Date of Award

1996

Degree Name

Biomedical Sciences

College

Joan C. Edwards School of Medicine

Type of Degree

Ph.D.

Document Type

Dissertation

First Advisor

Susan DeMesquita

Second Advisor

Ronald Millecchia

Third Advisor

Vernon E. Reichenbecher

Fourth Advisor

Sasha N. Zill

Fifth Advisor

Ruu-Tong Wang

Sixth Advisor

Leonard J. Deutsch

Abstract

Postnatal retinal development was studied in a marsupial opossum, Monodelphis domestica using light microscopy and 3H-thymidine autoradiography. For the light microscopic study, opossum neonates at 1, 3, 7, 14, 21, 25 and 28 days of age were euthanized, fixed and processed into paraffin sections for hematoxylin and eosin staining. The distinct ganglion cell layer, first observed on postnatal day (P) 7, was separated from the outer neuroblasts by the inner plexiform layer. The neuroblast layer was divided into inner and outer nuclear layers on P25 by the presumptive outer plexiform layer, indicated by discrete intercellular spaces located between the nuclear laminae. Prior to P28, mitoses occurred along the ventricular margin of the neuroblast retina bordering on the intraretinal space. The retina achieved an adult-like appearance at the fourth postnatal week, with mitoses restricted to the extreme retinal periphery in the outer nuclear layer.

The 3H-thymidine autoradiographic study traced the differentiation of neuroblasts into their respective retinal lamina during postnatal development. Neonatal opossums at 1, 3, 7, 14, 21 and 28 days of age received a single dose intraperitoneal injection of 3H-thymidine and survived for 1, 7, 14, 21 or 28 days post-injection. The opossums were euthanized and processed for paraffin sectioning and for autoradiography. The NTB-2 emulsion-dipped slides underwent 8 weeks of exposure before development into autoradiograms, followed by H/E counterstaining. This study showed constituent cells of each nuclear lamina differentiate concurrently in two phases. 3H-thymidine labeled cells differentiated in the first phase were ganglion cells, horizontal cells and cone photoreceptors from Pl to P3, with 3H-thymidine labeled bipolar cells, amacrine cells and rod photoreceptors differentiated in the second phase starting at P3 and extending to the fourth postnatal week. A central to peripheral gradient of cell differentiation was exhibited, with 3H-thymidine labeled cells first observed in the central retina and cells differentiated at later ages observed in increasingly peripheral positions within the retina. The pattern of cellular differentiation in Monodelphis domestica was similar to that found in placental mammals and other marsupial mammals. Monodelphis domestica is an ideal animal model for mammalian retinogenesis due to its extreme embryonic appearance at birth and to its rapid postnatal retinal development.

Subject(s)

Retina – Development.

Opossums – Anatomy.

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