Abstract
Purpose: :
There are at least nine morphological types of cone bipolar (CB) cells in the mammalian retina, which have been classified according to their branching pattern, the number of cones contacted and the shape and stratification of their axons in the IPL. During recent years several imunocytochemical markers of bipolar cells have been identified. However, most of them are expressed in different bipolar cell types amongst different species. We now try to present a unifying classification scheme by comparing the density and the axonal stratification pattern of the bipolar cells in different species.
Methods: :
Bipolar cells were labeled with antibodies against CaB5, synaptotagmin II (Syt2), CD15 and recoverin. They were studied in sections and whole mounts of the rat, rabbit, cat, ground squirrel and macaque monkey retina and compared with the types of bipolar cells in mouse retina. The stratification pattern was defined by the two dendritic strata of cholinergic amacrine cells.
Results: :
CaB5 labels in all species an OFF CB just below (inner to) the OFF cholinergic dendrites, and an ON CB just above (outer to) the ON cholinergic dendrites. CD15 labels in ground squirrel an ON CB in S5, comparable to the DB6 in monkey. Syt2 labels one OFF and one ON CB type in mouse and rat, but mainly amacrine cells in the other species. The Syt2 OFF CB cells are most likely the same in mouse and rat: they stratify in S1, have a high density and are recoverin positive. Whereas the Syt2 ON CB cells represent different types: they are a flat, in S4 stratifying CB cells in rat, and more diffusely in S4/5 stratifying CB cells in mouse. In rabbit, Syt2 labels a pair of mirror symmetric amacrine cells comparable to the glypho-immunoreactive amacrine cells in macaque.
Conclusions: :
Our data suggests that several bipolar cell types are common in all mammalian species. However, they also show that the same antisera may depict different types of neurons in different species.