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Biomedical subjects

M H Dixon

Publications and source records attributed to M H Dixon.

4 recordsLinked to original sources
PubMed2005

Physiological and metabolic adaptations of Potamogeton pectinatus L. tubers support rapid elongation of stem tissue in the absence of oxygen.

Tubers of Potamogeton pectinatus L., an aquatic pondweed, over-winter in the anoxic sediments of rivers, lakes and marshes. Growth of the pre-formed shoot that emerges from the tuber is remarkably tolerant to anoxia, with elongation of the stem occurring faster when oxygen is absent. This response, which allows the shoot to reach oxygenated waters, occurs despite a 69-81% reduction in the rate of ATP production, and it is underpinned by several physiological and metabolic adaptations that contribute to efficient energy usage. First, extension of the pre-formed shoot is the result of cell expansion, without the accumulation of new cellular material. Secondly, after over-wintering, the tuber and pre-formed shoot have the enzymes necessary for a rapid fermentative response at the onset of growth under anoxia. Thirdly, the incorporation of [(35)S]methionine into protein is greatly reduced under anoxia. The majority of the anoxically synthesized proteins differ from those in aerobically grown tissue, implying an extensive redirection of protein synthesis under anoxia. Finally, anoxia-induced cytoplasmic acidosis is prevented to an unprecedented degree. The adaptations of this anoxia-tolerant plant tissue emphasize the importance of the mechanisms that balance ATP production and consumption in the absence of oxygen.

Adaptation, Physiological↗
PubMed1978

The nature of standard control in children's matching-to-sample.

In Experiment I, six preschool-aged children were given matching-to-sample training with two figures in which they were required to choose one of two comparison stimuli that was identical in shape to the standard stimulus. Following this training, they were given intermittent test trials in which a novel stimulus figure was substituted for the previously correct comparison stimulus. Five of the six subjects consistently chose the substituted stimulus during test trials. Experiment II replicated the findings of Experiment I with three other preschool-aged children. Experiment II also provided controls for the possibility that the subjects of Experiment I were selecting the substituted stimulus because of its novelty. The investigators concluded that eight of the nine subjects were exhibiting the type of control described by Berryman, Cumming, Cohen, and Johnson (1965) as S-delta responding.

Journal Article↗
PubMed1976

Establishing conditional discriminations without direct training: stimulus classes and labels.

An attempt was made to expand the paradigm published by Spradlin, Cotter, and Baxley (1973). Spradlin et al. conditioned subjects to select a choice stimulus in response to two different sample stimuli and then conditioned them to select a new choice stimulus in response to one sample stimulus. The remaining sample stimulus then controlled the second choice stimulus. In the current investigation, two subjects were taught two classes of four symbols each through visual match-to-sample training. When auditory symbols were conditioned to control some members of these two classes, the reamining members came under auditory control without direct training.

Adolescent↗