Diversity of Ganglion Cell Responses to Saccade-Like Image Shifts in the Primate Retina

Saccades are a fundamental part of natural vision. They interrupt fixations of the visual gaze and rapidly shift the image that falls onto the retina. These stimulus dynamics can cause activation or suppression of different retinal ganglion cells, but how they affect the encoding of visual information in different types of ganglion cells is largely unknown. Here, we recorded spiking responses to saccade-like shifts of luminance gratings from ganglion cells in isolated marmoset retinas and investigated how the activity depended on the combination of presaccadic and postsaccadic images. All identified cell types, On and Off parasol and midget cells, as well as a type of Large Off cells, displayed distinct response patterns, including particular sensitivity to either the presaccadic or the postsaccadic image or combinations thereof. In addition, Off parasol and Large Off cells, but not On cells, showed pronounced sensitivity to whether the image changed across the transition. Stimulus sensitivity of On cells could be explained based on their responses to step changes in light intensity, whereas Off cells, in particular, parasol and the Large Off cells, seem to be affected by additional interactions that are not triggered during simple light-intensity flashes. Together, our data show that ganglion cells in the primate retina are sensitive to different combinations of presaccadic and postsaccadic visual stimuli. This contributes to the functional diversity of the output signals of the retina and to asymmetries between On and Off pathways and provides evidence of signal processing beyond what is triggered by isolated steps in light intensity.SIGNIFICANCE STATEMENT Sudden eye movements (saccades) shift our direction of gaze, bringing new images in focus on our retinas. To study how retinal neurons deal with these rapid image transitions, we recorded spiking activity from ganglion cells, the output neurons of the retina, in isolated retinas of marmoset monkeys while shifting a projected image in a saccade-like fashion across the retina. We found that the cells do not just respond to the newly fixated image, but that different types of ganglion cells display different sensitivities to the presaccadic and postsaccadic stimulus patterns. Certain Off cells, for example, are sensitive to changes in the image across transitions, which contributes to differences between On and Off information channels and extends the range of encoded stimulus features.

Intensification of strontium (II) ion biosorption on Sargassum sp via response surface methodology

A batch system was employed to investigate the biosorption of strontium (II) on Sargassum sp. The biosorption of strontium on Sargassum sp was studied with response surface methodology to determine the combined effect of temperature, initial metal ion concentration, biomass treatment, biosorbent dosage and pH. Under optimal conditions, the algae's biosorption capacity for strontium (initial pH 7.2, initial strontium concentration 300 mg/l for Mg-treated biomass and biosorbent dosage 0.1 g in 100 mL metal solution) was measured at 103.95 mg/g. In our analysis, equilibrium data were fitted to Langmuir and Freundlich isotherms. Results show that the best fit is provided by the Freundlich model. Biosorption dynamics analysis of the experimental data indicated that strontium (II) was absorbed into algal biomass in accordance with the pseudo-second-order kinetics model well.

Molecular Mechanisms Mediating the Transfer of Disease-Associated Proteins and Effects on Neuronal Activity

BACKGROUND

Various cellular pathways have been implicated in the transfer of disease-related proteins between cells, contributing to disease progression and neurodegeneration. However, the overall effects of protein transfer are still unclear.

OBJECTIVE

Here, we performed a systematic comparison of basic molecular mechanisms involved in the release of alpha-synuclein, Tau, and huntingtin, and evaluated functional effects upon internalization by receiving cells.

METHODS

Evaluation of protein release to the extracellular space in a free form and in extracellular vesicles using an optimized ultracentrifugation protocol. The extracellular effects of the proteins and extracellular vesicles in primary neuronal cultures were assessed using multi-channel electrophysiological recordings combined with a customized spike sorting framework.

RESULTS

We demonstrate cells differentially release free-forms of each protein to the extracellular space. Importantly, neuronal activity is distinctly modulated upon protein internalization in primary cortical cultures. In addition, these disease-related proteins also occur in extracellular vesicles, and are enriched in ectosomes. Internalization of ectosomes and exosomes by primary microglial or astrocytic cells elicits the production of pro-inflammatory cytokines, and modifies spontaneous electrical activity in neurons.

OBJECTIVE

Overall, our study demonstrates that released proteins can have detrimental effects for surrounding cells, and suggests protein release pathways may be exploited as therapeutic targets in different neurodegenerative diseases.

