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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 investigated in the retina of the lamprey, Lampetra fluviatilis. This organism constitutes one of the older representative vertebrates and possesses a peculiar organization, probably unique: two-thirds of the ganglion cells are in the classical amacrine cell layer and the nerve fiber layer is located in the scleral part of the inner plexiform layer. Calbindin-like immunoreactivity was demonstrated in large bipolar cells and in cell bodies located in the inner retina. Although the distinction between labelled ganglion cells and labelled amacrine cells was rendered difficult, we hypothesized that the majority of calbindin-immunoreactive cells observed in the inner retina are ganglion cells, because of the high number of labelled fibers in the nerve fiber layer. Calretinin-like immunoreactivity was detected in both large and small bipolar cells, and also in cells located in the inner retina. Since few calretinin-immunoreactive fibers were observed in the nerve fiber layer, we assume that the latter category of cells are amacrine cells. Horizontal cells were both negative for calbindin and calretin-like immunoreactivities. Calbindin and calretinin, which are present in cones from many species, could not be detected in the photoreceptor layer favouring the rod-dominated lamprey retina. Although their distribution differs from those observed in most vertebrates, the present results indicate the good conservation of both calcium binding proteins in the retina during the vertebrate evolution.

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Interplexiform cells (IPCs) have not been previously described as a component of the population of tyrosine hydroxylase (TH) immunoreactive (presumably dopaminergic) cells in the avian retina. In this study, carried out in both pigmented and imperfect albino mutant quails (Coturnix coturnix japonica), we initially describe TH immunoreactive cells in the inner nuclear layer whose internal dendritic arborization extends into strata 1 3 and 4/5 of the inner plexiform layer. Then, we describe ascending processes arising from the somata or proximal dendrites of these cells. These sclerally directed processes (100-1,000 μm long) run across the inner nuclear layer to terminate within the outer plexiform layer, sometimes even reaching the outer nuclear layer. Hence, the cells bearing such processes correspond well with the definition of IPCs. The number of scleral processes is higher in mutant (48 ± 19/retina) than in normal (12 ± 10/retina) quails and are distributed throughout the retina except the area surrounding the pecten. Comparison of biochemical assays for dopamine in the two strains reveals a significantly higher dopamine content in the mutant quails which could be related to its increased number of dopaminergic IPC processes.