Transforming growth factor alpha attenuates the functional expression of AMPA receptors in cortical GABAergic neurons

In the developing neocortex, brain-derived neurotrophic factor (BDNF) exerts a trophic activity to increase the expression and channel activity of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor subunits. Here, we demonstrate that the epidermal growth factor (EGF) receptor (ErbB1) ligands exert the opposite biological activity in cultured neocortical neurons. Subchronic stimulation of ErbB1 with transforming growth factor alpha (TGFalpha), EGF, or heparin-binding EGF (HB-EGF) down-regulated protein expression of the GluR1 AMPA receptor subunit in cultured neocortical neurons. In agreement, TGFalpha treatment decreased the Bmax of [3H] AMPA binding and GluR1 mRNA levels. Immunocytochemistry revealed that the decrease in GluR1 was most pronounced in multipolar GABAergic neurons. To examine the physiological consequences, we recorded AMPA-evoked currents as well as miniature excitatory postsynaptic currents in morphologically identified putative GABAergic neurons in culture. Subchronic TGFalpha treatment decreased AMPA-triggered currents as well as the amplitude and frequency of miniature excitatory postsynaptic currents. An ErbB1 tyrosine kinase inhibitor, PD153035, inhibited the TGFalpha effect. Moreover, TGFalpha counteracted the neurotrophic activity of BDNF on AMPA receptor expression. Co-application of TGFalpha with BDNF blocked the BDNF-triggered up-regulation of AMPA receptor expression and currents. These observations reveal a negative regulatory activity of the ErbB1 ligand, TGFalpha, which reduces the input sensitivity of cortical GABAergic neurons to attenuate their inhibitory function.

Amyloid beta induces neuronal cell death through ROS-mediated ASK1 activation

Amyloid beta (Abeta) is a main component of senile plaques in Alzheimer's disease and induces neuronal cell death. Reactive oxygen species (ROS), nitric oxide and endoplasmic reticulum (ER) stress have been implicated in Abeta-induced neurotoxicity. We have reported that apoptosis signal-regulating kinase 1 (ASK1) is required for ROS- and ER stress-induced JNK activation and apoptosis. Here we show the involvement of ASK1 in Abeta-induced neuronal cell death. Abeta activated ASK1 mainly through production of ROS but not through ER stress in cultured neuronal cells. Importantly, ASK1-/- neurons were defective in Abeta-induced JNK activation and cell death. These results indicate that ROS-mediated ASK1 activation is a key mechanism for Abeta-induced neurotoxicity, which plays a central role in Alzheimer's disease.

Enamel matrix derivative gel stimulates signal transduction of BMP and TGF-{beta}

It has been shown that Emdogain Gel (Emd-Gel) containing enamel matrix proteins promotes biomineralization, such as osteogenesis and cementogenesis, during the regeneration of periodontal tissues. However, the growth factors involved in these activities of Emd-Gel remain unclear. In this study, Emd-Gel was fractionated into 22 sub-fractions by size exclusion chromatography. The osteoinductive factors, TGF-beta and BMP, were examined by a specific luciferase reporter gene assay. In the unfractionated Emd-Gel, TGF-beta-like activity was detected, while BMP activity was not. In contrast, in the fractionated Emd-Gel samples, TGF-beta-like activity was detected from fractions 8 to 13, and BMP-like activity was detected from fractions 4 to 6. Also, it was confirmed that the BMP-like activity in Emd-Gel was inhibited by authentic TGF-beta1 and TGF-beta-like activity. These results indicate that Emd-Gel contains both TGF-beta- and BMP-like growth factors that contribute to the induction of biomineralization during periodontal regeneration.

Screening and determination of methamphetamine and amphetamine in the blood, urine and stomach contents in emergency medical care and autopsy cases

Methamphetamine (MA) and amphetamine (AMP) were screened and their levels were determined using the Toxi-Lab thin-layer chromatography system and gas chromatography-mass spectrometry, respectively, in the blood, urine and stomach contents from 211 emergency medical care and 417 autopsy cases. MA and AMP were detected in 5 emergency medical cases, and the blood MA and AMP concentrations ranged from 0.697-0.041 micromol/100 g and from 0.0944-0.0003 micromol/100 g, respectively. MA and AMP were detected in 19 autopsy cases, in which blood MA and AMP concentration ranged from 14.3-0.123 micromol/100 g and from 0.256-0.0017 micromol/100 g, respectively. The autopsy cases included 5 cases of sudden death with blood MA concentration of less than 3 micromol/100 g. MA and AMP screening and determination in emergency medical care and autopsy cases provide useful information and are indispenable in clarifying the dimensions of MA abuse in Japan.

