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The Journal of General Physiology Nov 1966The ionic mechanism of the electropositive olfactory receptor potential was studied in the bullfrog and the swamp frog. The positive receptor potential strikingly...
The ionic mechanism of the electropositive olfactory receptor potential was studied in the bullfrog and the swamp frog. The positive receptor potential strikingly decreased in amplitude in chloride-free solution. When the olfactory epithelium was immersed in high-KCl-Ringer's solution and then in Cl-free, high-K solution, the polarity of the positive potential could be reversed. This is supposed to be due to the exit of the increased internal chloride ion. From the above two experiments it is concluded that the positive olfactory receptor potential depends primarily upon the influx of the chloride ion through the olfactory receptive membrane. Some contribution by potassium and possibly other ions may occur. The ability of other anions to substitute for chloride was examined. It was found that only Br-, F-, and HCO2- could penetrate the olfactory receptive membrane. The sieve hypothesis in the inhibitory post-synaptic membrane (Coombs, Eccles, and Fatt, 1955) is not applicable to the olfactory receptive membrane on the basis of the size of hydrated ions, but it may be applicable on the basis of the sizes of naked ions.
Topics: Animals; Anions; Bicarbonates; Bromine; Cell Membrane Permeability; Chlorides; Iodine; Membrane Potentials; Olfactory Receptor Neurons; Potassium; Rana catesbeiana; Sulfates
PubMed: 11526841
DOI: 10.1085/jgp.50.2.473 -
Journal of Neurophysiology Aug 2008The basal ganglia (BG) play a critical role in the pathogenesis and pathophysiology of Parkinson's disease (PD). Recent studies indicate that serotoninergic systems...
The basal ganglia (BG) play a critical role in the pathogenesis and pathophysiology of Parkinson's disease (PD). Recent studies indicate that serotoninergic systems modulate BG activity and may be implicated in the pathophysiology and treatment of PD. The globus pallidus (GP), the rodent homologue of the primate GPe, is the main central nucleus of the basal ganglia, affecting the striatum, the subthalamic nucleus (STN), and BG output structures. We therefore studied the effect of serotonin (5-HT) and specific 5-HT agonists and antagonists on GP neurons from rat brain slices. Using intra- and extracellular recordings of GP neurons we found that serotonin increases the firing rate of GP neurons. Analyzing the effects of specific 5-HT agonists and antagonists on the firing rate of GP neurons showed that the increase in firing rate is due to the activation of 5-HT1B and 5-HT1A receptors. Intracellular recordings in both voltage- and current-clamp modes revealed that serotonin mediates its effect via pre- and postsynaptic mechanisms. The presynaptic effect is mediated by attenuation of gamma-aminobutyric acid release, probably through activation of 5-HT1B receptors. Postsynaptically, serotonin activates a hyperpolarization-activated cation channel, probably via 5-HT1A receptors. Furthermore, serotonin decreases the fast synaptic depression characteristic of the striatal afferent input. The decreased serotonin concentrations in the BG nuclei in PD may contribute to depressed GP activity and enhance the emergence of BG pathological synchronous oscillations. We therefore suggest that future therapeutics of PD should be directed toward restoration of normal serotonin levels in BG nuclei.
Topics: Animals; Animals, Newborn; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Electric Stimulation; GABA Antagonists; Globus Pallidus; In Vitro Techniques; Membrane Potentials; Neurons; Patch-Clamp Techniques; Presynaptic Terminals; Pyridazines; Rats; Serotonin; Serotonin Agents; Synapses; gamma-Aminobutyric Acid
PubMed: 18550726
DOI: 10.1152/jn.00845.2007 -
Brain Research Nov 1996The detailed mechanisms underlying long-term potentiation (LTP) are not known. In hippocampal CA1, translocation of protein kinase C (PKC) activity from cytosol to...
The detailed mechanisms underlying long-term potentiation (LTP) are not known. In hippocampal CA1, translocation of protein kinase C (PKC) activity from cytosol to membrane and subsequent phosphorylation of growth associated protein (GAP)-43 have been demonstrated to be critical events for the maintenance phase of LTP. LTP in mossy fiber (MF)-CA3 pathway and the Schaffer collateral/commissural (SC)-CA1 pathway differ in a number of ways: SC-CA1 LTP depends on NMDA receptors while MF-CA3 LTP does not, and SC-CA1 LTP is primarily postsynaptic while MF-CA3 LTP is primarily presynaptic. The role of PKC in MF-CA3 LTP has not been studied. We investigated the role of PKC in CA3 and show that PKC inhibitors prevent LTP, but that PKC activators produce a reversible synaptic potentiation, indicating that PKC activation is an essential but not sufficient component of LTP in CA3. Then using antibodies against specific PKC isozymes we have determined the membrane vs. cytosolic distribution of various PKC isozymes in slices subjected to low or tetanic stimulation, or perfused with phorbol esters (PDAc). Compared with control, LTP and PDAc slices show greater PKC-alpha and -epsilon immunoreactivity in the membrane fraction, indicating that both LTP and phorbol ester treatment induce translocation of PKC-alpha and -epsilon from cytosol to membrane. However, with PKC-beta and PKC-gamma the only detectable translocation from cytosol to membrane was in the phorbol ester-treated slices. Thus, while phorbol ester treatment causes translocation of PKC-alpha, -beta, -gamma and -epsilon, the only detectable translocation associated with CA3 LTP is that of PKC-alpha and -epsilon.
