Extended range and aberration-free autofocusing via remote focusing and sequence-dependent learning.

Rapid autofocusing over long distances is critical for tracking 3D topological variations and sample motion in real time. Taking advantage of a deformable mirror and Shack-Hartmann wavefront sensor, remote focusing can permit fast axial scanning with simultaneous correction of system-induced aberrations. Here, we report an autofocusing technique that combines remote focusing with sequence-dependent learning via a bidirectional long short term memory network.

Long-term depression links amyloid-β to the pathological hyperphosphorylation of tau.

In Alzheimer's disease, soluble oligomers of the amyloid-β peptide (Aβ) trigger a cascade of events that includes abnormal hyperphosphorylation of the protein tau, which is essential for pathogenesis. However, the mechanistic link between these two key pathological proteins remains unclear. Using hippocampal slices, we show here that an Aβ-mediated increase in glutamate release probability causes enhancement of synaptically evoked N-methyl-d-aspartate subtype glutamate receptor (NMDAR)-dependent long-term depression (LTD).

Heterosynaptic cross-talk of pre- and postsynaptic strengths along segments of dendrites.

Dendrites are crucial for integrating incoming synaptic information. Individual dendritic branches are thought to constitute a signal processing unit, yet how neighboring synapses shape the boundaries of functional dendritic units is not well understood. Here, we address the cellular basis underlying the organization of the strengths of neighboring Schaffer collateral-CA1 synapses by optical quantal analysis and spine size measurements.

Volumetric two-photon fluorescence imaging of live neurons using a multimode optical fiber.

Multimode optical fibers (MMFs), combined with wavefront control methods, have achieved minimally invasive in vivo imaging of neurons in deep-brain regions with diffraction-limited spatial resolution. Here, we report a method for volumetric two-photon fluorescence imaging with a MMF-based system requiring a single transmission matrix measurement. Central to this method is the use of a laser source able to generate both continuous wave light and femtosecond pulses.

A Novel Optical Quantal Analysis of Miniature Events Reveals Enhanced Frequency Following Amyloid β Exposure.

Non-evoked miniature release of neurotransmitters is increasingly recognized as playing an important role in neural function and is implicated in synaptic plasticity, metaplasticity, and homeostasis. Spontaneous miniature release events (minis) are usually measured electrophysiologically by recording the miniature postsynaptic currents (mEPSCs) that they evoke. However, this indirect technique can be confounded by changes within the postsynaptic neuron.

Compact and contactless reflectance confocal microscope for neurosurgery.

Visual guidance at the cellular level during neurosurgical procedures is essential for complete tumour resection. We present a compact reflectance confocal microscope with a 20 mm working distance that provided <1.2 µm spatial resolution over a 600 µm × 600 µm field of view in the near-infrared region.

Deconvolution for multimode fiber imaging: modeling of spatially variant PSF.

Focusing light through a step-index multimode optical fiber (MMF) using wavefront control enables minimally-invasive endoscopy of biological tissue. The point spread function (PSF) of such an imaging system is spatially variant, and this variation limits compensation for blurring using most deconvolution algorithms as they require a uniform PSF. However, modeling the spatially variant PSF into a series of spatially invariant PSFs re-opens the possibility of deconvolution.

A two-compartment model of synaptic computation and plasticity.

The synapse is typically viewed as a single compartment, which acts as a linear gain controller on incoming input. Traditional plasticity rules enable this gain control to be dynamically optimized by Hebbian activity. Whilst this view nicely captures postsynaptic function, it neglects the non-linear dynamics of presynaptic function.

Focusing light in biological tissue through a multimode optical fiber: refractive index matching.

Controlling light propagation through a step-index multimode optical fiber (MMF) has several important applications, including biological imaging. However, little consideration has been given to the coupling of fiber and tissue optics. In this Letter, we characterized the effects of tissue-induced light distortions, in particular those arising from a mismatch in the refractive index of the pre-imaging calibration and biological media.

Optical Quantal Analysis Using Ca Indicators: A Robust Method for Assessing Transmitter Release Probability at Excitatory Synapses by Imaging Single Glutamate Release Events.

Despite evidence that presynaptic efficacy and plasticity influence circuit function and behavior , studies of presynaptic function remain challenging owing to the difficulty of assessing transmitter release in intact tissue. Electrophysiological analyses of transmitter release are indirect and cannot readily resolve basic presynaptic parameters, most notably transmitter release probability ( ), at single synapses. These issues can be circumvented by optical quantal analysis, which uses the all-or-none optical detection of transmitter release in order to calculate .

Subcellular spatial resolution achieved for deep-brain imaging in vivo using a minimally invasive multimode fiber.

Achieving intravital optical imaging with diffraction-limited spatial resolution of deep-brain structures represents an important step toward the goal of understanding the mammalian central nervous system. Advances in wavefront-shaping methods and computational power have recently allowed for a novel approach to high-resolution imaging, utilizing deterministic light propagation through optically complex media and, of particular importance for this work, multimode optical fibers (MMFs). We report a compact and highly optimized approach for minimally invasive in vivo brain imaging applications.

Neuronal Receptors Display Cytoskeleton-Independent Directed Motion on the Plasma Membrane.

