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Biomedical subjects

D F Johnson

Publications and source records attributed to D F Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1990

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↗
PubMed1990

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↗
PubMed1990

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↗
PubMed1989

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↗
PubMed1989

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↗
PubMed1989

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↗
PubMed1988

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↗
PubMed1988

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↗
PubMed1988

Biosynthetic relationships between three rat apolipoprotein B peptides.

Rat liver is unique in secreting very low density lipoproteins (VLDL) with three size-isoforms of apolipoprotein B: PI and PIII correspond to B-100 and B-48, respectively, while PII is slightly smaller than PI and has no counterpart in other species. Antibodies against a fusion protein corresponding to the extreme C-terminal region of PI fail to react with PII, suggesting that the latter lacks this moiety. [35S]Methionine-labeled perfused rat liver and isolated hepatocytes secrete labeled PII, but intracellular apoB contains only PI and PIII. The absence of labeled PII from Golgi VLDL, and the absence of continued PII production within the plasma compartment, strongly suggest that PIII-containing VLDL are formed by a one-time proteolytic processing of a certain proportion of PI-containing VLDL at the time of secretion. In contrast, polysome run-off translation experiments and analysis of polysome-bound nascent apoB chains show that both rat liver and intestinal polysomes release PIII-sized peptides directly at the appropriate point of elongation, in a manner incompatible with their formation by posttranslational processing. These results strongly suggest that the large (PI, B-100) and small (PIII, B-48) apoB peptides are translated from separate mRNAs. Thus, although both PII and PIII are C-terminally truncated products of PI, the mechanisms involved are entirely different.

Amino Acid Sequence↗
PubMed1987

Photoaffinity labeling of the calcium channel antagonist receptor in the heart of the cardiomyopathic hamster.

The high affinity 1,4-dihydropyridine receptors of the cardiac membrane calcium channel from Syrian Cardiomyopathic hamsters were studied using [3H] PN200-110 and [3H]azidopine as ligands. [3H]Azidopine was photoincorporated covalently into bands of 180, 100, 79, 45 and 31 kDa, as determined by SDS/polyacrylamide gel electrophoresis. Photolabeling of the 180 kDa band is protected by 2 microM [1H]PN200-110 whereas the lower Mr bands are not. Thus, only the 180 kDa band is the calcium channel linked 1,4 dihydropyridine receptor. The photoincorporation into this 180 kDa band is doubled with samples of myopathic hamsters vs. control hamsters. It is suggested that the increase in calcium channel receptors may be involved in the pathogenesis of this cardiomyopathy.

Affinity Labels↗
PubMed1987

Metastatic basal cell carcinoma in acquired immunodeficiency syndrome-related complex.

Basal cell carcinoma is a common neoplasm that rarely metastasizes. Metastatic basal cell carcinoma has been associated with a deficiency of cellular immunity. Patients with acquired immunodeficiency syndrome, at greater risk for specific neoplasms, may be at greater risk for basal cell carcinoma and subsequent metastasis. We report a case of metastatic basal cell carcinoma in a patient with acquired immunodeficiency syndrome-related complex.

AIDS-Related Complex↗
PubMed1987

Caloric regulation and patterns of food choice in a patchy environment: the value and cost of alternative foods.

Rats in a laboratory foraging paradigm had 24-hr-per-day access to a feeder where they could search, by completing a fixed number of bar presses, for an opportunity to eat one of a pair of foods differing in caloric density (2.5, 3, 3.5, or 4 kcal/g) and, in Experiment 2, the price of food pellets (10 to 50 bar presses per pellet). The rats could either accept the opportunity, and eat a meal, or reject it in favor of further search. Daily caloric intake was relatively constant. The rats always included both foods in their diet, but, for any particular food, the degree of inclusion in the diet and of acceptance of meal opportunities, the meal size, and the rate of eating were all functions not only of the price and caloric value of that food but also of the price and value of the alternately-available food. The patterns of intake for one food relative to those for the other available food were strongly correlated with the relative rate of calorie intake during consumption of that food compared to the other. Although the rats appeared to be sensitive to the local rates of calorie flow, they did not maximize daily calories consumed per time spent feeding.

