Biomedical subjects

M I Michael

Publications and source records attributed to M I Michael.

At least 19 recordsLinked to original sources

PubMed1994

Effect of light and dark on the developing retina of the Egyptian toad, Bufo regularis.

The effect of light and dark on the retina of the Egyptian toad, Bufo regularis Reuss, was studied during its development from early larval stages till the end of metamorphosis. The observed changes in response to light and dark were restricted to the pigment epithelium and the photoreceptor cells. The animals examined were divided into four groups: 1-controls fixed in light (CL); 2-controls fixed in dark (CD); 3-animals maintained under continuous darkness (DD); and 4-animals exposed to continuous lighting (LL). In CD- and DD-animals, the location of melanin granules in the pigment epithelial processes (PEP) was restricted to the peripheral area between the apical portions of photoreceptor cells (scleral position). In CL-and LL-animals, on the contrary, abundant melanin granules were found in the PEP where they were dispersed more centripetally between the outer segments and ellipsoids of the visual cells (vitreal position). Photomechanical movements of the epithelial pigments were indicated in this species in response to light and dark before reaching the limb-bud stage. In DD-eye of the newly metamorphosed toadlets, the pigment epithelium appeared considerably thick and contained large lipid droplets when compared to that of the other three groups. Only in DD-animals some rod outer segments showed degeneration during the later stages of development. In addition, there was a remarkable reduction in the number of cones in the eyes of this group as a result of continuous light deprivation. Some differences in the position of cone nuclei were also observed in the retinae of the four groups.

Animals↗

PubMed1993

Effect of cyclophosphamide on limb regeneration in stages of Bufo regularis reuss.

Pre-amputation treatment in both stages (53 and 56) caused a profound decline in limb regeneration abilities and gave heteromorphic regenerates with smaller number of toes in the early stage, while in the later one, it suppressed completely the regeneration of toes or toe protuberances; otherwise partial or complete restoration of the shank. CY treatment concomitant with amputation caused intensive enhancement of regeneration in the early stage, while in the later one it activated regeneration to a lesser degree.

Amputation, Surgical↗

PubMed1992

Malformations of the eye in the exencephalic tail-short mice during its development.

Exencephalic tail-short (Ts/+) embryos were obtained from mating normal mice of Patch strain with Ts/+ mice from Babl/c strain. The most common eye malformations in the exencephalic embryos were exophthalmy, microphthalmy, eye ball irregularity and corneal opacity. Squint eye and unilateral anophthalmy occurred at a lower frequency. The eye abnormalities were recognized histologically by 11-days of gestation. The retina was retarded in development. Lens fibres were swollen and some of them appeared degenerated. Lens epithelium was protruded anteriorly, detached from the underlying lens and joined the corneal endothelium. The lens remained in close contact to the ectodermal layer, forming a thick lens stalk. At the 16-day stage, the corneal epithelium became irregular in thickness and the corneal stroma was discontinuous, having disarranged collagenous fibrils. In a few embryos the corneal endothelium was absent. In the squint-eyed embryo, the cornea bulged through the opened eyelids, while in an anophthalmic embryo it was thick and underdeveloped. Generally, the upper and lower eyelids of the exencephalic embryos were asymmetrical, and the lower lid appeared covered by a thick irregular peridermal layer.

Animals↗

PubMed1991

Changes in cell proliferation kinetics during organogenesis and differentiation of the brain and optic cup in the chick embryo.

The kinetics of cell proliferation on during early ontogenesis of the brain and formation of the eye was studied in the chick embryo. Kinetic parameters--the mitotic index (MI), proliferative activity (P), the duration of mitosis (tm) and the generation time (T)--were measured in various regions of the brain and eye cup, using colchicine as a stathmokinetic agent. It was found that MI could be taken as an indicator of P during early development. In stage 11 it is also clear that the shortest T occurs in areas of rapid proliferation. By stage 12, although the generation time in the various regions studied differs, P and MI are approximately the same. A short tm is not always restricted to areas with a high P. P is affected by variation of T rather than by tm or time of any other parameter of the cycle. With increasing age, tm values decrease and T increase, probably owing to the progress of differentiation during embryonic development.

Animals↗

PubMed1990

Mitotic activity in the blastema and stump tissues of regenerating hind limbs of Xenopus laevis larvae after amputation at ankle level. An autoradiographic study.

Mitotic activity, as indicated by DNA synthesis, was studied by autoradiographic analysis along the proximodistal axis of regenerating limbs in the early and later larval stages 53 and 57 of Xenopus laevis. Wound-healing, dedifferentiation, blastema formation and growth phases were studied. Most of the various stump tissues, as well as the cell mass of the regeneration blastema, were involved. The study showed an increase in DNA synthesis in the stump tissues during their dedifferentiation as well as during blastema formation. The increase was confined mainly to the distal portion (close to the amputation level), so that a proximodistal gradient was discernible. This could be regarded as valid evidence of contribution of the severed stump tissues to the blastema cells. The mesenchymal blastema cells formed after amputation at stage 53 displayed higher mitotic activity than the fibrocytoid blastema cells formed at stage 57. Although the latter were more differentiated than the former, they still showed DNA replication and mitotic division.

Amputation Stumps↗

PubMed1989

Embryonic development of the mouse, with reference to intrauterine position.

The degree of development of embryos in the same litter varied. In both the control and the experimental group the foetal weight curve followed a U-shaped course, with the lightest embryos in the intermediate position. A high incidence of split-face embryos was found in the lateral (ovarian) position in the uterus, while the highest frequency of exencephalic embryos occurred in the intermediate position.

Animals↗

PubMed1988