[Alzheimer's disease, amyloid peptide and synaptic dysfunction].

Alzheimer's disease (AD) is the first cause of dementia that leads to insidious and progressive loss of memory and cognitive functions. In the early stages of AD, there is a strong correlation between memory impairment and cortical levels of soluble amyloid-β peptide oligomers (Aβ). It has become clear that Aβ disrupt glutamatergic synaptic function, which in turn may lead to the characteristic cognitive deficits.

Early temporal short-term memory deficits in double transgenic APP/PS1 mice.

We tested single APP (Tg2576) transgenic, PS1 (PS1dE9) transgenic, and double APP/PS1 transgenic mice at 3 and 6 months of age on the acquisition of a hippocampal-dependent operant "differential reinforcement of low rate schedule" (DRL) paradigm. In this task mice are required to wait for at least 10 seconds (DRL-10s) between 2 consecutive nose poke responses. Our data showed that while single APP and PS1 transgene expression did not affect DRL learning and performance, mice expressing double APP/PS1 transgenes were impaired in the acquisition of DRL-10s at 6 months, but not at 3 months of age.

Local facilitation of hippocampal metabotropic glutamate receptor-dependent long-term depression by corticosterone and dexamethasone.

Long-term potentiation and long-term depression (LTD) of synaptic efficacy, two major forms of synaptic plasticity, are believed to underlie learning processes and memory storage. We have recently shown that acute stress, through corticosterone release and stimulation of glucocorticoid receptors (GRs), facilitates the LTD elicited by the group 1 metabotropic glutamate receptor (mGluR) agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG) in hippocampal CA1 neurons. However, it is unknown whether sustained corticosterone release, per se, is also able to facilitate DHPG-elicited LTD in control (i.

A comparison of image deconvolution algorithms applied to the detection of endocytic vesicles in fluorescence images of neural proteins.

In this work we present a comparative study of three image deconvolution methods applied to fluorescence images of neural proteins. The purpose of this work is to compare the efficiency of these methods, in order to establish which one performs better the restoration of this type o image. Moreover we show that image deconvolution improve not only image quality, but detection capabilities and thus the counting of endocytic vesicles.

Acute stress facilitates hippocampal CA1 metabotropic glutamate receptor-dependent long-term depression.

Acute stress affects NMDA receptor (NMDAR)-dependent synaptic plasticity in the CA1 region of the hippocampus, with long-term potentiation and long-term depression (LTD) being, respectively, diminished and facilitated by acute exposure to stress. Here, we examined whether this facilitatory effect of stress on NMDAR-dependent LTD extends to metabotropic glutamate receptor (mGluR)-dependent LTD at Schaffer collateral-CA1 synapses. Application of a low dose (50 microM) of the selective group 1 mGluR agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) promoted LTD in slices from stressed, but not from control, rats.

The calcium-sensing protein synaptotagmin 7 is expressed on different endosomal compartments in endocrine, neuroendocrine cells or neurons but not on large dense core vesicles.

Synaptotagmin (syt) isoforms function as calcium sensor in post-Golgi transport although the precise transport step and compartment(s) concerned are still not fully resolved. As syt7 has been proposed to operate in lysosomal exocytosis and in exocytosis of large dense core vesicles (LDCVs), we have addressed the distribution of endogenous syt7 in insulin-secreting cells. These cells express different syt7 isoforms comparable to neurons.

The cytosolic domain of APP induces the relocalization of dynamin 3 in hippocampal neurons.

Amyloid precursor protein (APP) has been the subject of intense research to uncover its implication in Alzheimer's disease. Its physiological function is, however, still poorly understood. Herein, we investigated its possible influence on the development of cultured hippocampal neurons.

Immunolocalization and high affinity interactions of acyl-CoAs with proteins: an original study with anti-acyl-CoA antibodies.

Anti-acyl-Coenzyme A (acyl-CoA) antibodies were used to detect fatty acyl-CoAs in cultured rat hippocampal neurons, in which important lipid metabolism and transport occur. Hippocampus was chosen because of his involvement in many cerebral functions and diseases. Immunofluorescence experiments showed an intense labelling within neurites and cell bodies.

