Vis Neurosci 4:595–604īeerman F, Schmid E, Schutz G (1992) Expression of the mouse tyrosinase gene during embryonic development: recapitulation of the temperature regulation in transgenic mice. J Comp Neurol 330:95–104īalkema GW, Drager UC (1990) Origins of uncrossed retinofugal projections in normal and hypopigmented mice. Second, as the bird retina is cone dominated, any deficits in albino strains may be relatively minor.īaker GE, Reese BE (1993) Chiasmatic course of temporal retinal axons in the developing ferret. Although there is a common time table for the development of the mammalian visual system when expressed in terms of the caecal period, which is between conception and eye opening, the pace of retinal development in birds is accelerated, which may alter interactions between these regions. First, normal mammalian retinal development may depend partly on time-dependent interactions in the maturation of the retinal pigment epithelium and the neural retina. There are two possible explanations for this result. Consequently, the underdevelopment of the central retina seen in hypopigmented mammals does not occur in this bird. Although there were variations in the measurements undertaken between the strains, none were pigment related or consistent with the abnormality found in the central retina in albino mammals. Each strain of bird had an area of increased retinal layer thickness in dorso-temporal regions, but not a fovea. Estimates of cone numbers were also made. Measurements of layer thickness, cell density and cell size were made at a range of locations in the ganglion cell layer and in the inner and the outer nuclear layers. Retinae from normally pigmented and two forms of hypopigmented budgerigars ( Melopsittacus undulatus) were studied. Also if one of the primary effects of albinism is centred on rods, then albino birds may not show a deficit, because their retinae are cone dominated. Consequently, examination of the retinae of hypopigmented birds will reveal whether there is a relationship between the two abnormalities. Birds have a highly developed central retina, but unlike most mammals they do not have a significant uncrossed retinal projection. This study addresses the question of whether pigment-related abnormalities occur in the central retina of a non-mammal, the bird. Also, many ganglion cells in temporal regions project inappropriately to the contralateral hemisphere. In the outer retina this deficit is confined to rods. The central retina in hypopigmented mammals is underdeveloped.
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