Hospital resource allocation and insurance coverage.
Explore the source record for details and available documents.
Health Care Rationing↗
Biomedical subjects
D F Johnson
Publications and source records attributed to D F Johnson.
Elimination of apolipoprotein B48 formation in rat hepatoma cell lines transfected with mutant human apolipoprotein B cDNA constructs.
Rat hepatoma McA-RH7777 cell lines transfected with full-length human apolipoprotein (apo) B constructs produce mostly human apoB48 and only small amounts of apoB100, as a result of mRNA editing at codon 2153 (C to U conversion at nucleotide 6666). To abolish the formation of apoB48 and increase the yield of apoB100 and other forms of apoB longer than apoB48, site-specific mutations were introduced at or near the site of apoB mRNA editing. Among four mutations examined, only that in which codon 2153 was converted from CAA (Gln) to CTA (Leu) effectively precluded the formation of apoB48. In this mutant, a stop codon would not be generated even if the C to U conversion occurred. The three other mutations were introduced to disrupt the proposed stem-loop structure encompassing the editing site. Changes made in the third positions of five codons on the 5' side of the edited base or of four codons 3' of the edited base failed to eliminate the production of a protein with the approximate size of apoB48. A construct in which codon 2153 was changed from CAA to GAT (Asp) also failed to eliminate the production of a protein the size of apoB48. Analysis of the region between nucleotides 6200 and 6900 of the cDNA did not detect any prevalent alternate editing sites. Immunoblot analysis using polyclonal antibodies raised against synthetic peptides of human apoB100 indicated that the carboxyl terminus of the apoB48-like proteins probably resides between amino acid residues 2068 and 2129 of apoB100. These results provide some insight into the mechanism of apoB mRNA editing and will facilitate further studies on apoB-containing lipoproteins.
Amino Acid Sequence↗
Consumption of salty food by rats: regulation of sodium intake?
The extent to which sodium levels may be regulated by consumption was examined in two experiments that offered rats foods varying in sodium chloride (NaCl) content. In the first, rats received single purified diets containing from 0% to 3% NaCl. There were no effects of NaCl level on the amount or pattern of daily food intake; water intake, however, increased with salt content. In the second study, rats had choices between a NaCl-free food and a food containing either 1, 2, or 3% NaCl for 1 week each. Total food intake was unaffected. Proportional intake of the salt-free option increased with the salt content of the alternate food, but not sufficiently to maintain a constant NaCl intake. After 8 weeks of exposure to a single food, intake of the salty option increased in the choice tests, but the level of NaCl (from 0.5 to 3.0%) in the exposure-phase food did not affect the subsequent choice. We conclude that when only one food is available, salt intake is governed by caloric requirements and sodium levels are regulated by excretion. When foods differing in NaCl content are available, consumption does contribute to the regulation of sodium balance, but the amount consumed is not tightly controlled. Rats' salt preference appears to increase with age or with experience eating the purified foods offered here, but experience eating salty food does not affect the preferred level of salt.
Aging↗
Characterization of apolipoprotein B mRNA editing from rabbit intestine.
Apolipoprotein (apo) B-48 is generated by a unique physiological process. Cytidine 6,666 of the apo B primary transcript is posttranscriptionally converted to a uridine by an RNA editing mechanism that transforms the codon for glutamine 2,153 to a termination codon. The editing reaction can be duplicated in a cell-free extract. In this study, the apo B-48 mRNA editing activity derived from partially purified extracts of rabbit enterocytes was characterized. The optimum conditions for the editing reaction were determined to be a salt concentration of 0.125-0.150 M NaCl or KCl, a pH of 8-8.5, and a temperature of 30 degrees C. The reaction rate was linear up to 45 minutes and was proportional to the editing extract concentration. No metal ion cofactors, DNA or RNA cofactors, or energy requirements were identified. At optimum conditions, the reaction followed Michaelis-Menten kinetics, with a Km of 0.4 nM for the rabbit RNA substrate. In addition, the reaction rate was enhanced by the addition of 25 micrograms/ml heparin or 40% glycerol. The characteristics of the editing reaction suggest that it is catalyzed by a nucleotide sequence-specific cytidine deaminase that is either a single enzyme or a multimeric protein.