Directed transport of transmembrane proteins is generally believed to occur via intracellular transport vesicles. However, using single-particle tracking in rat hippocampal neurons with a pH-sensitive quantum dot probe that specifically reports surface movement of receptors, we have identified a subpopulation of neuronal EphB2 receptors that exhibit directed motion between synapses within the plasma membrane itself. This receptor movement occurs independently of the cytoskeleton but is dependent on cholesterol and is regulated by neuronal activity.

Hippocampal mGluR1-dependent long-term potentiation requires NAADP-mediated acidic store Ca signaling.

Acidic organelles, such as endosomes and lysosomes, store Ca that is released in response to intracellular increases in the second messenger nicotinic acid adenine dinucleotide phosphate (NAADP). In neurons, NAADP and Ca signaling contribute to synaptic plasticity, a process of activity-dependent long-term potentiation (LTP) [or, alternatively, long-term depression (LTD)] of synaptic strength and neuronal transmission that is critical for neuronal function and memory formation. We explored the function of and mechanisms regulating acidic Ca store signaling in murine hippocampal neurons.

Intracellular Ca Release and Synaptic Plasticity: A Tale of Many Stores.

Ca is an essential trigger for most forms of synaptic plasticity. Ca signaling occurs not only by Ca entry via plasma membrane channels but also via Ca signals generated by intracellular organelles. These organelles, by dynamically regulating the spatial and temporal extent of Ca elevations within neurons, play a pivotal role in determining the downstream consequences of neural signaling on synaptic function.

Fast volume-scanning light sheet microscopy reveals transient neuronal events.

Light sheet fluorescence microscopy offers considerable potential to the cellular neuroscience community as it makes it possible to image extensive areas of neuronal structures, such as axons or dendrites, with a low light budget, thereby minimizing phototoxicity. However, the shallow depth of a light sheet, which is critical for achieving high contrast, well resolved images, adds a significant challenge if fast functional imaging is also required, as multiple images need to be collected across several image planes. Consequently, fast functional imaging of neurons is typically restricted to a small tissue volume where part of the neuronal structure lies within the plane of a single image.

Inhibition of lysosomal Ca signalling disrupts dendritic spine structure and impairs wound healing in neurons.

A growing body of evidence suggests that lysosomes, which have traditionally been regarded as degradative organelles, can function as Ca stores, regulated by the second messenger nicotinic acid adenine dinucleotide phosphate (NAADP). We previously demonstrated that in hippocampal pyramidal neurons, activity-dependent Ca release from these stores triggers fusion of the lysosome with the plasma membrane. We found that the physiological role of this Ca-dependent fusion was to maintain the long-term structural enlargement of dendritic spines induced by synaptic activity.

Glutamate is required for depression but not potentiation of long-term presynaptic function.

Hebbian plasticity is thought to require glutamate signalling. We show this is not the case for hippocampal presynaptic long-term potentiation (LTP), which is expressed as an increase in transmitter release probability (P). We find that LTP can be induced by pairing pre- and postsynaptic spiking in the absence of glutamate signalling.

Homeostatic Presynaptic Plasticity Is Specifically Regulated by P/Q-type Ca Channels at Mammalian Hippocampal Synapses.

Voltage-dependent Ca channels (VGCC) represent the principal source of Ca ions driving evoked neurotransmitter release at presynaptic boutons. In mammals, presynaptic Ca influx is mediated mainly via P/Q-type and N-type VGCC, which differ in their properties. Changes in their relative contributions tune neurotransmission both during development and in Hebbian plasticity.

Synaptic Transmission Optimization Predicts Expression Loci of Long-Term Plasticity.

Long-term modifications of neuronal connections are critical for reliable memory storage in the brain. However, their locus of expression-pre- or postsynaptic-is highly variable. Here we introduce a theoretical framework in which long-term plasticity performs an optimization of the postsynaptic response statistics toward a given mean with minimal variance.

Activity-Dependent Exocytosis of Lysosomes Regulates the Structural Plasticity of Dendritic Spines.

Lysosomes have traditionally been viewed as degradative organelles, although a growing body of evidence suggests that they can function as Ca stores. Here we examined the function of these stores in hippocampal pyramidal neurons. We found that back-propagating action potentials (bpAPs) could elicit Ca release from lysosomes in the dendrites.

A compact light-sheet microscope for the study of the mammalian central nervous system.

Investigation of the transient processes integral to neuronal function demands rapid and high-resolution imaging techniques over a large field of view, which cannot be achieved with conventional scanning microscopes. Here we describe a compact light sheet fluorescence microscope, featuring a 45° inverted geometry and an integrated photolysis laser, that is optimized for applications in neuroscience, in particular fast imaging of sub-neuronal structures in mammalian brain slices. We demonstrate the utility of this design for three-dimensional morphological reconstruction, activation of a single synapse with localized photolysis, and fast imaging of neuronal Ca(2+) signalling across a large field of view.

Rapid regulation of endoplasmic reticulum dynamics in dendritic spines by NMDA receptor activation.

Endoplasmic reticulum (ER) is motile within dendritic spines, but the mechanisms underlying its regulation are poorly understood. To address this issue, we have simultaneously imaged morphology and ER content of dendritic spines in cultured dissociated mouse hippocampal neurons. Over a 10 min period, spines were highly dynamic, with spines both increasing and decreasing in volume.