Análise fractal da vasculatura arteriolar e venular da retina em pessoas sem doença ocular

Although it has been suggested that retinal vasculature is a diffusion-limited aggregation (DLA) fractal, no study has been dedicated to standardizing its fractal analysis . The aims of this project was to standardize a method to estimate the fractal dimensions of retinal vasculature and to characterize their normal values; to determine if this estimation is dependent on skeletization and on segmentation and calculation methods; to assess the suitability of the DLA model and to determine the usefulness of log-log graphs in characterizing vasculature fractality . To achieve these aims, the information, mass-radius and box counting dimensions of 20 eyes vasculatures were compared when the vessels were manually or computationally segmented; the fractal dimensions of the vasculatures of 60 eyes of healthy volunteers were compared with those of 40 DLA models and the log-log graphs obtained were compared with those of known fractals and those of non-fractals. The main results were: the fractal dimensions of vascular trees were dependent on segmentation methods and dimension calculation methods, but there was no difference between manual segmentation and scale-space, multithreshold and wavelet computational methods; the means of the information and box dimensions for arteriolar trees were 1.29. against 1.34 and 1.35 for the venular trees; the dimension for the DLA models were higher than that for vessels; the log-log graphs were straight, but with varying local slopes, both for vascular trees and for fractals and non-fractals. This results leads to the following conclusions: the estimation of the fractal dimensions for retinal vasculature is dependent on its skeletization and on the segmentation and calculation methods; log-log graphs are not suitable as a fractality test; the means of the information and box counting dimensions for the normal eyes were 1.47 and 1.43, respectively, and the DLA model with optic disc seeding is not sufficient for retinal vascularization modeling

Encoding mechanisms based on fast oscillations in the retina of the cat and their dependencies on anesthesia

Processing in the visual system starts in the retina. Its complex network of cells with different properties enables for parallel encoding and transmission of visual information to the lateral geniculate nucleus (LGN) and to the cortex. In the retina, it has been shown that responses are often accompanied by fast synchronous oscillations (30 - 90 Hz) in a stimulus-dependent manner. Studies in the frog, rabbit, cat and monkey, have shown strong oscillatory responses to large stimuli which probably encode global stimulus properties, such as size and continuity (Neuenschwander and Singer, 1996; Ishikane et al., 2005). Moreover, simultaneous recordings from different levels in the visual system have demonstrated that the oscillatory patterning of retinal ganglion cell responses are transmitted to the cortex via the LGN (Castelo-Branco et al., 1998). Overall these results suggest that feedforward synchronous oscillations contribute to visual encoding. In the present study on the LGN of the anesthetized cat, we further investigate the role of retinal oscillations in visual processing by applying complex stimuli, such as natural visual scenes, light spots of varying size and contrast, and flickering checkerboards. This is a necessary step for understanding encoding mechanisms in more naturalistic conditions, as currently most data on retinal oscillations have been limited to simple, flashed and stationary stimuli. Correlation analysis of spiking responses confirmed previous results showing that oscillatory responses in the retina (observed here from the LGN responses) largely depend on the size and stationarity of the stimulus. For natural scenes (gray-level and binary movies) oscillations appeared only for brief moments probably when receptive fields were dominated by large continuous, flat-contrast surfaces. Moreover, oscillatory responses to a circle stimulus could be broken with an annular mask indicating that synchronization arises from relatively local interactions among populations of activated cells in the retina. A surprising finding in this study was that retinal oscillations are highly dependent on halothane anesthesia levels. In the absence of halothane, oscillatory activity vanished independent of the characteristics of the stimuli. The same results were obtained for isoflurane, which has similar pharmacological properties. These new and unexpected findings question whether feedfoward oscillations in the early visual system are simply due to an imbalance between excitation and inhibition in the retinal networks generated by the halogenated anesthetics. Further studies in awake behaving animals are necessary to extend these conclusions

