in surface GABA B1 involves enhanced recycling and is blocked by the NMDAR antagonist AP5. The decrease in surface GABA B2 is also blocked by AP5 and by inhibiting degradation pathways. These results indicate that NMDAR activity is critical in GABA BR trafficking and function and that the individual subunits can be separately controlled to regulate neuronal responsiveness and survival. 相似文献
8.
D 1- and D 2-types of dopamine receptors are located separately in direct and indirect pathway striatal projection neurons (dSPNs and iSPNs). In comparison, adenosine A 1-type receptors are located in both neuron classes, and adenosine A 2A-type receptors show a preferential expression in iSPNs. Due to their importance for neuronal excitability, Ca 2+-currents have been used as final effectors to see the function of signaling cascades associated with different G protein-coupled receptors. For example, among many other actions, D 1-type receptors increase, while D 2-type receptors decrease neuronal excitability by either enhancing or reducing, respectively, Ca V1 Ca 2+-currents. These actions occur separately in dSPNs and iSPNs. In the case of purinergic signaling, the actions of A 1- and A 2A-receptors have not been compared observing their actions on Ca 2+-channels of SPNs as final effectors. Our hypotheses are that modulation of Ca 2+-currents by A 1-receptors occurs in both dSPNs and iSPNs. In contrast, iSPNs would exhibit modulation by both A 1- and A 2A-receptors. We demonstrate that A 1-type receptors reduced Ca 2+-currents in all SPNs tested. However, A 2A-type receptors enhanced Ca 2+-currents only in half tested neurons. Intriguingly, to observe the actions of A 2A-type receptors, occupation of A 1-type receptors had to occur first. However, A 1-receptors decreased Ca V2 Ca 2+-currents, while A 2A-type receptors enhanced current through Ca V1 channels. Because these channels have opposing actions on cell discharge, these differences explain in part why iSPNs may be more excitable than dSPNs. It is demonstrated that intrinsic voltage-gated currents expressed in SPNs are effectors of purinergic signaling that therefore play a role in excitability. 相似文献
9.
N-methyl-D-aspartate receptors (NMDARs), critical mediators of both physiologic and pathologic neurological signaling, have previously been shown to be sensitive to mechanical stretch through the loss of its native Mg(2+) block. However, the regulation of this mechanosensitivity has yet to be further explored. Furthermore, as it has become apparent that NMDAR-mediated signaling is dependent on specific NMDAR subtypes, as governed by the identity of the NR2 subunit, a crucial unanswered question is the role of subunit composition in observed NMDAR mechanosensitivity. Here, we used a recombinant system to assess the mechanosensitivity of specific subtypes and demonstrate that the mechanosensitive property is uniquely governed by the NR2B subunit. NR1/NR2B NMDARs displayed significant stretch sensitivity, whereas NR1/NR2A NMDARs did not respond to stretch. Furthermore, NR2B mechanosensitivity was regulated by PKC activity, because PKC inhibition reduced stretch responses in transfected HEK 293 cells and primary cortical neurons. Finally, using NR2B point mutations, we identified a PKC phosphorylation site, Ser-1323 on NR2B, as a unique critical regulator of stretch sensitivity. These data suggest that the selective mechanosensitivity of NR2B can significantly impact neuronal response to traumatic brain injury and illustrate that the mechanical tone of the neuron can be dynamically regulated by PKC activity. 相似文献
10.
