Biology subjects

Papaioannou, S.

Publications and source records attributed to Papaioannou, S..

6 recordsLinked to original sources

bioRxiv2022

Multiphoton holographic photostimulation induces potassium-dependent spike silencing in label-free mouse cortex in vivo

Multiphoton microscopy allows measurement of network activity as well as the manipulation of cell type specific or functionally identified neuronal subpopulations with optogenetic holographic stimulation. When neurons co-express an activity reporter (e.g. calcium or voltage-sensitive indicators) and an (excitatory or inhibitory) opsin, such "all optical" interrogation approaches in vivo allows to draw causal links between function of cell-type specific microcircuits and behaviour. However, the net effects of near-infrared stimulation on network activity per se remain to be adequately investigated in vivo. Here we show that multicell holographic photostimulation with near-infrared radiation with total powers to sample used in current literature halves the spike rate of the non-illuminated neurons in label-free mouse cortex in vivo. The effect is not mediated by GABA release, but depends on NIR-dependent gating of potassium channels as it is absent when neurons are intracellularly perfused with the broad potassium channel blocker cesium ions, and are possibly mediated by heating. The phenomenon may contribute to set an upper limit to holographic photostimulation efficacy, calls for the need to control the effects of holographic stimulation protocols per se in label free preparations, and might be of relevance to interpret the therapeutical effects on infrared stimulation in psychiatry and neurology. Highlights- Holographic multi-cell, infrared illumination halves spike rates of no-target neurons - The effect happens with total powers to sample used in "all-optical" literature - Infrared-driven spike killing is GABA-independent but depends on potassium channels

neuroscience↗

bioRxiv2022

Liver sinusoidal endothelial cells orchestrate NK cell recruitment and activation in acute inflammatory liver injury

In both steady-state and during endotoxicosis, liver sinusoidal endothelial cells (LSECs) can rapidly clear lipopolysaccharide (LPS) from the bloodstream. They are located along blood sinusoids of the liver, and establish intimate contact with circulating and tissue-resident immune cells. However, their role in regulating immune responses during LPS-induced endotoxicosis remains poorly understood. Here, we show that LSECs play a dual role in regulating inflammatory responses, acting as modulators of NK cell pro-inflammatory output and as major producers of immune cell-attracting chemokines. We demonstrate that LSECs switch their chemokine expression pattern driven by LPS and IFN-{gamma}, resulting in the production of the myeloid-attracting chemokine CCL2 and the lymphoid-attracting chemokine CXCL10, which accumulate in the serum of LPS-challenged animals. In livers of LPS-injected mice, monocytes and Kupffer cells expressed highest amounts of the pro-inflammatory cytokine Il12a and Il18 transcripts, while NK cells expressed the highest amounts of Ifng. NK cell exposure to LSECs in vitro led to global transcriptomic changes, and primed NK cells to produce higher amounts of IFN-{gamma} in response to IL-12 and IL-18. LSECs required exposure to IFN-{gamma} for Cxcl10 expression, and Cxcl10 gene-deletion in endothelial cells abrogated NK cell accumulation in the liver after LPS treatment. Thus, our data indicate that LSECs occupy a unique temporal and spatial position acting as central regulators that respond to both LPS and immune-derived inflammatory signals, and fuel a positive feedback loop of immune cell attraction and activation in the inflamed liver tissue. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=96 SRC="FIGDIR/small/500206v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@653c53org.highwire.dtl.DTLVardef@5ba4bdorg.highwire.dtl.DTLVardef@9caad8org.highwire.dtl.DTLVardef@1945eb5_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2021

Visual stimulation with blue wavelength light drives V1 effectively eliminating stray light contamination during two-photon calcium imaging