Aspectos anatômicos do olho e neuroquímicos da retina do mocó (Kerodon rupestris)

The visual system is an important link between the animal and the environment, com profound influences on the habits and lifestyle in various habitats. Adaptive mechanismsto the temporal niche are present in the visual system of many vertebrates, involving changins in ocular dimensios and design, retinal cell distribution and organization of neurochemical circuits related to the retinal resolution or sensitivity. The sensory system of the eye is represented by the retina, whose organization is responsible by receipty, initial analysis, and transmission of the information to the brain. The knowledge of the position of the eyes in the head and the distribution of retinal cells allow to identify adaptive aspects of each species to its visual field, which is characteristic to the ecological niche it occupies. In this research, we study eye anatomical characteristics and retina neurochemical features of the rock cavy (Kerodon rupestris), a tipical Brazilian rodent from the suborder Hystricomorpha, family Caviidae. The rock cavy has lateral eyes well constitute bony orbit and well differentiated extrinsic muscle. The study of the descriptive and morphometric anatomy of the showed mean values of axial diameter 10.7±0,5mm and equatorial diameter 11.6±0.7mm. The pupil is slit shaped and the lens has mean axial diameter 5.4±0.03 mm, corresponding to ~45% of the axial diameter of the eye. The posterior nodal distance and the retinal magnification factor were estimated at 6.74 mm e 118 μm/grau, respectively. Flat mounts were processed for Nissl stain, and the topographic distribution of ganglion cells showed a moderate visual band, just below the optic disc, with higher density in the ventral retina. Retinal vertical sections and flat mounts were processed for immunohistochemistry to visualize tyrosine hydroxilase (TH) and thus two types of TH+ cells were detected. Type 1 cells had strong TH-immunoreactivity, the body cell varied from 120.047 to 269.373 μm2 stratifying in the sublamina 1 of the IPL. Type 2 cells were weakly TH-imunoreactive, had cell body located mostly in the IPL, varying from 54.848 to 177.142 μm2, constituting ~10% of the TH+ cells. Both cell types exhibited similar topographic distribution with higher density found in a horizontal band along of the naso-temporal axis in the dorsal retina. The total population of dopaminergic cells was 2,156±469,4 cells, occupying an average area of 198,164 μm2. The presence of cones and rods was detected by immunohistochemistry in vertical sections and flat mounts. S cones density is around 10 times smaller than L cones, with different degree of spatial organization. Other retinal neuronal populations of the rock cavy were also detected in vertical sections with specific markers. Comparative analysis of the anatomical characteristics of the rock cavy eye 12 suggest that it was designed to acquire higher sensitivity to light, at expense of image sharpness, compatible with a vision at mesopic conditions. Additionally, the distribution of the 2 subtypes of dopaminergic cells in a naso-temporal band in the dorsal retina seems suitable to a gain in sensitivity, coherent with an animal with predominantly crepuscular activity pattern

Prevalência de alterações fundoscópicas em estudantes na cidade de Natal/Brasil

Objetivo: Determinar a prevalência de alterações fundoscópicas em estudantes de escolas das redes pública e privada de Natal-RN. Métodos: Avaliação oftalmológica foi realizada em 990 alunos, de 5 a 21 anos, matriculados nas escolas das redes públicas e privada do município de Natal- RN, que estiveram cursando alguma série do ensino fundamental ou médio, no período de 03 a 06 de 2001. Resultados: Alterações fundoscópicas foram observadas em 5,3% dos estudantes. As anormalidades encontradas, por ordem de freqüência, foram: branco sem pressão, 1,0%; cicatriz de retinocoroidite sugestiva de toxoplasmose, 1,0%; atrofia do epitélio pigmentado da retina, 0,8%; nevos da coróide, 0,4%; escavação da cabeça do nervo óptico aumentada, 0,4%; degeneração em treliça, 0,3%; buraco operculado, 0,2%; fundus miópico, 0,2%; tortuosidade vascular aumentada, 0,2%; granuloma sugestivo de toxocaríase, 0,2%; hipoplasia da cabeça do nervo óptico, 0,1%; persistência da artéria hialoidea, 0,1%; persistência de fibras de mielina, 0,1%; retina sal e pimenta, 0,1%; retinosquise, 0,1%. Conclusão: Houve uma baixa prevalência de alterações fundoscópicas na população estudada

