Ultrastructure alterations of retinal photoreceptors of the black rat, Rattus rattus exposed to certain heavy metals

This study was designed to investigate the impact of lead and cadmium on the retinal photoreceptors of rats. Adult black rats, Rattus rattus, were selected and divided into control and exposed groups. The exposed group was housed in industrial car batteries room containing fumes of lead and cadmium. The retina prepared for scanning and transmission electron microscopy. The scanning electron microscopy revealed different lead-cadmium changes represented by gradual increasing in spaces between segments of the photoreceptors, associated with swelling of their inner segments and accompanied with rupture, degeneration and decreased numbers of some rods and cones in the outer segments. Disorganization, shortening, a decrease in number of the photoreceptors and a great deformity were the characteristic changes after prolonged exposure to the heavy metals. The aforementioned damages of the photoreceptors were confirmed at the ultrastructural level using transmission electron microscope in the form of progressive disorganization, shortening, swelling, widening of the intradiscal spaces, vacuolization and degeneration of the lamellae of the outer segments [OS], followed by the damage of mitochondria of the inner segments[IS]. Excessive penetration of the processes of the pigmented epithelium [PE] filled with pigments of different shapes and sizes between the damaged segments were noted. These pathological changes were considered the first symptoms in the retinal toxicity. The present results are alarming and call for further investigations to elucidate the impact of exposure to these heavy metals for longer periods on the rat vision and eye structure

Visual and acoustic communication in non-human animals: a comparison.

The visual and auditory systems are two major sensory modalities employed in communication. Although communication in these two sensory modalities can serve analogous functions and evolve in response to similar selection forces, the two systems also operate under different constraints imposed by the environment and the degree to which these sensory modalities are recruited for non-communication functions. Also, the research traditions in each tend to differ, with studies of mechanisms of acoustic communication tending to take a more reductionist tack often concentrating on single signal parameters, and studies of visual communication tending to be more concerned with multivariate signal arrays in natural environments and higher level processing of such signals. Each research tradition would benefit by being more expansive in its approach.

Electrophysiological measurements of spectral sensitivities: a review

Spectral sensitivities of visual systems are specified as the reciprocals of the intensities of light (quantum fluxes) needed at each wavelength to elicit the same criterion amplitude of responses. This review primarily considers the methods that have been developed for electrophysiological determinations of criterion amplitudes of slow-wave responses from single retinal cells. Traditional flash methods can require tedious dark adaptations and may yield erroneous spectral sensitivity curves which are not seen in such modifications as ramp methods. Linear response methods involve interferometry, while constant response methods involve manual or automatic adjustments of continuous illumination to keep response amplitudes constant during spectral scans. In DC or AC computerized constant response methods, feedback to determine intensities at each walvelength is derived from the response amplitudes themselves. Although all but traditional flash methods have greater or lesser abilities to provide on-line determinations of spectral sensitivities, computerized constant response methods are the most satisfatory due to flexibility, speed and maintenance of a constant adaptation level.

The opossum photoreceptors: a model for evolutionary trends in early mammalian retina

The topography and spectral characteristics of mammalian photoreceptors correlate with both, the present ecological demands and the evolutionary history. The South American Opossum is a marsupial mammal with unspecialized habitus and crepuscular lifestyle. A sparse population of cones (max. = 3000/mm2) can be differentiated into four subtypes by morphological, topographical and immunocytochemical criteria. In spite of this unusual diversity the cone types can be split into two functional groups: The population of single cones labeled by antibody OS-2 for short wavelenght sensitive pigments was ubiquitous but at very low densities (200/mm2). The single cones labeled by antibody (COS-1) against long wavelength sensitive pigments constitute the dominant population in the area centralis (2300/mm2). These two single cone types correlate with the pair typically present in placental mammals. Discrimination of spatial and color contrast may be provided by this "modern" set. The COS-1 labeled double and single cones bearing an oil droplet, display a different pattern by being restricted to the inferior (non-tapetal) half of the retina (max = 800/mm2). This additional set of cones with oil droplets and long wavelength pigments is a conservative feature of the opossum retina and other marsupials. As an accessory cone system it is possibly providing enhanced sensitivity at mesopic conditions. During the early evolution of nocturnal mammals with its prominent expansion of rod vision these cone types were conserved but then were lost in placental mammals. Thus the unique features of mammalian are the result of two evolutionary steps: first a reduction of cone based vision, followed by a secondary differentiation of photopic vision and behaviour relying on the remaining set of cones.

The internal horizontal cell of the frog: spatial summation

En la Rana pipiens se estudiaron las propiedades del campo receptivo de las células horizontales internas (CHI). Se determinó la constante de espacio de cada célula usando puntos luminosos de diferentes tamaños o moviendo una abertura luminosa rectangular a lo largo de la retina. Con el primer método, la constante varió entre 100 - 500 um y con el segundo, entre 100 - 720 um. Se describió un rango de valores similar en el Xenopus, aunque sus SHI son más grandes que las de la Rana. Aparentemente, el acoplamiento entre las CHI es más eficiente en la retina de la Rana que en aquellá del Xenopus. El amplio rango de los valores sugiere que entre las células de la misma retina hay una variación importante en la eficiencia del acoplamiento