Synaptic Membranes: Cell membranes associated with synapses. Both presynaptic and postsynaptic membranes are included along with their integral or tightly associated specializations for the release or reception of transmitters.Membranes: Thin layers of tissue which cover parts of the body, separate adjacent cavities, or connect adjacent structures.Synaptosomes: Pinched-off nerve endings and their contents of vesicles and cytoplasm together with the attached subsynaptic area of the membrane of the post-synaptic cell. They are largely artificial structures produced by fractionation after selective centrifugation of nervous tissue homogenates.Cell Membrane: The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.Membrane Lipids: Lipids, predominantly phospholipids, cholesterol and small amounts of glycolipids found in membranes including cellular and intracellular membranes. These lipids may be arranged in bilayers in the membranes with integral proteins between the layers and peripheral proteins attached to the outside. Membrane lipids are required for active transport, several enzymatic activities and membrane formation.Intracellular Membranes: Thin structures that encapsulate subcellular structures or ORGANELLES in EUKARYOTIC CELLS. They include a variety of membranes associated with the CELL NUCLEUS; the MITOCHONDRIA; the GOLGI APPARATUS; the ENDOPLASMIC RETICULUM; LYSOSOMES; PLASTIDS; and VACUOLES.Receptors, Neurotransmitter: Cell surface receptors that bind signalling molecules released by neurons and convert these signals into intracellular changes influencing the behavior of cells. Neurotransmitter is used here in its most general sense, including not only messengers that act to regulate ion channels, but also those which act on second messenger systems and those which may act at a distance from their release sites. Included are receptors for neuromodulators, neuroregulators, neuromediators, and neurohumors, whether or not located at synapses.Enkephalin, Leucine: One of the endogenous pentapeptides with morphine-like activity. It differs from MET-ENKEPHALIN in the LEUCINE at position 5. Its first four amino acid sequence is identical to the tetrapeptide sequence at the N-terminal of BETA-ENDORPHIN.Membrane Potentials: The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).Membranes, Artificial: Artificially produced membranes, such as semipermeable membranes used in artificial kidney dialysis (RENAL DIALYSIS), monomolecular and bimolecular membranes used as models to simulate biological CELL MEMBRANES. These membranes are also used in the process of GUIDED TISSUE REGENERATION.Brain: The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.Arthropod Venoms: Venoms from animals of the phylum Arthropoda. Those most investigated are from scorpions and spiders of the class Arachnidae and from ant, bee, and wasp families of the Insecta order Hymenoptera. The venoms contain protein toxins, enzymes, and other bioactive substances and may be lethal to man.Neprilysin: Enzyme that is a major constituent of kidney brush-border membranes and is also present to a lesser degree in the brain and other tissues. It preferentially catalyzes cleavage at the amino group of hydrophobic residues of the B-chain of insulin as well as opioid peptides and other biologically active peptides. The enzyme is inhibited primarily by EDTA, phosphoramidon, and thiorphan and is reactivated by zinc. Neprilysin is identical to common acute lymphoblastic leukemia antigen (CALLA Antigen), an important marker in the diagnosis of human acute lymphocytic leukemia. There is no relationship with CALLA PLANT.Synaptic Vesicles: Membrane-bound compartments which contain transmitter molecules. Synaptic vesicles are concentrated at presynaptic terminals. They actively sequester transmitter molecules from the cytoplasm. In at least some synapses, transmitter release occurs by fusion of these vesicles with the presynaptic membrane, followed by exocytosis of their contents.Erythrocyte Membrane: The semi-permeable outer structure of a red blood cell. It is known as a red cell 'ghost' after HEMOLYSIS.Rats, Inbred Strains: Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations or by parent x offspring matings carried out with certain restrictions. This also includes animals with a long history of closed colony breeding.Membrane Fluidity: The motion of phospholipid molecules within the lipid bilayer, dependent on the classes of phospholipids present, their fatty acid composition and degree of unsaturation of the acyl chains, the cholesterol concentration, and temperature.Glutamates: Derivatives of GLUTAMIC ACID. Included under this heading are a broad variety of acid forms, salts, esters, and amides that contain the 2-aminopentanedioic acid structure.Nerve Tissue ProteinsBrain Chemistry: Changes in the amounts of various chemicals (neurotransmitters, receptors, enzymes, and other metabolites) specific to the area of the central nervous system contained within the head. These are monitored over time, during sensory stimulation, or under different disease states.Elapid Venoms: Venoms from snakes of the family Elapidae, including cobras, kraits, mambas, coral, tiger, and Australian snakes. The venoms contain polypeptide toxins of various kinds, cytolytic, hemolytic, and neurotoxic factors, but fewer enzymes than viper or crotalid venoms. Many of the toxins have been characterized.Microscopy, Electron: Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.Cell Membrane Permeability: A quality of cell membranes which permits the passage of solvents and solutes into and out of cells.Synapses: Specialized junctions at which a neuron communicates with a target cell. At classical synapses, a neuron's presynaptic terminal releases a chemical transmitter stored in synaptic vesicles which diffuses across a narrow synaptic cleft and activates receptors on the postsynaptic membrane of the target cell. The target may be a dendrite, cell body, or axon of another neuron, or a specialized region of a muscle or secretory cell. Neurons may also communicate via direct electrical coupling with ELECTRICAL SYNAPSES. Several other non-synaptic chemical or electric signal transmitting processes occur via extracellular mediated interactions.Receptors, Glutamate: Cell-surface proteins that bind glutamate and trigger changes which influence the behavior of cells. Glutamate receptors include ionotropic receptors (AMPA, kainate, and N-methyl-D-aspartate receptors), which directly control ion channels, and metabotropic receptors which act through second messenger systems. Glutamate receptors are the most common mediators of fast excitatory synaptic transmission in the central nervous system. They have also been implicated in the mechanisms