Amplitude changes in the electrophysiological response of retinal cells during simultaneous current stimulation

Purpose : Ocular electrical stimulation exhibit potential for the treatment of neurodegenerative ocular diseases. However, the underlying mechanism in the retinal cells remains subject of research. Studies applying transcranial electrical stimulation show that direct current stimulation (DCS) over the visual cortex manipulates the amplitudes of visual evoked potentials. An anodal DCS leads to increased amplitudes while a cathodal DCS decreased these amplitudes. We hypothesize that the retinal cells show similar reactions. Methods : We stimulated 15 volunteers (8m, 7f, 23.5 ± 1.6 years, one eye) with a cathodal DCS of 500 µA (DC-stimulator MC, neuroConn GmbH, Ilmenau) for 10 minutes. For DCS we used six cup electrodes (diameter: 0.95 cm) placed around one eye . Before, during and after DCS we measured the electrophysiological answer of the retinal ganglion cells using a pattern-reversal stimulus (stimulus field: 1° individual checks, 16° total; reversals per second: 4; Michelson contrast: 99%; mean luminance: 186 cd/m^2). For recording, we used Ag/AgCl ring electrodes located at the lower eyelid and the earlobe. For statistical analysis the Friedman test for paired samples and a confidence interval analysis was performed. Results : The characteristic amplitudes of the the electrophysiological answer (P50 and N95 component) as well as its peak-to-peak difference (PPD) were decreased during the stimulation. The visible trend was statistically not significant (Friedman test P50/N95/PPD: p = 0.527/0.574/0.297). Under consideration of specific volunteers (showed expected reduction of the N95 component, n = 9) we found a significant change of the N95 component for the difference between before and during DCS (confidence interval analysis, lower limit: -2.45 µV; upper limit: -0.38 µV; after Bonferroni correction α = 0.0143). Conclusions : The performed study indicates a trend that a cathodal DCS decreasing electrophysiological activity in the retina

Pulsed electrical stimulation of the human eye enhances retinal vessel reaction to flickering light

Recent studies indicate therapeutic benefits of electrical stimulation in cases of specific ophthalmic diseases that are associated with dysfunctional ocular microcirculation. This suggests effects of electrical stimulation on vascular functions. In the present study, we investigated the effects of electrical stimulation on retinal vessel reactions using dynamic vessel analysis (DVA). Eighty healthy subjects were randomly assigned to one of three groups receiving electrical stimulation with different current intensities: 400 μA (n = 26); 800 μA (n = 27); 1200 μA (n = 27). The electrode montage for electrical stimulation consisted of a ring-shaped active electrode surrounding one eye and a square return electrode at the occiput. Rectangular, monophasic, positive current pulses were applied at 10 Hz for a duration of 60 s per stimulation period. DVA was used to observe the stimulation-induced reactions of retinal vessel diameters in response to different provocations. In three DVA measurements, three stimulus conditions were investigated: flicker light stimulation (FLS); electrical stimulation (ES); simultaneous electrical and flicker light stimulation (ES+FLS). Retinal vasodilation caused by these stimuli was compared using paired t-test. The subjects receiving electrical stimulation with 800 μA showed significantly increased retinal vasodilation for ES+FLS compared to FLS (p < 0.05). No significant differences in retinal vessel reactions were found between ES+FLS and FLS in the 400 and 1200 μA groups. No retinal vasodilation was observed for ES for all investigated current intensities. The results indicate that positive pulsed electrical stimulation of an adequate intensity enhances the flicker light-induced retinal vasodilation

Re-structuring of marine communities exposed to environmental change

Species richness is the most commonly used but controversial biodiversity metric in studies on aspects of community stability such as structural composition or productivity. The apparent ambiguity of theoretical and experimental findings may in part be due to experimental shortcomings and/or heterogeneity of scales and methods in earlier studies. This has led to an urgent call for improved and more realistic experiments. In a series of experiments replicated at a global scale we translocated several hundred marine hard bottom communities to new environments simulating a rapid but moderate environmental change. Subsequently, we measured their rate of compositional change (re-structuring) which in the great majority of cases represented a compositional convergence towards local communities. Re-structuring is driven by mortality of community components (original species) and establishment of new species in the changed environmental context. The rate of this re-structuring was then related to various system properties. We show that availability of free substratum relates negatively while taxon richness relates positively to structural persistence (i.e., no or slow re-structuring). Thus, when faced with environmental change, taxon-rich communities retain their original composition longer than taxon-poor communities. The effect of taxon richness, however, interacts with another aspect of diversity, functional richness. Indeed, taxon richness relates positively to persistence in functionally depauperate communities, but not in functionally diverse communities. The interaction between taxonomic and functional diversity with regard to the behaviour of communities exposed to environmental stress may help understand some of the seemingly contrasting findings of past research