Topics: Analysis of Variance; Animals; Biological Transport; Cytosol; Electric Stimulation; Hippocampus; In Vitro Techniques; Isoenzymes; Long-Term Potentiation; Male; Membranes; Nerve Fibers; Protein Kinase C; Rats; Rats, Wistar; Subcellular Fractions; Synapses
PubMed: 8955949
DOI: 10.1016/s0006-8993(96)00836-0 -
The Journal of Neuroscience : the... Sep 2008Ionotropic glutamate receptors play important roles in spinal processing of nociceptive sensory signals and induction of central sensitization in chronic pain. Here we...
Ionotropic glutamate receptors play important roles in spinal processing of nociceptive sensory signals and induction of central sensitization in chronic pain. Here we applied highly sensitive freeze-fracture replica labeling to laminae I-II of the spinal dorsal horn of rats and investigated the numbers, densities, and colocalization of AMPA- and NMDA-type glutamate receptors at individual postsynaptic membrane specializations with a high resolution. All glutamatergic postsynaptic membranes in laminae I-II expressed AMPA receptors, and most of them (96%) were also immunoreactive for the NR1 subunit of NMDA receptors. The numbers of gold particles for AMPA and NMDA receptors at individual postsynaptic membranes showed a linear correlation with the size of postsynaptic membrane specializations and varied in the range of 8-214 and 5-232 with median values of 37 and 28, whereas their densities varied in the range of 325-3365/microm(2) and 102-2263/microm(2) with median values of 1115/microm(2) and 777/microm(2), respectively. Virtually all (99%) glutamatergic postsynaptic membranes expressed GluR2, and most of them (87%) were also immunoreactive for GluR1. The numbers of gold particles for pan-AMPA, NR1, and GluR2 subunits showed a linear correlation with the size of postsynaptic surface areas. Concerning GluR1, there may be two populations of synapses with high and low GluR1 densities. In synapses larger than 0.1 microm(2), GluR1 subunits were recovered in very low numbers. Differential expression of GluR1 and GluR2 subunits suggests regulation of AMPA receptor subunit composition by presynaptic mechanism.
Topics: Animals; Dendrites; Freeze Fracturing; Male; Posterior Horn Cells; Rats; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Synapses
PubMed: 18815255
DOI: 10.1523/JNEUROSCI.1551-08.2008 -
Biophysical Journal May 1970Evidence from electron microscopy indicates that the separation between adjacent membranes of the central nervous system (CNS) is less than 500 A and perhaps as small as...
Evidence from electron microscopy indicates that the separation between adjacent membranes of the central nervous system (CNS) is less than 500 A and perhaps as small as 100-250 A. The rapid K(+) efflux associated with the neural action potential may therefore be sufficient to affect the local extracellular potassium concentration and, via their partial dependence upon the potassium equilibrium potential, alter the electrical states of nearby neural and glial membranes. This new concept of a transient and local depolarizing "ionic interaction" between active and inactive membranes of the CNS is here examined theoretically and its magnitude calculated as a function of (a) the intermembrane separation, (b) the membranes' electrochemical characteristics, and (c) the rate at which K(+) can diffuse away from the vicinity of the active (neural) membrane. My results indicate that the interaction is in the millivolt range and therefore significant in the modulation of postsynaptic and presynaptic information processing; in particular configurations the postulated interaction alone may be suprathreshold. Membrane noise and local synchrony in groups of neurons may reflect these local, K(+)-mediated interactions. The transient ionic interaction between active neural and nearby glial membrane is also in the millivolt range; however, the relevance of neuroglia to neuronal function is obscure. Certain pathological states, such as seizure and spreading depression, have an obvious phenomenological correspondence to the results presented here and are briefly discussed.
Topics: Action Potentials; Cell Membrane; Cell Membrane Permeability; Central Nervous System; Diffusion; Kinetics; Membrane Potentials; Microscopy, Electron; Models, Neurological; Neuroglia; Potassium; Synaptic Transmission
PubMed: 4314730
DOI: 10.1016/S0006-3495(70)86310-X -
Proceedings of the National Academy of... Feb 1999At the synapse, presynaptic membranes specialized for vesicular traffic are linked to postsynaptic membranes specialized for signal transduction. The mechanisms that...
