Types and density of calretinin-containing retinal ganglion cells in mouse

Calcium-binding proteins are present in a number of retinal cell types. Types and density of parvalbumin-immunoreactive (IR) retinal ganglion cells (RGCs) in the mouse retina were previously reported using a newly developed single-cell injection technique following immunocytochemistry [Kim, T.J., Jeon, C.J., 2006. Morphological classification of parvalbumin-containing retinal ganglion cells in mouse: single-cell injection after immunocytochemistry. Invest. Ophthalmol. Vis. Sci. 47, 2757–2764]. The present study was aimed at describing the types and density of calretinin-containing RGCs in the mouse. Calretinin-containing RGCs were first identified by immunocytochemistry and were then iontophoretically injected with a lipophilic dye, DiI. Subsequently, confocal microscopy was used to characterize the morphologic classification of the calretinin-IR ganglion cells on the basis of the dendritic field size, branching pattern, and stratification within the inner plexiform layer (IPL). The results indicated that at least 10 morphologically different types of RGCs express calretinin in the mouse retina. They were heterogeneous in morphology: monostratified to bistratfied, small-to-large dendritic field size, and sparse-to-dense dendritic arbors. The present study showed that 86.59% (38,842/44,857) of RGCs contained calretinin. The density of calretinin-IR ganglion cell in the mouse retina was 2795 cells/mm2. The combined approach of cell morphology and the selective expression of a particular protein would provide valuable data for further knowledge on functional features of the RGCs.