Reorganization of visual pathways following posthatching removal of one retina in pigeons

Abstract

Organization of visual pathways was studied in 2-month-old pigeons that underwent unilateral retinal removal on either the day of hatching (ERA, i.e., early retinal ablated) or the 9th day after hatching (LRA, i.e., late retinal ablated). A general size reduction of visual areas contralateral to the removed retina was found in ERA pigeons, which additionally showed an altered differentiation of thalamic visual targets as well as a different cytoarchitectonic arrangement of the superficial layers of the optic tectum. No comparable modifications were found in LRA pigeons. The retinal projections of the remaining eye were studied following intraocular injections of 3H-proline. Both in ERA and LRA pigeons, the distribution of retinofugal afferents to primary visual regions contralateral to the injected eye was similar to that of control pigeons. Anomalous ipsilateral projections from the remaining retina to primary retinorecipient regions were found in ERA pigeons only. Effects of early ablation of one retina on second-order visual connections were also studied. Following injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the visual Wulst contralateral to the operated eye, a smaller number of ipsilateral projecting thalamo-Wulst neurons was found as compared with control pigeons. In contrast, the contralateral thalamo-Wulst projections were increased. No changes in thalamo-Wulst projections were found following tracer injections into the opposite Wulst, i.e., ipsilateral to the operated eye. The present study demonstrates a substantial anatomical reorganization of both primary and secondary visual pathways following unilateral retinal removal immediately after hatching, when maturation of the visual system is not yet completed.

Binocularity in the Little Owl, <i>Athene noctua</i>

“…According to previous results obtained in different avian species, Wulst-projecting neurons appear to be more numerous in the ipsiiateral thalamus than on the contralateral brain side [24,27], In contrast, our find ing of comparable numbers of ipsilaterally and contralaterally projecting thalamic neurons indicates that in the little owl the uncrossed and crossed pathways to the Wulst are almost equivalent. This is in keeping with the electrophysiological results obtained with visually evoked potentials recorded from the Wulst surface that show similar responses to stimulation of either eye [13].…”

Dendrite development and target innervation of displaced retinal ganglion cells of the chick (Gallus gallus)

“…These processes occur for the most part between E9 and E12. The initial differentiation of RGC dendrites takes place before retinal or central connections are formed (Nishimura, 1980), and the independence in development of retina and retinorecipient structures has been established by studies, where either the eye primordia or the tectal primordia were surgically removed (Kelly and Cowan, 1972;Cowan, 1983, 1984;Bagnoli et al, 1989;Vanselow et al, 1990). Even after bilateral resection of the eye cups, the gross histological development of the optic tectum is at first not affected, with the exception, of course, that the stratum opticum cannot form.…”

“…Later, when normal innervation of the retinorecipient strata is due, tectal neurons degenerate in the input-deprived layers. This will occur only if the eye cups are removed before the projection has formed (Kelly and Cowan, 1972;Bagnoli et al, 1989;Macdonald and Wilson, 1996). Similarly, RGC differentiation in the absence of tectal primordia begins normally, including the formation of different morphological types.…”

Development of the retinotectal system in the pigeon: a cytoarchitectonic and tracing study with cholera toxin

“…Therefore it is conceivable that the formation of this feature is influenced by retinal input. It has been shown that the differentiation of the outer retinoreceptive layers depends upon the ingrowth of retinal fibers (Kelly and Cowan 1972;Bagnoli et al 1989Bagnoli et al , 1992. The different retinorecipient layers of the OT are innervated by retinal fibers with different terminal arbor morphology, possibly belonging to different ganglion cell types (Repérant and Angaut 1977).…”