Análise fractal da vasculatura retínica: métodos de segmentação e de cálculo dimensional

Embora tenha sido proposto que a vasculatura retínica apresenta estrutura fractal, nenhuma padronização do método de segmentação ou do método de cálculo das dimensões fractais foi realizada. Este estudo objetivou determinar se a estimação das dimensões fractais da vasculatura retínica é dependente dos métodos de segmentação vascular e dos métodos de cálculo de dimensão. Métodos: Dez imagens retinográficas foram segmentadas para extrair suas árvores vasculares por quatro métodos computacionais (“multithreshold”, “scale-space”, “pixel classification” e “ridge based detection”). Suas dimensões fractais de “informação”, de “massa-raio” e “por contagem de caixas” foram então calculadas e comparadas com as dimensões das mesmas árvores vasculares, quando obtidas pela segmentação manual (padrão áureo). Resultados: As médias das dimensões fractais variaram através dos grupos de diferentes métodos de segmentação, de 1,39 a 1,47 para a dimensão por contagem de caixas, de 1,47 a 1,52 para a dimensão de informação e de 1,48 a 1,57 para a dimensão de massa-raio. A utilização de diferentes métodos computacionais de segmentação vascular, bem como de diferentes métodos de cálculo de dimensão, introduziu diferença estatisticamente significativa nos valores das dimensões fractais das árvores vasculares. Conclusão: A estimação das dimensões fractais da vasculatura retínica foi dependente tanto dos métodos de segmentação vascular, quanto dos métodos de cálculo de dimensão utilizados

Prevalência de alterações fundoscópicas em estudantes na cidade de Natal-Brasil

Objetivo: Determinar a prevalência de alterações fundoscópicas em estudantes de escolas das redes pública e privada de Natal-RN. Métodos: Avaliação oftalmológica foi realizada em 990 alunos, de 5 a 21 anos, matriculados nas escolas das redes públicas e privada do município de Natal-RN, que estiveram cursando alguma série do ensino fundamental ou médio, no período de 03 a 06 de 2001. Resultados: Alterações fundoscópicas foram observadas em 5,3% dos estudantes. As anormalidades encontradas, por ordem de freqüência, foram: branco sem pressão, 1,0%; cicatriz de retinocoroidite sugestiva de toxoplasmose, 1,0%; atrofia do epitélio pigmentado da retina, 0,8%; nevos da coróide, 0,4%; escavação da cabeça do nervo óptico aumentada, 0,4%; degeneração em treliça, 0,3%; buraco operculado, 0,2%; fundus miópico, 0,2%; tortuosidade vascular aumentada, 0,2%; granuloma sugestivo de toxocaríase, 0,2%; hipoplasia da cabeça do nervo óptico, 0,1%; persistência da artéria hialoidea, 0,1%; persistência de fibras de mielina, 0,1%; retina sal e pimenta, 0,1%; retinosquise, 0,1%. Conclusão: Houve uma baixa prevalência de alterações fundoscópicas na população estudada

Incidência e fatores de risco da retinopatia diabética em pacientes do Hospital Universitário Onofre Lopes, Natal-RN