At the synapse, presynaptic membranes specialized for vesicular traffic are linked to postsynaptic membranes specialized for signal transduction. The mechanisms that connect pre- and postsynaptic membranes into synaptic junctions are unknown. Neuroligins and beta-neurexins are neuronal cell-surface proteins that bind to each other and form asymmetric intercellular junctions. To test whether the neuroligin/beta-neurexin junction is related to synapses, we generated and characterized monoclonal antibodies to neuroligin 1. With these antibodies, we show that neuroligin 1 is synaptic. The neuronal localization, subcellular distribution, and developmental expression of neuroligin 1 are similar to those of the postsynaptic marker proteins PSD-95 and NMDA-R1 receptor. Quantitative immunogold electron microscopy demonstrated that neuroligin 1 is clustered in synaptic clefts and postsynaptic densities. Double immunofluorescence labeling revealed that neuroligin 1 colocalizes with glutamatergic but not gamma-aminobutyric acid (GABA)ergic synapses. Thus neuroligin 1 is a synaptic cell-adhesion molecule that is enriched in postsynaptic densities where it may recruit receptors, channels, and signal-transduction molecules to synaptic sites of cell adhesion. In addition, the neuroligin/beta-neurexin junction may be involved in the specification of excitatory synapses.
Topics: Aging; Animals; Brain; COS Cells; Cell Adhesion Molecules; Cell Adhesion Molecules, Neuronal; Cerebellum; Disks Large Homolog 4 Protein; Embryonic and Fetal Development; Gene Expression Regulation, Developmental; Guanylate Kinases; Hippocampus; Intracellular Signaling Peptides and Proteins; Membrane Proteins; Mice; Mice, Inbred C57BL; Microscopy, Immunoelectron; Neocortex; Nerve Tissue Proteins; Pyramidal Cells; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Synapses; Synaptophysin; Transfection
PubMed: 9927700
DOI: 10.1073/pnas.96.3.1100 -
Journal of Cell Science May 2013Lethal Giant Larvae (LGL) is a cytosolic cell polarity scaffold whose loss dominantly enhances neuromuscular junction (NMJ) synaptic overgrowth caused by loss of the...
Lethal Giant Larvae (LGL) is a cytosolic cell polarity scaffold whose loss dominantly enhances neuromuscular junction (NMJ) synaptic overgrowth caused by loss of the Fragile X Mental Retardation Protein (FMRP). However, direct roles for LGL in NMJ morphological and functional development have not before been tested. Here, we use confocal imaging and two-electrode voltage-clamp electrophysiology at the Drosophila larval NMJ to define the synaptic requirements of LGL. We find that LGL is expressed both pre- and postsynaptically, where the scaffold localizes at the membrane on both sides of the synaptic interface. We show that LGL has a cell autonomous presynaptic role facilitating NMJ terminal branching and synaptic bouton formation. Moreover, loss of both pre- and postsynaptic LGL strongly decreases evoked neurotransmission strength, whereas the frequency and amplitude of spontaneous synaptic vesicle fusion events is increased. Cell-targeted RNAi and rescue reveals separable pre- and postsynaptic LGL roles mediating neurotransmission. We show that presynaptic LGL facilitates the assembly of active zone vesicle fusion sites, and that neuronally targeted rescue of LGL is sufficient to ameliorate increased synaptic vesicle cycling imaged with FM1-43 dye labeling. Postsynaptically, we show that loss of LGL results in a net increase in total glutamate receptor (GluR) expression, associated with the selective elevation of GluRIIB subunit-containing receptors. Taken together, these data indicate that the presynaptic LGL scaffold facilitates the assembly of active zone fusion sites to regulate synaptic vesicle cycling, and that the postsynaptic LGL scaffold modulates glutamate receptor composition and function.
Topics: Animals; Drosophila Proteins; Drosophila melanogaster; Gene Expression Regulation; Larva; Receptors, Glutamate; Synaptic Membranes; Synaptic Transmission; Tumor Suppressor Proteins
PubMed: 23444371
DOI: 10.1242/jcs.120139 -
The Journal of Neuroscience : the... Sep 2003Kainate receptors function as mediators of postsynaptic currents and as presynaptic modulators of synaptic transmission at mossy fiber synapses. Despite intense research...
