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Biomedical subjects

M M David

Publications and source records attributed to M M David.

11 recordsLinked to original sources
PubMed2001

Response to seasonal drought in three cultivars of Ceratonia siliqua: leaf growth and water relations.

Responses of leaf growth and leaf water relations to seasonal drought were monitored during two successive years in three cultivars (Galhosa, Espargal and Mulata) of Ceratonia siliqua L. growing in the field in southern Portugal. Leaf water relations of fully expanded leaves were characterized by pressureâ volume analysis, and morphometric measurements of petiolar xylem were made. The three cultivars differed with respect to onset of leaf initiation. In Galhosa, there was a sharp peak of leaf initiation in June that was immediately followed by a period when leaf expansion rates were highest. The onset of leaf growth occurred earlier in Espargal and Mulata than in Galhosa, and both cultivars continued producing new leaves throughout the summer period. The diurnal pattern of water relations in recently expanded leaves indicated that, during midsummer, Galhosa was the only cultivar in which leaf water potential did not fall below the turgor loss point and leaf relative water content remained above 90%. The occurrence of osmotic adjustment in recently expanded leaves of Galhosa was not demonstrated conclusively. However, during the dry season following leaf formation, a seasonal decrease in osmotic potential sufficient to maintain turgor was detected in 1-year-old leaves of Galhosa but not in 1-year-old leaves of the other cultivars. Among cultivars, Galhosa petioles had the widest xylem conduits, which may partly explain why midday leaf water potential in Galhosa never decreased below -2.0 MPa even at the end of the summer drought.

Fabaceae↗
PubMed2000

Thyroid function and response to 48-hour sleep deprivation in treatment-resistant depressed patients.

BACKGROUND: Clinical depression is associated with abnormalities of the hypothalamic-pituitary-thyroid axis. Changes in thyroid function during sleep deprivation may be related to its antidepressant effects. METHODS: Levels of thyroid-stimulating hormone, tri-iodothyronine, tri-iodothyronine uptake, thyroxine, and free thyroxine were measured before, during, and after a 48-hour sleep deprivation in nine treatment-resistant depressed patients. Clinical state was assessed every 4 hours. A retrospective study of 26 similar patients was added for cross-validation. RESULTS: Significant increases in thyroid-stimulating hormone and tri-iodothyronine during sleep deprivation were not correlated with clinical improvement. Sleep deprivation responders had lower tri-iodothyronine uptake levels than nonresponders in both the prospective (p <.02) and the retrospective (p <.03) samples. CONCLUSIONS: The lower tri-iodothyronine uptake values in responders may identify a subgroup of depressed patients who respond to sleep deprivation by virtue of some abnormality of the hypothalamic-pituitary-thyroid axis that is temporarily corrected by sleep deprivation.

Adult↗
PubMed1996

Respiratory symptoms in urban Hispanic and non-Hispanic white women.

The prevalence and predictors of wheeze syndromes, including asthma, were examined among 475 non-Hispanic (NH) white and 371 Hispanic pregnant women enrolled in a population-based study in East Boston, Massachusetts. Respiratory symptoms and risk factors were ascertained by questionnaire early in pregnancy. Hispanic and NH white women were of similar age (mean +/- SD, 26 +/- 5 yr), but Hispanics reported less schooling (30 versus 50% completed high school), a lower frequency of household pets (4 versus 47%), and a lower frequency of parental asthma (6 versus 12%). Hispanics smoked significantly less than NH whites did, both in prevalence (8 versus 50%) and number of cigarettes per day among current smokers (12 +/- 9 versus 22 +/- 10; p < 0.0001). Hispanics reported a lower frequency than NH whites did of doctor-diagnosed asthma (6 versus 12%), persistent wheeze (5 versus 19%), and either persistent wheeze or asthma (11 versus 30%). In multivariate analysis, active cigarette smoking and parental history of asthma were associated most strongly with wheeze syndromes. When these two factors as well as educational level, presence of household pets, and height2-adjusted FEV1 were controlled, Hispanics remained at lower risk of asthma (odds ratio [OR] 0.71; 95% confidence interval [CI], 0.37-1.37) and persistent wheeze (OR 0.48; 95% CI, 0.25-0.95) than NH whites. These results suggest that chronic wheeze syndromes are common among young urban women and are associated with both active smoking and a parental history of asthma. Hispanic women from Central and South America living in urban environments in the United States may be at less risk for these conditions than NH white women, in contrast to those from Puerto Rico.

