Effects of monocular deprivation on the dendritic features of retinal ganglion cells / Efectos de la privación monocular sobre las características dendríticas de las células ganglionares de la retina

Monocular deprivation results in anatomical changes in the visual cortex in favor of the non-deprived eye. Although the retina forms part of the visual pathway, there is scarcity of data on the effect of monocular deprivation on its structure. The objective of this study was to describe the effects of monocular deprivation on the retinal ganglion cell dendritic features. The study design was quasi-experimental. 30 rabbits (18 experimental, 12 controls) were examined. Monocular deprivation was achieved through unilateral lid suture in the experimental animals. The rabbits were observed for three weeks. Each week, 6 experimental and 3 control animals were euthanized, their retina harvested and processed for light microscopy. Photomicrographs of the retina were taken using a digital camera then entered into FIJI software for analysis. The number of primary branches, terminal branches and dendritic field area among the non-deprived eyes increased by 66.7%(p=0.385), 400%(p=0.002), and 88.4%(p=0.523) respectively. Non-deprived eyes had 114.3% more terminal dendrites (p=0.002) compared to controls. Among deprived eyes, all variables measured had a gradual rise in the first two weeks followed by decline with further deprivation. There were no statistically significant differences noted between the deprived and control eyes. Monocular deprivation results in increase in synaptic contacts in the non-deprived eye, with reciprocal changes occurring in the deprived eye.

La privación monocular de la visión resulta en cambios anatómicos en la corteza visual en favor del ojo no privado. Aunque la retina forma parte de la vía visual, hay escasez de datos sobre el efecto de la privación monocular en su estructura. El objetivo de esta investigación fue describir los efectos de la privación monocular en las características de las dendritas de las células ganglionares de la retina. Se diseñó un estudio cuasi-experimental. Se examinaron 30 conejos (18 experimentales, 12 controles). La privación monocular se logró a través de la sutura unilateral del párpado en los animales de experimentación. Los conejos fueron observados durante tres semanas. Cada semana, 6 animales experimentales y 3 control fueron eutanasiados, donde se obtuvo la retina y fue procesada para realizar microscopía óptica. Las microfotografías de la retina fueron tomadas con una cámara digital y luego se utilizó el software FIJI para su análisis. El número de dendritas primarias, terminales y el área del campo de dendritas en los ojos no privados aumentó un 66,7% (p=0,385), 400% (p=0,002), y 88,4% (p=0,523), respectivamente. Los ojos no privados, tenían 114,3% más dendritas terminales (p=0,002) en comparación con los controles. Entre los ojos privados, todas las variables medidas tuvieron un aumento gradual en las dos primeras semanas, seguido de descenso con mayor privación. No se observaron diferencias estadísticamente significativas entre los ojos privados y el grupo control. En conclusion, la privación monocular produce un aumento de los contactos sinápticos en los ojos no privados, con cambios recíprocos que se manifiestan en los ojos privados de la visión.

The Influence of Contrasts on Directional and Spatial Frequency Tuning in Visual Cortex Areas 17/18 of the Cat

PURPOSE: The purpose of this study was to investigate the effects of contrast display exposure on neuronal directional and spatial frequency tuning. Neuronal responses were recorded from ninety-four neurons in cortical areas 17 and 18 in two adult cats. METHODS: A multi-channel microelectrode was implanted in cortical areas 17 and 18 of two paralyzed and anaesthetized cats. Various drifting sinusoidal grating contrast displays were presented to one of the cats' eyes in the visual field. Contour plots based on the neuronal responses to the drifting sinusoidal grating displays using various contrasts (i.e., 0.4, 0.7, and 1.0) and velocities (i.e., 4.6, 13.9, 23.1, 32.3, 41.5, 50.8, and 60.0 deg/sec) were plotted as a function of the spatial frequency and the direction associated with each velocity and contrast used. RESULTS: Five parameters were extracted from these contour plots: 1) optimum response, 2) preferred direction, 3) optimum spatial frequency, 4) directional tuning width, and 5) spatial frequency bandwidth. To determine the optimal velocity, each parameter was plotted against each of the specific display contrasts used, and a 'best fit' line was established. Response amplitudes were dependent on the type of contrast utilized; however, the spatial frequency and directional tuning properties were stable for the cortical neurons assessed. CONCLUSIONS: The results of the presentation of different contrasts on neuronal directional and spatial frequency tuning are consistent with behavioral results when medium and high contrast displays are used.

Intrinsic projections of cebus-monkey area 17: cell morphology and axon terminals

Metric features of the axon terminals and cell morphology of intrinsic projections of area 17 were studied in the Cebus apella. Anterograde and retrograde labeled cell appendages were obtained using saturated pellets and iontophoretic injections of biocytin in the operculum. Details of the histological and histochemical procedures have been described elsewhere (Amorim and Picanço-Diniz, 1996). We distinguished three labeled cell types: pyramidal, star pyramidal and stellate cells and three distinct morphologies of axon terminals were found: Ia, Ib and II, located at supragranular layers. Axon terminals of the group I innervate larger extent of striate cortex through longer intermediate segments, and acute branching angles compared to group II. Group II present on average similar characteristics of the smooth neurons axon terminals. The results taken together with the occurrence of only two types of synapses (I and II) from Gray's ultrastructural studies, seem to give an additional support to extend to the Cebus apella the major subdivision of neocortical neuronal morphology that classified them as smooth and spine neurons.

Effect of pre and postnatal retinal deprivation on the striate-peristriate cortical connections in the rat

The tangential distribution of the striate-peristriate cortical connections in normal, postnatally eye nucleated and congenitally anophthalmic rats, was studied after a single injection of wheat germ agglutinin conjugated with horseradish peroxidase into the striate cortex. The typical normal pattern of separate fields in the peristriate cortex is altered in eye enucleated animals, in such a way that their areal distribution in the cerebral cortex is increased and each field tends to fuse with the adjacent one. This process is more marked in anophthalmic animals, a finding that is in agreement with the notion that ganglion cells exert their influence before the visual pathway is functional

A dual arrangement pattern of the cells of corticotectal origin in the cat

Utilizando o transporte retrógrado da peroxidase da raiz forte (HRP) e a técnica de aplanamento do córtex cerebral, foi estudado o arranjo das células corticotectais nas diversas áreas visuais do gato. Demonstraram-se dois padröes diferentes de distribuiçäo, sendo um focal, evidenciado pela injeçöes de HRP no colículo superfícial, e outro difuso, revelado pela injeçäo de HRP no colículo profundo. Esses dados säo analisados tendo em vista a hipótese da existência de dois sistemas corticotectais, anatômica e fisiologicamente distintos

The visual cortex of the agouti (Dasyprocta agouti): architectonic subdivisions

1. We have studied the cytoarchitecture and myeloarchitecture of the agouti's cortical surface that can be activated by visual stimulation. Five architectonic subdivisions that correspond to distinctive visuotopic representations were characterized. 2. The largest portion of the visual cortex is occupied by area 17 which is situated lateral to the cingulate cortex, medial to area 18, posterior to the parietal cortex, and anterior to the agranular retrosplenial cortex. Additionally, four architectonic subdivisions in the extrastriate visual cortex were distingished, i. e., from medial to lateral: area 18, area 19, anterior lateral area, and temporal posterior area. 3. Along the border of the extrastriate cortex a ring of nonvisual cortical fiels was encountered encompassing parietal (somatic sensorial) cortex, temporal anterior and temporal intermediate (auditory) areas, a band of pre-rhinal cortex, and agranular retrosplenial cortex