Animals↗
The magnitude-of-reinforcement function in closed and open economies.
It has been hypothesized that the magnitude-of-reinforcement effect may differ in closed and open experimental economies. We determined the relationship between magnitude of reinforcement and response rate in three feeding conditions: a closed economy in which total intake was unrestricted, a closed economy in which total intake was restricted so as to maintain body weight at 85% of free-feeding weight, and a traditional open economy in which subjects received food outside the experimental session. In the closed economies, regardless of body weight, the rats responded faster for smaller pellets and when the fixed ratio for pellets was higher. In the open economy, there was no reliable effect of pellet size or pellet cost on response rate. It is concluded that although there are circumstances in which response rate is an immediate function of the parameters of reinforcement, rate is not necessarily a measure of response strength. Response rate may instead, or additionally, contribute to a strategy of reducing the costs associated with resource utilization.
Adult↗
The economics of water and salt balance.
Two environmental features often associated are a shortage of water and an excess of electrolytes. We explored the economics of this situation by jointly manipulating the instrumental cost of consuming water and the amount of salt in the diet of rats. As the dietary salt increased, water intake increased; and as water cost increased, water intake fell. Food intake also declined as water cost increased, and the rats maintained a minimum ratio of water: salt consumed across all conditions. For all diets, as water intake fell, food intake and body weight also declined, perhaps defending the ratio of body water to lean body mass. There was no evidence that the slope of the demand curve for water changed as a function of dietary salt.
Animal Feed↗
The relationship between feeding rate and patch choice.
Rats in a laboratory foraging simulation searched for sequential opportunities to feed in two patches that differed in the rate at which food pellets were delivered (controlled by fixed-interval schedules) and in the size of the pellets. The profitability of feeding in each patch was calculated in terms of time (grams per minute) and in terms of effort (grams per bar press). These values were the result of the imposed fixed interval, the size of the pellets, and the rate at which the rats pressed the bar in each condition. The rats ate more food and larger meals, but not more frequent meals, at the patch offering the higher rate of food consumption, calculated as grams per minute. The relative intake at any patch was a function of the relative rate of intake during meals at that patch compared to the other patch. Rats respond to explicit manipulations of feeding time in the same manner as they respond to manipulations of feeding effort.
Animals↗
Apolipoprotein B mRNA editing. Direct determination of the edited base and occurrence in non-apolipoprotein B-producing cell lines.
In humans, apolipoprotein (apo) B48 is synthesized in the intestine as an obligatory constituent of chylomicrons. Apolipoprotein B48 is identical to the amino-terminal 2152 amino acids (240 kDa) of apoB100 and is translated from an edited apoB mRNA in which codon 2153 has been converted from glutamine (CAA) to what is recognized as a premature stop codon (UAA). To determine whether the apoB mRNA editing in fact converts cytosine 6666 in codon 2153 to uracil, we incubated a synthetic apoB RNA containing 32P-labeled cytosines in an in vitro editing system prepared from rabbit enterocytes. The in vitro edited RNA was purified and digested to nucleoside 5'-monophosphates, which were analyzed on two-dimensional thin-layer chromatography. We found that the edited base co-migrated with authentic uridine 5'-monophosphate. Thus, cytosine 6666 is converted to uracil, most likely by a nucleotide-specific cytosine deaminase. To determine whether apoB mRNA editing occurs in cell lines that do not synthesize apoB, we stably transfected a high expression vector containing 354 base pairs of apoB sequence into 18 different cell lines. We found apoB mRNA editing activity in five osteosarcoma cell lines and one epidermoid cell line, none of which synthesizes any detectable apoB. Thus, apoB mRNA editing occurs in cell lines that do not synthesize apoB, which suggests that mRNA editing may be a common biological phenomenon in eukaryotic cells.
