Glial Cell Activation and Oxidative Stress in Retinal Degeneration Induced by β-Alanine Caused Taurine Depletion and Light Exposure

We investigate glial cell activation and oxidative stress induced by taurine deficiency secondary to β-alanine administration and light exposure. Two months old Sprague-Dawley rats were divided into a control group and three experimental groups that were treated with 3% β-alanine in drinking water (taurine depleted) for two months, light exposed or both. Retinal and external thickness were measured in vivo at baseline and pre-processing with Spectral-Domain Optical Coherence Tomography (SD-OCT). Retinal cryostat cross sections were immunodetected with antibodies against various antigens to investigate microglial and macroglial cell reaction, photoreceptor outer segments, synaptic connections and oxidative stress. Taurine depletion caused a decrease in retinal thickness, shortening of photoreceptor outer segments, microglial cell activation, oxidative stress in the outer and inner nuclear layers and the ganglion cell layer and synaptic loss. These events were also observed in light exposed animals, which in addition showed photoreceptor death and macroglial cell reactivity. Light exposure under taurine depletion further increased glial cell reaction and oxidative stress. Finally, the retinal pigment epithelial cells were Fluorogold labeled and whole mounted, and we document that taurine depletion impairs their phagocytic capacity. We conclude that taurine depletion causes cell damage to various retinal layers including retinal pigment epithelial cells, photoreceptors and retinal ganglion cells, and increases the susceptibility of the photoreceptor outer segments to light damage. Thus, beta-alanine supplements should be used with caution.

The antennal scape organ of Scutigera coleoptrata (Myriapoda) and a new type of arthropod tip-pore sensilla integrating scolopidial components

Background Centipedes are terrestrial, predatory arthropods with specialized sensory organs. However, many aspects of their sensory biology are still unknown. This also concerns hygroreception, which is especially important for centipedes, as their epicuticle is thin and they lose water rapidly at low humidity. Thus, the detection of humid places is vital but to date no definite hygroreceptor was found in centipedes. House centipedes (Scutigeromorpha) possess a peculiar opening at the base of their antenna, termed ‘scape organ’, that houses up to 15 cone-shaped sensilla in a cavity. Lacking wall and tip-pores, these socket-less sensilla may be hypothesized to function as hygroreceptors similar to those found in hexapods. Results The cone-shaped sensilla in the scape organ as well as nearby peg-shaped sensilla are composed of three biciliated receptor cells and three sheath cells. A tip-pore is present but plugged by a highly electron-dense secretion, which also overlays the entire inner surface of the cavity. Several solitary recto-canal epidermal glands produce the secretion. Receptor cell type 1 (two cells in cone-shaped sensilla, one cell in peg-shaped sensilla) possesses two long dendritic outer segments that project to the terminal pore. Receptor cell type 2 (one cell in both sensilla) possesses two shorter dendritic outer segments connected to the first (proximal) sheath cell that establishes a scolopale-like structure, documented for the first time in detail in a myriapod sensillum. Conclusions The nearly identical configuration of receptor cells 1 with their long dendritic outer segments in both sensilla is similar to hexapod hygroreceptors. In Scutigera coleoptrata, however, the mechanism of stimulus transduction is different. Water vapor may lead to swelling and subsequent elongation of the plug pin that enters the terminal pore, thus causing stimulation of the elongated dendritic outer segments. The interconnection of receptor cell 2 with short outer dendritic segments to a scolopale-like structure potentially suits both sensilla for vibration or strain detection. Thus, both sensilla located at the antennal base of scutigeromorph centipedes fulfill a dual function.

Foveal bulge as a predictor of high visual function in rhegmatogenous retinal detachment

Introduction. The integrity of photoreceptor's inner segment/outer segment connection plays great importance in predicting visual acuity in eyes with retinal pathology. However, even optical coherence tomographic study showed the intact of retinal layers, including photoreceptor's inner segment/outer segment line, after surgery due to rhegmatogenous retinal detachment (RRD), low visual acuity is observed. Purpose. to identify predictors of high visual acuity in the foveolar zone in patients after successful RRD repair according to SD-OCT. Material and methods. Group 1 consisted of 20 cases – eyes after successful primary RRD repair performed through pars plana vitrectomy using silicone oil tamponade (1300 cSt), followed by removal of silicone oil with a replacement for sterile air. Group 2 – control, followed eyes without ophthalmopathology and visualisation of foveolar bulge according to OCT. All patients underwent a standard ophthalmological examination and OCT on the 30th day after silicone oil removal. OCT examination was performed by Retina Map and Cross Line modes. The lengths of the outer segments of photoreceptors, inner segments of photoreceptors and the outer nuclear layer of the layer were measured in manual mode. Retina Map was used to measure retinal foveolar thickness. Results. During the study, the data of the foveolar thickness of the retina, the outer nuclear layer and the length of the outer segment of photoreceptors in the main group showed a significant decrease in comparison with the control group (p=0.002, p=0.006, p=0.02, respectively). In this case, a strong correlation was obtained only between the length of the outer segments of photoreceptors and visual acuity (r=0.68). Conclusion. The length of the outer segments of the cones in the central retinal area, or foveolar bulge, should considers a predictor of high visual acuity twostage surgical treatment of primary RRD using silicone oil. Key words: retinal detachment, foveolar bulge, ellipsoid zone, vitrectomy, OCT.