Estudar a incidência e fatores de risco (tempo de doença e presença de hipertensão arterial sistêmica) para retinopatia diabética em 1002 pacientes encaminhados pelo Programa de Diabetes do Hospital Universitário Onofre Lopes no período de 1992 – 1995. Métodos: Estudo retrospectivo de pacientes com diagnóstico de diabetes mellitus encaminhados ao Setor de Retina do Departamento de Oftalmologia pelo Programa de Diabetes do Hospital Universitário e submetido, sob a supervisão do autor, a exame oftalmológico, incluindo medida da acuidade visual corrigida (tabela de Snellen), biomicroscopia do segmento anterior e posterior, tonometria de aplanação e oftalmoscopia binocular indireta sob midríase(tropicamida 1% + fenilefrina 10%). Foi realizada análise dos prontuários referente ao tempo de doenças e diagnostico clínico de hipertensão arterial sistêmica. Resultados: Dos 1002 diabéticos examinados (em 24 deles a fundoscopia foi inviável), 978 foram separados em 4 grupos: sem retinopatia diabética (SRD), 675 casos (69,01%); com retinopatia diabética não proliferativa (RDNP), 207 casos (21,16%); com retinopatia diabética proliferativa (RDP), 70 casos (7,15%); e pacientes já fotocoagulados (JFC), 26 casos (2,65%). Do total, 291 eram do sexo masculino (29%) e 711 do sexo feminino (71%). Os 4 grupos foram ainda avaliados quanto ao sexo, a faixa etária, a acuidade visual, tempo de doença, presença de catarata e hipertensão arterial sistêmica e comparados entre si. Com relação ao tipo de diabetes, 95 eram do tipo I (9,4%), 870 pacientes eram do tipo II (86,8%), e em 37 casos(3,7%) o tipo de diabetes não foi determinado. Conclusões: Comprovou-se que os pacientes com maior tempo de doença tinham maior probabilidade de desenvolver retinopatia diabética, e que a hipertensão arterial sistêmica não constituiu fator de risco em relação à diminuição da acuidade visual nos pacientes hipertensos

"O núcleo supraquiasmático e o folheto intergeniculado do mocó (Kerodon rupestris): Projeções retinianas e caracterização imuno-histoquímica

In this study, two circadian related centres, the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) were evaluated in respect to their cytoarchitecture, retinal afferents and chemical content of major cells and axon terminals with a tract tracer and immunohistochemical techniques in the rock cavy (Kerodon rupestris), a Brazilian caviidae rodent species. The rock cavy SCN is innervated in its ventral portion by terminals from the predominantly contralateral retina. It also contains neurophisin and vasoactive intestinal polypeptide immunoreactive cell bodies and neuropeptide Y and enkephalin immunopositive fibres and terminals and is marked by intense GFAP immunoreactivity. The IGL receives a predominantly contralateral retinal projection, contains neuropeptide Y and nitric oxide synthase producing neurons and enkephalin immunopositive terminals and is characterized by dense GFAP immunoreactivity. This is the first report examining the neural circadian system in a crepuscular rodent species for which circadian properties have been described. The results are discussed comparing with what has been described for other species and in the context of the functional significance of these centres

Centros subcorticais dos sistemas visual primário e óptico acessório no mocó (kerodon rupestris): caracterização pela projeção retiniana e citoarquitetura.

The primary and accessory optic systems comprise two set of retinorecipient neural clusters. In this study, these visual related centers in the rock cavy were evaluated by using the retinal innervations pattern and Nissl staining cytoarchigtecture. After unilateral intraocular injection of cholera toxin B subunit and immunohistochemical reaction of coronal and sagittal sections from the diencephalon and midbrain region of rock cavy. Three subcortical centres of primary visual system were identified, superior colliculus, lateral geniculate complex and pretectal complex. The lateral geniculate complex is formed by a series of nuclei receiving direct visual information from the retina, dorsal lateral geniculate nucleus, intergeniculate leaflet and ventral lateral geniculate nucleus. The pretectal complex is formed by series of pretectal nuclei, medial pretectal nucleus, olivary pretectal nucleus, posterior pretectal nucleus, nucleus of the optic tract and anterior pretectal nucleus. In the accessory optic system, retinal terminals were observed in the dorsal terminal, lateral terminal and medial terminal nuclei as well as in the interstitial nucleus of the superior fasciculus, posterior fibres. All retinorecipient nuclei received bilateral input, with a contralateral predominance. This is the first study of this nature in the rock cavy and the results are compared with the data obtained for other species. The investigation represents a contribution to the knowledge regarding the organization of visual optic systems in relation to the biology of species.