Adolescent↗
PubMed1991

Rapid eye movement latency and mood following a delay of bedtime in healthy subjects: do the effects mimic changes in depressive illness?

The phase advance hypothesis proposes that a phase advance of certain circadian rhythms (such as rapid eye movement (REM) sleep propensity) relative to the sleep-wake cycle is implicated in the pathophysiology and pathogenesis of depression. In an earlier study, we reported that a 6-h delay of sleep in normals produced REM changes that resembled the depressive pattern. Mood change was generally modest, although 2 of the 10 subjects became noticeably depressed. This study assessed the replicability of these results, and introduced a phase advance control condition. Predicted changes were observed in REM parameters. Modest but reliable mood change was confined to the first night of the phase delay, and was attributed to sleep loss. These results suggest that the effects of the phase shift were relatively benign, except in a minority of cases. Such individuals may have a susceptibility to depression that manifests itself under certain conductive physiological conditions.

Adolescent↗
PubMed1991

Sleep disturbance in depression reconsidered.

The well documented observation of a characteristic sleep disturbance in depression has been accorded a good deal of significance. Several current hypotheses regarding the etiology of depression, are based on these findings. However, a review of the descriptive studies shows that care has not generally been taken either to restrict or objectively measure daytime sleep. Evidence is presented suggesting that daytime sleep may occur in depressed patients more frequently than commonly thought and that, in normal subjects, daytime napping can result in nocturnal sleep changes similar to those seen in depressed patients. A model is proposed in which the nocturnal sleep disturbance in depression reflects the occurrence, during the daytime, of frank slow wave sleep or periods of large amplitude, slow wave EEG activity as a consequence of a dampening of the circadian rhythm of sleep propensity.

Arousal↗
PubMed1990

Sleep deprivation in depression: pattern of relapse and characteristics of preceding sleep.

The pattern of relapse following therapeutic response to 40-hr sleep deprivation (SD) was examined in nine depressed patients. On the night ending SD patients were awakened from polygraphically recorded sleep on one or more occasions, in order to assess the clinical state. All subjects were found to demonstrate a precipitous and full relapse over this night, the timing of the relapse varying considerably between individuals. No association was found between deterioration in the clinical state and characteristics of preceding sleep. These results are consistent with the notion that, in predisposed individuals, some process associated with sleep has a depressogenic effect. However, they necessitate revision of theories of SD and depression that emphasize the infrastructure of sleep.

Adult↗
PubMed1981

Erythrocruorin from the crustacean Caenestheria inopinata. Quaternary structure and arrangement of subunits.

The subunit structure of erythrocruorin from the crustacean Caenestheria inopinata was studied. The native protein was found to have a sedimentation coefficient of 12.0 S and a molecular weight, as determined by sedimentation equilibrium, of 302,000. Iron and heme determinations gave 0.346 and 3.98% corresponding to minimal molecular weights of 16,100 and 15,500, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis gave one band with mobility corresponding to a molecular weight of 30,000. The molecular weight of the polypeptide chain was determined to be 30,500 by sedimentation equilibrium in 6 M guanidine hydrochloride and 0.1 M 2-mercaptoethanol. Dissociation of the 12S molecule was observed at acidic and alkaline pH. A dissociation species of 2.7 S was isolated and its molecular weight determined to be 28,000 by sedimentation equilibrium. On a molecular weight basis, the native molecule is composed of ten 2.7S subunits, each of which consists of a single polypeptide chain carrying two hemes. We propose a model for the molecule composed of ten spheres, each representing a 2.7S subunit, arranged in two layers stacked in an eclipsed orientation, in five spheres of each layer occupying the vertices of a regular pentagon. Support for this arrangement is provided by a comparison of projections of the model with molecular profiles seen in the electron microscope.

Animals↗
PubMed1975

[Odontogenesis, organogenic model using teratomas].

The study of odontogenesis in teratomas, leads to the following observations. Conspicuous odontogenic fields are present in the vicinity of pluri-differentiated cystic structures. Tooth germs are connected to the walls of the cysts by an anastomosed dental laminar. The teeth developing in teratoma are not comparable to the normal process which is harmonized when the formation and the distribution of the various parts are concerned. They are deformed in appearance but not in the same way as the classic genetic malformations. The origin of both epithelial and mesenchymal parts is still not completely understood.

Adult↗