Studies of membrane composition and factors affecting the analytical use of potassium responsive ion-selective electrodes

PhD ThesisIn this work, optimization of the performance of potassium / PVC electrodes based on valinomycin, with respect to the composition of the membrane, i. e. the ratio of valinomycin to plasticizer, and the type of PVC matrix has been investigated, in an attempt to reduce the cost of the commercially available electrode. The behaviour of a number of PVC electrodes based on a series of novel bis-crown compounds towards potassium and sodium ions has been evaluated. The influence of the internal reference system, particularly the internal reference solution, on the electrode charateristics was examined by varying the concentration and type of the reference solution. The presence of negative sites in the PVC membrane as an origin of the selectivity, maintaining the electroneutrality in the bulk of the membrane, has been investigated by making pH measurements on solutions in contact with the membrane constituents. The anion response of the potassium / valinomycin electrode with the variation of the concentration of valinomycin, type of plasticizer and PVC have been clarified. Automatic calibration and selectivity determination has been carried out on the membrane using a continuous dilution method, and examination of the effect of the liquid junction potential, type of junction and concentration of the bridge solution on the response of the electrode were ascertained. A high concentration of the valinomycin (>1% w/w) and plasticizer (<70% w/w), independent of the type of PVC and plasticizer, was found to show the best performance. The bis-crowns, except bis-naphthol crowns, did not display competitive results in the determination of potassium and sodium ions. The potentials of the internal and external surfaces of the membrane are established separately of one another, and the magnitude of the membrane potential did not simply depend on the ratio of sensed ion activity in the inner and outer solutions. There is however, strong supporting evidence that the presence of impurities in the membrane components are responsible for the selectivity and electroneutrality of the membrane. The anion response of the membrane is shown to be influenced by the nature of membrane and concentration of valinomycin. The source of the bias in the Corning 902 Analyser in relation to flame photometry was explained and the continuous dilution method was applied to the evaluation of the sensor instruments.University of Razi Bakhtaran, Ira

Balance strategy in hoverboard control.

This study examines how people learn to perform lower limb control in a novel task with a hoverboard requiring to maintain dynamic balance. We designed an experiment to investigate the learning of hoverboard balance and two control strategies: A hip strategy, which mainly uses hip movements to change the angle of the foot, and an ankle strategy relying more on ankle motion to control the orientation of hoverboard plates controlling the motion. Motor learning was indicated by a significant [Formula: see text]% decrease in the trial completion time (p < 0.001) and a significant 24 ± 11% decrease in total muscle activation (p < 0.001). Furthermore, the participants, who had no prior experience riding a hoverboard, learned an ankle strategy to maintain their balance and control the hoverboard. This is supported by significantly stronger cross-correlation, phase synchrony, lower dynamic time warping distance between the hoverboard plate orientation controlling hoverboard motion, and the ankle angle when compared to the hip angle. The adopted ankle strategy was found to be robust to the foot orientation despite salient changes in muscle group activation patterns. Comparison with results of an experienced hoverboard rider confirmed that the first-time riders adopted an ankle strategy

Cable-driven robotic interface for lower limb neuromechanics identification.

This paper presents a versatile cable-driven robotic interface to investigate the single-joint joint neuromechanics of the hip, knee and ankle in the sagittal plane. This endpoint-based interface offers highly dynamic interaction and accurate position control (as is typically required for neuromechanics identification), and provides measurements of position, interaction force and EMG of leg muscles. It can be used with the subject upright, corresponding to a natural posture during walking or standing, and does not impose kinematic constraints on a joint, in contrast to existing interfaces. Mechanical evaluations demonstrated that the interface yields a rigidity above 500 N/m with low viscosity. Tests with a rigid dummy leg and linear springs show that it can identify the mechanical impedance of a limb accurately. A smooth perturbation is developed and tested with a human subject, which can be used to estimate the hip neuromechanics

Maturation of NMDA receptor-mediated spontaneous postsynaptic currents in the rat locus coeruleus neurons

Introduction: During mammalian brain development, neural activity leads to maturation of glutamatergic innervations to locus coeruleus. In this study, fast excitatory postsynaptic currents mediated by N-methyl-Daspartate (NMDA) receptors were evaluated to investigate the maturation of excitatory postsynaptic currents in locus coeruleus (LC) neurons. Methods: NMDA receptor-mediated synaptic currents in LC neurons were evaluated using whole-cell voltage-clamp recording during the primary postnatal weeks. This technique was used to calculate the optimum holding potential for NMDA receptor-mediated currents and the best frequency for detecting spontaneous excitatory postsynaptic currents (sEPSC). Results: The optimum holding potential for detecting NMDA receptor-mediated currents was + 40 to + 50 mV in LC neurons. The frequency, amplitude, rise time, and decay time constant of synaptic responses depended on the age of the animal and increased during postnatal maturation. Conclusion: These findings suggest that most nascent glutamatergic synapses express functional NMDA receptors in the postnatal coerulear neurons, and that the activities of the neurons in this region demonstrate an age-dependent variation. © 2020 Akademiai Kiado, Budapest

A simple tool to measure spasticity in spinal cord injury subjects.

