An Ultrastructural and Immunohistochemical Analysis of the Outer Plexiform Layer of the Retina of the European Silver Eel (Anguilla anguilla L)

Jan Klooster,Maarten Kamermans

doi:10.1371/journal.pone.0152967

Jan Klooster, Maarten Kamermans

Open Access

https://doi.org/10.1371/journal.pone.0152967

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Abstract

Here we studied the ultrastructural organization of the outer retina of the European silver eel, a highly valued commercial fish species. The retina of the European eel has an organization very similar to most vertebrates. It contains both rod and cone photoreceptors. Rods are abundantly present and immunoreactive for rhodopsin. Cones are sparsely present and only show immunoreactivity for M-opsin and not for L-, S- or UV-cone opsins. As in all other vertebrate retinas, Müller cells span the width of the retina. OFF-bipolar cells express the ionotropic glutamate receptor GluR4 and ON-bipolar cells, as identified by their PKCα immunoreactivity, express the metabotropic receptor mGluR6. Both the ON- and the OFF-bipolar cell dendrites innervate the cone pedicle and rod spherule. Horizontal cells are surrounded by punctate Cx53.8 immunoreactivity indicating that the horizontal cells are strongly electrically coupled by gap-junctions. Connexin-hemichannels were found at the tips of the horizontal cell dendrites invaginating the photoreceptor synapse. Such hemichannels are implicated in the feedback pathway from horizontal cells to cones. Finally, horizontal cells are surrounded by tyrosine hydroxylase immunoreactivity, illustrating a strong dopaminergic input from interplexiform cells.

Highlights

The genus Anguila consists of 18 species that are widely distributed throughout the world
The eye of the European silver eel does not differ from the general organization of the vertebrate eye
One striking deviation from this general scheme is present in the posterior eye segment

Summary

Introduction

The genus Anguila consists of 18 species that are widely distributed throughout the world. The American eel (Anguilla rostrata), the Japanese eel (Anguilla japonica) and the European eel (Anguilla anguilla) migrate over long distance [1]. European eels spawn in the Sargasso Sea. After hatching the larvae migrate across the Atlantic Ocean to the European coastal waters over about a 6 month period [1]. The European eel undergoes metamorphosis twice in its life. The larvae metamorphose into glass eels and move inwards to freshwater rivers and lakes. There they stay for several years to become yellow eels [1]. The yellow eels change to silver eels in preparation for the transatlantic journey back to the Sargasso sea where they spawn and die [2,3]

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