Hippocampal and Cortical Pyramidal Neurons Swell in Parallel with Astrocytes during Acute Hypoosmolar Stress

Normal nervous system function is critically dependent on the balance of water and ions in the extracellular space (ECS). Pathological reduction in brain interstitial osmolarity results in osmotically-driven flux of water into cells, causing cellular edema which reduces the ECS and increases neuronal excitability and risk of seizures. Astrocytes are widely considered to be particularly susceptible to cellular edema due to selective expression of the water channel aquaporin-4 (AQP4). The apparent resistance of pyramidal neurons to osmotic swelling has been attributed to lack of functional water channels. In this study we report rapid volume changes in CA1 pyramidal cells in hypoosmolar ACSF (hACSF) that are equivalent to volume changes in astrocytes across a variety of conditions. Astrocyte and neuronal swelling was significant within 1 min of exposure to 17 or 40% hACSF, was rapidly reversible upon return to normosmolar ACSF, and repeatable upon re-exposure to hACSF. Neuronal swelling was not an artifact of patch clamp, occurred deep in tissue, was similar at physiological vs. room temperature, and occurred in both juvenile and adult hippocampal slices. Neuronal swelling was neither inhibited by TTX, nor by antagonists of NMDA or AMPA receptors, suggesting that it was not occurring as a result of excitotoxicity. Surprisingly, genetic deletion of AQP4 did not inhibit, but rather augmented, astrocyte swelling in severe hypoosmolar conditions. Taken together, our results indicate that neurons are not osmoresistant as previously reported, and that osmotic swelling is driven by an AQP4-independent mechanism

Effects of Astrocyte Specific Swelling on Neuronal Excitability in Elevated Potassium

Abstract:Neurotransmitter and ion influx into astrocytes generates osmotic gradients coupled to water movement into the cell, resulting in transient or prolonged fluctuations in cell volume. Increases in cell volume reduce the size of the extracellular space (ECS) and are associated with elevated brain tissue excitability. However, the precise mechanisms at play in coupling astrocyte volume changes to ion movements remain controversial, as does the effect of acute astrocyte volume fluctuations on neuronal function. Here we set out to determine the effects of raised extracellular potassium concentrations ( [K+]o) on volume responses of CA1 pyramidal neurons and stratum radiatum astrocytes in the hippocampus. First, we found that elevated [K+]o within a physiological range (6.5 and 10.5 mM from a baseline of 2.5 mM) and up to 26 mM produces dose-dependent increases in astrocyte volume, with no effect on neuronal volume. Astrocyte volume increases in elevated [K+]o were not dependent on AQP4, Kir4.1, the sodium-bicarbonate cotransporter NBCe1, or the electroneutral cotransporter NKCC1, but were significantly attenuated in 1 mM BaCl2 and by the Na+/K+ pump inhibitor ouabain, suggesting that astrocyte volume increases are due to K+ influx from nonspecific K+ channels and/or the Na+/K+ ATPase. High [K+]o-induced astrocyte swelling resulted in significant increases in neuronal excitability in the form of NMDA receptor-dependent slow inward currents (SICs) and mixed AMPA/NMDA mEPSCs. Direct depolarizing effects of high [K+]o on neuronal spiking were prevented by application of TTX, and the amount of depolarization was insufficient to activate voltage-gated Ca2+ channels, suggesting that changes in neuronal excitability were not due to elevated [K+]o-related increases in synaptic transmission. Finally, we show that astrocyte-specific swelling in elevated [K+]o and effects on neuronal excitability can be completely negated by addition of mannitol, which we found selectively shrinks astrocytes. Overall, our findings suggest that astrocyte-selective volume increases in elevated [K+]o conditions are due to activity of the Na+/K+ ATPase, which result in astrocyte-specific increases in neuronal excitability independent of direct depolarizing effects of high [K+]o on neurons

Effects of Astrocyte Specific Swelling on Neuronal Excitability in Elevated Potassium

