IMMUNOHISTOCHEMICAL LOCALIZATION OF CALBINDIN-D28K AND CALRETININ IN THE LAMPREY RETINA

Calbindin-D28K and calretinin are homologous cytosolic calcium binding proteins localized in many retinal neurons from different species. In this report, location of cells immunoreactive to both proteins was in vestigated in the retina of the lamprey, Lampetra fluviatilis. This or ganism constitutes one of the older representative vertebrates and pos sesses a peculiar organization, probably unique: two-thirds of the gan glion cells are in the classical amacrine cell layer and the nerve fib er layer is located in the scleral part of the inner plexiform layer. Calbindin-like immunoreactivity was demonstrated in large bipolar cell s and in cell bodies located in the inner retina. Although the distinc tion between labelled ganglion cells and labelled amacrine cells was r endered difficult, we hypothetized that the majority of calbindin-immu noreactive cells observed in the inner retina are ganglion cells, beca use of the high number of labelled fibers in the nerve fiber layer. Ca lretinin-like immunoreactivity was detected in both large and small bi polar cells, and also in cells located in the inner retina. Since few calretinin-immunoreactive fibers were observed in the nerve fiber laye r, we assume that the latter category of cells are amacrine cells. Hor izontal cells were both negative for calbindin and calretinin-like imm unoreactivities. Calbindin and calretinin, which are present in cones from many species, could not be detected in the photoreceptor layer fa vouring the rod-dominated lamprey retina. Although their distribution differs from those observed in most vertebrates, the present results i ndicate the good conservation of both calcium binding proteins in the retina during the vertebrate evolution. (C) 1994 Wiley-Liss, Inc.