Efeitos da senescência no núcleo supraquiasmático do sagui (Callithrix Jacchus): plasticidade morfológica e neuroquímica

The circadian timing system (CTS) is responsible for the generation and synchronization and the suprachiasmatic nucleus (SCN) of the hypothalamus has been described as the major circadian pacemaker in many mammalian species. The internal temporal organization managed by SCN is disturbed with aging bringing many pathological disorders that range from loss of complex cognitive performance to simple physiological functions. Therefore, our aim was perform a comparative study of the morphological aspects and neurochemical composition in the SCN of marmosets (Callithrix jacchus) adults and older using immunohistochemical techniques. We found morphometric and neurochemical changes in th SCN o folder animals in comparison to adults, among these a possible decreased in retinal projection to the SCN of older animals, found through a decline in CTB immunostaining, which can occur due atrophy and/or decreasing of fibers from the retinohypothalamic tract (RHT). The Klüver-Barrera histological technique strongly suggests a decrease in those fibers from RHT. Also, by means of a morphometric study, it is found a atrophy and numerical decline of neurons in SCN of aged animals, investigated by Nissl technique, and immunostaining with NeuN and calbindin. Relative optical density (ROD) analysis were used to evaluate the expression of some neurochemical components in SCN, such as GFAP expression, which was increased in older, result that indirectly reinforces that morphological changes occurs due the aging; the vasoactive intestinal polipeptide (VIP) showed no expression alteration in SCN of older animals; the serotonin (5-HT) was descreased in the dorsomedial portion of the SCN, and neurpeptide Y (NPY) apparently also decrease due to the increase of age. Many of these modifications were seen in other animals, such as rodents, human primates and non-human primates. These data about marmoset comes to add new information of the effect of aging on structures responsibles for the circadian rhytmicity, and that some behavioral changes controlled by th SCN, and founded in aged animals, may be caused by these morphological and neurochemical changes. Although some results have been quantitatively negative, qualitatively all analysis show significant change comparing adult and older animals, perhaps due to a low sampling number. In conclusion, the marmoset presents several morphological and neurochemical changes in the SCN of aged animals compared to adults, which may result in behavioral changes that favor pathology aging related

O trato retino-hipotalâmico no mocó (Kerodon rupestris): Um estudo de traçado anterógrado com a subunidade b da toxina colérica

The light, besides the vision stimuli, controls other process completely independent of image formation, such as the synchronization of the organismic circadian rhythms to the enviromental light/dark cycle. In mammals, this adjust occurs through the retinohypothalamic tract, a direct retinal projection to the suprachiasmatic nucleus, considered to be the major circadian pacemaker. Early studies have identified only the suprachiasmatic nucleus as a retinal target in the hypothalamus. However, using more sensitive neuroanatomic tracers, other retinorecipient hypothalamic regions outside to suprachiasmatic nucleus were pointed in a great number of mammalian species. In this study, the retinohypothalamic tract was shown in the rock cavy (Kerodon rupestris), an endemic rodent of the semiarid region of the Brazilian Northeast, using unilateral intravitreal injections of cholera toxin subunit b as a neuronal tracer. The results reveal that in the rock cavy, besides the suprachiasmatic nucleus, several hypothalamic regions receive direct retinal projection, such as the ventrolateral preoptic nucleus, medial and lateral preoptic areas, the supraoptic nucleus and bordering areas, anterior, lateral and rectrochiasmatic hypothalamic areas, and the subparaventricular zone. The results are discussed by comparing with those of the literature, into a functional context

Caracaterização do núcleo pré-geniculado do sagüi (Callithrix jacchus) :projeção retiniana, neuroquímica e atividade celular (expressão de FOS)