Neuronal ion channels of different types often do not function independently but will inhibit or potentiate the activity of
other types of channels, a process called cross-talk. The N-methyl- D-aspartate receptor (NMDA receptor) and the γ-aminobutyric acid type A receptor (GABA A receptor) are important excitatory and inhibitory receptors in the central nervous system, respectively. Currently, cross-talk
between the NMDA receptor and the GABA A receptor, particularly in the central auditory system, is not well understood. In the present study, we investigated functional
interactions between the NMDA receptor and the GABA A receptor using whole-cell patch-clamp techniques in cultured neurons from the inferior colliculus, which is an important
nucleus in the central auditory system. We found that the currents induced by aspartate at 100 μmol L −1 were suppressed by the pre-perfusion of GABA at 100 μmol L −1, indicating cross-inhibition of NMDA receptors by activation of GABA A receptors. Moreover, we found that the currents induced by GABA at 100 μmol L −1 ( I
GABA) were not suppressed by the pre-perfusion of 100 μmol L −1 aspartate, but those induced by GABA at 3 μmol L −1 were suppressed, indicating concentration-dependent cross-inhibition of GABA A receptors by activation of NMDA receptors. In addition, inhibition of IGABA by aspartate was not affected by blockade of voltage-dependent Ca 2+ channels with CdCl 2 in a solution that contained Ca 2+, however, CdCl 2 effectively attenuated the inhibition of I
GABA by aspartate when it was perfused in a solution that contained Ba 2+ instead of Ca 2+ or a solution that contained Ca 2+ and 10 mmol L −1 BAPTA, a membrane-permeable Ca 2+ chelator, suggesting that this inhibition is mediated by Ca 2+ influx through NMDA receptors, rather than voltage-dependent Ca 2+ channels. Finally, KN-62, a potent inhibitor of Ca 2+/calmodulin-dependent protein kinase II (CaMKII), reduced the inhibition of I
GABA by aspartate, indicating the involvement of CaMKII in this cross-inhibition. Our study demonstrates a functional interaction
between NMDA and GABA A receptors in the inferior colliculus of rats. The presence of cross-talk between these receptors suggests that the mechanisms
underlying information processing in the central auditory system may be more complex than previously believed. 相似文献
11.
NMDA receptors (NMDARs) play a pivotal role in the regulation of neuronal communication and synaptic function in the central nervous system. The subunit composition and compartmental localization of NMDARs in neurons affect channel activity and downstream signaling. This review discusses the distinct NMDAR subtypes and their function at synaptic, perisynaptic, and extrasynaptic sites of excitatory and inhibitory neurons. Many neurons express more than one of the modulatory NR2 subunits that participate in the formation of di- and/or triheteromeric channel assemblies (e.g., NR1/NR2A, NR1/NR2B, and/or NR1/NR2A/NR2B). Depending on the subunit composition and presence or absence of intracellular binding partners along the postsynaptic membrane, these NMDAR subtypes are allocated to distinct synaptic inputs converging onto a neuron or are distributed differentially among synaptic or extrasynaptic sites. These sites can carry NR2A and NR2B subunits, supporting the hypothesis that the spatial distribution of scaffolding and signaling complexes critically determines the full spectrum of NMDAR signaling.The author thanks the Deutsche Forschungsgemeinschaft for financial support (Ko 1064/5). 相似文献
12.
Abstract: The effects of the divalent cations Ca 2+, Sr 2+, Ba 2+, Mg 2+, Mn 2+, and Cd 2+ were studied on γ-aminobutyric acid A (GABA A) responses in rat cerebral cortical synaptoneurosomes. The divalent cations produced bidirectional modulation of muscimol-induced 36Cl ? uptake consistent with their ability to permeate and block Ca 2+channels. The order of potency for inhibition of muscimol responses was Ca 2+ > Sr 2+ > Ba 2+, similar to the order for permeation of Ca 2+ channels in neurons. The order of potency for enhancement of muscimol responses was Cd 2+> Mn 2+ > Mg 2+, similar to the order for blockade of Ca 2+channels in neurons. Neither Ca 2+ nor Mg 2+ caused accumulation of GABA in the extravesicular space due to increased GABA release or decreased reuptake of GABA by the synaptoneurosomes. The inhibition of muscimol responses by Ca 2+ was most likely via an intracellular site of action because additional inhibition could be obtained in the presence of the Ca 2+ ionophore, A23187. This confirms electrophysiologic findings in cultured neurons from several species. In contrast, the effects of Cd 2+, Mn 2+, and Mg 2+ may be mediated via blockade of Ca 2+ channels or by intracellular sites, although the results of these studies do not distinguish between the two loci. The effects of Zn 2+ were also studied, because this divalent cation is reported to have widely divergent effects on GABA A responses. In contrast to other studies, we demonstrate that Zn 2+ inhibits GABA A responses in an adult neuronal preparation. Zn 2+ produced a concentration-dependent inhibition (limited to 40%) of muscimol responses with an EC 50 of 60 μ M. The inhibition of muscimol-induced 38Cl ? uptake by Zn 2+ was noncompetitive. The effect of Zn 2+was reduced in the presence of Mg 2+ in a competitive or allosteric manner. The portion of GABA A receptors sensitive to Zn 2+ may reflect a specific subunit composition in cerebral cortex as previously observed for recombinant GABA A receptors in several expression systems. The modulation of GABA A receptor function by Ca 2+ and other divalent cations may play an important role in the development and/or attenuation of neuronal excitability associated with pathologic conditions such as seizure activity and cerebral ischemia. 相似文献
13.
