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Biomedical subjects

M Cook

Publications and source records attributed to M Cook.

At least 127 records · Page 7Linked to original sources
PubMed1977

Esterase isozyme patterns in developing embryos of Brachydanio rerio (zebra danio), Brachydanio abolineatus (pearl danio), and their hybrids.

The ontogeny of esterase isozymes in Brachydanio rerio (zebra danio), Brachydanio albolineatus (pearl danio), and hybrids formed by their reciprocal crosses was investigated using polyacrylamide disc electrophoresis. Seven esterase isozymes were identified in each species from the unfertilized egg stage to nine days posthatch. Electrophoretic analysis of qualitative changes in enzyme pattern indicated that some esterases were present at all stages of development while other esterases abruptly appeared at a specific stage of morphological differentiation. The esterases of both species were classified on the basis differential substrate and inhibitor specificities. In developing hybrids formed by B. rerio eggs inseminated with B. albolineatus sperm, the maternal isozyme pattern persisted until Stage 17 (gastrulation). Embryonic extracts from Stage 17 onward showed a slow-moving, DFP-sensitive carboxylesterase of paternal origin. In developing hybrids formed by B. albolineatus eggs inseminated with B. rerio sperm, a paternal contribution to the esterase pattern was probably present by the end of gastrulation; esterase activity of distinctively paternal origin was present by Stage 22 (retinal pigmentation) The maternal contribution to the total esterase profile appeared to remain high through hatching. Additional evidence for gene activity at gastrulation was obtained in experiments utilizing actinomycin-D and cycloheximide. Results of exposing embryos of B. rerio to 15 mug/ml of actinomycin-D indicated that transcription of the template RNA coding for cholinesterase occurred during gastrulation or some 20-30 hours prior to the appearance of the isozyme at Stage 22. This template RNA was translated sometime during that 10-hour interval immediately preceding Stage 22.

Animals↗
PubMed1975

The role of gaze in impression formation.

Three hypotheses about the effects of amount of gaze on the impression created of six confederates were tested, using rating scales and free descriptions. The first hypothesis--that favourableness of impression would be a linear function of amount of gaze--was partly confirmed. The second hypothesis--that favourableness of impression would be a curvilinear function of amount of gaze--was not confirmed, nor was the third hypothesis--that effect of gaze would be a complex function of sex of subject and sex of gazer. The effects of gaze were not as marked as had been predicted. The free descriptions also provided data on the number and type of subjects who commented on the amount of gaze of the confederate. Three possible explanations of the results are discussed.

Eye Movements↗
PubMed1975

Anxiety and ritualized speech.

The experiment examines the effects on a number of words that seem irrevelant to semantic communication. The Units of Ritualized Speech (URSs) considered are: 'I mean', 'in fact', 'really', 'sort of', 'well', and 'you know'. Two hypotheses are tested: (i) that URS rate will increase with anxiety; and (ii) that the speaker's preferred URS will increase with anxiety. Subjects were interviewed on topics they had previously rated as anxiety-provoking and non-anxiety-provoking. Hypothesis (i) was supported, but hypothesis (ii) was not. More specifically, the use of 'I mean' and 'well' increases when the speaker is anxious. Explanation for this is sought in the grammatical location of these two units. Sex differences in the use of URSs, correlations between URSs and their relationship to other forms of disfluency are also considered.

Anxiety↗
PubMed1968

Encephalopathy of thiamine deficieny: studies of intracerebral mechanisms.

Thiamine-deficient encephalopathy is characterized by morphologic lesions in the brainstem and less extensively in the cerebellum, but the early neurologic signs reverse rapidly and fully with thiamine, indicating a metabolic disorder. The suggested causal mechanisms of the encephalopathy involve two thiamine-dependent enzymes: (a) impairment of pyruvate decarboxylase activity with decreased cerebral energy (ATP) synthesis, and (b) reduction of transketolase activity with possible impairment of the hexose monophosphate shunt and subsequent decrease in NADPH formation. The latter may be important in maintaining glutathione in a reduced form (GSH), which apparently functions by keeping enzymes in a reduced (active) conformation. To examine some of these postulated mechanisms, in this study we measured pyruvate decarboxylase and transketolase activity, lactate, ATP and GSH levels in the cerebral cortex, cerebellum, and brainstem, and thiamine concentration in whole brain of rats with diet-induced low thiamine encephalopathy. Pair-fed and normally fed asymptomatic control animals were similarly investigated. To assess the functional importance of some of our results, we repeated the studies in rats, immediately (16-36 hr) after reversal of the neurological signs with thiamine administration. THE DATA OBTAINED LED TO THE FOLLOWING CONCLUSIONS: (a) Brain contains a substantial reserve of thiamine in that thiamine level has to fall to below 20% of normal before the onset of overt encephalopathy and an increase in brain thiamine to only 26% of normal results in rapid reversal of neurologic signs. (b) Both cerebral transketolase and pyruvate decarboxylase activities are impaired in low thiamine encephalopathy and the abnormality in the pyruvate decarboxylase is reflected in a rise in brain lactate. These biochemical abnormalities occur primarily in the brainstem and cerebellum, the sites of the morphologic changes. (c) Although the fall in cerebral transketolase is about twofold greater than that of pyruvate decarboxylase activity during encephalopathy, both enzymes rise on reversal of neurologic signs and the degree of the transketolase rise is slight. Accordingly, this study cannot ascertain the relative functional importance of these two pathways in the induction of the encephalopathy. The data suggest, however, that the depression of transketolase is not functionally important per se, but may only be an index of some other critical aspect of the hexose monophosphate shunt. (d) The normal cerebral ATP concentration and small GSH fall during encephalopathy, with little GSH rise on reversal of neurologic signs, suggest that a depletion of neither substance is instrumental in inducing thiamine-deficient encephalopathy.

Adenosine Triphosphate↗