In rodents, the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) are the main components of the circadian system. The SCN is considerate the site of an endogenous biological clock because can to generate rhythm and to synchronize to the environmental cues (zeitgebers) and IGL has been related as one of the main areas that modulate the action of SCN. Both receive projections of ganglion cells of retina and this projection to SCN is called retinohypothalamic tract (RHT). Moreover, the IGL is connected with SCN through of geniculohypothalamic tract (GHT). In primates (include humans) was not still demonstrated the presence of a homologous structure to the IGL. It is believed that the pregeniculate nucleus (PGN) can be the answer, but nothing it was still proven. Trying to answer that question, the objective of our study is to do a comparative analysis among PGN and IGL through of techniques immunohystochemicals, neural tracers and FOS expression after dark pulses. For this, we used as experimental model a primate of the new world, the common marmoset (Callithrix jacchus). Ours results may contribute to the elucidation of this lacuna in the circadian system once that the IGL is responsible for the transmission of nonphotic information to SCN and participate in the integration between photic and nonphotic stimulus to adjust the function of the SCN. In this way to find a same structure in primates represent an important achieve in the understanding of the biological rhythms in those animals

Efeito do tratamento com as drogas antipsicóticas haloperidol e clozapina sobre a infecção de toxoplasma gondii em cultura de células retinianas embrionárias

T. gondii is an obligate intracellular protozoan and the main cause of retinochoroiditis in humans. The aim of this study was to evaluate the effect of the antipsychotic drugs haloperidol and clozapine on the course of infection by T. gondii of cultured embryonic retinal cells. Embryo retinas of Gallus gallus domesticus (E12) were used for the preparation of mixed monolayer cultures of retinal cells. Cultures were maintained on plates of 96 and 24 wells by 37°C in DMEM medium supplemented with 5% fetal bovine serum for 2 days. After this period, cultures were simultaneously infected with tachyzoites of T. gondii and treated with the antipsychotics haloperidol and clozapine for 48 hours. Treatment effects were determined by both assessing cell viability with the MTT method and evaluating infection outcomes in slides stained with Giemsa. The treatment with haloperidol and clozapine cells infected with T. gondii resulted in higher viability of these cells, suggesting a possible prevention of neuronal degeneration induced by T. gondii. Additionally, intracellular replication of this protozoan in cells treated with haloperidol and clozapine were significantly reduced, possibly by modulation of the parasite s intracellular calcium concentration

Projeção retiniana, caracterização citoarquitetônica e neuroquímica da zona incerta do moco (Kerodon rupestris)

The Zona Incerta (ZI) is embryologically derived from the ventral thalamus, in continuity with the reticular nucleus of the thalamus. Studies usingneural tracers technics have allowed identify a complex connectional map including the ZI. Futhermore, cytochemical, molecular and functional data have shown abundant variability in the neurochemical contend in the ZI, as well as,the involvement of the ZI in the modulation of nociception, attention, alertness, control and maintenance of posture and control of visceral activity. This work aims to characterize the cytoarchitecture, neurochemical content of the ZI in the rock cavy (Kerodon rupestris), and a direct retinal-ZI pathway present in this species. The Nissl staining is effective for the delineation and characterization of ZI citoarchitecture. ZIc receives a contralateral retinal projection showing varicosities, suggesting a modulatory character of photic information. The ZI in the rock cavy, as in others rodents and primates, is characterized by a complex neurochemical signature. The ZI neurochemistry presents great diversity, especially in the medial portion of ZIr, where we have found immunoreactivity of all neuroactive substances investigated, and that NOS-IR, GFAP and CR helped the delimitation of middle ZI in ZId and ZIv. Nevertheless, just 5-HT-IR fibers are present in all subdivisions of the ZI. These data demonstrate the great wealth of the neurochemistry of rock cavy s ZI and a direct retinal modulation in the ZI, helping to explain it s broad functional repertory