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M D Pagel

Publications and source records attributed to M D Pagel.

9 recordsLinked to original sources
PubMed1994

Solution structure of a core peptide derived from scyllatoxin.

An analysis of the sequences of scyllatoxin and charybdotoxin suggested that it would be possible to design a core peptide sequence which would still fold to give the beta-hairpin and helix seen in the toxins, but which would eliminate one disulfide and connecting residues. The core sequence was modeled, then synthesized and purified. The cysteines oxidize in air to give the same disulfide pairings as seen in the parent toxins as the major product. The three-dimensional structure of the core sequence peptide, termed Max, was determined using proton NMR spectroscopy and found to be identical in secondary structure to the toxins. However differences were found in the relative orientation of the beta-hairpin and helix. The use of this structural motif, found in many insect toxins, as a disulfide framework for exploring sequence/structure/activity relationships is discussed.

Amino Acid Sequence↗
PubMed1990

Psychosocial influences on new born outcomes: a controlled prospective study.

This paper reports the results of a prospective investigation of 100 women during their pregnancies to test the hypothesis that social and psychological factors influence pregnancy outcome after controlling for demographic, biomedical, and lifestyle variables. Subjects completed questionnaires that assessed family social supports, life events, and anxiety. In addition, data were collected on general biomedical and pregnancy risk, lifestyle practices including smoking and drinking, as well as demographic information. Four infant outcomes, birthweight, gestational age, and 1 and 5 min Apgar scores, were studied via hierarchical multiple regression analyses for their relationship to the social and psychological variables, after controlling for all other sets of variables. The results of these analyses showed that life events stress accounted for significant variation in birthweight, and social supports and anxiety were associated with the two pediatric Apgar scores. Gestational age bore a simple relationship to anxiety, with higher anxiety predictive of lower gestational age. Further analyses revealed that women with either low social supports or high anxiety were, on the average, younger, more often single, of lower education level, had less income, smoked more, and had higher general biomedical risk than women with adequate social supports or lower anxiety. This suggests the multiple ways in which social and psychological risk factors may be related to pregnancy outcome and emphasizes the need for well controlled studies in this area.

Anxiety↗
PubMed1989

Taxonomic differences in the scaling of brain on body weight among mammals.

Theories for the evolution of brain weight in mammals suggest that closely related species have diverged largely as a result of selection for differences in body weight, but that differences among more distantly related species have arisen due to greater net directional selection on brain weight. This pattern of changing selection causes brain weight to evolve more slowly than body weight among closely related species, such as those in the same genus, than among more distantly related species, such as those from different families or orders; a phenomenon known as the "taxon-level effect." Thus, brain weight differs more for a given difference in body weight as the species compared are more distantly related. An alternative explanation for the taxon-level effect is proposed. Distantly related species are more likely to inhabit different ecological conditions than are more closely related species. Where the taxon-level effect occurs, brain weight appears to have evolved in response to the demands of these different ecological conditions. As a consequence, brain weight differs more among distantly related species, for any given difference in body weight, than among closely related species. This effect, rather than a progressive pattern of changing selection pressures, may account for the taxon-level effect in mammals.

Animals↗
PubMed1989

Comparative methods for examining adaptation depend on evolutionary models.

Comparisons among taxa provide a powerful means for helping to understand why primate species differ from each other in morphology, behaviour and life history. Comparative tests can also mislead when not applied correctly, and correct application means taking into account the phylogenetic relationships among the species being compared. Adaptation is defined as a comparative concept. The reasons for phenotypic similarity among closely related taxa are summarized. Different models of evolutionary change dictate different methods for reconstructing ancestral character states and for performing comparative analyses on categorical and continuously varying character. All comparative methods rely either implicitly of explicitly on some model of how evolution proceeds. The choice of a particular method of analysis is, therefore, an implicit choice of a model of evolution.

Adaptation, Biological↗
PubMed1988

Recent developments in the analysis of comparative data.

