Scanning electron microscopic observations on differentiation and maintenance of photoreceptor cells in vitro.

Scanning electron microscopy was performed on cell cultures of embryonic and post-hatch chick retinas co-cultured with optic lobe neurons or in medium that had been pre-conditioned with optic lobe cells. The culture medium consisted of Eagles Basal Medium supplemented with glucose, fetal calf serum, glutamine and bicarbonate. Application of colchicine (5 micrograms/ml) to the cultures, encouraged the dissociation of retinal cell rosettes and optic lobe neuron aggregates, thereby allowing us to examine differentiation of isolated photoreceptor cells. Over time, developing photoreceptor cells gradually took on the morphological characteristics of rods and cones in the post-hatch chick: cells were polarized having a single neurite on one end of the cell and inner and outer segment-like structures on the other end. Developing cone cells elaborated an oil droplet and filopodial-like processes at the apical end of the inner segment. The latter may correspond to the calyceal processes which normally envelop the basal 1/3 of the outer segment. The sequence of events noted in vitro parallel those previously reported in vivo.