Biomedical subjects

R J Ulshafer

Publications and source records attributed to R J Ulshafer.

4 recordsLinked to original sources

PubMed1979

An SEM AND TEM study of suppression of eye development in eyeless mutant axolotls.

Morphology of the primary optic rudiment of normal eyed and mutant eyeless (e/e) axolotl embryos was studied at light. Tem and SEM levels. The presumptive eyeforming region of eyeless embryos differs from that of normal embryos in several important respects including premature formation of basal lamina, separation from overlying ectoderm by mesenchyme cells and persistence of granules in the interspace surrounding the optic anlage into relatively late developmental stages. These differences suggest that the gene that causes failure of eye formation in the mutant axolotls produces structural differences that interfer with normal physical and/or biochemical inductive interactions between neurectoderm and mesenchyme cells due primarily to the precocious development of basal lamina over the extermal surface of the optic primordia.

Ambystoma↗

PubMed1979

Cell death and optic fiber penetration in the optic stalk of the chick.

The role of dying cells in the optic stalk in relation to retinal fiber migration was investigated in the chick embryo. Cell death was analysed at various stages of development by counting pycnotic nuclei and also by the Gomori acid phosphatase reaction, while nerve fibers were visualised by the Bodian method. A wave of cell death, beginning in the neural retina at stage 18 and advancing with time through the stalk towards the diencephalon, occurred simultaneously or slightly prior to differentiation and migration of ganglion cell axons. Cell death stopped and gliogenesis occurred in the stalk after penetration by retinal fibers. Cell death occurred in the stalk even when fiber penetration was prevented by optic cup ablation. In this case, necrosis ensued until almost complete degeneration of the stalk, usually within three days after the operation, and gliogenesis did not occur. As the stalk degenerated, its cells became heavily pigmented. These observations suggest that the onset of cell death in the optic stalk is determined prior to and independently of retinal fiber penetration. On the other hand, cessation of cell death and subsequent gliogenesis occur only in the presence of ingrowing optic fibers.

Acid Phosphatase↗

PubMed1979

[Alterations in concanavalin A binding during retinal development in Xenopus laevis].

Changes in concanavalin A binding were observed in the retina of Xenopus laevis throughout development. Prior to stage 37, the optic cup and nervous sysetm displayed a light, diffuse staining. Abruptly at stage 37, however, intense staining reaction occurred in the ganglionic fibers, both plexiform layers and photoreceptor inner segments, remaining thus throughout larval and adult life. Our results suggest that important structural modifications occur in retinal cells at the time of establishment of connections with the tectum, preceedings, and possibility related to, electrical functioning of the visual system.

Animals↗

PubMed1979

The use of avian double monsters in studies on induction of the nervous system.

Ninety-eight duck double monsters (siamese twins) were studied between 48 and 72 h of incubation in whole-mount or serial-sectioned preparations. Each case was classified into one of four categories depending on the orientations of the two embryonic axes. In all classes, defects in primary neural induction of various parts of the embryonic nervous system were observed which depended to a large extent on the distance separating the anterior tips of the two notochords or on the relative positions of the notochords. Our observations suggest that: when the same inducing field of one embryo overlaps to a critical extent with that of the twin, the two inducers act as one; induction of forebrain and optic vesicles is purely prechordal; the notochord exerts an inhibition on induction of forebrain by prechordal mesoderm; and the presence of rhombencephalic structures depends on both prechordal and chordamesodermal interactions.

Animals↗