Biomedical subjects

Shigetada Nakanishi

Publications and source records attributed to Shigetada Nakanishi.

At least 19 recordsLinked to original sources

PubMed2006

Intrinsic ON responses of the retinal OFF pathway are suppressed by the ON pathway.

Parallel ON and OFF pathways conduct visual signals from bipolar cells in the retina to higher centers in the brain. ON responses are thought to originate by exclusive use of metabotropic glutamate receptor 6 (mGluR6) expressed in retinal ON bipolar cells. Paradoxically, we find ON responses in retinal ganglion cells of mGluR6-null mice, but they occur at long latency. The long-latency ON responses are not blocked by metabotropic glutamate or cholinergic receptor antagonists and are not produced by activation of receptive field surrounds. We show that these longer-latency ON responses are initiated in the OFF pathways. Our results expose a previously unrecognized intrinsic property of OFF retinal pathways that generates responses to light onset. In mGluR6-null mice, long-latency ON responses are observed in the visual cortex, indicating that they can be conducted reliably to higher visual areas. In wild-type (WT) mice, APB (DL-2-amino-4-phosphonobutyric acid), an mGluR6 agonist, blocks normal, short-latency ON responses but unmasks longer-latency ones. We find that these potentially confusing ON responses in the OFF pathway are actively suppressed in WT mice via two pharmacologically separable retinal circuits that are activated by the ON system in the retina. Consequently, we propose that a major function of the signaling of the ON pathway to the OFF pathway is suppression of these mistimed, and therefore inappropriate, light-evoked responses.

Action Potentials↗

PubMed2006

Membrane potential-regulated Ca2+ signalling in development and maturation of mammalian cerebellar granule cells.

In many developing neuronal cell types, the resting membrane potential is relatively depolarized, then gradually hyperpolarizes during the early postnatal period. The regulatory roles of membrane potential changes in neuronal development and maturation have been extensively studied in developing cerebellar granule cells, using primary culture under depolarizing and non-depolarizing conditions in combination with in vivo analysis. Depolarization enhances calcium entry via voltage-sensitive Ca2+ channels (VSCCs) and activates Ca2+-calmodulin-dependent protein kinase (CaMK) and calcineurin phophatase (CaN). The activation of CaN induces many genes encoding extracellular and intracellular signalling molecules implicated in granule cell development. The inactivation of CaN in turn up-regulates many other genes characteristic of mature granule cells, including NR2C NMDA receptor and GABAAalpha1 and alpha6 receptors. The induction of NR2C also requires CaMK-up-regulated brain-derived neurotrophic factor (BDNF), indicating a convergence of signalling mechanism of the CaMK and CaN cascades. The inactivation of CaN maintains the phosphorylated and sumoylated form of a transcriptional myocyte enhances factor 2A (MEF2A) regulator. This form of MEF2A acts as a transcriptional repressor and is essential for the dendritic morphogenesis of differentiated granule cells. Collectively, the membrane potential change and the resulting Ca2+ signalling play a pivotal role in development and maturation of neuronal cells.

Animals↗

PubMed2006

Expression profile of BDNF-responsive genes during cerebellar granule cell development.

With the aid of microarray and PCR analysis, this investigation sought expression profiles of BDNF-regulated genes in cultured mouse cerebellar granule cells and addressed their relevance to gene regulation in developing granule cells in vivo. Many of the BDNF-upregulated and downregulated genes identified were upregulated and downregulated, respectively, during cerebellar development. This developmental change was, at least partly, prevented in the TrkB receptor-deficient cerebellum. The BDNF-upregulated genes were distributed in either postmigratory or both premigratory and postmigratory granule cells at postnatal day 8 (P8) and were still present in mature granule cells at P21. In contrast, the BDNF-downregulated genes were predominantly expressed in premigratory granule cells at P8 and disappeared at P21. Furthermore, many of the BDNF-upregulated gene products are implicated in signaling cascades of N-methyl-D-aspartate receptors and MAP kinase. The results indicate that BDNF signaling plays a pivotal role in promoting gene expression in granule cell development and maturation.

