Morphological types and connectivity of horizontal cells found in the adult zebrafish (Danio rerio) retina

Abstract

We describe here different types of horizontal cells in the zebrafish retina and how they connect to photoreceptors. To label horizontal cells, crystals of DiI were placed onto the tips of pulled glass pipettes and inserted into the inner nuclear layer of fixed whole-mount retinas. The DiI-labeled horizontal cells were imaged by confocal microscopy and analyzed according to dendritic arborization, cell depth, dendritic terminal morphology, and connectivity with photoreceptors. Three types of horizontal cells were unequivocally identified: two cone-connecting (H1/2 and H3) and one rod-related cell. H1/2 cells have dendritic terminals that are arranged in "rosette" clusters and that connect to cone photoreceptors without any apparent specificity. H3 cells are larger and have dendritic terminal doublets arranged in a rectilinear pattern. This pattern corresponds to the mosaic of the single cones in the zebrafish photoreceptor mosaic and indicates that H3 cells connect specifically to either the blue-sensitive (long-single) or ultraviolet-sensitive (short-single) cones. Thus, H3 cells are likely to be chromaticity-type cells that process specific color information, whereas H1/2 cells are probably luminosity-type cells that process luminance information. Rod horizontal cells were identified by their shape and dendritic pattern, and they connect with numerous rod photoreceptors via small spherical terminals.

Immunocytochemical localization of NTPDases1 and 2 in the neural retina of mouse and zebrafish

“…In our immunostaining, NTPDase2 labeling extends from HC bodies to delineate interneuron somas in the INL as well. Furthermore, we cannot rule out the possibility that NTPDases1 and 2 are expressed by different subpopulations of HC (Song et al, 2008). The presence of both NTPDases in the outer synaptic layer suggests that nucleotides would be regulated in a different manner according to the type of NTPDase they encounter in or near their site of release.…”

Ultrastructural analysis of the glutamatergic system in the outer plexiform layer of zebrafish retina

“…Zebrafish contains at least three types and most likely four types of horizontal cell (Marc and Cameron, 2001;Connaughton et al, 2004;Song et al, 2008). All cone pedicles and rod spherules, with the classic and butterfly arrangements, were innervated by GluR2-immunoreactive dendrites of horizontal cells, suggesting that all types of horizontal cell in zebrafish express GluR2 subunits, the same as in goldfish retina (Klooster et al, 2001).…”

The visual system of zebrafish and its use to model human ocular Diseases

“…Comparable to other teleosts, the zebrafish contains four distinguishable horizontal cell types, as identified by a number of labeling methods (Connaughton and Dowling, 1998; Yazulla and Studholme, 2001; Connaughton et al, 2004; Song et al, 2008; Li et al, 2009). One large field horizontal cell is rod-specific(, while the two small field horizontal cells (H1, H2) connect solely to cones, just as a large field horizontal cell (H3), which responds best to UV light (Li et al, 2009; Connaughton and Nelson, 2010).…”