Root nutation modelled by two ion flux-linked growth waves around the root

A new model of root circumnutation is proposed, based on the correlation between nutation and ion flux oscillations in the elongation zone. The model considers that, in a small region on one side of the root and within the elongation zone, the growth rate is different from the average. This local disturbance to growth may have been caused by mechanical, chemical or other stimuli, or it may be merely an effect of existing nutation, tropisms or other asymmetric growth. If this disturbance is a reduction in the local growth rate, the root will be bending towards that side. The model provides that the region of growth reduction enlarges and spreads as a wave along and around the root. As the wave of growth reduction moves away, the initially disturbed region recovers. Viewing the root in the cross section containing the original region, the growth reduction moves from that region with different speeds in the two opposite directions around the circumference of the root. The mathematical formulation for the movement of the growth disturbance is given. The resulting bending of the root can be quite complex. The proposed model allows us to describe typical features of nutating roots reported in the literature and observed in our experiments. Results of simulation show a high correspondence with experimental observations. Some components of a possible physiological mechanism for the model are discussed.     

Extrinsic control and intrinsic computation in the hippocampal CA1 circuit

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Subcircuits of Deep and Superficial CA1 Place Cells Support Efficient Spatial Coding across Heterogeneous Environments

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Influence of O2- and CO2-concentrations on oscillations in the transpiration rate from oat plants in darkness

The effect of changed O₂- and CO₂-concentrations in air on oscillations in the transpiration rate of young oat plants in darkness has been investigated. Lowering the O₂-concentration to 5% did not affect the oscillations. When the CO₂ in the air was removed, the transpiration rate increased, and the oscillations ceased. When the CO₂-concentration was raised to 0.3 or 3% the transpiration rate temporarily decreased, but the period of the oscillations was not changed. Further increase of the CO₂-concentration caused, after a temporary decrease, an increased transpiration rate, and the oscillations eventually ceased. The period of the oscillations was influenced by the temperature: a lower temperature gave a longer period. It is concluded that substomatal O₂-deficit or high CO₂-concentration do not play a crucial role in the origin of these oscillations.     

Mitochondrial oscillation and activation of H+/cation exchange

Mitochondria incubated aerobically in the presence of tetrapropylammonium and weak acids and in the presence of trace amounts of tetraphenylboron undergo a series of damped oscillations reflecting cycles of osmotic swelling and shrinkage. The matrix volume changes are consequent to transport of tetrapropylammonium catalytically stimulated by tetraphenylboron. The amplitude and frequency of the oscillations increase with the concentration of tetrapropylammonium, as required for critical rates and extents of ion influx. Addition of bovine serum albumin abolishes both the uptake of tetrapropylammonium and the oscillations. Volume oscillations are paralleled by cyclic activation and depression of the respiratory rate. Two lines of evidence suggest that the train of damped oscillations depends on the cyclic activation of an electroneutral exchange of H⁺ with organic cations rather than on cyclic uncoupling. First, further increase of cation permeability due to a pulse of tetraphenylboron, after initiation of cation efflux, restores cation influx. Second, addition of Mg²⁺, which abolishes the oscillations, has a much more marked inhibitory effect on the process of cation efflux than on cation influx. Conversely, addition of A23187, which removes membrane-bound Mg²⁺, promotes cation efflux and thus the oscillations. It is suggested that, in the present system, stretching of the inner membrane and Mg²⁺ depletion result in activation of an electroneutral H⁺/organic cation exchange, and that cyclic activation of this reaction results in damped oscillations.     

In Vitro Slow Fluctuation in Horseradish Peroxidase Activity

In vitro slow fluctuations in the level of horseradish peroxidase activity were observed in long-range experiments (72-144 h). Besides random fluctuations, regular slow oscillatory patterns with period lengths ranging from 10.0 to 39.0 h were detected by statistical analysis. The possibility that these oscillations in enzyme activity could have reflected changes in the physical environment of the experimental setup has been thoroughly examined and ruled out. Periodic exposition of the enzyme solution, otherwise kept in darkness, to blue light illumination was shown to influence the period of the oscillations. The changes in enzyme activity were correlated with a modification of the Michaelis constant estimated using guaiacol as substrate. This result was confirmed by the action of chemical modifiers of the enzyme, such as ferulic acid and rutin. It is thought that the observed oscillations in horseradish peroxidase activity are due to spontaneous and specific changes in the tridimensional structure of the enzyme in the thermic reservoir.     