Animals↗

PubMed2005

Neuronal depolarization controls brain-derived neurotrophic factor-induced upregulation of NR2C NMDA receptor via calcineurin signaling.

In the developing cerebellum, switching of subunit composition of NMDA receptors occurs in granule cells from NR2B subunit-containing receptors to NR2C subunit-containing receptors. This switching of subunit composition plays an important role in the establishment of functional mossy fiber-granule cell synaptic transmission in the mature cerebellar network. The mechanism underlying NR2C upregulation in developing granule cells, however, has to date remained to be determined. In granule cells cultured in low (5 mm) KCl, brain-derived neurotrophic factor (BDNF) upregulated NR2C mRNA via the TrkB-extracellular signal-regulated kinase (ERK) 1/2 cascade and promoted the formation of an NR2C-containing NMDA receptor complex. In granule cells cultured in high (25 mm) KCl, depolarization stimulated voltage-sensitive Ca2+ channels. The resultant increase in intracellular Ca2+ activated Ca2+/calmodulin-dependent calcineurin phosphatase and blocked NR2C mRNA upregulation. Interestingly, the depolarization-induced Ca2+ increase simultaneously upregulated BDNF mRNA via Ca2+/calmodulin-dependent protein kinase (CaMK). Consequently, when calcineurin was inhibited by its inhibitor FK506 under the depolarizing condition, the CaMK-mediated increase in BDNF became a stimulatory signal, and the endogenous BDNF autocrine system was capable of upregulating NR2C mRNA via the common TrkB-ERK cascade. The importance of the BDNF-TrkB pathway was further supported by a significant reduction in NR2C in normally migrated granule cells of TrkB(-/-) knock-out mice in vivo. The convergent mechanism of the BDNF and Ca2+ signaling cascades thus plays an important regulatory role in NR2C induction in granule cells during cerebellar development.

Animals↗

PubMed2005

A pivotal role of calcineurin signaling in development and maturation of postnatal cerebellar granule cells.

Primary culture of postnatal cerebellar granule cells provides a model system that recapitulates many molecular events of developing granule cells in vivo. Depolarization of cultured granule cells increases intracellular Ca(2+) and activates Ca(2+)/calmodulin-dependent calcineurin (CaN) phosphatase. This Ca(2+) signaling mimics some of the signaling events for proliferation, migration, and differentiation of granule cells in vivo. We investigated the genome-wide expression profiles of depolarization- and CaN-regulated genes in cultured mouse granule cells and addressed their relevance to gene regulation in developing granule cells in vivo. Granule cells were cultured under a nondepolarization condition (5 mM KCl) and a depolarization condition (25 mM KCl) with and without the CaN inhibitor FK506. Gene expression profiles between depolarization and nondepolarization and between FK506 treatment and untreatment were analyzed by microarray techniques. Both depolarization and FK506 treatment influence expression levels of a large number of genes, most of which are overlapping, however, are conversely regulated by these two treatments. Importantly, many of the FK506-responsive genes are up- or down-regulated in parallel with gene expression in postnatal granule cells in vivo. The FK506-down-regulated genes are highly expressed in proliferating/premigratory granule cells and many of these genes encode cellular components involved in cell proliferation, migration, and differentiation. In contrast, the FK506-up-regulated genes are predominantly expressed in postmigratory granule cells, including many functional molecules implicated in synaptic transmission and modulation. This investigation demonstrates that the CaN signaling plays a pivotal role in development and synaptic organization of granule cells during the postnatal period.

Animals↗

PubMed2005

Enhanced cocaine responsiveness and impaired motor coordination in metabotropic glutamate receptor subtype 2 knockout mice.