of memory and of many diseases.Basement Membrane: A darkly stained mat-like EXTRACELLULAR MATRIX (ECM) that separates cell layers, such as EPITHELIUM from ENDOTHELIUM or a layer of CONNECTIVE TISSUE. The ECM layer that supports an overlying EPITHELIUM or ENDOTHELIUM is called basal lamina. Basement membrane (BM) can be formed by the fusion of either two adjacent basal laminae or a basal lamina with an adjacent reticular lamina of connective tissue. BM, composed mainly of TYPE IV COLLAGEN; glycoprotein LAMININ; and PROTEOGLYCAN, provides barriers as well as channels between interacting cell layers.Kinetics: The rate dynamics in chemical or physical systems.Cerebral Cortex: The thin layer of GRAY MATTER on the surface of the CEREBRAL HEMISPHERES that develops from the TELENCEPHALON and folds into gyri and sulchi. It reaches its highest development in humans and is responsible for intellectual faculties and higher mental functions.Subcellular Fractions: Components of a cell produced by various separation techniques which, though they disrupt the delicate anatomy of a cell, preserve the structure and physiology of its functioning constituents for biochemical and ultrastructural analysis. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p163)Calcium: A basic element found in nearly all organized tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.Protein Transport: The process of moving proteins from one cellular compartment (including extracellular) to another by various sorting and transport mechanisms such as gated transport, protein translocation, and vesicular transport.Flunitrazepam: A benzodiazepine with pharmacologic actions similar to those of DIAZEPAM that can cause ANTEROGRADE AMNESIA. Some reports indicate that it is used as a date rape drug and suggest that it may precipitate violent behavior. The United States Government has banned the importation of this drug.Calcium Chloride: A salt used to replenish calcium levels, as an acid-producing diuretic, and as an antidote for magnesium poisoning.Carrier Proteins: Transport proteins that carry specific substances in the blood or across cell membranes.Molecular Weight: The sum of the weight of all the atoms in a molecule.Protein Binding: The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.Binding, Competitive: The interaction of two or more substrates or ligands with the same binding site. The displacement of one by the other is used in quantitative and selective affinity measurements.Hippocampus: A curved elevation of GRAY MATTER extending the entire length of the floor of the TEMPORAL HORN of the LATERAL VENTRICLE (see also TEMPORAL LOBE). The hippocampus proper, subiculum, and DENTATE GYRUS constitute the hippocampal formation. Sometimes authors include the ENTORHINAL CORTEX in the hippocampal formation.Receptors, Cholinergic: Cell surface proteins that bind acetylcholine with high affinity and trigger intracellular changes influencing the behavior of cells. Cholinergic receptors are divided into two major classes, muscarinic and nicotinic, based originally on their affinity for nicotine and muscarine. Each group is further subdivided based on pharmacology, location, mode of action, and/or molecular biology.Electrophoresis, Polyacrylamide Gel: Electrophoresis in which a polyacrylamide gel is used as the diffusion medium.Endopeptidases: A subclass of PEPTIDE HYDROLASES that catalyze the internal cleavage of PEPTIDES or PROTEINS.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Receptors, AMPA: A class of ionotropic glutamate receptors characterized by their affinity for the agonist AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid).Neurons: The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.Receptors, N-Methyl-D-Aspartate: A class of ionotropic glutamate receptors characterized by affinity for N-methyl-D-aspartate. NMDA receptors have an allosteric binding site for glycine which must be occupied for the channel to open efficiently and a site within the channel itself to which magnesium ions bind in a voltage-dependent manner. The positive voltage dependence of channel conductance and the high permeability of the conducting channel to calcium ions (as well as to monovalent cations) are important in excitotoxicity and neuronal plasticity.Membrane Transport Proteins: Membrane proteins whose primary function is to facilitate the transport of molecules across a biological membrane. Included in this broad category are proteins involved in active transport (BIOLOGICAL TRANSPORT, ACTIVE), facilitated transport and ION CHANNELS.Oleic Acids: A group of fatty acids that contain 18 carbon atoms and a double bond at the omega 9 carbon.Bungarotoxins: Neurotoxic proteins from the venom of the banded or Formosan krait (Bungarus multicinctus, an elapid snake). alpha-Bungarotoxin blocks nicotinic acetylcholine receptors and has been used to isolate and study them; beta- and gamma-bungarotoxins act presynaptically causing acetylcholine release and depletion. Both alpha and beta forms have been characterized, the alpha being similar to the large, long or Type II neurotoxins from other elapid venoms.Phospholipases: A class of enzymes that catalyze the hydrolysis of phosphoglycerides or glycerophosphatidates. EC 3.1.-.Membrane Glycoproteins: Glycoproteins found on the membrane or surface of cells.Binding Sites: The parts of a macromolecule that directly participate in its specific combination with another molecule.Glycopeptides: Proteins which contain carbohydrate groups attached covalently to the polypeptide chain. The protein moiety is the predominant group with the carbohydrate making up only a small percentage of the total weight.Lipid Bilayers: Layers of lipid molecules which are two molecules thick. Bilayer systems are frequently studied as models of biological membranes.Glutamic Acid: A non-essential amino acid naturally occurring in the L-form. Glutamic acid is the most common excitatory neurotransmitter in the CENTRAL NERVOUS SYSTEM.Polyethylene Glycols: Polymers of ETHYLENE OXIDE and water, and their ethers. They vary in consistency from liquid to solid depending on the molecular weight indicated by a number following the name. They are used as SURFACTANTS, dispersing agents, solvents, ointment and suppository bases, vehicles, and tablet excipients. Some specific groups are NONOXYNOLS, OCTOXYNOLS, and POLOXAMERS.