Investigation of the origin of ephedrine and methamphetamine by stable isotope ratio mass spectrometry: a Japanese experience

Illicit drug abuse is a serious global problem that can only be solved through international cooperation. In Asian countries, the abuse of methamphetamine is one of the most pressing problems. To assist in the control of methamphetamine, the authors investigated in detail the character of ephedrine, which is a key precursor for the illicit manufacture of methamphetamine. Commercial ephedrine is produced by one of three methods: (a) extraction from Ephedra plants, (b) full chemical synthesis or (c) via a semi-synthetic process involving the fermentation of sugar, followed by amination. Although chemically there is no difference between ephedrine samples from different origins (natural, synthetic or semi-synthetic), scientific and analytical tools such as drug-characterization and impurity-profiling programmes may provide valuable information for law enforcement and regulatory activities as part of precursor control strategies. During the research under discussion in the present article, in addition to classical impurity profiling of manufacturing by-products, the use of stable isotope ratio mass spectrometry was investigated for determining the origin of the ephedrine that had been used as a precursor in seized methamphetamine samples. The results of carbon and nitrogen stable isotope ratio (delta13C and delta15N) analysis of samples of crystalline methamphetamine seized in Japan suggested that the drug had been synthesized from either natural or semi-synthetic ephedrine and not from synthetic ephedrine. Stable isotope ratio analysis is expected to be a useful tool for tracing the origins of seized methamphetamine. It has attracted much interest from precursor control authorities in Japan and the East Asian region and may prove useful in the international control of precursors.

Expression and characterization of disulfide bond use of oligomerized A2-Pancortins: Extracellular matrix constituents in the developing brain

The region-specific characteristics of the extracellular matrix are crucial for diverse functions in the brain. Pancortins/neuron-specific olfactomedin-related glycoproteins are components of the extracellular matrix. They comprise four alternatively spliced variants, Pancortin-1 to -4, which share a common portion, the B part, in the middle of their structure, have two pairs of alternatively spliced 5' regions, A1 and A2, and 3' regions, C1 and C2. Here we demonstrate that in mice, Pancortin-3 (A2-B-C1) and Pancortin-4 (A2-B-C2), which we have grouped together the A2-Pancortins, were transcribed early during the development of the brain in a region specific manner and were expressed very stably in vivo. They are N-glycosylated and secreted. Furthermore, we examined their ontogenetical expression profiles in the developing thalamus using antiserum against the common B region, since transient expressions of their mRNAs were notable there. In the developing thalami, they lasted long in oligomerized form even after the transcription of their mRNAs decreased to an undetectable level. Further analyses revealed that cysteine residues that are located in the common B part are important for homo- and hetero-oligomer formation of A2-Pancortins. When we substituted cysteine residues 45 and 47 with serine residues in that common B part, oligomerization of the A2-Pancortins was highly disturbed.

Conditioned Place Preference and Locomotor Sensitization after Repeated Administration of Cocaine or Methamphetamine in Rats Treated with Epidermal Growth Factor during the Neonatal Period

