SPATIAL AND TEMPORAL DIFFERENCES BETWEEN THE EXPRESSION OF SHORT-WAVEAND MIDDLE-WAVE SENSITIVE CONE PIGMENTS IN THE MOUSE RETINA - A DEVELOPMENTAL-STUDY

In an earlier study we found a topographic separation of middlewave-se nsitive (M) and shortwave-sensitive (S) cones in the adult mouse retin a. In the present study we investigated the development of the two col our-specific cone types to see whether there is also a temporal differ ence between the expression of the specific cone visual pigments. Usin g two anti-cone visual pigment antibodies, COS-1 and OS-2, we compared the densities of immunopositive cone outer segments on retinal whole mounts derived from mice of various ages. The first detectable cone ou ter segments were the S-cones which appeared in the inferior half of t he retina on postnatal day 4. At this stage, the density of the S-cone s was very low (30-40 cones/retina) but increased steadily on the foll owing days to reach a value comparable to that of adults by P30 (18,00 0/mm2). This cone type always remained much more abundant in the lower part of the retina throughout the whole retinal development. In the s uperior half of the retina, a few S-cones appeared from postnatal day 7; however, their number always remained about one order of magnitude lower than in the inferior part. In contrast, M-cone outer segments we re not identifiable earlier than postnatal day 11 and were confined ex clusively to the superior part of the retina during the whole developm ental process. On postnatal day 12, their density was l,900/MM2 and in creased to a value of 11,000/mm2 by postnatal day 30, which represente d the adult stage. As shown by comparison of isodensity lines derived from immunocytochemical reactions of whole mount retinas, the two cone types occupied complementary halves of the mouse retina with maximum density centres located in opposite retinal quadrants. We conclude tha t 1) in contrast to the primate retina, mouse S-cones precede the M-co nes in their development, and 2) the spatial arrangement of the two co ne types is maintained throughout the whole differentiation process.