Collapsin response mediator protein 2 (CRMP-2), traditionally viewed as an axon/dendrite specification and axonal growth protein, has emerged as nidus in regulation of both pre- and post-synaptic Ca 2+ channels. Building on our discovery of the interaction and regulation of Ca 2+ channels by CRMP-2, we recently identified a short sequence in CRMP-2 which, when appended to the transduction domain of HIV TAT protein, suppressed acute, inflammatory and neuropathic pain in vivo by functionally uncoupling CRMP-2 from the Ca 2+ channel. Remarkably, we also found that this region attenuated Ca 2+ influx via N-methylD-Aspartate receptors (NMDARs) and reduced neuronal death in a moderate controlled cortical impact model of traumatic brain injury (TBI). Here, we sought to extend these findings by examining additional neuroprotective effects of this peptide (TAT-CBD3) and exploring the biochemical mechanisms by which TAT-CBD3 targets NMDARs. We observed that an intraperitoneal injection of TAT-CBD3 peptide significantly reduced infarct volume in an animal model of focal cerebral ischemia. Neuroprotection was observed when TAT-CBD3 peptide was given either prior to or after occlusion but just prior to reperfusion. Surprisingly, a direct biochemical complex was not resolvable between the NMDAR subunit NR2B and CRMP-2. Intracellular application of TAT-CBD3 failed to inhibit NMDAR current. NR2B interactions with the post synaptic density protein 95 (PSD-95) remained intact and were not disrupted by TAT-CBD3. Peptide tiling of intracellular regions of NR2B revealed two 15-mer sequences, in the carboxyl-terminus of NR2B, that may confer binding between NR2B and CRMP-2 which supports CRMP-2''s role in excitotoxicity and neuroprotection. 相似文献
14.
Collapsin response mediator protein 2 (CRMP-2), traditionally viewed as an axon/dendrite specification and axonal growth protein, has emerged as nidus in regulation of both pre- and post-synaptic Ca 2+ channels. Building on our discovery of the interaction and regulation of Ca 2+ channels by CRMP-2, we recently identified a short sequence in CRMP-2 which, when appended to the transduction domain of HIV TAT protein, suppressed acute, inflammatory and neuropathic pain in vivo by functionally uncoupling CRMP-2 from the Ca 2+ channel. Remarkably, we also found that this region attenuated Ca 2+ influx via N-methylD-Aspartate receptors (NMDARs) and reduced neuronal death in a moderate controlled cortical impact model of traumatic brain injury (TBI). Here, we sought to extend these findings by examining additional neuroprotective effects of this peptide (TAT-CBD3) and exploring the biochemical mechanisms by which TAT-CBD3 targets NMDARs. We observed that an intraperitoneal injection of TAT-CBD3 peptide significantly reduced infarct volume in an animal model of focal cerebral ischemia. Neuroprotection was observed when TAT-CBD3 peptide was given either prior to or after occlusion but just prior to reperfusion. Surprisingly, a direct biochemical complex was not resolvable between the NMDAR subunit NR2B and CRMP-2. Intracellular application of TAT-CBD3 failed to inhibit NMDAR current. NR2B interactions with the post synaptic density protein 95 (PSD-95) remained intact and were not disrupted by TAT-CBD3. Peptide tiling of intracellular regions of NR2B revealed two 15-mer sequences, in the carboxyl-terminus of NR2B, that may confer binding between NR2B and CRMP-2 which supports CRMP-2's role in excitotoxicity and neuroprotection. 相似文献
15.