Animal Husbandry↗
PubMed1987

Influence of postnatal rearing conditions on the response of squirrel monkey infants to brief perturbations in mother-infant relationships.

This study was designed to determine the behavioral and pituitary-adrenal responses of squirrel monkey mother-infant dyads reared under different housing conditions to either 1- or 6-hr separations. Dyads were reared either in an individual cage or in social groups of 3 mother-infant dyads. The two separation conditions consisted of removing either the mother or the infant to a novel test cage while the other member remained in the home cage. Group-reared infants displayed lower levels of plasma cortisol, movement, and vocalization when they remained in the home cage during separation compared to their responses in the novel cage. However, individually-reared infants displayed high cortisol and activity levels in both separation environments, and vocalization levels were higher at 1 hr in the home cage than in the novel cage. These results indicate that familiarity with the separation environment, per se, does not attenuate the behavioral or physiological responses of infants, but that familiar conspecifics, even in the absence of alloparenting, can benefit an infant during separation from its mother. Two additional test conditions assessed the responses of mother-infant dyads when they were only momentarily separated and then immediately reunited in either the home cage or a novel cage. Reunion in the home cage evoked no cortisol or behavioral responses, but reunion in a novel cage resulted in significant elevations in infant cortisol levels and time in contact with the mother. The corticoid response of the mothers differed from their infants during separations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Husbandry↗
PubMed1986

Changes in rats' meal patterns as a function of the caloric density of the diet.

Rats in a laboratory foraging paradigm were offered each of four diets which differed in caloric density, and intakes, meal frequencies, meal sizes, and eating rates were monitored. The rats maintained a constant daily caloric intake by eating more frequent, larger meals of the lower density foods. However, caloric meal size was not regulated, and significant correlations between meal size and the length of the post-meal interval were rarely found. The 24-hour pattern of calorie intake was the same regardless of diet. Higher-calorie foods were consumed at a faster rate within meals than were lower-calorie foods. The feeding patterns observed suggest that caloric intake may be regulated over a time frame of several meals rather than on a meal-to-meal basis.

Adaptation, Physiological↗
PubMed1986

The economics of the law of effect.

A corollary of the law of effect predicts that the larger the reinforcement, the greater the rate of responding. However, an animal must eat more small portions than large portions to obtain the same daily intake, and one would predict, therefore, that when eating smaller portions an efficient animal would eat less (conserving time and energy) and/or respond faster (conserving time). The latter of these predictions was supported by the present experiments with free-feeding rats for which portion size (pellet size or duration of feeder presentation) and portion price within meals were varied. Response rate was a function of the unit price (responses/g) of food: Rats responded faster when portions were smaller or when prices were higher. Meal size and frequency were relatively unaffected by unit price, but were influenced by the price of meal initiation. The results are discussed in relation to the economic differences between traditional operant and free-feeding paradigms and to both traditional and more recent formulations of the law of effect.

Animals↗
PubMed1985

Human apolipoprotein B: identification of cDNA clones and characterization of mRNA.

Apolipoprotein B (apoB) is a major protein component of low density and very low density lipoproteins. Because of its large size and heterogeneity, molecular studies of apoB have been difficult, and its structure and regulation remain poorly understood. We now report the identification of human apoB cDNA clones by antibody screening of hepatoma libraries in the expression vector lambda gt11. Both oligo(dT) primed and random primed libraries were constructed and screened with polyclonal antibodies to intact apoB, as well as with antibodies raised against a synthetic peptide based on the limited amino acid sequence available for apoB. The identity of the clones was unambiguously established by comparisons of the cloned cDNA sequences with apoB amino acid sequences. The clones hybridize to an exceptionally large 20 kb mRNA that is present in liver and intestine but not other tissues examined, consistent with the distribution expected from protein biosynthetic studies. The properties of the mRNA have implications for the biogenesis of the multiple apoB molecular weight forms secreted by liver and intestine.

Apolipoproteins B↗
PubMed1985

Adenomatoid tumor of ejaculatory duct.

Adenomatoid tumors are generally restricted to the epididymal region and occasionally the spermatic cord in the male. Herein we report on a case of adenomatoid tumor apparently originating from the ejaculatory duct which to our knowledge has not been reported previously.

Aged↗