Animals↗
Use of the lac repressor in constructing sequential deletions and a new sequencing vector.
Large sequencing projects require an efficient strategy to generate a series of overlapping clones. This can be accomplished by protecting one end of a linear DNA molecule while sequential deletions are introduced into the other end by exonuclease digestion. We demonstrate that the lac repressor can protect the ends of linear nucleotide sequences from digestion by exonuclease if these ends contain the lac operator sequence. To exploit this, we have inserted the lac operator sequence between the primer-binding site and multiple cloning site of an M13 sequencing vector. Linearizing the replicative form and binding lac repressor protein protects the end next to the vector sequences. Sequential deletions are then introduced into the insert by digesting with exonuclease III or BAL 31. Because the rate and time of digestion are readily controlled, the region brought next to the sequencing primer site, after religation, can be selected in a timed series of reactions. This minimizes the screening needed to isolate an overlapping series of clones and facilitates sequencing of long regions.
Base Sequence↗
The time window of feeding.
This paper contrasts the traditional depletion/repletion model of food intake with a longer-term perspective which focuses on function rather than mechanism. We review naturalistic observations as well as the economic relationships we have discovered in the laboratory by a cost/benefit analysis of feeding in a closed economy. We have manipulated feeding costs by means of operant methodology and have explored two classes of cost, the cost of initiating meals and the cost of consuming food. We conclude that when an animal can detect the cost/benefit structure of its habitat, its feeding behavior will tend to maximize benefits relative to cost in apparent anticipation of its nutritional requirements and environmental conditions. The time window over which these feeding decisions are integrated may be minutes, hours, months, or seasons depending upon the animal's niche and current habitat. Feeding mechanisms based on momentary deficits and repletions are inadequate to explain these strategies, leaving the field of feeding mechanisms open for major discovery and revision.
Animals↗
Activity patterns in rats (Rattus norvegicus) as a function of the cost of access to four resources.
Patterns of eating, drinking, wheel running, and nesting were recorded in 2 experiments in which rats (Rattus norvegicus) lived in a laboratory environment that provided food, water, a running wheel, and a nest box. Access to each resource was contingent on the completion of a fixed ratio of bar presses and once earned remained available until the resource was not used for 10 consecutive min. In all cases an increase in the access price of a resource produced a decrease in the frequency with which the resource was accessed. This reduction in bout frequency was countered by an increase in bout size, which was compensatory for eating and nearly so for drinking, but which was only partially compensatory for wheel running. Nest bout size did not change significantly as nest price increased. The bout patterns of these 4 activities changed independently of one another, and the probabilities of behavioral transitions did not indicate strong links between any pairs of activities.
Animals↗
Behavior problems in children with the presenting problem of poor school performance.
Used 3 methods of assessing behavioral disturbance in 79 children presenting with poor school performance to an interdisciplinary evaluation center. Findings revealed a very high frequency of behavior problems, particularly of the internalizing type, but few differences in frequency or type of behavior problems among 4 subgroups: children with learning disabilities, mental retardation, borderline intellectual functioning, and without learning disabilities or cognitive impairment. Behavioral problems were associated with lower perceptions of self-worth and family functioning characterized as more controlling, and less supportive. Findings are discussed in terms of the need for interactional models of learning and behavior problems.
Adolescent↗
The effect of dexamethasone-21-acetate on meal size, meal frequency and macronutrient self-selection in rats.
In Experiment 1, the measurement of 24-hour food intake in two rats showed that treatment with dexamethasone-21-acetate (DEX) (0.5 mg/kg IP) produced a decrease in body weight which was at least partially due to a decrease in food intake (both meal frequency and meal size). In Experiment 2, the daily intake of three macronutrient sources was measured. These data showed that treatment with DEX (0.5 and 1.0 mg/kg IP) led to an acute increase in protein intake, a sustained decrease in fat intake and no change in carbohydrate consumption. We suggest that this change in macronutrient selection may be an adaptive response which serves to ameliorate some of the effects of DEX treatment.