Epidermal growth factor (EGF) and its structurally related proteins are involved in the developmental regulation of various brain neurons, including midbrain dopaminergic neurons. We recently reported EGF and EGF-receptor abnormalities in both the brain tissues and blood of schizophrenic patients. Administration of EGF to neonatal rats transiently increases tyrosine hydroxylase expression and subsequently results in behavioral abnormalities in prepulse inhibition of acoustic startle, locomotor activity, and social interaction after development. The enhanced locomotor and stereotypic responses of the neonatally EGF-treated rats are considered to be an animal model for positive schizophrenia symptoms. In the present study, we investigated psychostimulant sensitivity of neonatally EGF-treated rats. At the adult stage, EGF-treated rats were challenged with cocaine (15 mg/kg) or methamphetamine (1 mg/kg), and conditioned place preference and locomotor activity were examined. The rats that received EGF during the neonatal period had significantly higher conditioned place preference for where cocaine or methamphetamine was administered than controls. The neonatal EGF treatment enhanced behavioral response to methamphetamine and behavioral sensitization to cocaine at the adult stage. Drug-naive controls gradually increased locomotor responses to cocaine during their daily injections, whereas EGF-treated rats exhibited a larger increase in cocaine responses. These results indicate that overactivation of the EGF receptors (ErbB1) during the neonatal period influences future sensitivity to psychostimulants. Our findings indicate a potential link between EGF-receptor activation and drug addiction.

Relative levels of mRNA encoding enamel proteins in enamel organ epithelia and odontoblasts

Amelogenin, enamelin, sheathlin (ameloblastin/ amelin), enamelysin (MMP-20), and KLK4 (EMSP-1) are the major structural proteins and proteinases in developing tooth enamel. Recently, odontoblasts were reported to express amelogenin, the most abundant enamel protein. In this study, we hypothesized that odontoblasts express all enamel proteins and proteases, and we measured their relative mRNA levels in enamel organ epithelia and odontoblasts associated with porcine secretory- and maturation-stage enamel by RT-PCR, using a LightCycler instrument. The results showed that amelogenin mRNA in secretory-stage EOE is 320-fold higher than in odontoblasts beneath secretory-stage enamel, and over 20,000-fold higher than in odontoblasts under maturation-stage enamel. Similar results were obtained for enamelin and sheathlin. Enamelysin mRNA levels were equivalent in these two tissues, while KLK4 mRNA was higher in odontoblasts than in secretory-stage EOE. These results support the conclusion that odontoblasts are involved in the formation of the enamel layer adjacent to enamel-dentin junction.

[Spinal cord protection during thoracoabdominal aortic aneurysm repair; efficacy of distal aortic perfusion and segmental aortic clamping]

Despite improvement in adjuncts for thoracoabdominal aortic aneurysms (TAAA) repairs, many devastating complications remains after the surgery. Our experience with these aneurysms has been reviewed in order to identify those methods at risk of major morbidity, as well as which further improvements required. During last 16 years, 53 consecutive patients were operated on TAAA. The mean age was 58 years. Twenty patients had dissecting aneurysms and 13 patients had had prior aortic surgery. A femoro-femoral bypass was used to maintain distal aortic perfusion in most patients. Reimplantation of intercostal or lumbar arteries under the multi-segmental aortic clamping is consistent in our technique. Motor evoked potentials (MEP) were measured to monitor spinal cord protection since 2000. The hospital mortality was 9.4% (5/53), 22.2% (2/9) for emergency operation and 15.4% (2/13) for patients with prior aortic surgery. The mortality for the first and elective operations was 3.2% (1/31). No any neurologic dysfunction was observed in all patients including the hospital deaths. In view of clinical results, our adjuncts and techniques are useful for prevention of spinal cord ischemia during the TAAA surgery.

Distribution of marine birnavirus in cultured marine fish species from Kagawa Prefecture, Japan

To determine the distribution of marine birnavirus (MABV) in cultured populations of different marine fish species, 1291 pooled tissue samples from 2672 fish belonging to 22 species and one hybrid were collected from Kagawa Prefecture, Japan, during 1999-2001. Using cell-culture MABV was isolated from three species: yellowtail, Seriola quinqueradiata Temminck & Schlegel (positive number/sample number, 10/419), amberjack, S. dumerili (Risso) (4/72), and Japanese flounder, Paralichthys olivaceus (Temminck & Schlegel) (41/481). Using PCR on MABV-negative samples, the MABV genome was detected in the same three species [yellowtail (9/409), amberjack (4/68) and Japanese flounder (93/440)] and two additional species, spotted halibut, Verasper variegatus (Temminck & Schlegel) (5/11), and goldstriped amberjack, S. lalandi Valenciennes (1/5). These MABV-positive species can be taxonomically divided into two groups: the genus Seriola and flatfish. In Japanese flounder, MABV was detected during all seasons, and the infection rate was correlated with water temperature. Aquaculture sites with MABV-positive fish were evenly distributed over the surveyed area, suggesting that MABV is widely distributed at aquaculture sites in Kagawa Prefecture. The nucleotide sequence at the variable region, the VP2/NS junction, revealed that the 39th base mutation occurs host-specifically for flatfish. Flatfish are suspected to be the main reservoir of MABV and might be responsible for establishing the infection cycle in aquaculture environments.