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Receptors, Cell Surface: Cell surface proteins that bind signalling molecules external to the cell with high affinity and convert this extracellular event into one or more intracellular signals that alter the behavior of the target cell (From Alberts, Molecular Biology of the Cell, 2nd ed, pp693-5). Cell surface receptors, unlike enzymes, do not chemically alter their ligands.Magnesium: A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.Membrane Proteins: Proteins which are found in membranes including cellular and intracellular membranes. They consist of two types, peripheral and integral proteins. They include most membrane-associated enzymes, antigenic proteins, transport proteins, and drug, hormone, and lectin receptors.Mitochondrial Membranes: The two lipoprotein layers in the MITOCHONDRION. The outer membrane encloses the entire mitochondrion and contains channels with TRANSPORT PROTEINS to move molecules and ions in and out of the organelle. The inner membrane folds into cristae and contains many ENZYMES important to cell METABOLISM and energy production (MITOCHONDRIAL ATP SYNTHASE).Guinea Pigs: A common name used for the genus Cavia. The most common species is Cavia porcellus which is the domesticated guinea pig used for pets and biomedical research.Neurotransmitter Agents: Substances used for their pharmacological actions on any aspect of neurotransmitter systems. Neurotransmitter agents include agonists, antagonists, degradation inhibitors, uptake inhibitors, depleters, precursors, and modulators of receptor function.Radioligand Assay: Quantitative determination of receptor (binding) proteins in body fluids or tissue using radioactively labeled binding reagents (e.g., antibodies, intracellular receptors, plasma binders).Cells, Cultured: Cells propagated in vitro in special media conducive to their growth. Cultured cells are used to study developmental, morphologic, metabolic, physiologic, and genetic processes, among others.Adenosine Triphosphate: An adenine nucleotide containing three phosphate groups esterified to the sugar moiety. In addition to its crucial roles in metabolism adenosine triphosphate is a neurotransmitter.gamma-Aminobutyric Acid: The most common inhibitory neurotransmitter in the central nervous system.Cattle: Domesticated bovine animals of the genus Bos, usually kept on a farm or ranch and used for the production of meat or dairy products or for heavy labor.Chromatography, High Pressure Liquid: Liquid chromatographic techniques which feature high inlet pressures, high sensitivity, and high speed.Swine: Any of various animals that constitute the family Suidae and comprise stout-bodied, short-legged omnivorous mammals with thick skin, usually covered with coarse bristles, a rather long mobile snout, and small tail. Included are the genera Babyrousa, Phacochoerus (wart hogs), and Sus, the latter containing the domestic pig (see SUS SCROFA).Synaptic Transmission: The communication from a NEURON to a target (neuron, muscle, or secretory cell) across a SYNAPSE. In chemical synaptic transmission, the presynaptic neuron releases a NEUROTRANSMITTER that diffuses across the synaptic cleft and binds to specific synaptic receptors, activating them. The activated receptors modulate specific ion channels and/or second-messenger systems in the postsynaptic cell. In electrical synaptic transmission, electrical signals are communicated as an ionic current flow across ELECTRICAL SYNAPSES.Hydrolysis: The process of cleaving a chemical compound by the addition of a molecule of water.Rats, Sprague-Dawley: A strain of albino rat used widely for experimental purposes because of its calmness and ease of handling. It was developed by the Sprague-Dawley Animal Company.Receptors, GABA-A: Cell surface proteins which bind GAMMA-AMINOBUTYRIC ACID and contain an integral membrane chloride channel. Each receptor is assembled as a pentamer from a pool of at least 19 different possible subunits. The receptors belong to a superfamily that share a common CYSTEINE loop.Protease Inhibitors: Compounds which inhibit or antagonize biosynthesis or actions of proteases (ENDOPEPTIDASES).Tissue Distribution: Accumulation of a drug or chemical substance in various organs (including those not relevant to its pharmacologic or therapeutic action). This distribution depends on the blood flow or perfusion rate of the organ, the ability of the drug to penetrate organ membranes, tissue specificity, protein binding. The distribution is usually expressed as tissue to plasma ratios.Oligopeptides: Peptides composed of between two and twelve amino acids.Cell Line: Established cell cultures that have the potential to propagate indefinitely.Liposomes: Artificial, single or multilaminar vesicles (made from lecithins or other lipids) that are used for the delivery of a variety of biological molecules or molecular complexes to cells, for example, drug delivery and gene transfer. They are also used to study membranes and membrane proteins.Presynaptic Terminals: The distal terminations of axons which are specialized for the release of neurotransmitters. Also included are varicosities along the course of axons which have similar specializations and also release transmitters. Presynaptic terminals in both the central and peripheral nervous systems are included.Models, Biological: Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.Cell Fractionation: Techniques to partition various components of the cell into SUBCELLULAR FRACTIONS.Rats, Wistar: A strain of albino rat developed at the Wistar Institute that has spread widely at other institutions. This has markedly diluted the original strain.Protein Structure, Tertiary: The level of protein structure in which combinations of secondary protein structures (alpha helices, beta sheets, loop regions, and motifs) pack together to form folded shapes called domains. Disulfide bridges between cysteines in two different parts of the polypeptide chain along with other interactions between the chains play a role in the formation and stabilization of tertiary structure. Small proteins usually consist of only one domain but larger proteins may contain a number of domains connected by segments of polypeptide chain which lack regular secondary structure.Extraembryonic Membranes: The thin layers of tissue that surround the developing embryo. There are four extra-embryonic membranes commonly found in VERTEBRATES, such as REPTILES; BIRDS; and MAMMALS. They are the YOLK SAC, the ALLANTOIS, the AMNION, and the CHORION. These membranes provide protection and means to transport nutrients and wastes.Hydrogen-Ion Concentration: The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH = log 1/2[1/(H+)], where (H+) is the hydrogen ion concentration in gram equivalents per liter of solution. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Detergents: Purifying or cleansing agents, usually salts of long-chain aliphatic bases or acids, that exert cleansing (oil-dissolving) and antimicrobial effects through a surface action that depends on possessing both hydrophilic and hydrophobic properties.

