Multiscale vision model for event detection and reconstruction in two-photon imaging data

Reliable detection of calcium waves in multiphoton imaging data is challenging because of the low signal-to-noise ratio and because of the unpredictability of the time and location of these spontaneous events. This paper describes our approach to calcium wave detection and reconstruction based on a modified multiscale vision model, an object detection framework based on the thresholding of wavelet coefficients and hierarchical trees of significant coefficients followed by nonlinear iterative partial object reconstruction, for the analysis of two-photon calcium imaging data. The framework is discussed in the context of detection and reconstruction of intercellular glial calcium waves. We extend the framework by a different decomposition algorithm and iterative reconstruction of the detected objects. Comparison with several popular state-of-the-art image denoising methods shows that performance of the multiscale vision model is similar in the denoising, but provides a better segmenation of the image into meaningful objects, whereas other methods need to be combined with dedicated thresholding and segmentation utilities

Astrocyte dystrophy in ageing brain parallels impaired synaptic plasticity

Little is known about age-dependent changes in structure and function of astrocytes and of the impact of these on the cognitive decline in the senescent brain. The prevalent view on the age-dependent increase in reactive astrogliosis and astrocytic hypertrophy requires scrutiny and detailed analysis. Using two-photon microscopy in conjunction with 3D reconstruction, Sholl and volume fraction analysis, we demonstrate a significant reduction in the number and the length of astrocytic processes, in astrocytic territorial domains andin astrocyte-to-astrocyte coupling in the aged brain. Probing physiology of astrocytes with patch clamp, and Ca2+ imaging revealed deficits in K+ and glutamate clearance and spatiotemporal reorganisation of Ca2+ events in old astrocytes. These changes paralleled impaired synaptic long-term potentiation (LTP) in hippocampal CA1 in old mice. Our findings may explain the astroglial mechanisms of age-dependent decline in learning and memory.The research was supported by the Russian Science Foundation grant 20‐14‐00241

Raman spectroscopy of protein crystal nucleation and growth

Using Raman spectroscopy and the lysozyme as model system, we investigate the differences in protein conformation before and after Langmuir- Blodgett nanotemplate-induced crystal nucleation and growth. It was found, that the main difference in lysozyme conformation is associated to the higher amount of S-S bonds in lysozyme of LB crystals, probably in C-end of protein, resulting in the higher stiffness of the lysozyme molecules and LB crystal in a whole. Growth in size of LB crystal over time is also accompanied by the formation of S-S bonds. Atomic structure determined by X-ray diffraction correlates to the above pointing to the main differences between LB classical crystals in terms of water molecules environment previously associated to the increased radiation stability of LB crystals

PREPROCESSING AND REGISTRATION OF MINISCOPE-BASED CALCIUM IMAGING OF THE RODENT BRAIN

Microscopic imaging is central to the brain and cognition studies in animals and often requires advanced image processing. In vivo recordings on awake behaving animals require stabilization of the images as the tissue in the images undergoes non-rigid deformations due to animal movement, pulse beat and breathing of the animal. Here we propose an approach to compensation for the tissue motion in calcium imaging data acquired with miniaturized wearable microscopes (miniscopes) from live rodent brains. Our approach includes preprocessing of the images in which we compensate for non-uniform illumination, remove calcium transients and instrument-specific noise. For image registration we use the multiscale mutual information based non-rigid algorithm with B-spline transformation model. We present the preliminary results of such motion compensation approach applied to the real miniscope image stacks

Sodium–Calcium Exchanger Can Account for Regenerative Ca2+ Entry in Thin Astrocyte Processes

Calcium transients in thin astrocytic processes can be important in synaptic plasticity, but their mechanism is not completely understood. Clearance of synaptic glutamate leads to increase in astrocytic sodium. This can electrochemically favor the reverse mode of the Na/Ca-exchanger (NCX) and allow calcium into the cell, accounting for activity-dependent calcium transients in perisynaptic astrocytic processes. However, cytosolic sodium and calcium are also allosteric regulators of the NCX, thus adding kinetic constraints on the NCX-mediated fluxes and providing for complexity of the system dynamics. Our modeling indicates that the calcium-dependent activation and also calcium-dependent escape from the sodium-mediated inactive state of the NCX in astrocytes can form a positive feedback loop and lead to regenerative calcium influx. This can result in sodium-dependent amplification of calcium transients from nearby locations or other membrane mechanisms. Prolonged conditions of elevated sodium, for example in ischemia, can also lead to bistability in cytosolic calcium levels, where a delayed transition to the high-calcium state can be triggered by a short calcium transient. These theoretical predictions call for a dedicated experimental estimation of the kinetic parameters of the astrocytic Na/Ca-exchanger

Astrocytes monitor cerebral perfusion and control systemic circulation to maintain brain blood flow

Astrocytes provide neurons with essential metabolic and structural support, modulate neuronal circuit activity and may also function as versatile surveyors of brain milieu, tuned to sense conditions of potential metabolic insufficiency. Here we show that astrocytes detect falling cerebral perfusion pressure and activate CNS autonomic sympathetic control circuits to increase systemic arterial blood pressure and heart rate with the purpose of maintaining brain blood flow and oxygen delivery. Studies conducted in experimental animals (laboratory rats) show that astrocytes respond to acute decreases in brain perfusion with elevations in intracellular [Ca2+]. Blockade of Ca2+-dependent signaling mechanisms in populations of astrocytes that reside alongside CNS sympathetic control circuits prevents compensatory increases in sympathetic nerve activity, heart rate and arterial blood pressure induced by reductions in cerebral perfusion. These data suggest that astrocytes function as intracranial baroreceptors and play an important role in homeostatic control of arterial blood pressure and brain blood flow