Brain-derived neurotrophic factor upregulates and maintains AMPA receptor currents in neocortical GABAergic neurons

The regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors is implicated in synaptic plasticity. Although we have found that brain-derived neurotrophic factor (BDNF) triggers surface translocation of AMPA receptor proteins, the physiological significance of the BDNF effect remained to be determined. The present immunohistochemical studies revealed that cortical GABAergic neurons exhibited the most striking response to BDNF. Accordingly, we monitored AMPA-triggered currents through GABAergic neurons: Chronic BDNF treatment increased the AMPA-triggered currents but not NMDA-triggered currents in culture. In parallel, the amplitude, but not frequency, of spontaneous miniature excitatory postsynaptic currents (mEPSCs) was elevated in GABAergic neurons. In agreement, BDNF enhanced GABA release triggered by AMPA compared to the amount triggered by high potassium. Conversely, there was a significant decrease in the mEPSC amplitude of GABAergic neurons in heterozygous BDNF-knockout mice. These findings indicate that the neurotrophin enhances the input sensitivity of GABAergic neurons to facilitate their inhibitory function in the neocortex.

Formation mechanism of nitrifying granules observed in an aerobic upflow fluidized bed (AUFB) reactor

The influences of trace metals in the wastewater and shear stress by aeration were particularly examined to clarify the formation mechanism of nitrifying granules in an aerobic upflow fluidized bed (AUFB) reactor. It was found that Fe added as a trace element to the inorganic wastewater accumulated at the central part of the nitrifying granules. Another result obtained was that suitable shear stress by moderate aeration (0.07-0.20 L/min/L-bed) promoted granulation. Furthermore, it was successfully demonstrated that pre-aggregation of seed sludge using hematite promoted core formation, leading to rapid production of nitrifying granules. From these results, a nitrifying granulation mechanism is proposed: 1) as a first step, nitrifying bacteria aggregate along with Fe precipitation, and then the cores of granules are formed; 2) as a second step, the aggregates grow to be spherical or elliptical in form due to multiplication of the nitrifying bacteria and moderate shear stress in the reactor, and then mature nitrifying granules are produced. Fluorescence in situ hybridization (FISH) analysis successfully visualized the change in the spatial distribution of nitrifying bacteria in the granules, which supports the proposed granulation mechanism.

Distinct glutamate receptors govern differential levels of nitric oxide production in a layer-specific manner in the rat cerebellar cortex

To evaluate roles of nitric oxide (NO) in neural functions, it is critical to know how neural inputs activate neuronal NO synthase in individual sites. Although NMDA receptor-dependent mechanism well explains postsynaptic, robust NO production, this sole mechanism does not explain some aspects of NO production in the brain, such as the low-level production of NO and the mechanism for presynaptic NO production. We hypothesized that the glutamate receptor involved in NO production is site-specific and controls the initial NO concentration in each site. We visualized NO production mediated by NMDA, AMPA and type-1 metabotropic glutamate (mGlu-1) receptors in rat cerebellar slices and granule cells in culture, with an NO-specific fluorescent indicator, diaminofluorescein-2. AMPA receptor, but not NMDA or mGlu-1 receptor, was responsible for NO production at parallel fiber terminals, which was blocked by CNQX, tetrodotoxin or voltage-dependent calcium channel blockers. More numbers of electrical stimulation were required for NO production in the molecular layer than in other layers, suggesting that AMPA receptor activation generates NO at lower concentrations through a remote interaction with NO synthase. Although Purkinje cell does not express NO synthase, we detected NO production in Purkinje cell layer following electrical stimulation in the white matter at 50 Hz, but not at 10 Hz. This NO production was tetrodotoxin-sensitive, suggesting occurrence in the basket cell terminals, and required synergistic activation of mGlu-1 and NMDA receptors. In the granule cell layer, activation of AMPA or mGlu-1 receptor produced NO uniformly, while NMDA receptor activation produced NO in discontinuous areas of this layer. Thus, distinct glutamate receptors, including non-NMDA receptors, govern occurrence and level of NO production in a layer-specific manner.