Bound forms of Ca taken up by the synaptic plasma membrane. (1/900)

Temperature dependent Ca-binding by the synaptic plasma membrane was increased in the presence of ATP and Mg++. Apparent Km for ATP was about 2.8 X 10(-5) M and optimal concentration of Mg++ was 2 mM in the presence of 2 mM ATP. After preincubation with nonradioactive Ca++, ATP and Mg++ to attain a steady state, addition of 45Ca resulted in remarkable labelling of the membrane, indicating rapid turnover of most of the membrane bound Ca. The presence of oxalate (60 mM) greatly increased Ca up-take on prolonged incubation. The Ca uptake in presence and absence of oxalate had similar substrate specificity and was similarly influenced by various monovalent cations. Furthermore, activities for Ca-uptake in the presence and absence of oxalate could not be separated by sucrose density gradient centrifugation of the synaptic plasma membrane fraction. Accordingly, it was considered that Ca++ in the medium was taken up by surface of the membrane, ATP- and temperature-dependently and then transferred into a cavity where the Ca-oxalate complex is formed.  (+info)

Rapid dendritic morphogenesis in CA1 hippocampal dendrites induced by synaptic activity. (2/900)

Activity shapes the structure of neurons and their circuits. Two-photon imaging of CA1 neurons expressing enhanced green fluorescent protein in developing hippocampal slices from rat brains was used to characterize dendritic morphogenesis in response to synaptic activity. High-frequency focal synaptic stimulation induced a period (longer than 30 minutes) of enhanced growth of small filopodia-like protrusions (typically less than 5 micrometers long). Synaptically evoked growth was long-lasting and localized to dendritic regions close (less than 50 micrometers) to the stimulating electrode and was prevented by blockade of N-methyl-D-aspartate receptors. Thus, synaptic activation can produce rapid input-specific changes in dendritic structure. Such persistent structural changes could contribute to the development of neural circuitry.  (+info)

In vivo modulation of rodent glutathione and its role in peroxynitrite-induced neocortical synaptosomal membrane protein damage. (3/900)

