Navegando por Assunto "Células ganglionares da retina"

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Propriedades espaciais das respostas isoladas de cones L e M ao eletrorretinograma: implicações sobre a atividade das vias visuais paralelas
(Universidade Federal do Pará, 2015-06-16) JACOB, Mellina Monteiro; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718; GOMES, Bruno Duarte; http://lattes.cnpq.br/4932238030330851
We studied the spatial arrangement of L- and M-cone driven electroretinograms (ERGs) reflecting the activity of magno- and parvocellular pathways. L- and M-cone isolating sine wave stimuli were created with a four primary LED stimulator using triple silent substitution paradigms. Temporal frequencies were 8 and 12 Hz, to reflect cone opponent activity, and 30, 36 and 48 Hz to reflect luminance activity. The responses were measured for full-field stimuli and for different circular and annular stimuli. The ERG data confirm the presence of two different mechanisms at intermediate and high temporal frequencies. The responses measured at high temporal frequencies strongly depended upon spatial stimulus configuration. In the full-field conditions, the L-cone driven responses were substantially larger than the full-field M-cone driven responses and also than the L-cone driven responses with smaller stimuli. The M-cone driven responses at full-field and with 70° diameter stimuli displayed similar amplitudes. The L- and M-cone driven responses measured at 8 and 12 Hz were of similar amplitude and approximately in counter-phase. The amplitudes were constant for most stimulus configurations. The results indicate that, when the ERG reflects luminance activity, it is positively correlated with stimulus size. Beyond 35° retinal eccentricity, the retina mainly contains L-cones. Small stimuli are sufficient to obtain maximal ERGs at low temporal frequencies where the ERGs are also sensitive to cone-opponent processing.
Acesso aberto (Open Access)
Topografia de células ganglionares alfa na retina de roedores da Amazônia
(Universidade Federal do Pará, 2022-05) SAMPAIO, Gabriela Santos Alvarez; SOUZA, Givago da Silva; http://lattes.cnpq.br/5705421011644718; https://orcid.org/0000-0002-4525-3971
Introduction: The visual system of Amazonian rodents of the suborder Hystrichomorpha has been widely described, but little is known about the topography of alpha ganglion cells, which play a role in processing the vision of moving stimuli. Agouti (Dasyprocta aguti), paca (Cuniculus paca) and capybara (Hydrochoerus hydrochaeris) rodents are three different species of Hystrichomorpha that have a different circadian cycle and lifestyle. Objectives: To quantify alpha ganglion cell density and analyze cell body size according to eccentricity in the retina of agouti, paca and capybara. Methods: Three agouti, paca and capybara retinas from the pre-existing retinal collection at the Eduardo Oswaldo Cruz Laboratory of Neurophysiology at UFPA were used. Retinal collection were stained by the Nissl corpuscle staining method and direct counting was performed under a Zeiss optical microscope. The density of alpha-like ganglion cells was analyzed in different retinal eccentricities, such as in the visual range, area centralis, dorsal and ventral regions. Result: Analyzing the entire retina, the mean density of alpha-like ganglion cells in the agouti was 94.7±5.05 cells/μm2, in the paca it was 28.7±2.03 cells/μm2 and in the capybara it was 28.7±2.03 cells/μm2. of 101.03±24.42 cells/μm2. The presence of areas with high density of alpha ganglion cells was observed in the temporal region of the retina of the three rodents, and the agouti was the species that showed the most accentuated specialization of this type of ganglion cells. The cell body area of alpha ganglion cells that showed the highest frequency in the agouti retina was 200 μm², in the paca retina it was 300 to 600 μm² and in the capybara it was 300 to 500 μm². Conclusion: It is concluded that there is a relationship between ecology and density of alpha ganglion cells in the retina of large Brazilian rodents, so that those with diurnal habits have retinas with a greater number of these cells and with greater specialization in the temporal region.