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J. De Juan, J. M. Romero, G. R. G. Queiroz, C. Iñiguez; The Size of Cone and Horizontal Cells Shows Significant Changes During Light and Dark Adaptation in Teleost Retinas. Invest. Ophthalmol. Vis. Sci. 2007;48(13):52.
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© ARVO (1962-2015); The Authors (2016-present)
In teleost retinas, cone photoreceptors (CPh) and horizontal cells (HC) show dramatic changes related to light and dark adaptation. Light induces cone contraction and invaginations of fingerlike protrusions (spinules) into cone pedicles from HC dendrites, whilst darkness causes the opposite to happen. The aim of this study is to determine changes in CPh and HC cell size during adaptation to light and darkness, for subsequent correlation with CPh contraction/elongation and spinule formation/dissolution.
The experiments were performed on two species of teleost fish (Dicentrarchus labrax and Morone Americana), belonging to the Perciform order and the Moronidae family. The animals were kept in an aquarium for a 12h:12h light-dark cycle. Fish were adapted to light and darkness (>1h), killed and their retinas processed for transmission electron microscopy. Thin and semi-thin vertical sections of the retinas were observed in both optic and electron microscopes. The area and thickness of HC bodies, the area of CPh nuclei and the spinule number per pedicle from the light and dark-adapted retinas were calculated.
In dark-adapted retinas, the HC cell size, calculated from its profile areas and from the HC layer width, is 30 to 40 % greater than in light-adapted retinas. On the other hand, the CPh nuclei profile area is 20% larger in light-adapted retinas than in dark-adapted retinas. However, the cone pedicle profile area is greater in dark-adapted retinas. The maximal size of pedicles is reached after 60 minutes in darkness. Finally, the spinule number per pedicle, ranges from eight (Dicentrarchus labrax) to ten (Morone Americana) in light-adapted retinas, and is close to zero in dark-adapted retinas.
Our data shows that in the outer retina, the cone and horizontal cell size presents marked changes related to light and dark-adaptation in an inverse manner. In light adaptation, the size of the HC body and the cone pedicle decreases and the spinule number increases, whilst the CPh nuclei size increases. During dark adaptation, the opposite occurs. These data can be considered as a new type of retinomotor movement, which is closely related to the other dramatic changes observed in teleost outer retinas.
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