Publication: Fine structure of the retina and pigment epithelium in the creek chub, Semotilus atromaculatus (Cyprinidae, Teleostei)
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Date
1996
Authors
Collin, S.P. ; Collin, H.B. ; Ali, M.A.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The structure of the light- and dark-adapted
retina, the pigment epithelium and the choroid of the
creek chub, Semotilus atromaculatus (Cyprinidae,
Teleostei) is examined by light and electron microscopy.
An extensive network of vitreal blood vessels emanating
from the hyaloid artery enters the eye with the optic
nerve and overlies the inner limiting membrane. This
membrane closely apposes the fine protrusions of the
Müller cell processes which traverse the entire retina,
dividing the inner retina into alternating fascicles of
ganglion cells and optic axons. The inner nuclear layer
consists of bipolar, amacrine, Müller cell soma and two
layers of horizontal cells. The outer plexiform layer
possesses both rod spherules and cone pedicles. Each
rod spherule consists of a single synaptic ribbon in either
a triad or quadrad junctional arrangement within the
invaginating terminal endings of the bipolar and
horizontal cell processes. In contrast, cone pedicles
possess multiple synaptic ribbons within their junctional
complexes and, in the light-adapted state, the horizontal
cell processes show spinule formation. Four
photoreceptor types are identified on morphological
criteria; unequal double cones, large single cones, small
single cones and rods. Al1 but the small single cones are
capable of retinomotor responses. The rod to cone ratio
is approximately 5:l and the rods form two ill-defined
rows in the light-adapted condition. The retinal pigment
epithelium possesses two types of osmiophilic granules. These are bound within slender microvilli and migrate
vitread to surround the photoreceptors in response to
light. Bruch's membrane is trilaminar and the
vascularised choroid consists of up to three layers of
melanocytes. The endothelial borders of the choroidal
blood vessels abutting the outer lamina of Bruch's
membrane are fenestrated.
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