Peroxynitrite, formed by the reaction between nitric oxide and superoxide, leads to the oxidation of proteins, lipids, and DNA, and nitrates thiols such as cysteine and glutathione, and amino acids like tyrosine. Previous in vitro studies have shown glutathione to be an efficient scavenger of peroxynitrite, protecting synaptosomal membranes from protein oxidation, the enzyme glutamine synthetase from inactivation, and preventing the death of hippocampal neurons in culture. The current study was undertaken to see if in vivo modulation of glutathione levels would affect brain cortical synaptosomal membrane proteins and their subsequent reaction with peroxynitrite. Glutathione levels were depleted, in vivo, by injecting animals with 2-cyclohexen-1-one (CHX, 100 mg/kg body weight), and levels of glutathione were enhanced by injecting animals with N-acetylcysteine (NAC, 200 mg/kg body weight), which gets metabolized to cysteine, a precursor of glutathione. Changes in membrane protein conformation and structure in synaptosomes subsequently isolated from these animals were examined using electron paramagnetic resonance, before and after in vitro addition of peroxynitrite. The animals injected with the glutathione depletant CHX showed greater damage to the membrane proteins both before and after peroxynitrite treatment, compared to the non-injected controls. The membrane proteins from animals injected with NAC were comparable to controls before peroxynitrite treatment and were partially protected against peroxynitrite-induced damage. This study showed that modulation of endogenous glutathione levels can affect the degree of peroxynitrite-induced brain membrane damage and may have potential therapeutic significance for oxidative stress-associated neurodegenerative disorders.  (+info)

Diversity of thyrotropin-releasing hormone receptors in the pituitary and discrete brain regions of rats. (4/900)

In order to analyze the receptor properties of central nervous system (CNS)-stimulant thyrotropin-releasing hormone (L-pyroglutamyl-L-histidyl-L-prolinamide, TRH), we evaluated the binding of TRH and its analog taltirelin hydrate ((-)-N-[(S)-hexahydro-1-methyl-2,6-dioxo-4-pyrimidinylcarbonyl]-L- histidyl-L-prolinamide tetrahydrate; taltirelin, TA-0910) in rat anterior pituitary and several brain regions. There was a specific binding of [3H]methyl TRH (MeTRH) in the anterior pituitary, hypothalamus, brain stem, cerebral cortex and cerebellum with Kd values of 1.0-1.6 nM. The inhibition of [3H]MeTRH binding by TRH and taltirelin was monophasic in the anterior pituitary, hypothalamus and brain stem with Ki values of 6.3-8.0 nM and 145.5-170.4 nM for TRH and taltirelin, respectively. In contrast, the biphasic inhibition was revealed in the cerebral cortex and cerebellum. The Ki values for TRH and taltirelin were 4.1-4.3 nM and 67.8-73.4 nM for the high affinity binding site and 3.6-4.2 microM and 82.3-197.5 microM for the low affinity binding site, respectively. Addition of 100 microM GTP or its analog 5'-guanylylimidodiphosphate (Gpp[NH]p) affected neither the biphasic inhibition by TRH nor that by taltirelin. Thus the results suggest the presence of distinct high and low affinity TRH receptors in the CNS in contrast to the pituitary.  (+info)

Studies of excitable membranes. II. A comparison of specializations at neuromuscular junctions and nonjunctional sarcolemmas of mammalian fast and slow twitch muscle fibers. (5/900)

Mammalian fast and slow twitch skeletal muscles are compared by freeze-fracture, thick and thin sectioning, and histochemical techniques using conventional and high voltage electron microscopy. Despite gross morphological differences in endplate structure visualized at relatively low magnifications in this sections, rat extensor digitorum longus (EDL) (fast twitch) and soleus (slow twitch) fibers cannot be distinguished on the basis of size, number, or distribution of molecular specializations of the pre- and postsynaptic junctional membranes exposed by freeze fracturing. Specializations in the cortex of the juxtaneuronal portions of the junctional folds are revealed by high voltage electron stereomicroscopy as a branching, ladder-like filamentous network associated with the putative acetylcholline receptor complexes. These filaments are considered to be involved in restricting the mobility of receptor proteins to the perineuronal aspects of the postynaptic membrane. Although the junctional membranes of both EDL and soleus appear similar, a differential specialization of the secondary synaptic cleft was noted. The extracellular matrix in the bottom of soleus clefts was observed as an ordered system of filamentous "combs," These filamentous arrays have not been detected in EDL junctions. Examination of the extrajunctional sarcolemmas of EDL and soleus reveal additional differences which may be correlated with variations in electrical and contractile properties. For example, particle aggregates termed "square arrays" previously described in the sarcolemmas of some fibers of the rat diaphragm were observed in large numbers in sarcolemmas of EDL fibers but were seldom encountered in soleus fibers. These gross compositional differences in the membranes are discussed in the light of functional differences between fiber types.  (+info)

Effects of specific modifications of several hydroxyls of tetrodotoxin on its affinity to rat brain membrane. (6/900)