Extensive pharmacological studies have recently emerged indicating that group 2 metabotropic glutamate receptors (mGluRs) comprising mGluR2 and mGluR3 subtypes are associated with several neurological and psychiatric disorders. mGluR2 is widely distributed both presynaptically and postsynaptically in a variety of neuronal cells, but the physiological role of mGluR2 in brain function is poorly understood. This investigation involves a comprehensive behavioral analysis of mGluR2-/- knockout (KO) mice to explore the physiological role of mGluR2 in brain function. Although, under general observation, mGluR2-/- KO mice appeared to have no behavioral abnormalities, they exhibited several lines of behavioral alterations in the enforcing and defined behavioral tests. They showed a significant increase in locomotor sensitization and conditioned place preference in association with repeated cocaine administration, indicating that mGluR2 contributes to behavioral responses implicated in reinforcement and addiction of cocaine. Upon in vivo microdialysis analysis after cocaine administration, not only did extracellular levels of dopamine increase but also the response pattern of glutamate release markedly changed in the nucleus accumbens of mGluR2-/- KO mice. The mGluR2-/- KO mice also showed significant impairment in motor coordination in the accelerating rota-rod test and exhibited hyperlocomotion in novel environmental and stressful conditions, when assessed by the open-field and forced-swim tests. These results indicate that the inhibitory mGluR2 plays a pivotal role in synaptic regulation of glutamatergic transmission in the neural network.

Animals↗

PubMed2005

Synaptic mechanisms of the cerebellar cortical network.

The cerebellar cortex forms a defined array of relatively simple neural networks. Considerable progress has been made towards understanding the synaptic mechanisms of these networks. It has been revealed that inhibitory GABA receptors and distinct types of glutamate receptor cooperatively and differentially regulate and integrate glutamate-mediated transmission within cerebellar cortical circuits. In addition, molecular assembly of receptor-interacting scaffolding proteins and signaling molecules is dynamically controlled and underlies the functional synaptic organization of cerebellar cortical circuits. This article discusses some of the recent progress in this area, focusing on newly explored aspects of the synaptic mechanisms of glutamate-mediated transmission in the cerebellar cortical network.

Animals↗

PubMed2005

Opposite effects of Zn on the in vitro binding of [3H]LY354740 to recombinant and native metabotropic glutamate 2 and 3 receptors.

We investigated the effect of Zn on agonist binding to both recombinant and native mGlu2 and mGlu3 receptors. Zn had a biphasic inhibitory effect on recombinant mGlu2 with IC(50) values for the high- and low-affinity components of 60 +/- 10 microM and 2 +/- 0.7 mM, respectively. Zn induced a complex biphasic effect of inhibition and enhancement of [(3)H]LY354740 binding to mGlu3. Observations with a series of chimeric mGlu2/3 receptors suggest that the Zn effect resides in the N-terminal domain of mGlu2 and mGlu3. We observed that the His56 of mGlu2, which corresponds to Asp63 in mGlu3 was largely accountable for the second phase of the Zn effect. As revealed by quantitative receptor radioautography, the addition of up to 100 microm Zn to brain sections of wild-type mice resulted in significant decreases in binding density in most brain regions. In particular, the mid-molecular layer of the dentate gyrus (DGmol) and the CA1 lacunosum moleculare of hippocampus (CA1-LMol) showed reductions of 62 and 67%, respectively. In contrast, the addition of 300 microM Zn to brain sections of mGlu2(-/-) mice caused large increases in binding density of 289 and 242% in DGmol and CA1-LMol, respectively. Therefore, Zn might play a role as a physiological modulator of group II mGlu receptor function.

Amino Acid Sequence↗

PubMed2004

Distinct ontogenic and regional expressions of newly identified Cajal-Retzius cell-specific genes during neocorticogenesis.

