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Biomedical subjects

J M Kennedy

Publications and source records attributed to J M Kennedy.

16 recordsLinked to original sources
PubMed1992

Repression of the embryonic myosin heavy chain phenotype in regenerating chicken slow muscle is dependent on innervation.

Ventricular-like and fast myosin heavy chains (VL-MHC and FMHC) are transiently expressed during slow skeletal muscle development. The influence of innervation on repression of these MHC isoforms is investigated over an 84-day time course in: (1) normal anterior latissimus dorsi (N-ALD) muscles, (2) regenerating ALD (R-ALD) muscles, (3) denervated ALD (D-ALD) muscles, and (4) regenerating and denervated ALD (RD-ALD) muscles. Western blotting demonstrates that the VL-MHC is expressed in R-, D-, and RD-ALD muscles, but not in N-ALD muscles. Expression of the VL-MHC is transient in R-ALD muscles. In contrast, VL-MHC expression persists in RD-ALD muscles, and appears with time in D-ALD muscles. FMHC was not detected in N-ALD muscles by Western blotting. Two FMHCs are seen in R-ALD and RD-ALD muscles, and in 13-day embryonic ALD muscles. The slower migrating FMHC (FMHCA) comigrates with developmentally regulated FMHCs in fast pectoralis muscle, while the faster migrating FMHC (FMHCB) comigrates with the faster migrating FMHC in embryonic ALD muscle (13 days in ovo). FMHCB decreases in amount over the time course in R-ALD muscles, while FMHCA persists. In contrast, substantial levels of both FMHCs persist in RD-ALD muscles, and appear with time in D-ALD muscles. The cellular distribution of MHCs is followed by immunocytochemistry. Regenerating cells expressing VL-MHC and FMHC are replaced by a mature population in R-ALD muscles. Some of the mature myofibers in R-ALD muscles express FMHC, but not VL-MHC. In RD-ALD and D-ALD muscles, both regenerating and mature muscle cells are seen which express VL-MHC and FMHC. Our results indicate that innervation is required for the repression of VL-MHC and FMHCB during regeneration of slow muscle.

Animals↗
PubMed1992

Drawing development: from similarity of features to direction.

Children often are said to pass through a series of stages in learning to represent 3-dimensional objects, such as cubes, on a 2-dimensional picture surface. Drawings of cubes from 1,734 children and adults were collected. They were classified into 10 drawing types (5 distinguished by Willats, and some additional types, one taken from Caron-Pargue). Over 80% of 5-year-olds produced a single square to represent a cube. Also, over 80% of 14- and 15-year-olds and over 80% of adults produced a parallel-projection drawing. However, there are several routes between these two milestones of drawing development, since no other drawing type captured more than 23% of the drawings at any age between 6 and 13. It is instructive that some children produced drawings that never were made by any of the adults, while some adults produced drawings of cubes that young children did not. We suggest that these differences between children and adults show that the younger children use a similarity geometry with "feature-based" criteria, while the older children and adults use a vantage-point geometry that includes "direction-based" criteria.

Adolescent↗
PubMed1991

Mitochondrial DNA replication and transcription are dissociated during embryonic cardiac hypertrophy.

Cardiac hypertrophy was produced in embryonic chicks by decreasing the incubation temperature from 38 degrees C to 32 degrees C on day 11. Increases in ventricular protein, RNA, and DNA support the cardiac enlargement. Cytochrome-c oxidase activity and citrate synthase activity were depressed in hypothermic ventricles by 63% and 56%, respectively. No significant differences were seen in enzyme activities in pectoralis muscles. The involvement of mitochondrial gene replication and transcription was evaluated using a cDNA clone for the mitochondrially encoded subunit III of cytochrome-c oxidase (CO III). Quantitative slot-blot analysis demonstrated that the relative CO III mRNA concentration was reduced in hypothermic ventricles. In contrast, the relative mitochondrial DNA concentration was increased in hypothermic ventricles. Taken together, these data indicate that a hypothermia-induced decrease in cytochrome-c oxidase activity is associated with a decrease in CO III mRNA, which is not coupled to a decrease in the mitochondrial DNA copy number. This dissociation of mitochondrial gene replication and transcription may provide a useful model for examining the regulation of mitochondrial biogenesis.

Amino Acid Sequence↗
PubMed1978

Illusory contours can arise in dot figures.

Frisby and Clatworthy have suggested that subjective contours depend on special contrast effects acting at the tips of lines and at right angles to the lines. Their suggestion depends in part on the absence of such contours in dot figures. However, if the dots are grouped regularly and make a 'good figure', strong subjective contours appear, including a pattern comparable to Kaniza's triangle. The kind of contrast explanation required for these figures would be one in which individual dots create small contrast effects which are only manifest in perception when the effects are grouped together, by Gestalt form indicators, overlap cues, or the like.

Form Perception↗
PubMed1978

Illusory contours and the ends of lines.

A series of lines pointing towards a central region induces an illusory brightness effect that is systematically related to the angle formed by the lines and the contour of the illusory brightness. As the lines veer to become tangents the illusory brightness decreases.

Adult↗
PubMed1977

Aged in cities: residential segregation in 10 USA central cities.

This study focuses on the segregation of the aged in ten USA cities. The objectives are to determine the degree of segregation of elderly within cities, and how the pattern varied from 1960 to 1970 by size of city, age of city, and for cities that are growing and declining in population. Census data were used to compare proportions of the population 65 and over living in central city and suburban locations, and a summary Index of Dissimilarity was computed to measure the degree of age segregation by census tracts. In all metropolitan areas there was a disproportionate share of the elderly residing within the central city and considerable segregation in certain census tracts within the city. However, the degree of segregation showed no pattern of increase between 1960 and 1970. There was less segregation of the aged in older, declining cities and greater segregation in younger, growing cities. These findings suggest that age segregation is in part a function of the urbanization process.

Aged↗
PubMed1976

A figure-density hypothesis and illusory contour brightness.

Perceived figures tend to have surface colour and to be comparatively dense in texture and saturated. These figure characteristics are found in many of the illusory contour figures examined heretofore but new figures presented here do not conform to these characteristics. Consequently, rather than explain subjective brightness effects as offshoots of figural processes, it may be better to begin with concepts of local brightness effects induced by the display, which are made perceptually effective when grouped by the eye.

Color Perception↗