Abstract:Neurotransmitter and ion influx into astrocytes generates osmotic gradients coupled to water movement into the cell, resulting in transient or prolonged fluctuations in cell volume. Increases in cell volume reduce the size of the extracellular space (ECS) and are associated with elevated brain tissue excitability. However, the precise mechanisms at play in coupling astrocyte volume changes to ion movements remain controversial, as does the effect of acute astrocyte volume fluctuations on neuronal function. Here we set out to determine the effects of raised extracellular potassium concentrations ( [K+]o) on volume responses of CA1 pyramidal neurons and stratum radiatum astrocytes in the hippocampus. First, we found that elevated [K+]o within a physiological range (6.5 and 10.5 mM from a baseline of 2.5 mM) and up to 26 mM produces dose-dependent increases in astrocyte volume, with no effect on neuronal volume. Astrocyte volume increases in elevated [K+]o were not dependent on AQP4, Kir4.1, the sodium-bicarbonate cotransporter NBCe1, or the electroneutral cotransporter NKCC1, but were significantly attenuated in 1 mM BaCl2 and by the Na+/K+ pump inhibitor ouabain, suggesting that astrocyte volume increases are due to K+ influx from nonspecific K+ channels and/or the Na+/K+ ATPase. High [K+]o-induced astrocyte swelling resulted in significant increases in neuronal excitability in the form of NMDA receptor-dependent slow inward currents (SICs) and mixed AMPA/NMDA mEPSCs. Direct depolarizing effects of high [K+]o on neuronal spiking were prevented by application of TTX, and the amount of depolarization was insufficient to activate voltage-gated Ca2+ channels, suggesting that changes in neuronal excitability were not due to elevated [K+]o-related increases in synaptic transmission. Finally, we show that astrocyte-specific swelling in elevated [K+]o and effects on neuronal excitability can be completely negated by addition of mannitol, which we found selectively shrinks astrocytes. Overall, our findings suggest that astrocyte-selective volume increases in elevated [K+]o conditions are due to activity of the Na+/K+ ATPase, which result in astrocyte-specific increases in neuronal excitability independent of direct depolarizing effects of high [K+]o on neurons

A Novel Approach to Integrate Human Biomonitoring Data with Model Predicted Dietary Exposures: A Crop Protection Chemical Case Study Using Lambda-Cyhalothrin.

The appropriate use of human biomonitoring data to model population chemical exposures is challenging, especially for rapidly metabolized chemicals, such as agricultural chemicals. The objective of this study is to demonstrate a novel approach integrating model predicted dietary exposures and biomonitoring data to potentially inform regulatory risk assessments. We use lambda-cyhalothrin as a case study, and for the same representative U.S. population in the National Health and Nutrition Examination Survey (NHANES), an integrated exposure and pharmacokinetic model predicted exposures are calibrated to measurements of the urinary metabolite 3-phenoxybenzoic acid (3PBA), using an approximate Bayesian computing (ABC) methodology. We demonstrate that the correlation between modeled urinary 3PBA and the NHANES 3PBA measurements more than doubled as ABC thresholding narrowed the acceptable tolerance range for predicted versus observed urinary measurements. The median predicted urinary concentrations were closer to the median measured value using ABC than using current regulatory Monte Carlo methods

Polysomnography versus limited respiratory monitoring and nurse-led titration to optimise non-invasive ventilation set-up: a pilot randomised clinical trial

International audienc

Hypoosmolar dose-dependent swelling occurs in both pyramidal neurons and astrocytes in acute hippocampal slices

AbstractNormal nervous system function is critically dependent on the balance of water and ions in the extracellular space. Pathological reduction in brain interstitial osmolarity results in osmotically-driven flux of water into cells, causing cellular edema which reduces the extracellular space and increases neuronal excitability and risk of seizures. Astrocytes are widely considered to be particularly susceptible to cellular edema due to selective expression of the water channel aquaporin-4 (AQP4). The apparent resistance of pyramidal neurons to osmotic swelling has been attributed to lack of functional water channels. In this study we report rapid volume changes in CA1 pyramidal cells in hypoosmolar ACSF (hACSF) that are equivalent to volume changes in astrocytes across a variety of conditions. Astrocyte and neuronal swelling was significant within 1 minute of exposure to 17 or 40% hACSF, was rapidly reversible upon return to normosmolar ACSF, and repeatable upon re-exposure to hACSF. Neuronal swelling was not an artifact of patch clamp, occurred deep in tissue, was similar at physiological vs. room temperature, and occurred in both juvenile and adult hippocampal slices. Neuronal swelling was neither inhibited by TTX, nor by antagonists of NMDA or AMPA receptors, suggesting that it was not occurring as a result of excitotoxicity. Surprisingly, genetic deletion of AQP4 did not inhibit, but rather augmented, astrocyte swelling in severe hypoosmolar conditions. Taken together, our results indicate that neurons are not osmoresistant as previously reported, and that osmotic swelling is driven by an AQP4-independent mechanism.</jats:p

Controlling the Orientation and Synaptic Differentiation of Myotubes with Micropatterned Substrates

Micropatterned poly(dimethylsiloxane) substrates fabricated by soft lithography led to large-scale orientation of myoblasts in culture, thereby controlling the orientation of the myotubes they formed. Fusion occurred on many chemically identical surfaces in which varying structures were arranged in square or hexagonal lattices, but only a subset of patterned surfaces yielded aligned myotubes. Remarkably, on some substrates, large populations of myotubes oriented at a reproducible acute angle to the lattice of patterned features. A simple geometrical model predicts the angle and extent of orientation based on maximizing the contact area between the myoblasts and patterned topographic surfaces. Micropatterned substrates also provided short-range cues that influenced higher-order functions such as the localization of focal adhesions and accumulation of postsynaptic acetylcholine receptors. Our results represent what we believe is a new approach for musculoskeletal tissue engineering, and our model sheds light on mechanisms of myotube alignment in vivo