Biology subjects

Emptage, N. J.

Publications and source records attributed to Emptage, N. J..

6 recordsLinked to original sources

bioRxiv2021

Homeostatic regulation of presynaptic NMDA receptor subunit composition modulates action potential driven Ca2+ influx into boutons setting the bandwidth for information transfer

N-Methyl-D-aspartate receptors (NMDARs) play a pivotal role in both short and long-term plasticity. While the functional role of postsynaptic NMDARs is well established, a framework of presynaptic NMDAR (preNMDAR) function is missing. Differences in subunit composition of preNMDARs are documented at central synapses, raising the possibility that subtype composition plays a role in transmission performance. Here, we use electrophysiological recordings at Schaffer collateral - CA1 synapses and Ca2+ imaging coupled to focal glutamate uncaging at boutons of CA3 pyramidal neurones to reveal two populations of presynaptic NMDARs that contain either the GluN2A or GluN2B subunit. Activation of the GluN2B population decreases action potential (AP)-evoked Ca2+ influx via modulation of small conductance Ca2+-activated K+ channels (SK-channels) while activation of the GluN2A containing population does the opposite. Moreover, the level of functional expression of each receptor population can be homeostatically modified, bidirectionally affecting short-term facilitation during burst firing, thus providing a capacity for a fine adjustment of the presynaptic integration time window and therefore the bandwidth of information transfer.

neuroscience↗

bioRxiv2020

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 {micro}m spatial resolution over a 600 {micro}m x 600 {micro}m field of view in the near-infrared region. A physical footprint of 200 mm x 550 mm was achieved using only standard off-the-shelf components. Theoretical performance of the optical design was first evaluated via commercial Zemax software. Then three specimens from rodents: fixed brain, frozen calvaria and live hippocampal slices, were used to experimentally assess system capability and robustness. Results show great potential for the proposed system to be translated into use as a next generation label-free and contactless neurosurgical microscope.

neuroscience↗

bioRxiv2020

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 neighbouring synapses shape the boundaries of functional dendritic units are not well understood. Here we addressed the cellular basis underlying the organization of the strengths of neighbouring Schaffer collateral-CA1 synapses by optical quantal analysis and spine size measurements. Inducing potentiation at clusters of spines produced NMDA receptor-dependent heterosynaptic plasticity. The direction of postsynaptic strength change showed distance-dependency to the stimulated synapses where proximal synapses predominantly depressed whereas distal synapses potentiated; potentiation and depression were regulated by CaMKII and calcineurin, respectively. By contrast, heterosynaptic presynaptic plasticity was confined to weakening of presynaptic strength of nearby synapses, which required CaMKII and the retrograde messenger nitric oxide. Our findings highlight the parallel engagement of multiple signalling pathways, each with characteristic spatial dynamics in shaping the local pattern of synaptic strengths.

neuroscience↗

bioRxiv2020

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. The chromatic spreading of pulses generated an axially elongated excitation focus, which we used to demonstrate volumetric imaging of neurons and their dendrites in live rat brain slices through a 60 m-core MMF.

neuroscience↗

bioRxiv2018

Minimally invasive deep-brain imaging through a 50 μm-core multimode fibre.

Achieving optical access to deep-brain structures represents an important step towards the goal of understanding the mammalian central nervous system. The complex refractive index distribution within brain tissue introduces severe aberrations to long-distance light propagation thereby prohibiting image reconstruction using currently available non-invasive techniques. In an attempt to overcome this challenge endoscopic approaches have been adopted, principally in the form of fibre bundles or GRIN-lens based endoscopes. Unfortunately, these approaches create substantial mechanical lesions of the tissue precipitating neuropathological responses that include inflammation and gliosis. Together, lesions and the associated neuropathology may compromise neural circuit performance. By replacing Fourier-based image relay with a holographic approach, we have been able to reduce the volume of tissue lesion by more than 100-fold, while preserving diffraction-limited imaging performance. Here we demonstrate high-resolution fluorescence imaging of neuronal structures, dendrites and synaptic specialisations, in deep-brain regions of living mice. These results represent a major breakthrough in the compromise between high-resolution imaging and tissue damage, heralding new possibilities for deep-brain imaging in vivo.

neuroscience↗

bioRxiv2018

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 which 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.

cell biology↗