Development of the neonatal rabbit retina in organ culture .1. Comparison with histogenesis in vivo, and the effect of a gliotoxin (alpha-aminoadipic acid)

Organ cultures from neonatal rabbit retinae grew well over periods of up to 2 weeks in vitro. Proliferation in vitro declined in parallel with the decline seen in vivo, although the rate of proliferation in the explants was slightly reduced. The proliferation of progenitor cells in vitro produced the same cell types produced postnatally in vivo. Postnatally generated cell clones, labeled by means of a retroviral vector, consisted mainly of rods and Muller cells. The layers of the retinae developed as in vivo; an outer plexiform layer occurreed after the first 2 days in vitro. Ultrastructurally, ribbon synapses (outer and inner plexiform layer) and conventional synapses (inner plexiform layer) were observed. The photoreceptor cells grew well-developed inner segments and cilia but no mature outer segments. The cultured retinae contained a well-developed, regular lattice of Muller cells expressing vimentin as in vivo. The neuron-to-Muller cell-ratios were essentially the same as in vivo, viz. about 15 to 16 neurons, among them about 10 to 11 (rod) photoreceptor cells per Muller cell. When the glia cell-specific toxin alpha-aminoadipic acid (alpha AAA) was applied, the pattern of vimentin-positive Muller cells became irregular, or even locally missing. In such cases, the tissue became disorganized as indicated by a local disappearance of the regular layering, and development of many rosettes. It is concluded that an intact lattice of Muller cells is necessary for the migration of young neurons, and for correct formation of retinal layers.