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The S334ter-line-3 rat is a transgenic model of retinal degeneration developed to express a rhodopsin mutation similar to that found in human retinitis pigmentosa (RP) patients. Previous studies have focused on physiological changes in retinal cells and higher centers of the visual system with this model of retinal degeneration. However, little is known about the morphological changes in retinal cells during the development of the S334ter-line-3 rat. In order to understand and aid vision-rescue strategies, our aim has been to describe the retinal degeneration pattern in this model. We focus on changes in the morphologies of horizontal, bipolar, and amacrine cells in developing S334ter-line-3 rat retinas. Degeneration of photoreceptors begins in the central retina and progresses toward the periphery. In retinas at post-natal day 15 (P15), horizontal and rod bipolar cells show normal morphology. However, at P21, horizontal and rod bipolar cells exhibit abnormal processes at the outer plexiform layer, whereas the outer nuclear layer is significantly thinner. A glial reaction occurs concomitantly. In contrast, modifications in cone-bipolar and amacrine cells are much slower and do not occur until P90 and P180, respectively. The density of horizontal and rod-bipolar cells significantly drops after P60. Overall, the S334ter-line-3 model exhibits the hallmarks of cellular remodeling caused by photoreceptor degeneration. Its moderately fast time course makes the S334ter-line-3 a good model for studying vision-rescue strategies.

Precise positioning of a stimulating electrode in the eye is not possible by simple visualization. However, reliable measurement of responses to retinal stimulation requires consistent positioning. The present study focuses on impedance measurement techniques to sense the proximity of the electrode to the retina. A platinum-iridium stimulation electrode was placed inside the rat eye and impedance was recorded at different positions of the stimulating electrode relative to the retina. The presence of robust electrically evoked response in the superior colliculus indicates that the electrode may not have to be in absolute contact in order to elicit a neural response. Optical coherence tomography imaging confirmed the distance-impedance relationship.

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To function successfully, a retinal prosthesis needs to provide effective stimulation in a safe manner. To date, most studies have been dedicated to assessing proper stimulation parameters, for example, determining stimulus threshold. Few studies have looked at the effects of prolonged stimulation on retinal morphology. One previous study did show gross morphological changes in the rat retina due to mechanical pressure, with and without electrical stimulation (Colodetti et al., 2007). Here, we used immunocytochemistry to investigate the effects of the same experimental conditions on neuronal structure in finer detail. For this purpose, we first defined four experimental groups. In Group 1, the stimulating electrode was near but did not contact the retina, and we did not apply current pulses. In Group 2, the electrode also did not contact the retina, but we applied current pulses of 0.09 μC/phase. In Group 3, the stimulating electrode directly contacted the retina, but we did not apply current pulses. In Group 4, the stimulating electrode directly contacted the retina, and we applied current pulses of 0.09 μC/phase. We found neural damage only in the outer retina, including a disturbance of synaptic vesicle proteins in the photoreceptor terminals and a remodeling of horizontal and rod bipolar cells' processes. These results show that, although gross morphological changes are mainly concentrated around the area of electrode contact, immunocytochemistry can reveal changes in adjacent areas as well.

Measurements of Hall effect and Zn self-diffusio,n on single crsytals of ZnSe doped with various amounts of A1 or As were performed at 800% 900 ~ and 1000~ when the crystals were in equilibrium with atmospheres of welldefined zinc pressures; Hall effect measurements were also performed on crystals cooled after high temperature equilibration. Analysis of the results leads to the conclusion that Schottky disorder is the main type of atomic disorder. Values of the parameters for various equilibrium constants are determined.ZnSe has potential as a material for electroluminescent diodes and windows for high power infrared lasers. Knowledge of the high temperature defect structure is important for predicting the properties of materials made under different preparative conditions. A considerable amount of work has been devoted to the determination of the position of energy levels of various defects in the forbidden gap. Some levels are unambiguously assigned to certain foreign defects, while others are attributed to native defects, the exact nature of which (vacancies or interstitials, state of ionization) is not known. So far efforts to reach an understanding of the defect structure of ZnSe have been limited. High temperature Hall effect and conductivity measurements (1, 2) and self-diffusion measurements (3) were interpreted differently and no single model has emerged on the basis of which all the observations on ZnSe can be explained. In this investigation we attempt to determine the defect structure of ZnSe by high temperature measurements of the Hall effect and zinc tracer self-diffusion for A1-and Asdoped ZnSe crystals. Measurements of the electron concentration at room temperature on-ZnSe crystals quenched from high temperature after equilibration with atmospheres with well-defined zinc pressures provide information on the processes taking place during cooling.

The existing “quotidian equation state” model, based on Thomas-Fermi theory, is modified so as to improve the low density region of phase diagram of metals. A scheme for estimating the critical parameters of liquid-vapor phase transition is proposed. The new model reproduces experimental critical isotherms to a good degree of accuracy. Furthermore, the proposed model is validated with thermodynamic data in the liquid-vapor co-existence region, including results on isobaric expansion as well as released isentropes.