Particulate and dissolved elemental loads in the Kuji River related to discharge rate

In order to investigate influences of discharge rates on fluvial transport behavior of elements in the Kuji River, Japan, suspended and dissolved phase concentrations in the river water were measured together with the water flow rates. The concentrations of suspended particulate matter (SPM) increased by two or three orders of magnitude with the water discharge, and also had seasonal variations. Adsorptive elements or heavy metal elements, which tend to form insoluble compounds, were present generally as suspended forms in the river waters, and their dissolved form concentrations tended to increase with the water discharge. On the other hand, non-adsorptive elements such as alkali and alkaline-earth elements were present as dissolved forms under a normal flow rate condition, but equivalent quantity of suspended species also occurred under a high flow condition. In this case, the dissolved form concentrations decreased with the water discharge. Characterization of SPM with analyses of chemical compositions, scanning electron microscopy (SEM) and X-ray diffractometry (XRD) indicated that clay mineral such as montmorillonite would be the main carrier material of trace and major elements during the fluvial transport in the Kuji River. Variations of contents of selected elements in SPM with the water discharge indicated that river bottom sediments, which are probably potential sources of SPM added due to high water flow rates, would be different in chemical compositions from SPM floating under a normal flow condition. Variations of chemical compositions of SPM as well as of suspended or dissolved form concentrations of elements in the river waters were formulated as a function of the water discharge rates.

Odontoblasts enhance the maturation of enamel crystals by secreting EMSP1 at the enamel-dentin junction

The temporal expression patterns and activity distributions of enamelysin and EMSP1, which are the major proteinases in immature enamel, were characterized. Extracellular matrix fractions from developing porcine incisors, individually comprised of predentin, dentin, and four secretory-stage enamel samples, including the highly mineralized enamel (HME) at the enamel-dentin junction (EDJ), were isolated, and their resident proteinases were identified by zymography. Soft-tissue fractions, which included cells from the extension site of enamel formation (ESEF), secretory- and maturation-stage ameloblasts, and odontoblasts, were characterized histologically and by RT-PCR for their expression of enamelysin and EMSP1. A significant finding was that EMSP1, expressed by odontoblasts, concentrates in the HME, but is not detected in predentin or dentin. We conclude that odontoblasts deposit EMSP1 via their cell processes into the deepest enamel layer, which facilitates the hardening of this layer and contributes significantly to the functional properties of the EDJ.

Amelogenin gene expression in porcine odontoblasts

Amelogenin is the major organic component in the enamel matrix of developing teeth and plays an important role in enamel biomineralization. Amelogenin has been reported to be a specific secretory product of ameloblasts. In this study, we examined amelogenin gene expression in various cell layers prepared from a porcine permanent tooth germ using reverse transcription-polymerase chain-reaction (RT-PCR). Amelogenin amplification products were detected only in the secretory ameloblast layer after 20 cycles of PCR. After 30 cycles of PCR, amelogenin amplification products were detected in secretory and maturation-stage ameloblasts and in odontoblasts. The relative levels of amelogenin gene expression in secretory and maturation-stage ameloblasts and odontoblasts were determined. Secretory ameloblasts expressed over 1000 times the level of amelogenin mRNA found in odontoblasts. Amelogenin gene expression in odontoblasts was confirmed in an erupted porcine permanent first molar, which has no ameloblasts. Amelogenin PCR amplification products were identified from 4 different alternatively spliced transcripts in the ameloblast samples, and the same spliced forms were detected in the odontoblast samples.

