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Biomedical subjects

S Levitan

Publications and source records attributed to S Levitan.

10 recordsLinked to original sources
PubMed1998

Metrics for cortical map organization and lateralization.

Cerebral lateralization refers to the poorly understood fact that some functions are better controlled by one side of the brain than the other (e.g. handedness, language). Of particular concern here are the asymmetries apparent in cortical topographic maps that can be demonstrated electrophysiologically in mirror-image locations of the cerebral cortex. In spite of great interest in issues surrounding cerebral lateralization, methods for measuring the degree of organization and asymmetry in cortical maps are currently quite limited. In this paper, several measures are developed and used to assess the degree of organization, lateralization, and mirror symmetry in topographic map formation. These measures correct for large constant displacements as well as curving of maps. The behavior of the measures is tested on several topographic maps obtained by self-organization of an initially random artificial neural network model of a bihemispheric brain, and the results are compared with subjective assessments made by humans.

Brain Mapping↗
PubMed1983

The effect of 1,25-dihydroxyvitamin D3 on cartilage growth in neonatal mice.

The in vivo effects of 1,25(OH)2D3 on cell proliferation, tissue organization and matrix mineralization have been studied in condylar cartilage of neonatal mice. A relatively low dose of the metabolite, 50 ng/kg body weight, significantly reduced the incorporation of [3H]thymidine as well as the number of chondroblasts. The cartilage as a whole underwent a marked derangement in its organization, as many fibroblastlike cells appeared to occupy the zone of progenitor cells. There was a high degree of correlation observed between the effects of 1,25(OH)2D3 upon [3H]thymidine incorporation and the size of the condylar zone of chondroblasts. With increasing doses, enhanced mineralization was noted in the cartilaginous matrix, along with cartilage cell degeneration. These findings indicate that 1,25(OH)2D3 possesses an inhibitory effect upon both the proliferative activity of prechondroblasts and upon the capacity of those cells to differentiate into chondroblasts.

Animals↗
PubMed1979

Long bone growth during prolonged intermittent corticosteroid treatment and subsequent rehabilitation.

Immature A/J mice were treated for up to 7 weeks intermittent doses of triamcinolone hexacetonide and were thereafter allowed to recover for 7 weeks. Qualitative and quantitative morphological measurements were performed on the epiphyseal cartilage plate and diaphyseal bone of the humerus. By the third injection significant structural changes were noted in the cartilaginous tissue followed by a complete cessation of bone growth. The hormonal inhibitory effect on long bone growth lasted throughout the experimental period. However, at the end of the recovery period the length of the humerus was 96% of the normal. In contrast, the humeral width at midshaft and the width of its medullary cavity revealed slower recovery, achieving only 80% of the control values. Following rehabilitation, the growth of experimental epiphyseal plates exceeded that of nontreated animals as their width and the number of hypertrophic chondrocytes were 131% and 125% of their controls respectively. Thus, in A/J mice (a highly susceptible inbred strain of mice) intermittent (every four days) administration of a long-acting corticosteroid hormone arrested endochondral and periosteal bone formation; the former, however, underwent full recovery following the termination of the hormonal treatment.

Animals↗
PubMed1979

Corticosteroid-induced mandibular growth retardation and palatal malformation in the ICR mouse fetus.

Pregnant ICR mice were treated with triamcinolone hexacetonide at various stages of gestation. The mandibular ramus and its condylar cartilage were studied histologically in both viable and non-viable offspring. In addition, measurements were made of the overall height of the posterior vertical dimension of the mandible and of condylar height and width. Significant changes were noted in these parameters. Concomitantly, marked changes were observed in the various zones of the condylar cartilage. A very high incidence of cleft palate was noted in newborn and stillborn mice previously treated with triamcinolone. A possible correlation between mandibular growth retardation and palatal clefting is discussed.

Abnormalities, Drug-Induced↗
PubMed1977

Effects of corticosteroid hormone on the epiphyseal growth center of immature pregnant mice.

Immature pregnant mice treated with glucocorticoid hormone (triamcinolone hexacetonide) were killed 1 week following delivery. The epiphyseal growth plates of the humerus and their cellular constituents were analyzed quantitatively. It became evident that pregnancy per se evokes a marked suppressive effect upon young cartilage cells, thus interfering with the normal process of endochondral bone formation. Pregnant mice treated with glucocorticoid hormone experienced an even higher degree of chondrocytic derangement, however, to a lesser extent than chondroxytes of nonpregnant mice treated with the hormone. It therefore appears that pregnancy-induced elevation of systemic estrogens and progesterone provides some kind of a protection against the antianabolic activity of glucocorticoids upon chondrocytes.

Adrenal Cortex Hormones↗