This work presents a wearable device and the algorithms for quantitative modelling of joint spasticity and its application in a pilot group of subjects with different levels of spinal cord injury. The device comprises light-weight instrumented handles to measure the interaction force between the subject and the physical therapist performing the tests, EMG sensors and inertial measurement units to measure muscle activity and joint kinematics. Experimental tests included the passive movement of different body segments, where the spasticity was expected, at different velocities. Tonic stretch reflex thresholds and their velocity modulation factor are computed, as a quantitative index of spasticity, by using the kinematics data at the onset of spasm detected through thresholding the EMG data. This technique was applied to two spinal cord injury subjects. The proposed method allowed the analysis of spasticity at muscle and joint levels. The obtained results are in line with the expert diagnosis and qualitative spasticity characterisation on each individual

Nitric oxide in the nucleus raphe magnus modulates cutaneous blood flow in rats during hypothermia

Objective(s): Nucleus Raphe Magnus (NRM) that is involved in the regulation of body temperature contains nitric oxide (NO) synthase. Considering the effect of NO on skin blood flow control, in this study, we assessed its thermoregulatory role within the raphe magnus. Materials and Methods: To this end, tail blood flow of male Wistar rats was measured by laser doppler following the induction of hypothermia. Results: Intra�NRM injection of SNP (exogenous NO donor, 0.1� 0.2 μl, 0.2 nM) increased the blood flow. Similarly, unilateral microinjection of glutamate (0.1� 0.2 μl, 2.3 nM) into the nucleus increased the blood flow. This effect of L�glutamate was reduced by prior intra NRM administration of NO synthase inhibitor NG�methyl�L�arginine or NG�nitro�L�arginine methyl ester (L�NAME, 0.1 μl, 100 nM). Conclusion: It is concluded that NO modulates the thermoregulatory response of NRM to hypothermia and may interact with excitatory amino acids in central skin blood flow regulation. © 2015, Mashhad University of Medical Sciences. All rights reserved

Relative contribution of central and peripheral factors in superficial blood flow regulation following cold exposure

The aim of the present study was to evaluate the extent of contribution of thermal regulators in cold stress. Hypothermia is described as a diminution in core body temperature below 35°C. Thermoregulation is the equilibrium between heat generation (thermogenesis) and heat loss (thermolysis). Thermoregulatory control of skin blood flow (SBF) is critical to preserve body temperature homeostasis during thermal changes. The obtained results from different studies revealed that following cold exposure, some areas of the brain like preoptic/anterior hypothalamus, known as body thermostat, involve in thermoregulation by affecting on SBF. Furthermore, some peripheral factors participate in the thermal control through alteration of skin blood flow. Sympathetic neural control of SBF includes the noradrenergic vasoconstrictor system and a sympathetic active vasodilator system. Overall, further future studies are required to elucidate the imbalance of these regulators in some disorders. © 2020, Iranian Society of Physiology and Pharmacology. All rights reserved

Peripheral Ulcerative Keratitis: A Review

Peripheral ulcerative keratitis (PUK) is a rare but serious ocular condition that is an important clinical entity due to its ophthalmological and systemic implications. It is characterized by progressive peripheral corneal stromal thinning with an associated epithelial defect and can be associated with an underlying local or systemic pro-inflammatory condition, or present in an idiopathic form (Mooren ulcer). Associated conditions include autoimmune diseases, systemic and ocular infections, dermatologic diseases, and ocular surgery. Cell-mediated and autoantibody- mediated immune responses have been implicated in the pathogenesis of PUK, destroying peripheral corneal tissue via matrix metalloproteinases. Clinically, patients with PUK present with painful vision loss, a peripheral corneal ulcer, and often adjacent scleritis, episcleritis, iritis, or conjunctivitis. Diagnostic evaluation should be focused on identifying the underlying etiology and ruling out conditions that may mimic PUK, including marginal keratitis and Terrien marginal degeneration. Treatment should be focused on reducing local disease burden with topical lubrication, while simultaneously addressing the underlying cause with antimicrobials or anti-inflammatory when appropriate. Existing and emerging biologic immunomodulatory therapies have proven useful in PUK due to autoimmune conditions. Surgical treatment is generally reserved for cases of severe thinning or corneal perforation

Effects of the hydroalcoholic extract of Rosa damascena on hippocampal long-term potentiation in rats fed high-fat diet

High-fat diets (HFDs) and obesity can cause serious health problems, such as neurodegenerative diseases and cognitive impairments. Consumption of HFD is associated with reduction in hippocampal synaptic plasticity. Rosa damascena (R. damascena) is traditionally used as a dietary supplement for many disorders. This study was carried out to determine the beneficial effect of hydroalcoholic extract of R. damascena on in vivo hippocampal synaptic plasticity (long-term potentiation, LTP) in the perforant pathway (PP)�dentate gyrus (DG) pathway in rats fed with an HFD. Male Wistar rats were randomly assigned to four groups: Control, R. damascena extract (1 g/kg bw daily for 30 days), HFD (for 90 days) and HFD + extract. The population spike (PS) amplitude and slope of excitatory post-synaptic potentials (EPSP) were measured in DG area in response to stimulation applied to the PP. Serum oxidative stress biomarkers total thiol group (TTG) and superoxide dismutase (SOD) were measured. The results showed the HFD impaired LTP induction in the PP-DG synapses. This conclusion is supported by decreased EPSP slope and PS amplitude of LTP. R. damascena supplementation in HFD animals enhanced EPSP slope and PS amplitude of LTP in the granular cell of DG. Consumption of HFD decreased TTG and SOD. R. damascena extract consumption in the HFD animals enhanced TTG and SOD. These data indicate that R. damascena dietary supplementation can ameliorate HFD-induced alteration of synaptic plasticity, probably through its significant antioxidant effects and activate signalling pathways, which are critical in controlling synaptic plasticity. © 2021, The Author(s)