Animals↗
Ambient temperature and food costs: effects on behavior patterns in rats.
Eating, drinking, wheel running, and nesting were recorded continuously in animals living in cages where they foraged for and consumed food by completing operant bar-press requirements. The ambient temperature was either 24 or 0 degrees C. Two food costs, that of initiating meals and that of pellets within meals, were separately manipulated at each temperature. Compared with room temperature, the cold temperature produced a doubling of food and water intake and a greater than twofold increase in nesting time each day. Running behavior was not altered. Regardless of temperature, the cost of initiating meals influenced the frequency and size of meals but did not affect total food intake or time spent feeding, and this cost had no effect on any other activity. As the cost of pellets within meals increased, the time spent feeding increased and there was a decline in daily food intake. The change in intake was greater at the cold temperature because in the cold the rats did not increase daily feeding time sufficiently to maintain intake as pellet cost increased. Such an increase in feeding time would have required that less time be spent in one of the other activities.
Acclimatization↗
The role of central nervous system functioning and family functioning in behavioral problems of children with myelodysplasia.
This study examined the frequency and type of behavioral problems in 50 children with myelodysplasia and investigated the hypothesized roles of central nervous system (CNS) functioning and family functioning in behavioral problem outcome. The findings revealed that 50% of the children with myelodysplasia had a behavioral problem pattern and another 2% had low social skills, yielding an overall problem pattern rate of 52%. There was a high frequency of internalizing behavior problem profiles and a very low frequency of externalizing behavior problem profiles. Although there was little support for the hypothesized mediating role of central nervous system functioning, considerable support was provided for the association of family functioning and behavior problem outcomes.
Adolescent↗
Structural analysis of the calcium channel by photoaffinity labelling and limited proteolysis.
The L-type calcium channel of rabbit skeletal muscle triads, purified from digitonin extracts, was photolabelled with the dihydropyridine (+)[3H]PN 200-110. This photolabelled form was then subjected to limited proteolysis with papain and staphylococcus V-8 protease and analyzed by polyacrylamide gel electrophoresis. In the absence of proteolysis, the photolabelled channel was represented by a single protein with an apparent molecular weight of 160 kDa in the presence or absence of reducing agents. Following proteolysis, numerous photoadducts were observed with smaller molecular weights. The V-8 protease digestion pattern indicated that photoinsertion occurred in at least two distinct domains of 33 and 28 kDa. Papain digests were more extensive, generating smaller fragments of 28 and ca. 10 kDa. The results suggest that at least two distinct regions of the calcium channel interface at or near the dihydropyridine binding site, and that the binding site for these calcium antagonists resides within the channel proper, thereby modulating calcium influx.
Affinity Labels↗
Changes in macronutrient selection as a function of dietary tryptophan.
It has been hypothesized that the serotonergic system is involved in the regulation of carbohydrate and/or protein intake. Tests of this hypothesis using added dietary tryptophan and diets varying in the ratio of carbohydrate/protein resulted in depressed intakes of high carbohydrate/low protein diets, elevated intakes of low carbohydrate/high protein diets, and a reduction of total caloric intake. The present studies gave rats increased options for adjusting to added tryptophan by providing them with separate sources of protein, carbohydrate, and fat. The results showed the expected decrease in carbohydrate intake, but also increases in fat intake and, to a lesser extent, protein intake. Total caloric intake was conserved. Hypothalamic concentrations of serotonin and 5-hydroxyindole acetic acid indicated increased activity of the serotonergic system. These results lend support to serotonin's involvement in nutrient selection, in that carbohydrate consumption decreased in response to tryptophan loading, but indicate that other nutrients may also be affected. Given the option of altering fat intake, the animals maintained a constant caloric intake despite the reduction of carbohydrate consumption.
Animals↗