Abstract
Purpose:
Fish grow throughout life. As the fish retina grows, new cells are continuously added. Even though new rods originate from precursors present throughout the retina and are homogeneously distributed, rod-driven cells are added at the retinal margin and little is known about their distribution. The scope of this study was to investigate whether goldfish mixed-input ON bipolar cells (ON mBCs), which communicate with both rods and cones, follow the distribution and density of rods during retinal growth.
Methods:
ON mBCs of 57 goldfish ranging from 32 to 185 mm in standard length were immunostained for PKC and the cell density and distribution of labeled neurons was studied on whole-mounted retinas. The values obtained were correlated with morphometrical data for the same animals, and the maximal acuity of the ON mBC mosaic was calculated for each case.
Results:
The distribution of ON mBCs is homogeneous. Even though the absolute number of cells increases 6.4 times with growth, mean density decreases 4.17 times and intercellular spacing increases 1.84 times when one compares values from the smallest and largest animals. Because the eye lens grows in proportion to other eye structures (lens diameter = 3.33 times; eye length = 3.04 times; eye diameter = 2.91 times), so does the image projected onto the retina. Thereby, the maximal acuity of the ON mBC mosaic actually increases from one cycle/degree in small animals to two cycles/degree in large animals.
Conclusions:
Although ON mBCs are predominantly rod-driven, their proliferation and density do not follow those of rods during growth, since retinal stretch predominates over neurogenesis for this neuronal population. Nonetheless, the changes suffered by the retinal magnification factor during growth overcompensate for the concomitant decay in cell density. As a result, the maximal acuity of the goldfish ON mBC mosaic increases as the goldfish grows.
Keywords: 689 retina: distal (photoreceptors, horizontal cells, bipolar cells) •
754 visual acuity •
497 development