Ectosomes and exosomes modulate neuronal spontaneous activity

Extracellular vesicles (EVs) are important mediators in intercellular communication. However, understanding the biological origin and functional effects of EVs subtypes has been challenging due to the moderate differences in their physical properties and absence of reliable markers. Here, we characterize the proteomes of ectosomes and exosomes using an improved differential ultracentrifugation protocol and quantitative proteomics. Our analyses revealed singular proteomic profiles for ectosomes and exosomes that enabled us to establish specific protein markers that can be used for their biochemical distinction. Cytoskeleton and glycolytic proteins are distinctively present in ectosomes, while endosomal sorting complexes proteins and tetraspanins are enriched in exosomes. Furthermore, annexin-A2 was identified as a specific marker for ectosomes derived from cell media and human cerebrospinal fluid. Expression of EGFP as a cytosolic reporter leads to its incorporation in EVs and enables their imaging with higher resolution. Assessment of neuronal network activity using multi-electrode array recordings demonstrated that spontaneous neuronal activity can be modulated by EVs. Ectosomes and exosomes internalization in neuronal cells disrupted their regular synchronized bursting activity, resulting in overall lower and more disorganized spiking activity. Our findings suggest that EVs cargoes reflect core intracellular processes, and their functional properties might regulate basic biological and pathological processes. SIGNIFICANCE: This article presents novel approaches for studying the origin, composition, and biological effects in neuronal activity of ectosomes and exosomes. Our findings suggest that EVs cargoes reflect core intracellular processes, and their functional properties might regulate basic biological and pathological processes. Ultimately, our study also forms the foundation for future biomarker studies and for the understanding of the molecular basis of different diseases.

Investigation of uranium (VI) adsorption by polypyrrole

The purpose of this study was to investigate the adsorption of uranium (VI) ions on the polypyrrole adsorbent. Polypyrrole was synthesized by a chemical method using polyethylene glycol, sodium dodecylbenzenesulfonate, and cetyltrimethylammonium bromide as the surfactant and iron (III) chloride as an oxidant in the aqueous solution. The effect of various surfactants on the synthesized polymers and their performance as the uranium adsorbent were investigated. Adsorbent properties were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The effect of different parameters such as pH, contact time, initial metal ion concentrations, adsorbent dose, and the temperature was investigated in the batch system for uranium adsorption process. It has been illustrated that the adsorption equilibrium time is 7min. The results showed that the Freundlich model had the best agreement and the maximum adsorption capacity of polypyrrole for uranium (VI) was determined 87.72mg/g from Langmuir isotherm. In addition, the mentioned adsorption process was fast and the kinetic data were fitted to the Pseudo first and second order models. The adsorption kinetic data followed the pseudo-second-order kinetic model. Moreover, the thermodynamic parameters ΔG⁰, ΔH⁰ and ΔS⁰ showed that the uranium adsorption process by polypyrrole was endothermic and spontaneous.

Biosorption of strontium from aqueous solution by fungus Aspergillus terreus

INTRODUCTION

The biosorption characteristics of strontium ions using fungus Aspergillus terreus were investigated. Experimental parameters affecting the biosorption process such as pH, contact time, initial metal concentration, and temperature were studied.

MATHEMATICAL DESCRIPTION

Fungus A. terreus exhibited the highest strontium uptake capacity at 15°C at an initial strontium ion concentration of 876 mg L(-1) and an initial pH of 9. Biosorption capacity increased from 219 to 308 mg g(-1) with a decrease in temperature from 45°C to 15°C at this initial strontium concentration. The equilibrium data fitted very well to the Langmuir adsorption model in the concentration range of strontium ions and at all the temperatures studied.

CONCLUSION

Evaluation of the experimental data in terms of biosorption dynamics showed that the biosorption of strontium onto fungus followed the pseudo-second-order dynamics well (R(2) > 0.985). The calculated thermodynamics parameters (-1.64 < ∆G° < -1.93 kJ mol(-1) at temperatures of 45-15°C, ∆H° = -4.83 kJ mol(-1) and ∆S° = -0.01 kJ mol(-1) K(-1)) showed that the biosorption of strontium ions were feasible, spontaneous, and exothermic at the temperature ranges of 15-45°C.

Equilibrium, kinetic and thermodynamic study of the biosorption of uranium onto Cystoseria indica algae

Biosorption equilibrium, kinetics and thermodynamics of binding of uranium ions to Cystoseria indica were studied in a batch system with respect to temperature and initial metal ion concentration. Algae biomass exhibited the highest uranium uptake capacity at 15 degrees C at an initial uranium ion concentration of 500 mg l(-1) and an initial pH of 4. Biosorption capacity increased from 198 to 233 mg g(-1) with an decrease in temperature from 45 to 15 degrees C at this initial uranium concentration. The Langmuir isotherm model were applied to experimental equilibrium data of uranium biosorption depending on temperature. Equilibrium data fitted very well to the Langmuir model C. indica algae in the studied concentration range of Uranium ions at all the temperatures studied. The saturation type kinetic model was applied to experimental data at different temperatures changing from 15 to 45 degrees C to describe the batch biosorption kinetics assuming that the external mass transfer limitations in the system can be neglected and biosorption is chemical sorption controlled. The activation energy of biosorption (E(A)) was determined as -6.15 using the Arrhenius equation. Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of biosorption (DeltaG degrees , DeltaH degrees and DeltaS degrees ) were also evaluated.