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M Hoyt

Publications and source records attributed to M Hoyt.

6 recordsLinked to original sources
PubMed2000

Serological estimation of prey-protein gut-residence time and quantification of meal size for grass shrimp consuming meiofaunal copepods.

A series of experiments using serological reagents was conducted to examine predation, ingestion and digestion in a model predator-prey system. The harpacticoid copepod Amphiascoides atopus, obtained from mass culture, was used as prey and the grass shrimp, Palaemonetes pugio, as predator. Bulk-gut passage time in P. pugio was measured by visualization of latex beads and ranged from 0.5 to 4 h in starved and continuously-fed grass shrimp. A polyclonal antibody was prepared from crude extracts of A. atopus; cross reactions with P. pugio and three other crustaceans were either negligible or not detected using slide agar-gel-double-immunodiffusion (AGID) and Western blot preparations. The presence of A. atopus antigens was detected with great sensitivity (e.g., seven copepods, 35 µg dry weight, gave positive results) in grass shrimp gut contents even when proteins of other crustacean prey were present. Prey-proteins could be detected for as long as 4 h with AGID and 8 h with Western blot techniques. Individual grass shrimp that were fed A. atopus and consumed from 0 to 98 copepods h(-1) were subjected to Western-blot preparation with chemiluminescence detection and densitometric evaluation. There was a significant curvilinear relationship between protein content and the number of copepod prey ingested. Results suggest that serological techniques can be modified to estimate the mass or abundance of standard-sized prey ingested by field-collected predators.

Journal Article↗
PubMed1996

Mutations in the Ty3 major homology region affect multiple steps in Ty3 retrotransposition.

The Saccharomyces cerevisiae retroviruslike element Ty3 encodes the major structural proteins capsid (CA) and nucleocapsid in the GAG3 open reading frame. The Ty3 CA protein contains a sequence (QGX2EX5FX3LX3H, where H is a hydrophobic residue) which has not been observed in other retrotransposons but which is similar to the major homology region (MHR) described for retrovirus CA. In this study the effects of mutations in the Ty3 MHR on particle formation, processing, DNA synthesis, and transposition were examined. Each of the mutations tested resulted in severe defects in transposition, with disruption occurring prior to or at particle formation, subsequent to particle formation and prior to completion of DNA synthesis, and subsequent to DNA synthesis. Changing the Q in the motif to R had relatively little effect on particle formation but decreased transposition to about 13% of that of a wild-type element. Changing G to A or V almost completely eliminated the formation of intracellular particles, possibly by disruption of CA-CA interactions. Changes introduced at the position of E resulted in blocked processing, blocked DNA synthesis, or a block at some post-reverse transcription step, depending on the nature of the mutation introduced. These results showed that the integrity of the Ty3 MHR is required for multiple aspects of Ty3 replication involving CA. These functions are independent of extracellular budding and of infection, aspects of the retroviral life cycle which are not recapitulated in replication of the Ty3 retrotransposon.

Amino Acid Sequence↗
PubMed1990

Children's Activity Rating Scale (CARS): description and calibration.

A five-level Children's Activity Rating Scale (CARS) was designed to categorize the intensity of physical activities and discriminate between levels of energy expenditure in young children. The CARS was used by trained observers over a 12-month period to assess physical activities of 3-4 year-old children during field observations. Agreement among observers using the CARS was 84.1% for 389 paired observation periods. The energy expenditure for each level was assessed by measuring VO2s and heart rates of 5-6 year-old children (12 boys, 13 girls) while they performed eight activities representing the CARS levels. Mean VO2s for the eight activities in Levels 1-5 ranged from 7.1 to 37.5 ml.kg BW-1.min-1 (1 to 5.42 METS; 14.5% to 80.6% of VO2max). Mean heart rates ranged from 89 to 183 b.min-1 for activities in Levels 1-5. VO2s and heart rates at each level were significantly different from all other levels. These data demonstrate that the CARS encompasses a wide range of energy expenditures, discriminates between levels of energy expenditure, and can be used by trained observers to reliably evaluate physical activity and estimate energy expenditure of young children.

Body Weight↗
PubMedDate not supplied

Effects of intravenous test dose epinephrine on fetal sheep during acute fetal stress and acidosis.

Small IV doses of epinephrine (epi; 5.0-20.0 micrograms), similar to those advocated for epidural test dosing, cause a significant though transient (3 minutes) reduction in uterine blood flow in pregnant ewes but no subsequent adverse effect on the mature, unstressed fetus. The purpose of this study was to investigate the acute effects on the mature fetus of a maternal IV test dose of 12.5 mg bupivacaine and 50.0 micrograms fentanyl with or without 16.5 micrograms epi in the presence of acute placental insufficiency and fetal asphyxia. Two minutes after dosing and for 15 minutes thereafter, no changes were observed in maternal heart rate (HR), mean arterial pressure (MAP) or arterial blood gas values and catecholamine concentrations other than a statistically significant doubling in epi levels after epi dosing. Mildly (mean arterial pH, 7.23) and severely (mean pH, 6.87) acidotic fetuses differed with respect to arterial pO2, pCO2 and catecholamine values, but in neither group were any changes observed after maternal dosing. Under the conditions of acute fetal stress and acidosis produced in this experiment, inclusion of epi 16.5 micrograms in an epidural test dose does not significantly affect the HR, MAP, aortic flow, blood gases or catecholamine levels of the mature fetal sheep when injected intravenously.

Acidosis↗