Publication: Ultrastructure and organisation of the retina and pigment epithelium in the cutlips minnow, Exoglossum maxillingua (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, pigment epithelium and choriocapillaris of the
cutlips minnow, Exoglossum maxillingua (Cyprinidae,
Teleostei) is examined by light and electron microscopy.
A pronounced vitreal vascularisation overlies the inner
retina where the blood vessel walls, the inner limiting
membrane and the Müller cell endfeet are al1 closely
apposed. The thick Müller cell processes divide the imer
plexiform layer and nerve fibre layer into discrete
compartments. The ganglion cells do not form fascicles
and lie within both the ganglion cell and imer plexiform
layers. The inner nuclear layer consists of amacrine,
bipolar, Müller cell somata and two rows of horizontal
cells. The photoreceptor terminals comprise either
multiple (3-5 in cone pedicles) or single (rod spherules)
synaptic ribbons. These photoreceptor terminals form
either a triad (rods and cones) or a quadrad (cones)
mangement of contact with the invaginating processes
of the inner nuclear layer cells. The horizontal cell
processes of the cone photoreceptor terminals reveal
spinule formation in the light-adapted condition. Five
photoreceptor types are classified using morphological
criteria; triple cones, unequal double cones, large single
cones, small single cones and rods. The ratio of rods to cones is approximately 7: 1. Al1 photoreceptor types
show retinomotor responses. Only the cones possess
accessory outer segments but both rods (8-11) and cones
(15-19) possess calycal processes. The retinal pigment
epithelium displays retinomotor responses where
pigment granules within fine apical processes move
vitread to mask the rods in the light. The cells of the
retinal pigment epithelium are joined by various types of
junctions and contain numerous phagosomes,
mitochondria and polysomes. Bruch's membrane or the
complexus basalis is trilaminate with two types of
collagen fibrils comprising the central layer. The
endothelia of the blood vessels of the choriocapillaris,
facing Bruch's membrane, are fenestrated. Two to three layers of melanocytes interspersed between large thinwalled
capillaries and severa1 layers of collagen fibrils
comprise the choriocapillaris.
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