Enhancement of salivary secretion and neuropeptide (substance P, alpha-calcitonin gene-related peptide) levels in saliva by chronic anethole trithione treatment

Anethole trithione, a choleretic, has been reported to be effective in the treatment of dry mouth. We have examined the effects of chronic treatment with anethole trithione on salivary secretion, substance P immunoreactive substance (SP-IS) and alpha-calcitonin gene-related peptide immunoreactive substance (alpha-CGRP-IS) concentrations in human saliva. Anethole trithione caused significant increases of saliva SP-IS concentrations from the day 13 (25.3 +/- 1.6 pg mL(-1)) to day 14 (25.8 +/- 1.7 pg mL(-1)) compared with day 1 (19.9 +/- 1.9 pg mL(-1)). Anethole trithione caused significant increase in saliva alpha-CGRP-IS concentration on day 14 (39.9 +/- 4.7 pg mL(-1)) compared with day 1 (27.7 +/- 4.7 pg mL(-1)). Anethole trithione significantly increased the sialosis volumes from day 11 to day 14 (1.6 +/- 0.1-1.7 +/- 0.2 mL) compared with the day 1 (1.2 +/- 0.2 mL). Simple linear regression of the increase in sialosis volume with saliva SP-IS (r = 0.94) and alpha-CGRP-IS (r = 0.97) concentrations was found. These results demonstrated that chronic treatment with anethole trithione affected saliva SP-IS and alpha-CGRP-IS concentration in human saliva and sialosis volume.

Sphingosine 1-phosphate contracts canine basilar arteries in vitro and in vivo: possible role in pathogenesis of cerebral vasospasm

BACKGROUND AND PURPOSE

Sphingosine 1-phosphate (S1P) is a platelet-derived bioactive lipid that exerts a variety of biological responses, including vasocontraction. To understand the involvement of S1P in cerebral vasospasm, we investigated the effect of S1P on vasocontraction of the canine basilar artery in vitro and in vivo.

METHODS

We recorded isometric tension in basilar arterial rings from dogs in vitro and estimated time-course changes in the diameter of canine basilar arteries and the S1P concentration in cerebrospinal fluid (CSF) by angiography and radioreceptor assays, respectively, after administering S1P into the cisterna magna. Changes in the supernatant S1P concentration during clot formation were monitored by using the in vitro subarachnoid hemorrhage model, in which blood is mixed with CSF.

RESULTS

At concentrations ranging between 100 nmol/L and 10 micromol/L, S1P induced a dose-dependent contraction of the basilar artery in vitro. This effect was significantly inhibited by Y-27632, a highly selective Rho-kinase inhibitor. The administration of S1P into the CSF induced a 60% to 70% decrease in the arterial diameter within 15 minutes, and vasocontraction continued for 2 days thereafter. The concentration of S1P in the supernatant during clot formation in vitro reached approximately 300 nmol/L.

CONCLUSIONS

S1P induces vasocontraction in the canine basilar artery in vitro and in vivo, possibly through a mechanism involving activation of the Rho/Rho-kinase pathway. Thus, S1P might be considered as a novel spasmogenic substance involved in cerebral vasospasm after subarachnoid hemorrhage.

An outbreak of VHSV (viral hemorrhagic septicemia virus) infection in farmed Japanese flounder Paralichthys olivaceus in Japan

A rhabdoviral disease occurred in farmed populations of market sized Japanese flounder (hirame) Paralichthys olivaceus in the Seto Inland Sea of Japan in 1996. The causative agent was identified as viral hemorrhagic septicemia virus (VHSV) based on morphological, immunological, and genetic analyses. Diseased fish that were artificially injected with a representative virus isolate showed the same pathological signs and high mortality as observed in the natural outbreak. This is the first report of an outbreak of VHSV infection in cultured fish in Japan. Clinical signs of diseased fish included dark body coloration, an expanded abdomen due to ascites, congested liver, splenomegaly, and a swollen kidney. Myocardial necrosis was most prominent and accompanied by inflammatory reactions. Necrotic lesions also occurred in the liver, spleen and hematopoietic tissue, and were accompanied by circulatory disturbances due to cardiac failure. Hemorrhagic lesions did not always appear in the lateral musculature. Transmission electron microscopy revealed many rhabdovirus particles and associated inclusion bodies containing nucleocapsids in the necrotized myocardium. The histopathological findings indicated that the necrotizing myocarditis could be considered a pathognomonic sign of VHSV infection in Japanese flounder.

