First appearance of orthogonal arrays of particles in Müller cell membranes depends on retina maturation.

A freeze-fracture analysis was undertaken to investigate both the appearance of orthogonal arrays of particles (OAP) in the Müller cell endfoot membrane at the retina-vitreous border and the endfoot size during development of two avian species. Chickens and pigeons have a common length of development until hatching (21 days), but differ in maturation velocity. In the chicken, the first OAP appear in the central retina at embryonic day 18 (E18), in the peripheral retina at E19. The OAP density increases rapidly. In the pigeon, the first OAP appear 6 days after hatching when the eyes are opened. In both species, the size of endfeet is maximal when the OAP first appear and is reduced thereafter. In the chicken, during the time up to adulthood both the mean endfoot size and the retina area increase 6-fold suggesting that the number of endfeet remains constant during growth of their individual area. In the pigeon, after an initial increase of mean endfoot area this decreases until adulthood, despite continuous growth of the eye. This strongly suggests that during retina growth the number of Müller cell endfeet increases. It is concluded that these alterations of Müller cell membranes reflect some functional aspects of retina maturation.