Retinal structure

Proton translocation to the Schiff base nitrogen was proposed to occur by concerted double proton transfer (as shown in Fig. 15) leading to a retro retinal structure in the batho intermediate [127, 196], However, this model can be eliminated as it is inconsistent with the formation of batho intermediates from pigment analogs based on 5-desmethylretinal [145] and y-retroretinal [146,147], It also disagrees with the resonance Raman results. 

The process entails shifting of double bonds along the polyene chain, with the formation of a "retro-retinal" structure. Peters et al. (301) interpreted their observations by identifying PBAT with an excited state of rhodopsin, where single proton transfer toward the Schiff base nitrogen leads to the formation of bathorhodopsin. This approach has been supported by the theoretical interpretation of the spectrum of rhodopsin in terms of a nonprotonated Schiff base (214-216). A mechanism involving deprotonation of the Schiff base has also been suggested (310). All these models do not require cis-trans isomerization as a primary event in the chromo-phore. 

New versions of imaging devices are available with higher resolution and more rapid acquisition time. Future improvements will include the incorporation of adaptive optics that, at present, can resolve retinal structures at the cellular level. This technology will continue to improve and play a more critical role in the management of glaucoma and eye disease in general. 

The ganglion cell layer (GCL) contains the cell bodies of retinal ganglion cells, with their axons running across the retinal surface (nerve fiber layer) toward the optic nerve head, and on through the optic nerve to the lateral geniculate nucleus in the mid-brain. The inner retinal blood supply (outside the foveal avascular zone), the nerve fiber layer, and a thin membrane (the inner limiting membrane) form the most superficial retinal structures. 

Because the retina contains such high levels of DHA. it should be a good tissue in which to consider the effects of DHA deprivation. In order to do so. we need to understand retinal structure and function and the methods that can be used to study them. The following subsections will develop these issues. 

L. Beaudet, H.I. Browman, C.W. Hawryshyn (1993). Optic nerve response and retinal structure in rainbow trout of different sizes. Vision Res., 33,1739-1746. 

Liang FQ, Aleman TS, Dejneka NS, et al. Long-term protection of retinal structure but not function using rAAV. CNTF in animal models of retinitis pigmentosa. Mol Ther 2001 4 461 172. 

Bok D, Yasumura D, Matthes M, et al. Effects of adeno-associated virus-vectored ciliary neurotrophic factor on retinal structure and function in mice with a P216L rds/ peripherin mutation. Exp Eye Res 2002 74 719-735. 

Cis-trans isomerism is important in several biological processes, one of which is vision. When light strikes the retina, a cis double bond in the compound retinal (structurally related to vitamin A) is converted to a trans double bond. The conversion triggers a chain of events that finally results in our being able to see. 

Dartnall, H., Tansley, K. Physiology of vision Retinal structure and visual pigments. Annu. Rev. Physiol. 25, 433-458 (1963)... 

Relating the Function of Macular Pigment to Retinal Structure and Disease Pathogenesis... 

Vision begins when light rays (photons) are focused by the eye s lens on to the retina, the layer of cells lining the inside of the eye ball. The retina contains large numbers of photoreceptor cells known as rods and cones. The ends of the rods and cones contain a molecule called rhodopsin which consists of a protein (opsin) covalently bonded to a purple pigment molecule called retinal. Structural changes which occur around a carbon-carbon double bond in the retinal component of the rhodopsin trigger a series of chemical reactions that eventually result in vision. 

An intravitreal injection of 200 J4g sisomidn, which is also an aminoglycoside, irreversibly abolished the c-wave. The light rise, the hyperosmolarity response, the VEP and the retinal structure were severely damaged by 200 sisomidn. The responses related to the RPE, such as the c-wave, should be examined in studying toxic effects of chemicals with high melanin-affinity such as aminoglycosides. 

Electroretinograms in different species are related to the retinal structure and histology prevalence of rods in nocturnal animals (rats), prevalence of cones in diurnal animals (squirrel) and the aspect of electroretinogram is related to the species. 

The electroretinogram (ERG) is composed of responses of many different retinal cell types. Many studies have been made to separate the ERG into components and to link different components to different retinal structures. In theese studies, authors used microelectrodes and intact eyes of laboratory animals (Heynen and van Norren, 1985). However, in most clinical situations or during the course of toxicity studies, this technic is not suitable because it does not allow long-term studies on the same animal. Our first goal was to find a technic that permit to record global ERGs from the same animal at different times. 

---