A Pan-Canadian Framework for Cancer Survivorship Research

Background and context: Across all cancer types, two-thirds of Canadians diagnosed with cancer today will survive long-term, reflecting great progress in cancer detection and treatment. Many survivors, however, will experience substantial and long-term impacts of their diagnosis and treatment. Within this context, the Canadian Cancer Research Alliance (CCRA) sought to inform the cancer research funding community on how, and what kinds of research are needed, to enable research that will make a difference to patients as they move from treatment to the posttreatment phase. Aim: To develop and implement a national framework and recommendations to enable coordinated and strategic action among cancer research funders that advances cancer survivorship research in Canada in ways that improve survivors' care and experiences. Strategy/Tactics: Multiple approaches were used to inform framework development: a strategic literature review; an analysis of cancer survivorship research funding from 2005-13; and an online survey and key informant interviews from the broader stakeholder community. An Expert Panel and Patient Advisory Committee were also engaged to provide guidance and feedback. Program/Policy process: Over the course of one year, the project team and a working group of CCRA members met regularly to steer framework development. This involved activities such as developing data collection approaches and tools, reviewing data and emerging findings, and translating findings into priority areas and recommendations. In total, > 200 Canadian and international stakeholders provided input through the survey and interviews. Outcomes: Released March 2017, the Pan-Canadian Framework for Cancer Survivorship Research provides four recommendations for cancer research funders: 1) ensure ongoing and meaningful involvement of cancer survivors; 2) align funding calls with existing needs and potential for impact; 3) create opportunities for the translation of research into practice and policy; and 4) build and maintain infrastructure and expertise to advance research. Specific research priorities were emphasized across three research domains: survivors' experiences and outcomes; late and long-term effects; and models of care. The priorities ranged from investigating the mechanisms of late/long-term effects to conducting intervention research to improve psychosocial outcomes, prevent and ameliorate late effects, and improve integration of follow-up care. What was learned: A broad range of stakeholders came together to develop a national framework to maximize the impact of shared targeted research investment in cancer survivorship research. Survivors' voices were key to agreeing on definitional issues of survivorship, identifying priority research areas, and ultimately lending credibility to the resulting framework. Implementation of the framework is the next step of work for CCRA members. Planning has commenced on identifying an initial priority for joint action.

The Taq IA and Ser311 Cys polymorphisms in the dopamine D2 receptor gene and obesity

Dopamine D2 receptors (DRD2) in the central nervous system are involved in the regulation of feeding. It remains to be elucidated if mutations in the DRD2 gene contribute to the development of obesity. The aim of the present study was to investigate whether the Taq IA and Ser311Cys polymorphisms in the DRD2 gene are associated with obesity in Nauruan and Australian subjects. Subjects were selected based on extremes of the body mass index (BMI) distribution. Two groups of Australian women were selected. The leanest group had a mean BMI of 22.5 kg/m2 (range: 20.3-24.3) and the heaviest group had a mean of 36.1 kg/m2 (32.5-44.1). Four groups of Nauruan subjects were selected. Leanest men had a mean BMI of 33.0 kg/m2 (28.4-36.9), heaviest men had a mean of 52.8 kg/m2 (46.5-69.2), leanest women had a mean of 34.8 kg/m2 (28.2-41.8) and heaviest women had a mean of 55.1 kg/m2 (49.3-73.8). Subjects were genotyped for the Taq IA and Ser311Cys polymorphisms using polymerase chain reaction (PCR) restriction fragment length polymorphism analysis and allelic discrimination Taqman PCR respectively. Leanest and heaviest groups were examined for differences in genotype frequency. Taq IA and Ser311Cys genotype frequencies did not differ significantly between leanest and heaviest Nauruan groups, or between leanest and heaviest Australians. Haplotype frequencies of these polymorphisms did not differ between leanest and heaviest groups. The Taq IA and Ser311Cys polymorphisms in the DRD2 gene are unlikely to be common causes of obesity in these populations.

Calpain 3 gene expression in skeletal muscle is associated with body fat content and measures of insulin resistance

OBJECTIVE

To investigate whether skeletal muscle gene expression of calpain 3 is related to obesity and insulin resistance.

DESIGN

Cross-sectional studies in 27 non-diabetic human subjects and in Psammomys obesus, a polygenic animal model of obesity and type 2 diabetes.

MEASUREMENTS

Expression of CAPN3 in skeletal muscle was measured using Taqman fluorogenic PCR. In the human subjects, body composition was assessed by DEXA and insulin sensitivity was measured by euglycemic-hyperinsulinemic clamp. In Psammomys obesus, body composition was determined by carcass analysis, and substrate oxidation rates, physical activity and energy expenditure were measured by whole-body indirect calorimetry.

