The diurnal Dipsadidae snakes Philodryas olfersii and P. patagoniensis are closely related in their phylogeny but inhabit different ecological niches. P. olfersii is arboreal, whereas P. patagoniensis is preferentially terrestrial. The goal of the present study was tocompare the density and topography of neurons, photoreceptors, and cells in the ganglion cell layer in the retinas of these two species using immunohistochemistry and Nissl staining procedures and estimate the spatial resolving power of their eyes based on the ganglion cell peak density. Four morphologically distinct types of cones were observed by scanning electron microscopy, 3 of which were labeled with anti-opsin antibodies: large single cones and double cones labeled by the antibody JH492 and small single cones labeled by the antibody JH455. The average densities of photoreceptors and neurons in the ganglion cell layer were similar in both species (∼10,000 and 7,000 cells·mm-2, respectively). The estimated spatial resolving power was also similar, ranging from 2.4 to 2.7 cycles·degree-1. However, the distribution of neurons had different specializations. In the arboreal P. olfersii, the isodensity maps had a horizontal visual streak, with a peak density in the central region and a lower density in the dorsal retina. This organization might be relevant for locomotion and hunting behavior in the arboreal layer. In the terrestrial P. patagoniensis, a concentric pattern of decreasing cell density emanated from an area centralis located in the naso-ventral retina. Lower densities were observed in the dorsal region. The ventrally high density improves the resolution in the superior visual field and may be an important adaptation for terrestrial snakes to perceive the approach of predators from above.
To study the potential effect of a gene therapy, designed to rescue the expression of dystrophin Dp71 in the retinas of Dp71-null mice, on retinal physiology. METHODS.We recorded electroretinograms (ERGs) in Dp71-null and wild-type littermate mice. In dark-adapted eyes, responses to flashes of several strengths were measured. In addition, flash responses on a 25-candela/square meters background were measured. On-and Off-mediated responses to sawtooth stimuli and responses to photopic sinewave modulation (3-30 Hz) were also recorded. After establishing the ERG phenotype, the ShH10-GFP adeno-associated virus (AAV), which has been previously shown to target specifically Müller glial cells (MGCs), was delivered intravitreously with or without (sham therapy) the Dp71 coding sequence under control of a CBA promoter. ERG recordings were repeated three months after treatment. Real-time quantitative PCR and Western blotting analyses were performed in order to quantify Dp71 expression in the retinas. RESULTS.Dp71-null mice displayed reduced b-waves in dark-and light-adapted flash ERGs and smaller response amplitudes to photopic rapid-on sawtooth modulation and to sinewave stimuli. Three months after intravitreal injections of the ShH10-GFP-2A-Dp71 AAV vector, ERG responses were completely recovered in treated eyes of Dp71-null mice. The functional rescue was associated with an overexpression of Dp71 in treated retinas. CONCLUSIONS.The present results show successful functional recovery accompanying the reexpression of Dp71. In addition, this experimental model sheds light on MGCs influencing ERG components, since previous reports showed that aquaporin 4 and Kir4.1 channels were mislocated in MGCs of Dp71-null mice, while their distribution could be normalized following intravitreal delivery of the same ShH10-GFP-2A-Dp71 vector.
We have identified the photoreceptors of Trachemys scripta elegans, an intensely studied species that is a model for color vision work. To recognize and count the different photoreceptor types, we labeled them with a combination of morphological and immunohistochemistry markers. The counts for the determination of the density of each photoreceptor type were made in wholemount retinas. The percentages found for each cone type were 29, 23, 21, 12, and 6%, respectively, for L (both types), double, M, S, and ultraviolet cones. The cones were found to be organized horizontally in a visual streak, a linear region with a higher density of photoreceptors that ends temporally in the periphery and more centrally in the nasal side. This region of high density of photoreceptors was not symmetrical along its extension; there was a region with conspicuous central density peaks in the temporal area, suggestive of an area centralis. We also observed a dorsoventral asymmetry in photoreceptor density, with greater density in the ventral region. This asymmetry was observed in cones and rods, but it was more pronounced in the rods. Our results corroborate and extend the findings of previous work in the literature describing the retinal photoreceptors of T. s. elegans and their spatial organization. The higher cone density within the visual streak reflects increased spatial resolution and its existence suggests the possibility of binocular vision. It is remarkable that within this region the entire potential for color vision is also present.
Objective : to determine the functional and morphological effects at rabbits retina of PS80 concentration used in the preparation of intravitreal drugs. Methods: eleven New Zealand rabbits received a intravitreal injection of 0.1ml of PS80. As control, the contralateral eye of each rabbit received the same volume of saline. Electroretinography was performed according to a modified protocol, as well as biomicroscopy and retina mapping before injection and seven and ten days after. Animals were euthanized in the 30th day and the retinas were analyzed by light microscopy. Results: eyes injected with PS80 did not present clinical signs of intraocular inflammation. Electroretinography did not show any alteration of extent and implicit time of a and b waves at scotopic and photopic conditions. There were no morphological alterations of retinas at light microscopy. Conclusion: intravitreal injection of PS80 in the used concentration for intravitreal drug preparations do not cause any functional or morphological alterations of rabbit retinas. These results suggest that PS80 is not toxic to rabbit retinas and may be safely used in the preparation of new lipophilic drugs for intravitreal injection.
MPA vitreous half-life is 5.0 days. Intravitreal injection of 0.5 μg MPA and higher causes dose- and time-related photoreceptor sensitivity decrease in rabbits. The MPA dose of 0.05 μg may be safe for intravitreal use in rabbits.
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