2023 46 B2

Identifying Bipolar Cell Diversity in the Simplex Retina of Leucoraja erinacea (little skate)

By: Emma Alejandra Alvarez Castaneda

Department: Biology

Faculty Advisor: Dr. Ivan A. Anastassov

Purpose: The cartilaginous fish L. erinacea (Little skate) has a unique retina, which performs the same visual functions as ours, but with one type of light sensitive cell (rods), instead of two (rods and cones). Most vertebrates have a duplex retina, using rods and cones to respond to dim and bright light, respectively, and bipolar cells to transmit the signal down to ganglion cells. Interestingly, the retina of the little skate, can respond to bright and dim light with only rods. We have little information about the structure of this rod-only retina. For example, bipolar cells have a large diversity of cell subtypes in duplex retinas, but whether this is the case in skate is unknown. Bipolar cells are the first connecting partners to rods and cones and are essential for proper visual function. Here, we aim to determine if there is diversity in bipolar cell populations in the skate retina. We are using segmentation techniques in serial electron microscopy data to identify bipolar cell types, their differential anatomy, and spatial distribution. We hypothesize that the skate will have specialized bipolar cell types, as observed in duplex retinas, due to its ability to function under dim and bright light conditions.

Results: Preliminary results show 18 putative bipolar cell bodies obtained from the EM dataset. Six were traced within their dendritic trees and part of their axons, a 3D reconstruction of the traces of each cell was obtained for analysis.

Conclusions: Reconstructions of putative bipolar cells and cell bodies show differences in their shape, size, and location. These are attributes which support the existence of more than one subtype of bipolar cell in the skate retina. Work in ongoing to determine if these initial 13 bipolar cell types cluster into specific bipolar cell subtypes, as is often observed in duplex retinas.