Histology and histopathology Vol.11, nº 1 (1996)

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Browsing Histology and histopathology Vol.11, nº 1 (1996) by Subject "Fish"

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    Fine structure of the retina and pigment epithelium in the creek chub, Semotilus atromaculatus (Cyprinidae, Teleostei)
    (Murcia : F. Hernández, 1996) Collin, S.P.; Collin, H.B.; Ali, M.A.
    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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    Ultrastructure and organisation of the retina and pigment epithelium in the cutlips minnow, Exoglossum maxillingua (Cyprinidae, Teleostei)
    (Murcia : F. Hernández, 1996) Collin, S.P.; Collin, H.B.; Ali, M.A.
    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.