BACKGROUNDBrain visual circuits are often studied in vivo by imaging Ca2+ indicators with green-shifted emission spectra. Polychromatic white visual stimuli have a spectrum that partially overlaps indicators emission spectra, resulting in significant contamination of calcium signals. NEW METHODTo overcome light contamination problems we choose blue visual stimuli, having a spectral composition not overlapping with Ca2+ indicators emission spectrum. To compare visual responsiveness to blue and white stimuli we used electrophysiology (visual evoked potentials-VEPs) and 3D acousto-optic two-photon(2P) population Ca2+ imaging in mouse primary visual cortex (V1). RESULTSVEPs in response to blue and white stimuli had comparable peak amplitudes and latencies. Ca2+ imaging revealed that the populations of neurons responding to blue and white stimuli were largely overlapping, that their responses had similar amplitudes, and that functional response properties such as orientation and direction selectivities were also comparable. COMPARISON WITH EXISTING METHODSMasking or shielding the microscope are often used to minimize the contamination of Ca2+ signal by white light, but they are time consuming, bulky and thus can limit experimental design, particularly in the more and more frequently used awake set-up. Blue stimuli not interfering with imaging allow to omit shielding without affecting V1 physiological responsiveness. CONCLUSIONSOur results show that the selected blue light stimuli evoke physiological responses comparable to those evoked by white stimuli in mouse V1. This will make complex designs of imaging experiments in behavioral set-ups easier, and facilitate the combination of Ca2+ imaging with electrophysiology and optogenetics. HighlightsO_LIWhite and blue light trigger VEPs with similar amplitudes and latencies in mouse V1 C_LIO_LIBlue-and white-responding neurons are two largely overlapping neuronal populations C_LIO_LIBlue and white evoke Ca2+ responses similar in magnitude and latency C_LIO_LIBlue and white evoke Ca2+ responses similar in orientation/direction selectivity C_LIO_LIBlue stimuli could be an alternative to white ones in behavior and opto-physiological tests C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=149 SRC="FIGDIR/small/433182v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@66c0a2org.highwire.dtl.DTLVardef@1f0cce9org.highwire.dtl.DTLVardef@1ce97borg.highwire.dtl.DTLVardef@24a3f1_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2020

Goal-dependent tuning of muscle spindle receptors during movement preparation

Voluntary movements are believed to be advantageously prepared before they are executed, but the neural mechanisms at work have been unclear. For example, there are no overt changes in skeletal muscle activity during movement preparation. Here, using a delayed-reach manual task, we demonstrate a decrease in the firing rate of human muscle afferents (primary spindles) when preparing stretch rather than shortening of the spindle-bearing muscle. This goal-dependent modulation of proprioceptors begun early after target onset but was markedly stronger at the latter parts of the preparatory period. In two additional experiments, whole-arm perturbations during reach preparation revealed a congruent modulation of stretch reflex gains of shoulder and upper arm muscles. Our study shows that movement preparation can involve sensory elements of the peripheral nervous system. We suggest that central preparatory activity can also reflect sensory control, and preparatory tuning of muscle spindle mechanoreceptors is a component of planned reaching movements.

neuroscience↗

bioRxiv2019

Reconstruction of in-vivo subthreshold activity of single neurons from large-scale spiking recordings

Current developments in the manufacturing of silicon probes allow recording of spikes from large populations of neurons from several brain structures in freely moving animals. It is still, however, technically challenging to record the membrane potential from awake behaving animals. Routine access to the subthreshold activity of neurons would be of great value in order to understand the role of, for example, neuronal integration, oscillations, and excitability. Here we have developed a framework for reconstructing the subthreshold activity of single neurons using the spiking activity from large neuronal populations. The reconstruction accuracy and reliability have been evaluated with ground truth data provided from simultaneous patch clamp membrane potential recordings in-vivo. Given the abundance of large-scale spike recordings in the contemporary systems neuroscience society, this approach provides a general access to the subthreshold activity and hence could shed light on the intricate mechanisms of the genesis of spiking activity.

neuroscience↗

bioRxiv2018

In Silico Identification and In Vitro Validation of Novel KPC-2 β-lactamase Inhibitors

Bacterial resistance has become a worldwide concern, particularly after the emergence of resistant strains overproducing carbapenemases. Among these, the KPC-2 carbapenemase represents a significant clinical challenge, being characterized by a broad substrate spectrum that includes aminothiazoleoxime and cephalosporins such as cefotaxime. Moreover, strains harboring KPC-type {beta}-lactamases are often reported as resistant to available {beta}-lactamase inhibitors (clavulanic acid, tazobactam and sulbactam). Therefore, the identification of novel non {beta}-lactam KPC-2 inhibitors is strongly necessary to maintain treatment options. This study explored novel, non-covalent inhibitors active against KPC-2, as putative hit candidates. We performed a structure-based in silico screening of commercially available compounds for non-{beta}-lactam KPC-2 inhibitors. Thirty-two commercially available high-scoring, fragment-like hits were selected for in vitro validation and their activity and mechanism of action vs the target was experimentally evaluated using recombinant KPC-2. N-(3-(1H-tetrazol-5-yl)phenyl)-3-fluorobenzamide (11a), in light of its ligand efficiency (LE = 0.28 kcal/mol/non-hydrogen atom) and chemistry, was selected as hit to be directed to chemical optimization to improve potency vs the enzyme and explore structural requirement for inhibition in KPC-2 binding site. Further, the compounds were evaluated against clinical strains overexpressing KPC-2 and the most promising compound reduced the MIC of the {beta}-lactam antibiotic meropenem by four fold.

biochemistry↗