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Electron Microscopic Study of the Vertebrate Retina

The Journal of General Physiology
The Rockefeller University Press
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15.tif Electron Microscopic Study of the Vertebrate Retina GLORIA M. VILLEGAS From Laboratorio de Ultraestruetura, Instituto Venezolano de Investigaciones Cientffieas (I.V.I.C.), Caracas, Venezuela Morphological studies of the vertebrate retina with the use of the electron microscope have been carried out by several authors since 1949, most of them in relation to the structure of the receptors. These studies were devoted at first to the outer and inner segments of the receptors (1-8). More recently, the interest has been concentrated on the synaptic connections of the receptors (9-12). This work is intended to present a comparative study of all retinal layers of different vertebrates. A special attention has been given to a neuropile-like structure existing between the receptor endings and the bipolar cells. MATERIAL AND METHOD Retinae of the following vertebrates were used: monkey (Macaca rhesus, irus, and mulatta), chicken (Gallus domesticus var.), turtle (Pseudemys sp.), toad (Bufo marinus), and fish (Centropomidae). The animals were killed by decapitation, with the exception of monkeys, which were anesthetized with ether prior to decapitation. The retina, together with its pigment layer, was laid on a filter paper and cut into small pieces, together with the paper, and immediately immersed into an ice cold, buffered (pH 7.3 to 7.5) 2 per cent solution of osmium tetroxide for a period of 2 hours. Each fixative was diluted in the corresponding Ringer solution. After washing and dehydration through an ethanol series, small pieces were embedded in a prepolymerized mixture of n-butyl and methyl methacrylate. Ultrathin sections were made with a Moran ultramicrotome, equipped with a diamond knife (13), and examined with a Siemens Elmiskop I. RESULTS According to Walls (14), five layers can be distinguished in the retina (Fig. 1). The first is a receptor layer which comprises two zones separated by the outer 15 The Journal of General Physio

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