In the adult central nervous system, GABAergic synaptic inhibition is known to play a crucial role in preventing the spread of excitatory glutamatergic activity. This inhibition is achieved by a membrane hyperpolarization through the activation of postsynaptic γ-aminobutyric acid A (GABA A) and GABA B receptors. In addition, GABA also depress transmitter release acting through presynaptic GABA B receptors. Despite the wealth of data regarding the role of GABA in regulating the degree of synchronous activity in the adult, little is known about GABA transmission during early stages of development. In the following we report that GABA mediates most of the excitatory drive at early stages of development in the hippocampal CA3 region. Activation of GABA A receptors induces a depolarization and excitation of immature CA3 pyramidal neurons and increases intracellular Ca 2+ ([Ca 2+] i) during the first postnatal week of life. During the same developmental period, the postsynaptic GABA B-mediated inhibition is poorly developed. In contrast, the presynaptic GABA B-mediated inhibition is well developed at birth and plays a crucial role in modulating the postsynaptic activity by depressing transmitter release at early postnatal stages. We have also shown that GABA plays a trophic role in the neuritic outgrowth of cultured hippocampal neurons. © 1995 John Wiley & Sons, Inc. 相似文献
16.
Caffeine, a stimulant largely consumed around the world, is a non-selective adenosine receptor antagonist, and therefore caffeine actions at synapses usually, but not always, mirror those of adenosine. Importantly, different adenosine receptors with opposing regulatory actions co-exist at synapses. Through both inhibitory and excitatory high-affinity receptors (A1R and A2R, respectively), adenosine affects NMDA receptor (NMDAR) function at the hippocampus, but surprisingly, there is a lack of knowledge on the effects of caffeine upon this ionotropic glutamatergic receptor deeply involved in both positive (plasticity) and negative (excitotoxicity) synaptic actions. We thus aimed to elucidate the effects of caffeine upon NMDAR-mediated excitatory post-synaptic currents (NMDAR-EPSCs), and its implications upon neuronal Ca2+ homeostasis. We found that caffeine (30–200 μM) facilitates NMDAR-EPSCs on pyramidal CA1 neurons from Balbc/ByJ male mice, an action mimicked, as well as occluded, by 1,3-dipropyl-cyclopentylxantine (DPCPX, 50 nM), thus likely mediated by blockade of inhibitory A1Rs. This action of caffeine cannot be attributed to a pre-synaptic facilitation of transmission because caffeine even increased paired-pulse facilitation of NMDA-EPSCs, indicative of an inhibition of neurotransmitter release. Adenosine A2ARs are involved in this likely pre-synaptic action since the effect of caffeine was mimicked by the A2AR antagonist, SCH58261 (50 nM). Furthermore, caffeine increased the frequency of Ca2+ transients in neuronal cell culture, an action mimicked by the A1R antagonist, DPCPX, and prevented by NMDAR blockade with AP5 (50 μM). Altogether, these results show for the first time an influence of caffeine on NMDA receptor activity at the hippocampus, with impact in neuronal Ca2+ homeostasis. 相似文献
17.
N-Methyl- d-aspartate receptors (NMDARs) are ligand-gated ion channels that play an important role in neuronal development, plasticity, and excitotoxicity. NMDAR antagonists are neuroprotective in animal models of neuronal diseases, and the NMDAR open-channel blocker memantine is used to treat Alzheimer''s disease. In view of the clinical application of these pharmaceuticals and the reported expression of NMDARs in immune cells, we analyzed the drug''s effects on T-cell function. NMDAR antagonists inhibited antigen-specific T-cell proliferation and cytotoxicity of T cells and the migration of the cells toward chemokines. These activities correlated with a reduction in T-cell receptor (TCR)-induced Ca 2+ mobilization and nuclear localization of NFATc1, and they attenuated the activation of Erk1/2 and Akt. In the presence of antagonists, Th1 effector cells produced less interleukin-2 (IL-2) and gamma interferon (IFN-γ), whereas Th2 cells produced more IL-10 and IL-13. However, in NMDAR knockout mice, the presumptive expression of functional NMDARs in wild-type T cells was inconclusive. Instead, inhibition of NMDAR antagonists on the conductivity of K v1.3 and K Ca3.1 potassium channels was found. Hence, NMDAR antagonists are potent immunosuppressants with therapeutic potential in the treatment of immune diseases, but their effects on T cells have to be considered in that K v1.3 and K Ca3.1 channels are their major effectors. 相似文献
18.