Cajal-Retzius (CR) cells are early-generated transient neurons and are important in the regulation of cortical neuronal migration and cortical laminar formation. Molecular entities characterizing the CR cell identity, however, remain largely elusive. We purified mouse cortical CR cells expressing GFP to homogeneity by fluorescence-activated cell sorting and examined a genome-wide expression profile of cortical CR cells at embryonic and postnatal periods. We identified 49 genes that exceeded hybridization signals by >10-fold in CR cells compared with non-CR cells at embryonic day 13.5, postnatal day 2, or both. Among these CR cell-specific genes, 25 genes, including the CR cell marker genes such as the reelin and calretinin genes, are selectively and highly expressed in both embryonic and postnatal CR cells. These genes, which encode generic properties of CR cell specificity, are eminently characterized as modulatory composites of voltage-dependent calcium channels and sets of functionally related cellular components involved in cell migration, adhesion, and neurite extension. Five genes are highly expressed in CR cells at the early embryonic period and are rapidly down-regulated thereafter. Furthermore, some of these genes have been shown to mark two distinctly different focal regions corresponding to the CR cell origins. At the late prenatal and postnatal periods, 19 genes are selectively up-regulated in CR cells. These genes include functional molecules implicated in synaptic transmission and modulation. CR cells thus strikingly change their cellular phenotypes during cortical development and play a pivotal role in both corticogenesis and cortical circuit maturation.

Animals↗

PubMed2004

OFF-cholinergic-pathway-selective localization of P2X2 purinoceptors in the mouse retina.

It is known that, in the retina, extracellular adenosine triphosphate (ATP) inhibits acetylcholine (ACh) release from cholinergic neurons, but the types of purinoceptors on cholinergic neurons have not been examined. In the present work, we immunohistochemically examined the distribution of the purinoceptors P2X1, P2X2, P2X4, and P2X7 in relation to the cholinergic system of the retina in wild-type mice and transgenic mice expressing green fluorescent protein (GFP). Immunoreactivity for P2X2 was very strong in sublamina a of the inner plexiform layer but very weak in sublamina b of the inner plexiform layer of the retina. Immunoreactivity for P2X2 was colocalized with that for choline acetyltransferase (ChAT). When transgenic mice were treated with the immunotoxin-mediated cell-targeting technology to ablate cholinergic amacrine cells selectively, immunoreactivity for P2X2 and the signals for GFP disappeared in parallel and selectively in the OFF pathway. The distribution of immunoreactivity for P2X1, P2X4, and P2X7 differed from that of ChAT immunoreactivity. The selective distribution of P2X2 purinergic receptors in OFF-type cholinergic amacrine cells indicates that the P2X2 purinergic signaling systems in the ON and OFF pathways of the inner plexiform layer of the mouse retina are functionally different. The distribution of P2X2 purinoceptors may be responsible for the selective regulation of ACh release in the OFF pathway.

Acetylcholine↗

PubMed2004

The PDZ domain of PICK1 differentially accepts protein kinase C-alpha and GluR2 as interacting ligands.

The C terminus (ct) of protein kinase C-alpha (PKCalpha) has a type I PDZ binding motif, whereas GluR2 has a type II PDZ binding motif. Both motifs are recognized by the PDZ domain of protein interacting with protein kinase C (PICK1), and PICK1-PKCalpha-controlled phosphorylation regulates the synaptic expression and function of GluR2. Here, we show that a specific mutation within the carboxylate-binding loop of the PDZ domain of PICK1 (K27E; PICK1-KE) results in a loss of interaction with GluR2 but not with PKCalpha. In GST pull-down studies, PICK1-WT (wild type) but not PICK1-KE was retained by GST-ct-GluR2. Furthermore, PICK1-WT co-immunoprecipitated both PKCalpha and GluR2, whereas PICK1-KE only co-immunoprecipitated PKCalpha. In heterologous cells, PICK1-WT, but not PICK1-KE, clustered GluR2 and also clustered GluR1 in a GluR2-dependent manner. However, neither PICK1-WT nor PICK1-KE altered the distribution of PKCalpha, even after phorbol ester-induced redistribution of PKCalpha to the membrane. Finally, PICK1-KE showed no mislocalization when compared with PICK1-WT in neurons. Taken together, it appears that the PDZ domain of PICK1 is less sensitive to mutations for PKCalpha when compared with GluR2 binding. These results suggest that the PDZ domain of PICK1 has distinct PKCalpha and GluR2 binding subsite(s).