Synaptotagmin 8 is expressed both as a calcium-insensitive soluble and membrane protein in neurons, neuroendocrine and endocrine cells.

Synaptotagmins (syt) form a large family of transmembrane proteins and some of its isoforms are known to regulate calcium-induced membrane fusion during vesicular traffic. In view of the reported implication of the isoform syt8 in exocytosis we investigated the expression, localisation and calcium-sensitivity of syt8 in secretory cells. An immunopurified antipeptide antibody was generated which is directed against a C-terminal sequence and devoid of crossreactivity towards syt1 to 12.

A single in vivo exposure to cocaine abolishes endocannabinoid-mediated long-term depression in the nucleus accumbens.

In the nucleus accumbens (NAc), a key structure to the effects of all addictive drugs, presynaptic cannabinoid CB1 receptors (CB1Rs) and postsynaptic metabotropic glutamate 5 receptors (mGluR5s) are the principal effectors of endocannabinoid (eCB)-mediated retrograde long-term depression (LTD) (eCB-LTD) at the prefrontal cortex-NAc synapses. Both CB1R and mGluR5 are involved in cocaine-related behaviors; however, the impact of in vivo cocaine exposure on eCB-mediated retrograde synaptic plasticity remains unknown. Electrophysiological and biochemical approaches were used, and we report that a single in vivo cocaine administration abolishes eCB-LTD.

Active surface transport of metabotropic glutamate receptors through binding to microtubules and actin flow.

Receptors for neurotransmitters are concentrated and stabilized at given sites such as synapses through interactions with scaffolding proteins and cytoskeletal elements. The transport of receptors first involves directed vesicular trafficking of intracellularly stored receptors followed by their targeting to the plasma membrane. Once expressed at the cell surface, receptors are thought to reach their final location by random Brownian diffusion in the plasma membrane plane.

Dynamin 3 is a component of the postsynapse, where it interacts with mGluR5 and Homer.

The dynamins comprise a large family of mechanoenzymes known to participate in membrane modeling events. All three conventional dynamin genes (Dyn1, Dyn2, Dyn3) are expressed in mammalian brain and produce more than 27 different dynamin proteins as a result of alternative splicing. Past studies have suggested that Dyn1 participates in specialized neuronal functions such as rapid synaptic vesicle recycling, while Dyn2 may mediate the conventional clathrin-mediated uptake of surface receptors.

The metabotropic glutamate receptor mGluR5 is endocytosed by a clathrin-independent pathway.

Metabotropic glutamate receptors 5 (mGluR5) are members of the growing group C G protein-coupled receptor family. Widely expressed in mammalian brain, they are involved in modulation of the glutamate transmission. By means of transfection of mGluR5 receptors in COS-7 cells and primary hippocampal neurons in culture followed by immunocytochemistry and quantitative image analysis and by a biochemical assay, we have studied the internalization of mGluR5 splice variants.

Receptor activation and homer differentially control the lateral mobility of metabotropic glutamate receptor 5 in the neuronal membrane.

Glutamate receptors are clustered at the membrane through interactions with intracellular scaffolding proteins and cytoskeletal elements but can also be found in intracellular compartments or dispersed in the membrane. This distribution results from an equilibrium between the different pools of receptors whose dynamic is poorly known. The group I metabotropic glutamate receptor 5 (mGluR5) is concentrated in an annulus around the postsynaptic density but also found in large amounts in the extrasynaptic membrane.

Dendroaxonal transcytosis of transferrin in cultured hippocampal and sympathetic neurons.

Previous studies using overexpressed polymeric immunoglobulin receptor in cultured neurons have suggested that these cells may use a dendroaxonal transcytotic pathway (Ikonen et al., 1993; de Hoop et al., 1995).

Hairpin, dumbbell, and single-stranded phosphodiester oligonucleotides exhibit identical uptake in T lymphocyte cell lines.

The cellular binding, uptake, and intracellular distribution of structured double-stranded phosphodiester oligonucleotides (decoys) have been examined in T lymphocytes using fluorescein-labeled molecules. Intracellular localization of hairpin and dumbbell decoys was similar to that of single-stranded oligonucleotides. At short incubation times, oligonucleotides were localized only in cytoplasmic vesicles, whereas at longer times, they were also found in the nucleus.