The widely used sodium channel blocker tetrodotoxin (TTX) is a compound that has six hydroxyl residues at the C-4, C-6, C-8, C-9, C-10, and C-11 positions in addition to a guanidinium group, which is positively charged in biological pH range. Thirteen analogs of this toxin with structural modifications involving one or more of these hydroxyls were examined on their affinity to a rat brain membrane preparation, which is known to contain sodium channels abundantly. The equilibrium dissociation constants associated with the binding of TTX and its analogs to the sodium channels were estimated, from their ability to inhibit the binding of [3H]saxitoxin, as follows (in nM): TTX, 1.8; chiriquitoxin, 1.0; 11-oxoTTX, 1.5; 11-norTTX-6,6-diol, 1.6; 11-norTTX-6(S)-ol, 23; 11-norTTX-6(R)-ol, 31; 11-deoxyTTX, 37; 6-epiTTX, 39; 4-epiTTX, 68; 4,9-anhydroTTX, 180; TTX-8-O-hemisuccinate, >380; TTX-11-carboxylic acid, >2300; tetrodonic acid, >3600; 5,6,11-trideoxyTTX, >5000. The reduction of the affinity observed with the analogs involving reduction or translocation of the hydroxyls at C-6 and C-11 is indicative of the contribution of these residues to the binding to sodium channels as hydrogen bond donors. The especially large value of the dissociation constant for TTX-11-carboxylic acid is consistent with the idea that the C-11-hydroxyl forms a hydrogen bond with a carboxylic acid residue of the channel protein. The markedly low affinity of TTX-8-O-hemisuccinate may possibly be ascribable to intramolecular salt-bridge formation, which neutralizes the positive charge of the guanidinium group.  (+info)

Empty synaptic vesicles recycle and undergo exocytosis at vesamicol-treated motor nerve terminals. (7/900)

We investigated whether recycled cholinergic synaptic vesicles, which were not refilled with ACh, would join other synaptic vesicles in the readily releasable store near active zones, dock, and continue to undergo exocytosis during prolonged stimulation. Snake nerve-muscle preparations were treated with 5 microM vesamicol to inhibit the vesicular ACh transporter and then were exposed to an elevated potassium solution, 35 mM potassium propionate (35 KP), to release all preformed quanta of ACh. At vesamicol-treated endplates, miniature endplate current (MEPC) frequency increased initially from 0.4 to >300 s-1 in 35 KP but then declined to <1 s-1 by 90 min. The decrease in frequency was not accompanied by a decrease in MEPC average amplitude. Nerve terminals accumulated the activity-dependent dye FM1-43 when exposed to the dye for the final 6 min of a 120-min exposure to 35 KP. Thus synaptic membrane endocytosis continued at a high rate, although MEPCs occurred infrequently. After a 120-min exposure in 35 KP, nerve terminals accumulated FM1-43 and then destained, confirming that exocytosis also still occurred at a high rate. These results demonstrate that recycled cholinergic synaptic vesicles that were not refilled with ACh continued to dock and undergo exocytosis after membrane retrieval. Thus transport of ACh into recycled cholinergic vesicles is not a requirement for repeated cycles of exocytosis and retrieval of synaptic vesicle membrane during prolonged stimulation of motor nerve terminals.  (+info)

The subcellular localizations of atypical synaptotagmins III and VI. Synaptotagmin III is enriched in synapses and synaptic plasma membranes but not in synaptic vesicles. (8/900)

Multiple synaptotagmins are expressed in brain, but only synaptotagmins I and II have known functions in fast, synchronous Ca2+-triggered neurotransmitter release. Synaptotagmin III was proposed to regulate other aspects of synaptic vesicle exocytosis, particularly its slow component. Such a function predicts that synaptotagmin III should be an obligatory synaptic vesicle protein, as would also be anticipated from its high homology to synaptotagmins I and II. To test this hypothesis, we studied the distribution, developmental expression, and localization of synaptotagmin III and its closest homolog, synaptotagmin VI. We find that synaptotagmins III and VI are present in all brain regions in heterogeneous distributions and that their levels increase during development in parallel with synaptogenesis. Furthermore, we show by immunocytochemistry that synaptotagmin III is concentrated in synapses, as expected. Surprisingly, however, we observed that synaptotagmin III is highly enriched in synaptic plasma membranes but not in synaptic vesicles. Synaptotagmin VI was also found to be relatively excluded from synaptic vesicles. Our data suggest that synaptotagmins III and VI perform roles in neurons that are not linked to synaptic vesicle exocytosis but to other Ca2+-related nerve terminal events, indicating that the functions of synaptotagmins are more diverse than originally thought.  (+info)

