The number, morphology, and distribution of retinal ganglion cells and optic axons in the Australian lungfish Neoceratodus forsteri (Krefft 1870)

The number, morphology, and distribution of retinal ganglion cells and optic axons in the Australian lungfish Neoceratodus forsteri (Krefft 1870)

Authors:HELENA J. BAILES, ANN E.O. TREZISE, and SHAUN P. COLLIN

Abstract

Australian lungfish Neoceratodus forsteri may be the closest living relative to the first tetrapods and yet little is known about their retinal ganglion cells. This study reveals that lungfish possess a heterogeneous population of ganglion cells distributed in a horizontal streak across the retinal meridian, which is formed early in development and maintained through to adult stages. The number and complement of both ganglion cells and a population of putative amacrine cells within the ganglion cell layer are examined using retrograde labelling from the optic nerve and transmission electron-microscopic analysis of axons within the optic nerve. At least four types of retinal ganglion cells are present and lie predominantly within a thin ganglion cell layer, although two subpopulations are identified, one within the inner plexiform and the other within the inner nuclear layer. A subpopulation of retinal ganglion cells comprising up to 7% of the total population are significantly larger (>400 micrometer/m²) and are characterized as giant or alpha-like cells. Up to 44% of cells within the retinal ganglion cell layer represent a population of presumed amacrine cells. The optic nerve is heavily fasciculated and the proportion of myelinated axons increases with body length from 17% in subadults to 74% in adults. Spatial resolving power, based on ganglion cell spacing, is low (1.6–1.9 cycles deg^-1, n =2) and does not significantly increase with growth. This represents the first detailed study of retinal ganglion cells in sarcopterygian fish, and reveals that, despite variation amongst animal groups, trends in ganglion cell density distribution and characteristics of cell types were defined early in vertebrate evolution.

Keywords: Visual streak, Spatial resolving power, Amacrine cells, Optic nerve, Dipnoi

Download, click here / Para baixar, clique aqui. 

 

Displaced Amacrine Cells Disappear from the Ganglion Cell Layer in the Central Retina of Adult Fish during Growth

Displaced Amacrine Cells Disappear from the Ganglion Cell Layer in the Central Retina of Adult Fish during Growth
Authors: Andreas F. Mack, Christl Su¨ssmann, Bernhard Hirt, and Hans-Joachim Wagner

PURPOSE. Fish grow throughout life, including enlargement of eye and retina. Retinal growth involves several mechanisms of adjustment, such as cell addition and dendritic growth. To discover possible other means with which the animals adjust to changing eye size, the distribution of displaced amacrine cells (DACs) and ganglion cells (GCs) was analyzed in the retina of three sizes of a South American cichlid, the blue arcara Aequidens pulcher.
METHODS. DACs were identified by staining with antibodies specific for the calcium-binding protein parvalbumin. They were also weakly positive for staining against choline acetyl transferase (ChaT). GCs were labeled retrogradely with rhodamine dextran. Densities for both DACs and GCs were lower in the retinas of large fish. To distinguish changes due to eye size from specific adjustments, the proportions of DACs to GCs were examined, rather than the absolute cell densities, in various retinal regions in cryostat sections and wholemount preparations from fish of the three sizes.
RESULTS. The analyses suggest that, in small and large fish, DACs and GCs were produced in similar proportions (ratio of DACs to GCs, 0.62) in the retinal periphery where new retinal tissue was added by the germinal zone. However, in the central retina of large fish, this proportion was shifted toward GCs (DAC-GC ratio as low as 0.25).
CONCLUSIONS. During growth of the eye, the proportion of DACs in the ganglion cell layer decreases, indicating that these cells are eliminated from the ganglion cell layer by some unknown
mechanism. (Invest Ophthalmol Vis Sci. 2004;45: 3749–3755) DOI:10.1167/iovs.04-0190 

Download, Click here. Para baixar, clique aqui.

Morphology and Circuitry of Ganglion Cells

Morphology and Circuitry of Ganglion Cells
Author: Helga Kolb

General Morphology

Ganglion cells are the final output neurons of the vertebrate retina. The ganglion cell collects the electrical messages concerning the visual signal from the two layers of nerve cells preceding it in the retinal wiring scheme. A great deal of preprocessing has been accomplished by the neurons of the vertical pathways (photoreceptor to bipolar to ganglion cell chain), and by the lateral pathways (photoreceptor to horizontal cell to bipolar to a macrine to ganglion cell chain), before presentation to the ganglion cell, and so it represents the ultimate signaler to the brain of retinal information. Ganglion cells are larger on average than most preceding retinal inter neurons and have large diameter axons capable of passing the electrical signal, in the form of transient spike trains, to the retinal recipient areas of the brain many millimeters or centimeters distant from the retina. The optic nerve collects all of the axons of the ganglion cells, and this bundle of more than a million fibers (in humans, at least) then passes information to the next relay station in the brain for sorting and integrating into additional information-processing channels.

Para baixar / download, clique aqui / Click here.