Animals↗

PubMed2004

Phosphorylation and recruitment of Syk by immunoreceptor tyrosine-based activation motif-based phosphorylation of tamalin.

Tamalin is a scaffold protein that forms a multiple protein assembly including metabotropic glutamate receptors (mGluRs) and several postsynaptic and protein-trafficking scaffold proteins in distinct mode of protein-protein association. In the present investigation, we report that tamalin possesses a typical immunoreceptor tyrosine-based activation motif (ITAM), which enables Syk kinase to be recruited and phosphorylated by the Src family kinases. Coimmunoprecipitation analysis of rat brain membrane fractions showed that tamalin is present in a multimolecular protein assembly comprising not only mGluR1 but also c-Src, Fyn, and a protein phosphatase, SHP-2. The protein association of both tamalin and c-Src, as determined by truncation analysis of mGluR1 in COS-7 cells, occurred at the carboxyl-terminal tail of mGluR1. Mutation analysis of tyrosine with phenylalanine in COS-7 cells revealed that paired tyrosines at the ITAM sequence of tamalin are phosphorylated preferentially by c-Src and Fyn, and this phosphorylation can recruit Syk kinase and enables it to be phosphorylated by the Src family kinases. The phosphorylated tyrosines at the ITAM sequence of tamalin were highly susceptible to dephosphorylation by protein-tyrosine phosphatases in COS-7 cells. Importantly, tamalin was endogenously phosphorylated and associated with Syk in retinoic acid-treated P19 embryonal carcinoma cells that undergo neuron-like differentiation. The present investigation demonstrates that tamalin is a novel signaling molecule that possesses a PDZ domain and a PDZ binding motif and mediates Syk signaling in an ITAM-based fashion.

Alternative Splicing↗

PubMed2004

Seven in absentia homolog 1A mediates ubiquitination and degradation of group 1 metabotropic glutamate receptors.

Seven in absentia homolog 1A (Siah1A) is a member of the RING-finger-containing E3 ubiquitin ligases and has been shown to bind to the Siah-interacting domain (SID) at the carboxyl-terminal tails of the long splice forms of group 1 metabotropic glutamate receptors (mGluR1a and mGluR5). We examined the function of Siah1A in ubiquitination and degradation of group 1 mGluRs in heterologously expressing cell lines. Coexpression of Siah1A markedly decreased the SID-containing splice forms of group 1 mGluRs but not the SID-lacking mGluR1b splice form or the SID-deleted mGluR1a mutant. The decrease of mGluR1a resulted from accelerated protein turnover, as revealed by pulse-chase experiments. The Siah1A-mediated degradation of group 1 mGluRs was abrogated by not only mutations at the RING-finger domain of Siah1A but also treatment with a proteasome inhibitor. Siah1A coexpression induced strong ubiquitination of group 1 mGluRs. Replacements of lysine residues with arginine showed that Siah1A-mediated ubiquitination occurs at multiple lysine residues spanning both the seven-transmembrane region and carboxyl-terminal tail of mGluR5. In situ hybridization histochemistry showed a wide-spread distribution of Siah1 mRNAs, with high expression in the hippocampal pyramidal neurons and cerebellar Purkinje cells. Group 1 mGluRs play critical roles in the neural plasticity in both the hippocampal neurons and Purkinje cells. This investigation indicates that Siah1A serves as a selective ubiquitin ligase that mediates ubiquitination-dependent degradation of long splice variants of group 1 mGluRs and would contribute to posttranslational down-regulation of group 1 mGluRs.

Animals↗

PubMed2004

Generation of reelin-positive marginal zone cells from the caudomedial wall of telencephalic vesicles.