The Staphylococcus aureus enterotoxin B superantigen induces specific T cell receptor down-regulation by increasing its internalization.

Superantigens are able to stimulate T lymphocyte populations expressing T cell antigen receptors (TCR) belonging to particular V beta families. Moreover, the presence of these superantigens may induce long term unresponsiveness (anergy) of these sensitive cells. Some bacterial toxins are potent superantigens.

Endocytosis of interleukin 2 receptors in human T lymphocytes: distinct intracellular localization and fate of the receptor alpha, beta, and gamma chains.

Members of the cytokine receptor family are composed of several noncovalently linked chains with sequence and structure homologies in their extracellular domain. Receptor subfamily members share at least one component: thus the receptors for interleukin (IL) 2 and IL15 have common beta and gamma chains, while those for IL2, 4, 7, and 9 have a common gamma chain. The intracellular pathway followed by IL2 receptors after ligand binding and endocytosis was analyzed by immunofluorescence and confocal microscopy in a human T lymphocytic cell line.

Rapid endocytosis of interleukin 2 receptors when clathrin-coated pit endocytosis is inhibited.

The cytokine interleukin 2 (IL2) is produced by activated helper T lymphocytes and modulates the growth and activity of cells expressing high-affinity surface IL2 receptors that transduce its signaling. After ligand binding to receptors on the plasma membrane, receptor-ligand complexes are rapidly endocytosed and IL2 is degraded in acidic compartments. The best known receptor-mediated endocytosis pathway involves clathrin-coated pits.

Endocytosis of the beta chain of interleukin-2 receptor requires neither interleukin-2 nor the gamma chain.

Interleukin-2 (IL-2) and IL-2 receptors (IL-2R) critically regulate the magnitude and duration of T cell expansion required in an immune response. Modulation occurs at the level of receptor number and affinity. IL-2R is a multisubunit receptor which contains at least three chains, IL-2R alpha (p55), IL-2R beta (p70) and IL-2R gamma (p64).

Transcriptional and post-transcriptional mechanisms are involved in the absence of CD4 surface expression in two HIV-1 chronically infected T cell lines.

In vivo infection of human T cell lymphocytes by HIV-1 is mediated by the specific binding of the HIV-1 envelope glycoprotein gp120 to the T cell CD4 receptor. One of the post-infection events observed in vivo is the progressive loss of CD4+ T cells. One possible mechanism is the production of infected T cells which are lacking in surface expression of the CD4 receptor protein.

Both the alpha and beta chains of high-affinity interleukin 2 receptors are located in intracellular vesicles when their ligand is endocytosed.

The growth factor interleukin 2 (IL2) binds to high and low-affinity receptors (Kd approximately 10-100 pM and 10 nM, respectively) present on activated T lymphocytes. High-affinity receptors are composed of two non-convalently linked polypeptides, alpha and beta of 55 and 70 kDa. These two polypeptides do not share any sequence homology, but each of them, in the absence of the other, binds IL2: alpha with a Kd approximately 10 nM and beta with a Kd approximately 1 nM.

A triple helix-forming oligonucleotide-intercalator conjugate acts as a transcriptional repressor via inhibition of NF kappa B binding to interleukin-2 receptor alpha-regulatory sequence.

Oligonucleotide-directed triplex formation within upstream regulatory sequences is envisioned as a potential tool for gene inhibition. However, this approach requires that triple helix-forming oligonucleotides are chemically modified, so that the triplex is stable under physiological conditions. Here, we have compared several chemical modifications of an oligonucleotide, targeted to a natural 15-base pair homopyrimidine.

Activity of the kappa B enhancer of the interleukin-2 receptor alpha chain in somatic cell hybrids is accompanied by the nuclear localization of NF-kappa B.

The two nuclear proteins NF-kappa B (consisting of subunits p50 an dp65) and the DNA-binding subunit of NF-kappa B (p50) by itself, also called KBF1, are constitutively expressed and localized in the nucleus of the human T-cell line IARC 301.5. In order to define the roles of these two factors, which bind to the same kappa B enhancers, in transcription activation we have prepared somatic cell hybrids between IARC 301.