N-methyl-D-aspartate-induced alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) receptor down-regulation involves interaction of the carboxyl terminus of GluR2/3 with Pick1. Ligand-binding studies using Sindbis vectors carrying AMPA receptor decoys

The dynamics of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)-type glutamate receptors, as represented by their exocytosis, endocytosis and cytoskeletal linkage, has often been implicated in N-methyl-d-aspartate (NMDA)-dependent synaptic plasticity. To explore the molecular mechanisms underlying the AMPA receptor dynamics, cultured hippocampal neurons were stimulated with 100 microm NMDA, and the biochemical and pharmacological changes in the ligand binding activity of AMPA receptor complexes and its subunits, GluR1 and GluR2/3, were investigated. The NMDA treatment reduced the total amount of bound [(3)H]AMPA on the surface of the neurons but not in their total membrane fraction. This process was mimicked by a protein kinase C activator, phorbol ester, but blocked by an inhibitor of the same kinase, calphostin C. The NMDA-induced down-regulation of the ligand binding activity was also reflected by the decreased AMPA-triggered channel activity as well as by the cells' reduced immunoreactivity for GluR1. In parallel, the NMDA treatment markedly altered the interaction between the AMPA receptor subunits and their associating molecule(s); the association of PDZ molecules, including Pick1, with GluR2/3 was enhanced in a protein-kinase-C-dependent manner. Viral expression vectors carrying GluR1 and GluR2 C-terminal decoys, both fused to enhanced green fluorescent protein, were transfected into hippocampal neurons to disrupt their interactions. The overexpression of the C-terminal decoy for GluR2 specifically and significantly blocked the NMDA-triggered reduction in [(3)H]AMPA binding, whereas that for GluR1 had no effects. Co-immunoprecipitation using anti-Pick1 antibodies revealed that the overexpressed GluR2 C-terminal decoy indeed prevented Pick1 from interacting with the endogenous GluR2/3. Therefore, these observations suggest that the NMDA-induced down-regulation of the functional AMPA receptors involves the interaction between GluR2/3 subunits and Pick1.

Role of Rab3 GDP/GTP exchange protein in synaptic vesicle trafficking at the mouse neuromuscular junction

The Rab3 small G protein family consists of four members, Rab3A, -3B, -3C, and -3D. Of these members, Rab3A regulates Ca(2+)-dependent neurotransmitter release. These small G proteins are activated by Rab3 GDP/GTP exchange protein (Rab3 GEP). To determine the function of Rab3 GEP during neurotransmitter release, we have knocked out Rab3 GEP in mice. Rab3 GEP-/- mice developed normally but died immediately after birth. Embryos at E18.5 showed no evoked action potentials of the diaphragm and gastrocnemius muscles in response to electrical stimulation of the phrenic and sciatic nerves, respectively. In contrast, axonal conduction of the spinal cord and the phrenic nerve was not impaired. Total numbers of synaptic vesicles, especially those docked at the presynaptic plasma membrane, were reduced at the neuromuscular junction approximately 10-fold compared with controls, whereas postsynaptic structures and functions appeared normal. Thus, Rab3 GEP is essential for neurotransmitter release and probably for formation and trafficking of the synaptic vesicles.

Infectivity of aquabirnavirus strains to various marine fish species

To determine the infectivity of marine birnavirus (MABV) in various marine fish species, experimental infection was performed in combination groups of 5 fish species with 7 strains of MABV and 1 strain of infectious pancreatic necrosis virus (IPNV). Mortality was observed in yellowtail Seriola quinqueradiata and amberjack S. dumerili infected with MABV strains Y-6, Y-10K and H-1, but not in other infected species. MABV was reisolated from most combination groups, but the virus isolation rate and virus infectivity titer were often significantly different among groups with the same fish species or with the same virus strain. All MABV strains replicated well in makogarei Limanda yokohamae, but only slightly in tiger puffer Takifugu rubiipes. IPNV also replicated in all fish species without causing death. The isolation rate and infectivity titer of IPNV were similar to or higher than those of non-virulent strains of MABV. In conclusion, the infectivity of MABV for different fish species is considered to change, which is an important factor in the development of the infection cycle of this virus among marine organisms.