Kivonat:
PURPOSE. TO decide whether the transitory coexpression of cone visual
pigments described in the developing rat and gerbil retina is a
universal feature of dichromatic mammalian species.
METHODS. The rabbit, a species widely used in eye research, was
selected for the study and a search made for the presence of cones that
bound more than one cone antibody during the first postnatal week. To
plot the densities of individual cone types and to colocalize the two
visual pigments, immunocytochemistry on retinal wholemounts and
consecutive tangential sections, respectively, were used.
RESULTS. The sequence in which the visual pigments began to be
expressed was the same as that observed in other mammals: first,
rhodopsin; second, blue pigment; and last, green pigment. The striking
increase in blue cone density numbers observed in the rat, however, did
not occur in the rabbit. Instead, some days after the first blue cones
appeared, the green cones also started to express their visual pigment,
and this cone type soon outnumbered the blue cones. Within the limits
of the immunocytochemical method, it was established that unlike the
developing rat, the presence of double-labeled cones was not a
character of the rabbit retina.
CONCLUSIONS. Visual pigment coexpression is an interesting phenomenon
of retinal development, however, it is not the exclusive scenario of
photoreceptor differentiation. Each species must be carefully studied
before deciding whether its retinal cones synthesize both pigments
during retinal development.