An early and fundamental step of the laminar organization of developing neocortex is controlled by the developmental programs that critically depend on the activities of reelin-positive cells in the marginal zone. However, the ontogeny of reelin-positive cells remained elusive. To gain insights into the spatial and temporal regulation of reelin-positive marginal zone cell development, we used a transgenic mouse line in which we defined the green fluorescent protein (GFP) transgene as a novel reliable molecular marker of reelin-positive marginal zone cells from the early stages of their development. We further used exo utero electroporation-mediated gene transfer that allows us to mark progenitor cells and monitor the descendants in the telencephalon in vivo. We show here the generation of reelin-positive marginal zone cells from the caudomedial wall of telencephalic vesicles, including the cortical hem, where the prominent expression of GFP is initially detected. These neurons tangentially migrate at the cortical marginal zone and are distributed throughout the entire neocortex in a caudomedial-high to rostrolateral-low gradient during the dynamic developmental period of corticogenesis. Therefore, our findings on reelin-positive marginal zone cells, in addition to the cortical interneurons, add to the emerging view that the neocortex consists of neuronal subtypes that originate from a focal source extrinsic to the neocortex, migrate tangentially into the neocortex, and thereby underlie neural organization of the neocortex.

Animals↗

PubMed2004

Pharmacological and genetic evidence indicates that combined inhibition of NR2A and NR2B subunit containing NMDA receptors is required to disrupt prepulse inhibition.

RATIONALE: Glutamate signalling through the N-methyl-D-aspartate (NMDA) receptor is of critical importance for normal central nervous system (CNS) function, as indicated by the marked behavioural disturbances produced by non-subtype selective NMDA antagonists such as dizocilpine (MK-801). OBJECTIVE: The present studies were designed to investigate the involvement of the two major NMDA receptor subunits in the central nervous system, i.e. NR2A and NR2B, on sensorimotor gating in mice. METHODS: These experiments utilised the non-subtype-selective NMDA antagonist dizocilpine, a line of NR2A-KO mice and the selective NR2B antagonist Ro 63-1908, in the study of pre-pulse inhibition of the startle response (PPI). RESULTS: The non-selective NMDA receptor antagonist dizocilpine (0.1-1 mg/kg, IP) robustly disrupted PPI in wild-type mice. Conversely, selective genetic or pharmacological inhibition of either the NMDA NR2A or NR2B receptor subunit containing receptors, respectively, had no effect on PPI. Thus, NR2A KO mice showed normal PPI compared with wild-type littermate controls, and administration of Ro 63-1908 (1-10 mg/kg IP) to wild-type mice did not affect PPI. However, selective inhibition of NR2A and NR2B by administration of Ro 63-1908 to NR2A KO mice significantly disrupted PPI. CONCLUSIONS: These data imply that concomitant inhibition of both NR2A and NR2B subunit-containing NMDA receptors is necessary to disrupt PPI, suggesting that inhibition of NR2A and NR2B-containing NMDA receptors is required to elicit behaviours suggestive of psychomimetic effects in man.

Animals↗

PubMed2004

MGS0039: a potent and selective group II metabotropic glutamate receptor antagonist with antidepressant-like activity.

The present study describes the pharmacological profile of (1R,2R,3R,5R,6R)-2-Amino-3-(3,4-dichlorobenzyloxy)-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (MGS0039), a novel group II mGluR antagonist. MGS0039 showed high affinity for both mGluR2 (Ki = 2.2 nM) and mGluR3 (Ki = 4.5 nM), which are comparable to LY341495, another group II mGluR antagonist. MGS0039 attenuated both glutamate-induced inhibition of forskolin-evoked cyclic AMP formation in CHO cells expressing mGluR2 (IC50 = 20 nM) or mGluR3 (IC50 = 24 nM) and glutamate-increased [35S]GTPgammaS binding to mGluR2 (pA2 = 8.2), which means that MGS0039 acts as an antagonist. MGS0039 shifted the dose-response curve of glutamate-increased [35S]GTPgammaS binding rightward without altering the maximal response, and thereby indicating competitive antagonism. MGS0039 showed no significant effects on other mGluRs as well as the other receptors and transporters we studied. MGS0039 (0.3-3 mg/kg, i.p.) as well as LY341495 (0.1-3 mg/kg, i.p.) had dose-dependent antidepressant-like effects in the rat forced swim test and in the mouse tail suspension test. In contrast, MGS0039 (0.3-3 mg/kg, i.p.) had no apparent effect in the rat social interaction test and in the rat elevated plus-maze. These results indicate that MGS0039 is a potent and selective antagonist of group II mGluR, and that group II mGluR antagonists, like MGS0039, have an antidepressant-like potential in experimental animal models.

