Development of astrocytes and their relation to blood vessels in fetal monkey retina

To determine the development of astrocytes and their vascular relations in Macaca monkey retina.

Sections and wholemounts of retinas from fetal day (Fd) 65 to adult animals were analyzed immunohistochemically to detect glial fibrillary acidic protein (GFAP) and vimentin.

Astrocytes appeared first near the optic disc, then subsequently further peripherally, but avoided the fovea. In the nerve fiber layer, round and ovoid cells extended processes parallel to ganglion cell axons. In the ganglion cell layer, ovoid and stellate cells exhibited anisotropic processes or a honeycomb network. The inner lamina of astrocytes developed ahead of the outer lamina, and both reached their final positions before birth. Astrocytes lay more peripherally than did developing blood vessels, and the growing edge of nerve fiber layer vessels lay between the two astrocytic layers. Spindle cells, which may be vascular precursor cells, often aligned along linear astrocytic processes. Occasional spindle-shaped cells containing GFAP or vimentin were identified as immature glia. Astrocytes and blood vessels coincided regionally during development, but astrocyte processes were typically not in register with the meshwork of growing blood vessels. Astrocyte-vessel associations increased during fetal life and postnatally.

During development, astrocytes display the same bilaminar pattern and morphologies present in adult retina. Astrocytes and blood vessels exhibit a similar regional distribution, but develop in distinct spatial patterns. Vessel investment by astrocytic processes increases during fetal life but is variable at all ages.