Comparative methods can be used to test ideas about adaptation by identifying cases of either parallel or convergent evolutionary change across taxa. Phylogenetic relationships must be known or inferred if comparative methods are to separate the cross-taxonomic covariation among traits associated with evolutionary change from that attributable to common ancestry. Only the former can be used to test ideas linking convergent or parallel evolutionary change to some aspect of the environment. The comparative methods that are currently available differ in how they manage the effects brought about by phylogenetic relationships. One method is applicable only to discrete data, and uses cladistic techniques to identify evolutionary events that depart from phylogenetic trends. Techniques for continuous variables attempt to control for phylogenetic effects in a variety of ways. One method examines the taxonomic distribution of variance to identify the taxa within which character variation is small. The method assumes that taxa with small amounts of variation are those in which little evolutionary change has occurred, and thus variation is unlikely to be independent of ancestral trends. Analyses are then concentrated among taxa that show more variation, on the assumption that greater evolutionary change in the character has taken place. Several methods estimate directly the extent to which ancestry can predict the observed variation of a character, and subtract the ancestral effect to reveal variation of phylogeny. Yet another can remove phylogenetic effects if the true phylogeny is known. One class of comparative methods controls for phylogenetic effects by searching for comparative trends within rather than across taxa. With current knowledge of phylogenies, there is a trade-off in the choice of a comparative method: those that control phylogenetic effects with greater certainty are either less applicable to real data, or they make restrictive or untestable assumptions. Those that rely on statistical patterns to infer phylogenetic effects may not control phylogeny as efficiently but are more readily applied to existing data sets.

Adaptation, Physiological↗
PubMed1987

Social networks: we get by with (and in spite of) a little help from our friends.

Studies of social support networks have almost exclusively measured only their positive aspects. In this research, we investigated both the helpful or positive and the upsetting or negative aspects of social networks in a longitudinal study of spouses caring for a husband or wife with Alzheimer's disease, a progressive senile dementia. Measures of helpful and upsetting aspects of the care givers' networks, derived from interviews and daily interaction ratings, were studied for their relations with overall network satisfaction and depression at an initial interview period (n = 68) and at a follow-up period about 10 months later (n = 38). Results from hierarchical multiple regression analyses, in which care givers' age and sex and a measure of the spouses' health status were controlled, showed that the care givers' degree of upset with their networks was strongly associated with lower network satisfaction and increased depression at both time periods. Helpful aspects bore little or no direct relation to either depression or network satisfaction. Helpful aspects of the network did, however, interact with network upset in predicting network satisfaction, and depression (combined probabilities test, p less than .05). Longitudinal predictions of follow-up depression, after age, sex, care givers' health status, and initial depression levels were controlled, showed that changes in upsetting aspects of one's network were predictive of changes in depression over time. We interpreted these results within an attributional framework that emphasizes the salience of upsetting events within a social network.

Adaptation, Psychological↗
PubMed1984

A comparison of three social-psychological models of attitude and behavioral plan: prediction of contraceptive behavior.

We compared the predictive validities of three prominent models of attitudes and behavioral decisions: Rosenberg's instrumentality-value model, Fishbein's belief-evaluation model, and Beach's adaptation of subjective expected utility theory. Seventy female undergraduates rated each of the models' components and reported their attitudes and behavioral plans toward using three different methods of contraception. With the traditional across-subjects prediction procedure, the Rosenberg model generally accounted for 5-25% less variance in subjects' attitudes and behavioral plans than the Fishbein an Beach models, which were not different. With a within-subject prediction procedure, the Rosenberg model was again the least accurate, and the Fishbein and Beach models had similar predictive accuracy. As hypothesized, within-subject predictions were more accurate than across-subjects predictions. The relatively poor performance of the Rosenberg model was attributable to the instrumentality component. In addition, we found that the Beach model could be simplified with no appreciable loss in predictive accuracy. Finally, a subject's personal normative beliefs emerged as a strong independent predictor of behavioral plan.

Adult↗
PubMed1982

Acetate and bicarbonate fluctuations and acetate intolerance during dialysis.

Plasma bicarbonate losses during acetate dialysis were prevented by using a combination of acetate and bicarbonate in the dialysate. In 21 patients who were treated with combination dialysate, the fall in mean blood pressure (MBP), and frequency of symptoms, and post-dialysis task performance were all similar to that observed during dialysis with acetate alone. Furthermore, dialysis performed with bicarbonate dialysate resulted in significantly smaller MBP drops, fewer symptoms, and an improved task performance compared to either an acetate or a combination dialysis. These findings indicate that the presence of acetate, rather than a bicarbonate loss, was responsible for the patients' intolerance to acetate dialysis. Patients symptomatic on acetate dialysis had a similar ultrafiltration rate, weight loss, MBP drops, and postdialysis serum acetate levels; they were similar in age and weight to symptom-free patients. Thus, the toxic effect of acetate was not related to serum acetate level. There was no difference in bicarbonate dialysis between patients with symptoms on acetate and the symptom-free patients in reference to MBP drops and task performance. This finding suggests that symptomatic patients were not simply less tolerant to the process of dialysis, but differed from symptom-free patients in their response to the presence of acetate.

Acetates↗