Long-term potentiation of synaptic transmission in the hippocampus is the primary experimental model for investigating the synaptic basis of learning and memory in vertebrates. The best understood form of long-term potentiation is induced by the activation of the N-methyl-D-aspartate receptor complex. This subtype of glutamate receptor endows long-term potentiation with Hebbian characteristics, and allows electrical events at the postsynaptic membrane to be transduced into chemical signals which, in turn, are thought to activate both pre- and postsynaptic mechanisms to generate a persistent increase in synaptic strength.

A synaptic model of memory: long-term potentiation in the hippocampus

▪ Abstract Synaptic transmission is a dynamic process. Postsynaptic responses wax and wane as presynaptic activity evolves. This prominent characteristic of chemical synaptic transmission is a crucial determinant of the response properties of synapses and, in turn, of the stimulus properties selected by neural networks and of the patterns of activity generated by those networks. This review focuses on synaptic changes that result from prior activity in the synapse under study, and is restricted to short-term effects that last for at most a few minutes. Forms of synaptic enhancement, such as facilitation, augmentation, and post-tetanic potentiation, are usually attributed to effects of a residual elevation in presynaptic [Ca2+]i, acting on one or more molecular targets that appear to be distinct from the secretory trigger responsible for fast exocytosis and phasic release of transmitter to single action potentials. We discuss the evidence for this hypothesis, and the origins of the different kinetic phases...

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Short-Term Synaptic Plasticity

This work was supported by grants from the National Institutes of Health (R01 AG048814, B.A.B.; RO1 DA15043, B.A.B.; P50 NS38377, V.L.D. and T.M.D.) Christopher and Dana Reeve Foundation (B.A.B.), the Novartis Institute for Biomedical Research (B.A.B.), Dr. Miriam and Sheldon G. Adelson Medical Research Foundation (B.A.B.), the JPB Foundation (B.A.B., T.M.D.), the Cure Alzheimer’s Fund (B.A.B.), the Glenn Foundation (B.A.B.), the Esther B O’Keeffe Charitable Foundation (B.A.B.), the Maryland Stem Cell Research Fund (2013-MSCRFII-0105-00, V.L.D.; 2012-MSCRFII-0268-00, T.M.D.; 2013-MSCRFII-0105-00, T.M.D.; 2014-MSCRFF-0665, M.K.). S.A.L. was supported by a postdoctoral fellowship from the Australian National Health and Medical Research Council (GNT1052961), and the Glenn Foundation Glenn Award. L.E.C. was funded by a Merck Research Laboratories postdoctoral fellowship (administered by the Life Science Research Foundation). W.-S.C. was supported by a career transition grant from NEI (K99EY024690). C.J.B. was supported by a postdoctoral fellowship from Damon Runyon Cancer Research Foundation (DRG-2125-12). L.S. was supported by a postdoctoral fellowship from the German Research Foundation (DFG, SCHI 1330/1-1).

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Neurotoxic reactive astrocytes are induced by activated microglia

Foundations of Confocal Scanned Imaging in Light Microscopy -- Fundamental Limits in Confocal Microscopy -- Special Optical Elements -- Points, Pixels, and Gray Levels: Digitizing Image Data -- Laser Sources for Confocal Microscopy -- Non-Laser Light Sources for Three-Dimensional Microscopy -- Objective Lenses for Confocal Microscopy -- The Contrast Formation in Optical Microscopy -- The Intermediate Optical System of Laser-Scanning Confocal Microscopes -- Disk-Scanning Confocal Microscopy -- Measuring the Real Point Spread Function of High Numerical Aperture Microscope Objective Lenses -- Photon Detectors for Confocal Microscopy -- Structured Illumination Methods -- Visualization Systems for Multi-Dimensional Microscopy Images -- Automated Three-Dimensional Image Analysis Methods for Confocal Microscopy -- Fluorophores for Confocal Microscopy: Photophysics and Photochemistry -- Practical Considerations in the Selection and Application of Fluorescent Probes -- Guiding Principles of Specimen Preservation for Confocal Fluorescence Microscopy -- Confocal Microscopy of Living Cells -- Aberrations in Confocal and Multi-Photon Fluorescence Microscopy Induced by Refractive Index Mismatch -- Interaction of Light with Botanical Specimens -- Signal-to-Noise Ratio in Confocal Microscopes -- Comparison of Widefield/Deconvolution and Confocal Microscopy for Three-Dimensional Imaging -- Blind Deconvolution -- Image Enhancement by Deconvolution -- Fiber-Optics in Scanning Optical Microscopy -- Fluorescence Lifetime Imaging in Scanning Microscopy -- Multi-Photon Molecular Excitation in Laser-Scanning Microscopy -- Multifocal Multi-Photon Microscopy -- 4Pi Microscopy -- Nanoscale Resolution with Focused Light: Stimulated Emission Depletion and Other Reversible Saturable Optical Fluorescence Transitions Microscopy Concepts -- Mass Storage, Display, and Hard Copy -- Coherent Anti-Stokes Raman Scattering Microscopy -- Related Methods for Three-Dimensional Imaging -- Tutorial on Practical Confocal Microscopy and Use of the Confocal Test Specimen -- Practical Confocal Microscopy -- Selective Plane Illumination Microscopy -- Cell Damage During Multi-Photon Microscopy -- Photobleaching -- Nonlinear (Harmonic Generation) Optical Microscopy -- Imaging Brain Slices -- Fluorescent Ion Measurement -- Confocal and Multi-Photon Imaging of Living Embryos -- Imaging Plant Cells -- Practical Fluorescence Resonance Energy Transfer or Molecular Nanobioscopy of Living Cells -- Automated Confocal Imaging and High-Content Screening for Cytomics -- Automated Interpretation of Subcellular Location Patterns from Three-Dimensional Confocal Microscopy -- Display and Presentation Software -- When Light Microscope Resolution Is Not Enough:Correlational Light Microscopy and Electron Microscopy -- Databases for Two- and Three-Dimensional Microscopical Images in Biology -- Confocal Microscopy of Biofilms — Spatiotemporal Approaches -- Bibliography of Confocal Microscopy.

