Retinogeniculate projection fibers in the monkey optic nerve: A demonstration of the fiber pathways by retrograde axonal transport of WGA‐HRP

Abstract

Seven Japanese monkeys (Macaca fuscata) were used to investigate the fiber pathways of the optic nerve. Optic nerve fibers and retinal ganglion cells were retrogradely labeled by iontophoretic injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into electrophysiologically defined positions of the lateral geniculate nucleus (LGN). By gross anatomical observation, the optic nerve usually had one distinct bend, which flexed dorsally 3-4 mm from the eyeball, and occasionally another ventrally directed bend was found just behind the eyeball. In the optic nerve head, fibers from the various retinal areas were arranged in a wedge according to the fiber trajectory on the retinal surface. For about a 3 mm distance from the disc, fibers rapidly spread out radially. Subsequently, rather than scattering dorsoventrally, they progressed to the chiasm with a gradual increase in the degree of mediolateral (nasotemporal) scatter. The degree of the scatter was different depending on the retinal site from which the axons originated. Fibers from the peripheral retina spread out widely for a few millimeters behind the eyeball. Thereafter the scatter was rather limited until the chiasm. On the other hand, the scatter of fibers from the foveal and parafoveal areas progressed gradually through the nerve. The present study also suggests that the difference in scatter depends on the types of cells of origin. Fibers from large ganglion cells displayed more extensive scatter than fibers from medium-sized cells. In spite of the extensive scatter of fibers, two clear segregations were found; one was a dorsoventral segregation, which was displayed by both central and peripheral retinal fibers, and the other was a center-peripheral segregation in which the fibers from the nasal central (papillomacular) retina were located almost exclusively in the central part of the optic nerve surrounded by peripheral retinal fibers. However, the temporal central retinal fibers were located in the lateral periphery of the nerve, and they overlapped significantly with fibers from the temporal peripheral retina. Furthermore, a broad intermingling was found between nasal and temporal peripheral retinal fibers owing to their mediolateral scatter. Thus, the present findings based on more precise anatomical techniques indicate that the classical notion of the retinal quadrant topography in the monkey optic nerve probably is suspect. In addition, the "rotation" of the fiber arrangement was not demonstrated.

Long Term Transneuronal Retrograde Degeneration of the Retinal Ganglion Cells in Patients with Cerebral Infarction

“…Furthermore, the 6 th and 12 th month examinations showed a statistically significant decrease in the RNFL thicknesses in the superior, inferior, and temporal sectors when compared with the baseline thicknesses in both the contralateral and ipsilateral eyes. The first, 6 th , and 12 th month nasal RNFL thicknesses differed significantly in only the contralateral eyes, and these findings are accordance with the results of Park, Jindahra, and Naito et al 13,20 Visual field loss following stroke has been largely attributed to cortical strokes in which the visual pathway is damaged. Following a stroke, the loss of the visual field is usually more peripheral in nature.…”

“…This region has considerably greater intermingling of crossed and uncrossed fibers. 20 Theoretically, the superior and inferior peripapillary retina may contain crossed fibers, uncrossed fibers, or both from the more temporally located papillomacular bundle. An RNFL thickness change in the superior and inferior peripapillary retina was observed in both the contralateral and ipsilateral eyes in the study by Naito.…”

Developmental determinants at the mammalian optic chiasm

“…The clearest evidence against an ordered arrangement in the optic nerve came from Horton et al (1979) who labeled eight closely adjacent ganglion cells in the retina by injecting horseradish peroxidase (HRP) into the adult cat's lateral geniculate nucleus and then showed that of these eight axons, each took a different, independent course through the optic nerve. Axonal tracing studies in cat, ferret, and monkey have also shown the loss of retinotopic order as the axons were traced from the eye to the chiasm (Naito, 1986(Naito, , 1989Reese and Baker, 1993), and it is clear that in the adult rodent the crossed and the uncrossed components do not occupy different parts of the optic nerve near the chiasm (Baker and Jeffery, 1989), as would be expected from a retinotopically organized pathway. The loss of retinotopic order seen along the adult nerve also characterizes the earliest developmental stages.…”

Circulation and axonal transport in the optic nerve

“…4 The organisation within the retrobulbar part of the nerve is relatively straightforward, in that axons from peripheral retina pass in the peripheral part of the nerve, while those from more central retinal loci pass through central aspects of the nerve. 6 Even so, the precision with which parts of the optic nerve are retinotopically demarcated is coarse, with considerable overlap between the regions. 6 To achieve this order it has been suggested that more centrally arising axons pass through overlying axons so that they lie in the more superficial part of the nerve.…”

“…6 Even so, the precision with which parts of the optic nerve are retinotopically demarcated is coarse, with considerable overlap between the regions. 6 To achieve this order it has been suggested that more centrally arising axons pass through overlying axons so that they lie in the more superficial part of the nerve. 3 Tracing studies of individual axon paths suggest that this may not be the case and that some axons undergo a complex partial decussation at the margin of the optic nerve head, in which axons from peripheral and central retinal ganglion cells mingle to adopt the correct location within the retrobulbar optic nerve.…”