DNA synthesis in the embryonic chick lens epithelium is arrested after experimental lens rotation.

Using autoradiographic technique, we have studied DNA synthesis in normal embryonic chick lens epithelium and after experimental lens rotation. Analysis of the autoradiograms clearly demonstrates that when the lens primordium was rotated 180 degrees, so that lens epithelium was placed facing the interior of the optic cup, the lens epithelial cells completely stop DNA synthesis. This fact suggests that some retinal and vitreal factors are responsible for differentiation and replicative capacity of the lens epithelial cells.

Late events in the migrative behaviour of the retinal ganglion cells. A Golgi study in the chick retina.

The final displacement of the prospective ganglion neurons toward the ganglion cell layer (GCL) has been analyzed in chicken embryos during days 8 and 9 of incubation with the help of the Golgi method and computer-assisted image processing. Our findings indicate that some ganglionar soma are still located in the inner nuclear layer (INL) while others pierce the inner plexiform layer (IPL), exhibiting morphological adaptation of their perikaryon. The changing morphology of these delayed retinal ganglion neuroblasts seems to be due to the late translocation of the cell perikaryon to the GCL. This late migrative displacement of the ganglionar population is discussed in relation to the presence of displaced ganglion cells of Dogiel.

Developmental study of axon formation in the horizontal neurons of the retina of the chick embryo.

Among the types of horizontal cells of the avian retina, one has been described that has an axon terminating in a typical structure. The present study analyses the histogenesis of this axon whose initial outgrowth occurs on day 14 of incubation (HH-40). The axon terminal is first detectable, towards day 15 of incubation (HH-41), in the form of a varicose thickening possessing short filopodia. The formation of the axon and the growth of the axon terminal is coincident with a retraction of the perikaryal process. The axon usually originates from one of the principal dendrites and in these stages shows short and fine filopodia throughout its length. From day 16 onwards (synaptic) spines may be distinguished, both in the dendritic field and on the axon terminal. The growth of the axon, in the phase when the axon terminal still has not formed, may exhibit deflections and deviations in its course, the possible cause and mechanism of which are discussed.

The midget bipolar cells in the chick retina.

This paper reports the existence of midget bipolar cells on the chick retina, as determined by the staining methods of Golgi-Stensaas and Golgi-Colonnier. We date the appearance of these cell types at days 13 (HH-39) and 14 (HH-40) of incubation and describe them morphologically throughout their development until the time of hatching, at which time the cells show an adult structure. As an adjunct to this work we classify the midget bipolar cells into four groups.

Transplantation of the chick early eye primordium into a lensectomized optic cup of a host embryo.

Eye primordia of young chick embryos (stage XII) were transplanted into lensectomized optic cups of older embryos (stage XVII) to analyze the influence of the host retina on the degree of morphological differentiation attained by the donor lens. Embryos were sacrificed 24-96 h later. The donor lens primordium showed a differentiation more in correlation with the host eye cup (stage XXIII) after 24-96 h of incubation.