Handbook of biological confocal microscopy

Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions.

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Astrocytes: biology and pathology

Presynaptic and post-synaptic cells of the squid giant synapse were voltage-clamped simultaneously to study the relationship between presynaptic Ca current and transmitter-induced post-synaptic current (p.s.c.). Local Ca application was used to restrict Ca current and transmitter release to a limited region of the presynaptic terminal and thus minimize errors due to spatial heterogeneity of presynaptic membrane potential. Presynaptic terminals were depolarized by brief (3-6 ms) voltage-clamp pulses of varying amplitude to collect graded series of presynaptic Ca current and p.s.c. records. During presynaptic depolarization at 14 degrees C, Ca current activation preceded initial onset of p.s.c. (on-p.s.c.) by an interval of approximately 1 ms. The main component of on-p.s.c. followed Ca current activation by about 2 ms. The delay between a brief Ca tail current and peak response of the p.s.c. produced after pulse termination (off-p.s.c.) was also approximately 2 ms. Curves relating both Ca current and p.s.c. magnitudes to presynaptic potential were bell shaped with peaks near -10 mV, but the p.s.c. curve showed stronger voltage dependence on both sides of the peak. With very small and very large presynaptic command pulses, Ca current could be observed without measureable p.s.c. Synaptic transfer curves, plotting p.s.c. as a function of presynaptic Ca current, resembled third-power functions. On the average, p.s.c.s fit a curve representing the 2.9 power of Ca current (range 2.4-3.5 in eighteen experiments). Transfer curves consisted of two limbs: one from presynaptic pulses below -10 mV and the other from more positive pulses. These two limbs were similar and generally resembled power functions of identical exponent. It is thus likely that the third-power function accurately reflects synaptic current transfer, rather than interference from some other voltage-dependent process. Power functions fitting small-pulse and large-pulse limbs of some transfer curves had different scale coefficients, even though exponent values were the same. Consideration of synaptic transmission kinetics suggests that the voltage dependence of Ca channel opening rates can probably explain the difference in transfer curve limbs. Our experiments provide no evidence for an intrinsic voltage dependence of the transmitter release process.

Calcium entry and transmitter release at voltage‐clamped nerve terminals of squid.

Ionic Currents in Molluscan Soma

To explore the relationship between axon arbor growth and synaptogenesis, developing retinal ganglion cell (RGC) axon arbors in zebrafish optic tectum were imaged in vivo at high temporal and spatial resolution using two-photon microscopy. Individual RGC axons were dually labeled by expression of a cytosolic red fluorescent protein (DsRed Express) to mark arbor structure and a fusion of the synaptic vesicle protein synaptophysin with green fluorescent protein (Syp:GFP) to mark presynaptic vesicles. Analysis of time-lapse sequences acquired at 10 min intervals revealed unexpectedly rapid kinetics of both axon branch and vesicle cluster turnover. Nascent axonal branches exhibited short average lifetimes of 19 min, and only 17% of newly extended axonal processes persisted for periods exceeding 3 h. The majority (70%) of Syp:GFP puncta formed on newly extended axonal processes. Syp:GFP puncta also exhibited short average lifetimes of 30 min, and only 34% of puncta were stabilized for periods exceeding 3 h. Moreover, strongly correlated dynamics of Syp:GFP puncta and branch structure suggest that synaptogenesis exerts strong influences on both the extension and the selective stabilization of nascent branches. First, new branches form almost exclusively at newly formed Syp:GFP puncta. Second, stabilized nascent branches invariably bear Syp:GFP puncta, and the detailed dynamics of branch retraction suggest strongly that nascent synapses can act at branch tips to arrest retraction. These observations thus provide evidence that synaptogenesis guides axon arbor growth by first promoting initial branch extension and second by selective branch stabilization.

https://www.jneurosci.org/content/jneuro/26/13/3604.full.pdf

Evidence from In Vivo Imaging That Synaptogenesis Guides the Growth and Branching of Axonal Arbors by Two Distinct Mechanisms

IN the adult mammalian retina, the principal direction of information flow is along a vertical pathway from photoreceptors to retinal interneurons to ganglion cells, the output neurons of the retina. We report here, however, that initially in development, at a time when the photoreceptors are not yet even present, there are already functionally defined networks within the retina. These networks are spontaneously active rather than visually driven, and they involve horizontal rather than vertical pathways. By means of optical recording using the calcium-sensitive dye Fura-2, we have found that sets of retinal ganglion cells and amacrine cells, a type of retinal interneuron, undergo synchronized oscillations in intracellular calcium concentration. These oscillations are highly correlated among subgroups of neighbouring cells, and spread in a wave-like fashion tangentially across the retina. Thus, in development of retinal circuitry, the initial patterning of neuronal function occurs in the horizontal domain before the adult pattern of vertical information transfer emerges.

Early functional neural networks in the developing retina.

High-contrast en bloc staining of neuronal tissue for field emission scanning electron microscopy

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Stephen J. Smith

Papers

Calcium entry and transmitter release at voltage‐clamped nerve terminals of squid.

Ionic Currents in Molluscan Soma

Evidence from In Vivo Imaging That Synaptogenesis Guides the Growth and Branching of Axonal Arbors by Two Distinct Mechanisms

Early functional neural networks in the developing retina.

High-contrast en bloc staining of neuronal tissue for field emission scanning electron microscopy