Kainate receptors function as mediators of postsynaptic currents and as presynaptic modulators of synaptic transmission at mossy fiber synapses. Despite intense research into the physiological properties of mossy fiber kainate receptors, their subunit composition in the presynaptic and postsynaptic compartments is unclear. Here we describe the distribution of kainate receptor subunits in mossy fiber synapses using subunit-selective antibodies and knock-out mice. We provide morphological evidence for the presynaptic localization of KA1 and KA2 receptor subunits at mossy fiber synapses. Immunogold staining for KA1 and KA2 was commonly seen at synaptic contacts and in vesicular structures. Postsynaptic labeling in dendritic spines was also observed. Although KA1 predominantly showed presynaptic localization, KA2 was concentrated to a greater degree on postsynaptic membranes. Both subunits coimmunoprecipitated from hippocampal membrane extracts with GluR6 but not GluR7 subunits. These results demonstrate that KA1 and KA2 subunits are localized presynaptically and postsynaptically at mossy fiber synapses where they most likely coassemble with GluR6 subunits to form functional heteromeric kainate receptor complexes.
Topics: Animals; Antibody Specificity; Brain Chemistry; Cell Line; Cell Membrane; Hippocampus; Humans; Immunohistochemistry; Kidney; Mice; Mice, Knockout; Mossy Fibers, Hippocampal; Protein Subunits; Receptors, Kainic Acid; Synapses; Transfection; GluK2 Kainate Receptor; GluK3 Kainate Receptor
PubMed: 12954862
DOI: 10.1523/JNEUROSCI.23-22-08013.2003 -
Neuroscience Feb 2015Syntaxins are a family of transmembrane proteins that participate in SNARE complexes to mediate membrane fusion events including exocytosis. Different syntaxins are...
Syntaxins are a family of transmembrane proteins that participate in SNARE complexes to mediate membrane fusion events including exocytosis. Different syntaxins are thought to participate in exocytosis in different compartments of the nervous system such as the axon, the soma/dendrites or astrocytes. It is well known that exocytosis of synaptic vesicles at axonal presynaptic terminals involves syntaxin 1 but distributions of syntaxins on neuronal somal and dendritic, postsynaptic or astroglial plasma membranes are less well characterized. Here, we use pre-embedding immunogold labeling to compare the distribution of two plasma membrane-enriched syntaxins (1 and 4) in dissociated rat hippocampal cultures as well as in perfusion-fixed mouse brains. Comparison of Western blots of neuronal cultures, consisting of a mixture of hippocampal neurons and glia, with glial cultures, consisting of mostly astrocytes, shows that syntaxin 1 is enriched in neuronal cultures, whereas syntaxin 4 is enriched in glial cultures. Electron microscopy (EM)-immunogold labeling shows that syntaxin 1 is most abundant at the plasma membranes of axons and terminals, while syntaxin 4 is most abundant at astroglial plasma membranes. This differential distribution was evident even at close appositions of membranes at synapses, where syntaxin 1 was localized to the plasma membrane of the presynaptic terminal, including that at the active zone, while syntaxin 4 was localized to nearby peri-synaptic astroglial processes. These results show that syntaxin 4 is available to support exocytosis in astroglia.
Topics: Animals; Astrocytes; Cell Membrane; Cells, Cultured; Hippocampus; Qa-SNARE Proteins; Rats; Syntaxin 1
PubMed: 25485479
DOI: 10.1016/j.neuroscience.2014.11.054 -
Neuron Sep 2007NF-kappaB signaling has been implicated in neurodegenerative disease, epilepsy, and neuronal plasticity. However, the cellular and molecular activity of NF-kappaB...
NF-kappaB signaling has been implicated in neurodegenerative disease, epilepsy, and neuronal plasticity. However, the cellular and molecular activity of NF-kappaB signaling within the nervous system remains to be clearly defined. Here, we show that the NF-kappaB and IkappaB homologs Dorsal and Cactus surround postsynaptic glutamate receptor (GluR) clusters at the Drosophila NMJ. We then show that mutations in dorsal, cactus, and IRAK/pelle kinase specifically impair GluR levels, assayed immunohistochemically and electrophysiologically, without affecting NMJ growth, the size of the postsynaptic density, or homeostatic plasticity. Additional genetic experiments support the conclusion that cactus functions in concert with, rather than in opposition to, dorsal and pelle in this process. Finally, we provide evidence that Dorsal and Cactus act posttranscriptionally, outside the nucleus, to control GluR density. Based upon our data we speculate that Dorsal, Cactus, and Pelle could function together, locally at the postsynaptic density, to specify GluR levels.
Topics: Alleles; Animals; Blotting, Western; Cytoplasm; Drosophila; Electrophysiology; I-kappa B Proteins; Image Processing, Computer-Assisted; Immunohistochemistry; Interleukin-1 Receptor-Associated Kinases; Membranes; Microscopy, Electron; Muscles; Mutation; NF-kappa B; Neuromuscular Junction; Protein Processing, Post-Translational; Receptors, Glutamate; Reverse Transcriptase Polymerase Chain Reaction; Synapses
PubMed: 17880891
DOI: 10.1016/j.neuron.2007.08.005