Major pelvic ganglia (MPG) are relay centers for autonomic reflexes such as micturition and penile erection. MPG innervate the urogenital system, including bladder. γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian central nervous system, and may also play an important role in some peripheral autonomic ganglia, including MPG. However, the electrophysiological properties and function of GABA A receptor in MPG neurons innervating bladder remain unknown. This study examined the electrophysiological properties and functional roles of GABA A receptors in bladder-innervating neurons identified by retrograde Dil tracing. Neurons innervating bladder showed previously established parasympathetic properties, including small membrane capacitance, lack of T-type Ca 2+ channel expression, and tyrosine-hydroxylase immunoreactivity. GABA A receptors were functionally expressed in bladder innervating neurons, but GABA C receptors were not. GABA elicited strong depolarization followed by increase of intracellular Ca 2+ in neurons innervating bladder, supporting the hypothesis GABA may play an important role in bladder function. These results provide useful information about the autonomic function of bladder in physiological and pathological conditions. 相似文献
19.
BackgroundZinc distributes widely in the central nervous system, especially in the hippocampus, amygdala and cortex. The dynamic balance of zinc is critical for neuronal functions. Zinc modulates the activity of N-methyl-D-aspartate receptors (NMDARs) through the direct inhibition and various intracellular signaling pathways. Abnormal NMDAR activities have been implicated in the aetiology of many brain diseases. Sustained zinc accumulation in the extracellular fluid is known to link to pathological conditions. However, the mechanism linking this chronic zinc exposure and NMDAR dysfunction is poorly understood. Methodology/Principal FindingsWe reported that chronic zinc exposure reduced the numbers of NR1 and NR2A clusters in cultured hippocampal pyramidal neurons. Whole-cell and synaptic NR2A-mediated currents also decreased. By contrast, zinc did not affect NR2B, suggesting that chronic zinc exposure specifically influences NR2A-containg NMDARs. Surface biotinylation indicated that zinc exposure attenuated the membrane expression of NR1 and NR2A, which might arise from to the dissociation of the NR2A-PSD-95-Src complex. ConclusionsChronic zinc exposure perturbs the interaction of NR2A to PSD-95 and causes the disorder of NMDARs in hippocampal neurons, suggesting a novel action of zinc distinct from its acute effects on NMDAR activity. 相似文献
20.
BackgroundThe initiation of behavioral sensitization to cocaine and other psychomotor stimulants is thought to reflect N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic plasticity in the mesolimbic dopamine (DA) circuitry. The importance of drug induced NMDAR mediated adaptations in ventral tegmental area (VTA) DA neurons, and its association with drug seeking behaviors, has recently been evaluated in Cre- loxp mice lacking functional NMDARs in DA neurons expressing Cre recombinase under the control of the endogenous dopamine transporter gene (NR1 DATCre mice). Methodology and Principal FindingsUsing an additional NR1 DATCre mouse transgenic model, we demonstrate that while the selective inactivation of NMDARs in DA neurons eliminates the induction of molecular changes leading to synaptic strengthening, behavioral measures such as cocaine induced locomotor sensitization and conditioned place preference remain intact in NR1 DATCre mice. Since VTA DA neurons projecting to the prefrontal cortex and amygdala express little or no detectable levels of the dopamine transporter, it has been speculated that NMDA receptors in DA neurons projecting to these brain areas may have been spared in NR1 DATCre mice. Here we demonstrate that the NMDA receptor gene is ablated in the majority of VTA DA neurons, including those exhibiting undetectable DAT expression levels in our NR1 DATCre transgenic model, and that application of an NMDAR antagonist within the VTA of NR1 DATCre animals still blocks sensitization to cocaine. Conclusions/SignificanceThese results eliminate the possibility of NMDAR mediated neuroplasticity in the different DA neuronal subpopulations in our NR1 DATCre mouse model and therefore suggest that NMDARs on non-DA neurons within the VTA must play a major role in cocaine-related addictive behavior. 相似文献
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