  • Analysis of the major raft lipids revealed a slight age-related increase in cholesterol levels and such increases might enhance membrane lipid order and prevent further loss of PMCA activity. (
  • Here, we investigate electrical signaling in dendritic spines using voltage-sensitive dye imaging in cortical pyramidal neurons during backpropagating action potentials and synaptic input. (
  • The dendritic trees of neurons are structurally and functionally complex integrative units receiving thousands of synaptic inputs that have excitatory and inhibitory, fast and slow, and electrical and biochemical effects. (
  • The authors review recent data from patch-clamp recordings that provide new estimates of the passive membrane properties of hippocampal neurons, and show, with examples, how these properties affect the shaping and attenuation of synaptic potentials as they propagate in the dendrites, as well as how they affect the measurement of current from synapses located in the dendrites. (
  • Here, we have analyzed the endocytic sorting of GABA A Rs in neurons, revealing that over short time periods internalized GABA A Rs are rapidly recycled to the cell surface membrane, whereas over longer periods receptors are also targeted for lysosomal degradation. (
  • they do not affect the membrane potential of neurons. (
  • The first part of the study focuses on gephyrin's membrane association in neurons with the aim to elucidate the molecular mechanisms and significance of membrane tethering. (
  • This pathogenic variant acted dominant-negatively on regular gephyrin and disrupted the normal gephyrin scaffold and synaptic GABAAR clustering in hippocampal neurons. (
  • Bulbar respiratory neurons display rhythmic fluctuations of membrane potential in synchrony with the respiratory cycle. (
  • However, since these neurons in tissue slices usually lack the spontaneous rhythmic modulation in membrane potential, the identification of the neuron type based upon the spontaneous patterns of firing and membrane potential fluctuations is yet uncertain. (
  • The present study was aimed at elucidating the possible synaptic and non-synaptic mechanisms by which the periodic fluctuations of membrane potential are shaped in bulbar respiratory neurons of the ventral respiratory group. (
  • Ganglionic parasympathetic neurons located in the airways in several species, including humans, have anatomical and electrophysiological properties that limit transmission of preganglionic synaptic input. (
  • These results provide evidence that in contrast to the characteristics of airway parasympathetic neurons reported in other species, including human, the electrophysiological and synaptic properties, and anatomical characteristics of mouse lower airway ganglionic neurons, are less associated with integration of presynaptic input. (
  • Although the active and passive (electrophysiological) membrane properties of airway ganglionic neurons have been reported for several mammalian species ( 13 ), including humans ( 8 ), no studies have focused on mice, a species commonly used in airway asthma and allergy studies ( 23 ). (
  • In humans ( 9 ) and guinea pigs ( 16 ), airway parasympathetic ganglionic neurons display anatomical and electrophysiological characteristics that contribute to regulation of synaptic activity, including tonic and phasic action potential accommodation patterns, long- and short-action potential afterhyperpolarizations (AHPs), and multiple populations of fast excitatory postsynaptic potentials (fEPSPs). (
  • In addition, neurons are highly polarized cells with often long axons, extensively branched dendritic trees and many synaptic contacts. (
  • NG2 expressing oligodendrocyte precursor cells stand out from other types of glial cells by receiving classical synaptic contacts from many neurons. (
  • In fact, synaptic currents recorded in NG2 cells are so similar to synaptic currents recorded in neurons that even experts have a hard time diagnosing the type of cell when judging the electrophysiological recording only. (
  • however, in neurons and glia, specific membrane molecules are concentrated in cellular microdomains to overcome the randomizing effects of free diffusion. (
  • Recent QD-SPT experiments have provided critical insights into the mechanism and physiological relevance of membrane self-organization in neurons and astrocytes in the brain. (
  • Based on these findings, we propose that the behavior of membrane molecules reflects the condition of neurons in pathological disease states. (
  • Another crucial factor regulating synaptic transmission by neurons and hormone release by neuroendocrine cells is membrane tension. (
  • Such gradients relax by membrane flows, which are extremely slow in plasma membranes of non-neuronal cells, or non-terminal regions of neurons. (
  • Synapses connected by various synaptic adhesion molecules are communication spaces between neurons for transmitting information. (
  • Neurons react to learning and memory by activating synaptic connections. (
  • The data are consistent with an initial release of trace amines by simple diffusion, followed by an activity-dependent regulation of synaptic levels via one or more transporter proteins. (
  • It has been hypothesized that neuronal gangliosides are involved in receptors for biogenic amines (1-3) and certain neuro-toxins (4,5), and it is generally, although not universally (6), believed that, in the central nervous system, gangliosides are to be found concentrated in synaptic membranes. (
  • The putative intracellular location of Trace Amine-Associated Receptors necessitate that membrane transport processes be present in order for post-synaptic effects to occur. (
  • The synaptic cleft bridging pre- and post-synaptic compartments is an adhesive zone ~20 nm thick, containing adhesion proteins and neurotransmitter receptors. (
  • The arrival of an impulse at the site of the synapse causes the release of a chemical neurotransmitter which then diffuses across a narrow gap and binds onto the receptors of the postsynaptic neuron, altering the behaviour of the membrane and allowing the movement of ions between the intracellular and extracellular regions. (