A Metabolic Landscape for Maintaining Retina Integrity and Function

Neurons have high metabolic demands that are almost exclusively met by glucose supplied from the bloodstream. Glucose is utilized in complex metabolic interactions between neurons and glia cells, described by the astrocyte-neuron lactate shuttle (ANLS) hypothesis. The neural retina faces similar energy demands to the rest of the brain, with additional high anabolic needs to support continuous renewal of photoreceptor outer segments. This demand is met by a fascinating variation of the ANLS in which photoreceptors are the central part of a metabolic landscape, using glucose and supplying surrounding cells with metabolic intermediates. In this review we summarize recent evidence on how neurons, in particular photoreceptors, meet their energy and biosynthetic requirements by comprising a metabolic landscape of interdependent cells.

Functional results of surgical treatment of retinal detachment

The article analyzes the state of patients visual acuity after successful surgical treatment of retinal detachment. On the basis of gathered data, it was concluded that in case of detachment of the macula only in 50% of cases it is possible to increase visual acuity to 0.4 and higher. Restoration of visual functions continues for at least 6 months after the operation and is determined by the restoration of the structure of the outer segments of the photoreceptor cells. During this time, it is advisable to conduct drug therapy aimed at normalizing blood flow and functional activity of the retina. Visual functions recovery continues for at least 6 months after the operation and is connected with the restored structure of the outer segments of the photoreceptor cells. Important prognostic factors of central vision restoration in the postoperative period are visual acuity before surgery, duration of existence and height of macular detachment. Data on which of the methods of surgical treatment of retinal detachment allows to achieve higher visual acuity are contradictory. There is practically no data on the comparison of the effect on visual acuity of scleral buckling and vitrectomy in the long-term period, in patients with phakic eyes and with artiphakia. On visual acuity after fitting detachment of the macula may affect macular edema, epiretinal membrane formation and retinal folds, and edema of the peripapillary optic nerve head, progressive deterioration of blood flow in the basin of the central retinal artery, short posterior ciliary arteries and ophthalmic artery. It is believed that these factors are significantly more pronounced after scleral buckling than after vitrectomy. Some indicators of optical coherence tomography correlate with visual acuity after surgical treatment of retinal detachment: the state of the articulation line of the external and internal segments of the photoreceptors, as well as the state of the external limiting membrane.

THE CIRCADIAN CLOCK IN THE RETINAL PIGMENT EPITHELIUM CONTROLS THE DIURNAL RHYTHM OF PHAGOCYTIC ACTIVITY

The diurnal peak of phagocytosis by the retinal pigment epithelium (RPE) of photoreceptor outer segments (POS) is under circadian control, and it is believed that this process involves interactions from both the retina and RPE. Previous studies have demonstrated that a functional circadian clock exists within multiple retinal cell types and RPE cells. Thereby, the aim of the current study was to determine whether the circadian clock in the retina and or RPE controls the diurnal phagocytic peak of photoreceptor outer segments and whether selective disruption of the circadian clock in the RPE would affect RPE cells function and the viability during aging. To that aim, we first generated and validated an RPE tissue-specific KO of the essential clock gene, Bmal1, and then we determined the daily rhythm in phagocytic activity by the RPE in mice lacking a functional circadian clock in the retina or RPE. Then using electroretinography, spectral domain-optical coherence tomography, and optomotor response measurements of visual function we determined the effect of Bmal1 removal in young (6-month old) and old (18-month old) mice. RPE morphology and lipofuscin accumulation was also determined in young and old mice. Our data show that the circadian clock in the RPE controls the daily diurnal phagocytic peak of POS. Surprisingly, the lack of a functional RPE circadian clock or the diurnal phagocytic peak does not result in any detectable age-related degenerative phenotype in the retina or RPE. Thus, our results demonstrate that the loss of the circadian clock in the RPE or the lack of the daily peak in phagocytosis of POS does not result in deterioration of photoreceptors or the RPE during aging.