CHANGING PATTERNS OF VASCULATURE IN THE DEVELOPING AMPHIBIAN RETINA

Patterns of vascularisation were examined in whole-mounted retinae fro m tadpole stages to adulthood in the tree frog Litoria moorei using pe rfusion with Indian ink, Changing cell densities in the underlying gan glion cell layer were studied in a parallel Cresyl-stained series, Thr oughout development, the vasculature was pan-retinal and the hyaloid v essel was prominent, In early tadpole stages, capillaries were arrange d as a honeycomb, and their number increased at a rate sufficient to m aintain high densities in the face of increasing retinal area; major a rteries and veins condensed within the capillary network, By early pos t-metamorphic life, the retinal vasculature was remodelled by the loss of four-fifths of the capillaries; the reduction in their density was far greater than could be accounted for by continuing retinal growth, This loss resulted in a change from the honeycomb appearance to one w ith largely parallel vessels linked by fewer connecting ones, an arran gement that became increasingly pronounced, In post-metamorphic life, the number of branch points increased such that their density decrease d only slightly in the face of considerable increases in retinal area, The density of branch points varied across the retina and changed wit h age, Initially, the vasculature was most dense centrally, but by mid -larval life densities were highest in two patches located in the mid- temporal and mid-nasal retina, Thereafter, the vasculature increasingl y assumed gradients resembling an area centralis and visual streak, a profile that survived the vascular remodelling, The development of den sity gradients in the vasculature preceded that of cells in the gangli on cell layer, the latter appearing only following metamorphosis, Howe ver, in post-metamorphic life, the topographies of the retinal vascula ture and cells in the ganglion cell layer were closely related.