  • The results obtained indicated that although the majority of the anti‐GBP Abs were not directed against the glutamate recognition site of the GBP and of presumed synaptic membrane receptors, they were effective in blocking the activation of receptor‐associated ion channels. (
  • one example is the accumulation of neurotransmitter receptors at the postsynaptic neuronal membrane, which enables efficient synaptic transmission. (
  • The regulated internalization has been characterized as a principal mechanism for removing cell-surface receptors from the plasma membrane, and signaling to downstream targets of receptors. (
  • Here we examine the ability of trace amines to cross synthetic (Fluorosomes) and native (synaptosomes) lipid bilayer membranes. (
  • Here, we show that synaptic activity, one of the most important inducers of neurite growth, transcriptionally regulates the expression of neuronal glucose transporter Glut3 and rate‐limiting enzymes of glycolysis, resulting in enhanced glucose uptake and metabolism that is partly used for lipid synthesis. (
  • Analysis of the major raft lipids revealed a slight age-related increase in cholesterol levels and such increases might enhance membrane lipid order and prevent further loss of PMCA activity. (
  • In addition, we have identified the 35 S-labeled lipid-soluble material in these membrane fractions as cerebroside sulfate. (
  • The polypeptide composition of the purified synaptic plasma membranes was compared with the microsomes and mitochondria by polyacrylamide gel electrophoresis in sodium dodecyl sulphate. (
  • In this report we provide biochemical evidence that a highly purified synaptic plasma membrane fraction derived from rat brain, after intraventricular injection of 35S-labeled sodium sulfate, is enriched in a number of large sulfated glycoproteins compared with a purified myelin fraction studied concurrently. (
  • The visual system of the blowfly Calliphora vicina is a good model system to study synaptic transmission in vivo during sensory stimulation. (
  • To dissociate the roles of action potentials and graded potential changes in synaptic transmission we used voltage-clamp-controlled current-clamp techniques to suppress the graded membrane potential changes without affecting action potentials. (
  • If you look at the patient e.g. of Alzheimer's disease, you find a lot of aggregates all over the place, but even then in the path of pathogenesis the first thing that happens is the dysfunction of the synapses - something happens at the synaptic terminals and changes the property of the synaptic transmission. (
  • Vesicle trafficking and remodeling of the cytoskeleton, which are closely linked, are widely accepted to be the pivotal mechanisms of spine growth and contribute to strengthening synaptic transmission. (
  • We use these muscles as well as the superficial, tonic abdominal flexor muscle to demonstrate properties in synaptic transmission. (
  • Two aspects that influence a cell's membrane potential and which we address in these experiments are: (1) Ion concentration of K + on the outside of the membrane, and (2) the permeability of the membrane to specific ions. (
  • The coaxial multi-barrelled microelectrode technique 6 can partly overcome these difficulties as it allows an in vivo intracellular recording of membrane potential in conjunction with an extracellular iontophoresis of drugs which could block action potentials and synaptic waves in the recorded neuron. (
  • However, we have shown that at least one process, conversion by methyltransferase Iodine of phosphatidylethanolamine to phosphatidyl-N-monomethylethanolamine, remained enhanced twofold in neural membranes of rats killed while anesthetized with halothane or isoflurane. (
  • The specific binding of L-[3H]glutamate to hippocampal synaptic membranes was examined in rats kindled by tetanic stimulation of the angular bundle. (
  • Therefore, enriched preparations of synaptic particles called synaptosome are necessary to study synapse function. (
  • In a recent issue of Neuron , published on June 21, 2017, a research team led by Professor Ho Min Kim at the Graduate School of Medical Science and Engineering of KAIST reported the three-dimensional structure of MDGA1/Neuroligin-2 complex and mechanistic insights into how MDGAs negatively modulate synapse development governed by Neurexins/Neuroligins trans -synaptic adhesion complex. (
  • Jung A Kim at KAIST, first author in this study, said, "Our discovery from integrative investigations are an important first step both for a better understanding of Neuroligin/Neurexin synaptic adhesion pathways and MDGA-mediated regulation of synapse development as well as the development of potential new therapies for autism, schizophrenia, and epilepsy. (
  • Here, we sought to localize PDK1 in the NMJ and investigate the hypothesis that synaptic activity and muscle contraction regulate in parallel PDK1 and cPKCβI phosphorylation in the membrane fraction. (
  • We propose that subtle defects in these homeostatic processes can lead to late onset synaptic degeneration. (
  • In this review I aimed to provide a comprehensive view of the cellular processes and molecular key players involved in spatiotemporal regulation of spine growth, starting from the Ca2+ influx as a resultant of synaptic activity. (
  • Integrin alpha-3/beta-1 provides a docking site for FAP (seprase) at invadopodia plasma membranes in a collagen-dependent manner and hence may participate in the adhesion, formation of invadopodia and matrix degradation processes, promoting cell invasion. (
  • Moreover, it is hard to know at what timing any specific ionic conductance becomes active in the respiratory cycle change in membrane potential observed in different types of the respiratory neuron. (
  • The pattern of activation of these synaptic inputs determines if the neuron will fire an action potential at any given point in time and how it will respond to similar inputs in the future. (
  • We recorded extracellularly from an identified motion-sensitive neuron while simultaneously measuring and controlling the membrane potential of individual elements of its presynaptic input ensemble. (