Albino rats were maintained in varying illuminances of cyclic light (12L:12D) from birth through 15 weeks. Upon sacrifice, several retinal parameters were tested for differences between animals raised in one illuminance and another. These parameters were: (1) dark-adapted whole retina rhodopsin level, (2) steady-state whole retina rhodopsin level, (3) rod outer segment length throughout the retina, (4) photoreceptor cell density throughout the retina, (5) in situ rhodopsin absorbance throughout the retina, and (6) rhodopsin regeneration rate in vivo. The range of illuminances in the animals' habitats was 3 lux to 800 lux. / Results proved that albino rats were able to change a combination of the above parameters in order to adapt to the illuminance of their environment. Specifically, there was four times more rhodopsin in the whole retina extract of dark-adapted animals which were raised in 3 lux than those raised in 400 lux. Changes in the transverse absorbance, determined by microspectrophotometry, and the length of outer segments accounted for this difference. The microspectrophotometry was carried out on fixed and frozen sections of retina. The transverse absorbance measures were the absorbance in small volumes of the outer segment layer, and took into account both the density of cells and the density of pigment within cells. The change in dark-adapted rhodopsin content, coupled with the ability to alter their pigment regeneration rate, allowed the animals to control the amount of pigment in their retinas at steady-state bleach. By altering this amount, the rats controlled the number of photons their retinas caught each day with great accuracy. Animals raised in cyclic illuminances ranging from 3 to 400 lux caught a statistically equal number of photons (2.03 (+OR-) 0.2 x 10('16)) during the light period. / This study detailed a continuum of adaptation over a wide range of cyclic illuminances and revealed a retinal plasticity previously unknown in vertebrates. The possible evolutionary significance of this plasticity was briefly considered. / Source: Dissertation Abstracts International, Volume: 45-09, Section: B, page: 3109. / Thesis (Ph.D.)--The Florida State University, 1984.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_75420 |
| Contributors | PENN, JOHN SIDNEY., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 99 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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