Animals↗

PubMed2004

Pharmacological manipulation of mGlu2 receptors influences cognitive performance in the rodent.

Atrophy of the medial temporal lobes, including the glutamatergic cortical-hippocampal circuitry, is an early event in Alzheimer's disease (AD) and probably contributes to the characteristic short-term mnemonic decline. Pharmacological strategies directly targeted to ameliorating this functional decline may represent a novel approach for the symptomatic treatment of AD. Presynaptic group II metabotropic glutamate receptors (i.e. mGlu2 and mGlu3) exert a powerful modulatory influence on the function of these pathways, in particular the perforant pathway. Using a combination of mGlu2 receptor knockout mice and the group II agonist LY354740, we show that activation of mGlu2 receptors produces a cognitive impairment, i.e. a delay-dependent deficit in delayed matching and non-matching to position, and impaired spatial learning in a Morris water maze. Conversely, a group II antagonist, LY341495, improved acquisition of spatial learning. LY354740 potently reduced field excitatory postsynaptic potentials in hippocampal slices from wild type but not mGlu2 receptor knockout mice. Taken together, these results suggest that activation of mGlu2 receptors evokes a powerful inhibitory effect on hippocampal synaptic transmission and mGlu2 agonists produce a cognitive deficit consistent with this change. Conversely, mGlu2 receptor antagonists may improve certain aspects of cognition and thus represent a novel approach for the symptomatic treatment of AD.

Amino Acids↗

PubMed2004

Characterization of N-methyl-D-aspartate receptor subunits involved in acute ammonia toxicity.

Rapid administration of large doses of ammonia leads to death of animals, which is largely prevented by pretreatment with N-methyl-D-aspartate (NMDA) receptor antagonists. The present study focuses on a subunit(s) of NMDA receptor involved in ammonia-induced death by use of NMDA receptor GluRepsilon subunit-deficient (GluRepsilon(-/-)) mice and the selective GluRepsilon2 antagonist CP-101,606. Acute ammonia intoxication was induced in mice (eight per group) by a single intraperitoneal (i.p.) injection of ammonium chloride. Appearance of neurological deteriorations depended on the doses of ammonium chloride injected. While wild-type, GluRepsilon1(-/-), GluRepsilon4(-/-), and GluRepsilon1(-/-)/epsilon4(-/-) mice all died by ammonium chloride at 12 mmol/kg during the first tonic convulsions, two of eight GluRepsilon3(-/-) mice survived. Pretreatment of wild-type mice with CP-101,606 prevented two mice from ammonia-induced death. Pretreatment of GluRepsilon3(-/-) mice with CP-101,606 prevented the death of three mice and prolonged the time of death of non-survivors. Similarly, the neuronal form of nitric oxide synthase (NOS) inhibitor 7-nitroindazole (7-NI) as well as the nonselective NOS inhibitor L-NMMA, but not the inducible NOS inhibitor 1400W, partially prevented the death of mice and prolonged the period of death. Furthermore, ammonium chloride prolonged the increase in intracellular free Ca2+ concentration ([Ca2+]i) and subsequent NO production induced by NMDA in the cerebellum. These results suggest that activation of NMDA receptor containing GluRepsilon2 and GluRepsilon3 subunits and following activation of neuronal NOS are involved in acute ammonia intoxication which leads to death of animals.

Ammonia↗