Developmental changes in astrocyte density in the macaque perifoveal region.

We studied astrocyte density both in the perifoveal region and in extrafoveal regions within the same distance of the optic disc (OD) over a time period from foveal pit formation (embryonic day E112) until 2 months after birth. The study was prompted by earlier observations that the adult macaque displays an almost astrocyte-free region around the fovea which, however, at birth is occupied by astrocytes. Thus, we wanted to determine if the perifoveal region is invaded by astrocytes during early development to the same degree as other regions in the central retina, and how the reduction in density can be explained. From the earliest age we studied (embryonic day 112), less astrocytes were found in the perifovea than in other regions equidistant from the OD. In addition, the number of astrocytes steadily declined both in the perifovea and outside until birth. During the first week after birth, there was a further dramatic decline in perifoveal astrocyte density. Double-labelling with glial fibrillary acidic protein (GFAP) immunocytochemistry and the TUNEL method showed that during the whole observation period astrocytes undergo DNA fragmentation and presumably die. However, the rate of TUNEL-positive astrocytes did not significantly differ between perifovea and other regions equidistant to the OD, and at no time did we find a significant peak of apoptosis rate. Thus, the reduction in perifoveal astrocyte density cannot be explained by missing invasion or by selectively elevated apoptosis rates in the foveal and perifoveal regions. Alternative hypotheses are discussed.

Astrocyte invasion and vasculogenesis in the developing ferret retina.

We studied the time course of astrocyte invasion and blood vessel formation in the developing ferret retina using glial fibrillary acidic protein (GFAP)-immunohistochemistry for astrocytes and isolectin B4 histochemistry for blood vessels. As in other mammals, strongly GFAP positive astrocytes invade the ferret retina from the optic nerve. At birth, strongly GFAP positive astrocytes have reached about 22% of the distance between optic disc and outer retinal edge whereas weakly GFAP positive processes already extend to the edge of the retina. At postnatal days P30-P37 about 82% of the distance between optic disc and outer retinal edge and in the adult 88% of this distance is covered with strongly labelled astrocytes. Superficial blood vessels form from the optic disc. They reach up to about 24% of the retinal radius at birth and grow radially across the retina during further development. At P30-P37, the whole retina is covered with superficial blood vessels. The deep vascular layer forms later (around P30) through sprouting from superficial vessels. The radial pattern of astrocyte and vessel growth from the optic disc is not affected by the formation of the area centralis and visual streak.

Macroglia cells of the macaque monkey retina.

There are two types of macroglia cells in the macaque monkey retina: Müller cells and astrocytes. Both cell types are in close contact with neuronal structures as well as with the retinal vasculature and are thus well suited for their many physiological tasks. Müller cells ubiquitously traverse the whole thickness of the retina whereas astrocytes are only found in the ganglion cell and nerve fiber layers of vascularized retinal regions. In the adult, astrocytes are very scarce in the central 4 mm around the fovea, a region coinciding with peak Müller cell densities. During development this area is transiently occupied by astrocytes which then disappear during the first postnatal weeks at least in part through apoptosis. Possible reasons for this transiency will be discussed.

Macroglia cells of the macaque monkey retina

There are two types of macroglia cells in the macaque monkey retina: Müller cells and astrocytes. Both cell types are in close contact with neuronal structures as well as with the retinal vasculature and are thus well suited for their many physiological tasks. Müller cells ubiquitously traverse the whole thickness of the retina whereas astrocytes are only found in the ganglion cell and nerve fiber layers of vascularized retinal regions. In the adult, astrocytes are very scarce in the central 4mm around the fovea, a region coinciding with peak Müller cell densities. During development this area is transiently occupied by astrocytes which then disappear during the first postnatal weeks at least in part through apoptosis. Possible reasons for this transiency will be discussed.