RESULTS

In human subjects, calpain 3 gene expression was negatively correlated with total (P = 0.022) and central abdominal fat mass (P = 0.034), and with blood glucose concentration in non-obese subjects (P = 0.017). In Psammomys obesus, calpain 3 gene expression was negatively correlated with circulating glucose (P = 0.013) and insulin (P = 0.034), and with body fat mass (P = 0.049). Indirect calorimetry revealed associations between calpain 3 gene expression and carbohydrate oxidation (P = 0.009) and energy expenditure (P = 0.013).

CONCLUSION/INTERPRETATION

Lower levels of expression of calpain 3 in skeletal muscle were associated with reduced carbohydrate oxidation and elevated circulating glucose and insulin concentrations, and also with increased body fat and in particular abdominal fat. Therefore, reduced expression of calpain 3 in both humans and Psammomys obesus was associated with phenotypes related to obesity and insulin resistance.

Taste, intake rate, and food choice in rats

The contribution of taste to the food choices of foraging rats was examined. Rats in a laboratory foraging paradigm searched for sequential opportunities to eat at two feeders containing chow-based food pellets that were plain or flavored with saccharin or citric acid. Pellets cost the same number of bar presses at both feeders. Saccharin adulteration had no effect on intake parameters. Citric-acid-flavored pellets were eaten more slowly and in smaller meals. If there was no alternative food, daily intake was slightly reduced. When the alternative food was plain, fewer meals and fewer pellets were taken of the citric-acid-flavored than plain pellets. When we gradually increased the price of the plain pellets at one feeder, while the price at the alternative feeder (which contained either plain or citric-acid-flavored pellets) remained low, the rate of eating (profitability) decreased at the higher-price feeder, and the rats shifted their intake toward the less-costly, more profitable pellets. We compared the relationship between the relative eating rate at each feeder and the relative meal size (or daily intake) at each feeder when the low-priced food was plain and when it was flavored with citric acid, and found no differences. This indicates that taste may influence choice via its effect on rate of intake.

Sucrose intake as a function of its cost and the cost of chow

The avid consumption of pure carbohydrate solutions, which often results in a distortion of nutrient balance, is generally presumed to be driven by their taste. In the first of two experiments, we examined the effect of consumption cost on rats' intake of three concentrations of sucrose solution (8%, 16%, and 32%) when a nutritionally complete chow was concurrently freely available. In the second experiment, we examined the intake of 24% sucrose solution and chow as the consumption costs of both were varied. Increasing the cost of sucrose resulted in a reduction in the percent calories taken from sucrose; the steepness of the decline in intake with price was inversely related to the sucrose concentration and to the cost of chow. Chow calories were substituted for relatively expensive sucrose calories. An increase in the cost of chow resulted in a reduction in the percent of calories taken from chow and a protein-poor diet. The cost of sucrose did not affect the slope of the chow intake curve, presumably because, despite its sweet taste, sucrose was not a substitute for the protein, fat, and micronutrients in chow. Total caloric intake was conserved in all cases.Thus, the avid consumption of sucrose solution is curtailed when it is costly; but the degree of change in intake with cost depends on the cost of an alternative food. These results suggest that diet selection involves a comparison not only of the taste and post-ingestive consequences of available foods, but also of the cost of calories and nutrients in the foods. Selection appears to be guided first by caloric requirements and the relative cost of calories, then by nutrient requirements and the relative cost of nutrients, and finally by taste.

Effects of exercise on GLUT-4 and glycogenin gene expression in human skeletal muscle

To investigate the effect of exercise on GLUT-4, hexokinase, and glycogenin gene expression in human skeletal muscle, 10 untrained subjects (6 women and 4 men, 21.4 +/- 1.2 yr, 66.3 +/- 5.0 kg, peak oxygen consumption = 2.30 +/- 0.19 l/min) exercised for 60 min on a cycle ergometer at a power output requiring 73 +/- 4% peak oxygen consumption. Muscle samples were obtained by needle biopsy before, immediately after, and 3 h after exercise. Gene expression was quantified, relative to 29S ribosomal protein cDNA, by RT-PCR. GLUT-4 gene expression was increased immediately after exercise (1.7 +/- 0.4 vs. 0.9 +/- 0.3 arbitrary units; P < 0.05) and remained significantly higher than baseline 3 h after the end of exercise (2. 2 +/- 0.4 vs. 0.9 +/- 0.3 arbitrary units; P < 0.05). Hexokinase II gene expression was significantly higher than the resting value 3 h after the end of exercise (2.9 +/- 0.4 vs. 1.3 +/- 0.3 arbitrary units; P < 0.05). Exercise increased glycogenin mRNA more than twofold (2.8 +/- 0.6 vs. 1.2 +/- 0.2 arbitrary units; P < 0.05) 3 h after the end of exercise. For the first time, we report that a single bout of exercise is sufficient to cause upregulation of GLUT-4 and glycogenin gene expression in human skeletal muscle. Whether these increases, together with the associated increase in hexokinase II gene expression, lead to increased expression of these key proteins in skeletal muscle and contribute to the enhanced skeletal muscle glucose uptake, glycogen synthesis, and insulin action observed following exercise remains to be determined.