Modelling corticothalamic feedback and the gating of the thalamus by the cerebral cortex

Morphological studies have shown that excitatory synapses from the cortex constitute the major source of synapses in the thalamus. However, the effect of these corticothalamic synapses on the function of the thalamus is not well understood because thalamic neurones have complex intrinsic firing properties and interact through multiple types of synaptic receptors. Here we investigate these complex interactions using computational models. We show first, using models of reconstructed thalamic relay neurones, that the effect of corticothalamic synapses on relay cells can be similar to that of afferent synapses, in amplitude, kinetics and timing, although these synapses are located in different regions of the dendrites. This suggests that cortical EPSPs may complement (or predict) the afferent information. Second, using models of reconstructed thalamic reticular neurones, we show that high densities of the low-threshold Ca2+ current in dendrites can give these cells an exquisite sensitivity to cortical EPSPs, but only if their dendrites are hyperpolarized. This property has consequences at the level of thalamic circuits, where corticothalamic EPSPs evoke bursts in reticular neurones and recruit relay cells predominantly through feedforward inhibition. On the other hand, with depolarized dendrites, thalamic reticular neurones do not generate bursts and the cortical influence on relay cells is mostly excitatory. Models therefore suggest that the cortical influence can either promote or antagonize the relay of information, depending on the state of the dendrites of reticular neurones. The control of these dendrites may therefore be a determinant of attentional mechanisms. We also review the effect of corticothalamic feedback at the network level, and show how the cortical control over the thalamus is essential in co-ordinating widespread, coherent oscillations. We suggest mechanisms by which different modes of corticothalamic interaction would allow oscillations of very different spatiotemporal coherence to coexist in the thalamocortical system.     

Predictive visuo-motor communication through neural oscillations

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Thyroid Feedback Quantile-Based Index Is Associated With Blood Pressure and Other Hemodynamic Measures: A Cross-sectional Study

ObjectivePrevious studies have reported inconsistent relationships between thyroid function and blood pressure (BP) levels. We aimed to explore the associations between thyroid hormone sensitivity and BP parameters.MethodsThis retrospective study included 6272 participants who underwent a health examination at the First Hospital of China Medical University between January 2017 and December 2018. The Thyroid Feedback Quantile-based Index (TFQI), Parametric TFQI, thyroid-stimulating hormone index, and thyrotroph thyroxine resistance index were calculated to reflect thyroid hormone sensitivity. Mean arterial pressure, pulse pressure, and rate-pressure product were used to indirectly represent arterial stiffness.ResultsThe TFQI was positively associated with systolic BP (β = 3.22), diastolic BP (β =2.32), and mean arterial pressure (β = 2.62) (P < .001, for all). Analyses of the Parametric TFQI, thyroid-stimulating hormone index, and thyrotroph thyroxine resistance index yielded similar results. The TFQI was positively related to pulse pressure and rate-pressure product. With a 1 SD increase in the TFQI, the adjusted odds ratio for hypertension was 1.11 (95% CI 1.04-1.18). When comparing the fourth quartile of the TFQI with the first, the odds ratio for hypertension was 1.27 (95% CI 1.07-1.51, P_{for trend} = .006). These relationships remained significant when stratified by age, sex, and body mass index. Similar results were observed in a euthyroid or normotensive population.ConclusionThe TFQI was positively associated with BP and markers of arterial stiffness. Impaired thyroid hormone sensitivity was related to increased risk for hypertension.     

FFAR4 regulates cardiac oxylipin balance to promote inflammation resolution in HFpEF secondary to metabolic syndrome

Heart failure with preserved ejection fraction (HFpEF) is a complex clinical syndrome, but a predominant subset of HFpEF patients has metabolic syndrome (MetS). Mechanistically, systemic, nonresolving inflammation associated with MetS might drive HFpEF remodeling. Free fatty acid receptor 4 (Ffar4) is a GPCR for long-chain fatty acids that attenuates metabolic dysfunction and resolves inflammation. Therefore, we hypothesized that Ffar4 would attenuate remodeling in HFpEF secondary to MetS (HFpEF-MetS). To test this hypothesis, mice with systemic deletion of Ffar4 (Ffar4KO) were fed a high-fat/high-sucrose diet with L-NAME in their water to induce HFpEF-MetS. In male Ffar4KO mice, this HFpEF-MetS diet induced similar metabolic deficits but worsened diastolic function and microvascular rarefaction relative to WT mice. Conversely, in female Ffar4KO mice, the diet produced greater obesity but no worsened ventricular remodeling relative to WT mice. In Ffar4KO males, MetS altered the balance of inflammatory oxylipins systemically in HDL and in the heart, decreasing the eicosapentaenoic acid-derived, proresolving oxylipin 18-hydroxyeicosapentaenoic acid (18-HEPE), while increasing the arachidonic acid-derived, proinflammatory oxylipin 12-hydroxyeicosatetraenoic acid (12-HETE). This increased 12-HETE/18-HEPE ratio reflected a more proinflammatory state both systemically and in the heart in male Ffar4KO mice and was associated with increased macrophage numbers in the heart, which in turn correlated with worsened ventricular remodeling. In summary, our data suggest that Ffar4 controls the proinflammatory/proresolving oxylipin balance systemically and in the heart to resolve inflammation and attenuate HFpEF remodeling.