Dendritic morphology of retinal dopamine cells in carp of different sizes.

The dendritic morphology of dopamine (DA) cells in the inner plexiform layer of the retina of different-sized carp (8.6-33.6 cm in body length) was investigated by identifying their fluorescent cell bodies in isolated, aldehyde-fixed flatmounts and injecting them iontophoretically with Lucifer yellow (LY) under microscopic control. DA cells for LY injection were chosen in an intermediate region between the optic disc and the retinal margin, and their spatial parameters (cell density, nearest neighbor distance, dendritic field size and dendritic coverage) were compared between retinas of different sizes to explore whether this region is simply stretched by tissue expansion during retinal growth. It was shown that as the fish grow larger the dendritic field size of DA cells increases while the cell density is sharply reduced and the dendritic coverage gradually decreases. Differences in the dendritic coverage of DA cells between certain fish groups with different sizes were statistically significant. Further, the irregularity in cell distribution appeared to increase as the fish became larger. These results suggest that the dendritic tree of individual DA cells in the intermediate region is developed not only by tissue expansion but also by other unknown factors.