Clinical efficacy of metformin against insulin resistance parameters: sinking the iceberg

It has been increasingly recognised in recent years that type 2 (non-insulin-dependent) diabetes is part of a cluster of cardiovascular risk factors known as the metabolic syndrome, but also endorsed with such names as the deadly quartet, syndrome X and the insulin resistance syndrome. Atherosclerosis is the most common complication of type 2 diabetes among Europeans, and coronary artery, cerebrovascular and peripheral vascular disease are 2 to 5 times more common in people with this condition than in those without diabetes. These observations indicate that the treatment of type 2 diabetes requires agents that do more than simply lower blood glucose levels, and a therapy with both antihyperglycaemic effects and beneficial effects on dyslipidaemia, hypertension, obesity, hyperinsulinaemia and insulin resistance is likely to be most useful. In this respect, metformin has an important and established role: this drug has been shown to lower blood glucose and triglyceride levels, and to assist with weight reduction and to reduce hyperinsulinaemia and insulin resistance. Studies in the Israeli sand rat, Psammomys obesus, have indicated hyperinsulinaemia/insulin resistance to be the initial and underlying metabolic disorder in obesity and type 2 diabetes. Thus, the well established effect of metformin in reducing insulin resistance makes this drug an excellent candidate for the prevention of progression of impaired glucose tolerance to type 2 diabetes, and for the reduction of mortality associated with cardiovascular disease.

The relation between meal size and the time between meals: effects of cage complexity and food cost

Certain popular models of the regulation of food intake predict a positive correlation between the size of a meal and the preceding and/or following intermeal interval. However, the reported strength of these prandial correlations has varied widely in the literature. To determine what factors may influence the strength of these relationships, we measured the timing of and amount consumed in meals of laboratory rats as a function of 1) whether they were housed in isolation or with partial access to peers or a running wheel, 2) whether they were disturbed daily or weekly for maintenance procedures, and 3) whether food was free or contingent on operant responding. We also compared two definitions of "meal" and "intermeal interval." Strong prandial correlations were found only occasionally. Caging, food cost, and maintenance frequency did not affect the size of the correlations, although these factors did influence the rats' meal patterns. We conclude the regulation of food intake cannot be explained by models relying on a regular relationship between meal size and intermeal interval.

Prey size and prey density affect meal patterns of rats in depleting and nondepleting patches

We examined meal-ending decisions by rats feeding in depleting patches (where the rate of return decreased during a meal) and nondepleting patches (where the rate of return was constant) in a closed-economy, laboratory setting that allowed the precise measurement of feeding rates and meal patterns. The rats were free living in an environment where costs were imposed with bar-press requirements for (1) travelling to a patch to begin a meal and (2) earning prey during the ensuing meal in that patch. The prey in each patch were large or small, and dense or sparse. In both depleting and nondepleting patches, meals were larger as travel price increased. In nondepleting patches, meal size (in grams) was unaffected by the rate of return within the patch, but in depleting patches, meals were larger where the rate of return was higher. In depleting patches, the rats ate the same number of small and large prey per meal, suggesting that meals end when the rate of return reaches some level relative to a comparison value; however, the end-of-meal rate was lower than the average rate (calculated over foraging and feeding time), and thus meals were too large to maximize rate or minimize cost. No obvious rule of thumb explained meal size in both depleting and nondepleting patches. Copyright 1999 The Association for the Study of Animal Behaviour.

Behavioral strategies in the cold: effects of feeding and nesting costs

Animals can meet energetic challenges by acquiring or conserving energy. In the present experiment, we pitted these strategies against each other by housing rats in a cold environment and requiring them to bar press for food pellets and for access to a heated nest. Our question was how rats would exploit these resources to meet the added energetic demand of the cold when food was abundant or scarce. Results showed that rats' allocation of time and effort between competing activities was a function of demand. Feeding and nesting were partially substitutable in the cold: rats traded food for warmth and vice versa, economizing on both time and energy by adjusting their feeding and nesting patterns. Depending upon food abundance and the cost of nesting, rats acquired calories from food, conserved calories by nesting, and borrowed calories from the defense of body weight.

Neural mechanisms in human obesity-related hypertension

OBJECTIVE

Two hypotheses concerning mechanisms of weight gain and of blood pressure elevation in obesity were tested. The first hypothesis is that in human obesity sympathetic nervous system underactivity is present, as a metabolic basis for the obesity. The second hypothesis, attributable to Landsberg, is that sympathetic nervous activation occurs with chronic overeating, elevating blood pressure. These are not mutually exclusive hypotheses, since obesity is a heterogeneous disorder.

DESIGN AND METHODS

Whole body and regional sympathetic nervous system activity, in the kidneys and heart, was measured at rest using noradrenaline isotope dilution methodology in a total of 86 research voluteers in four different subject groups, in lean and in obese people who either did, or did not, have high blood pressure.

RESULTS

In the lean hypertensive patients, noradrenaline spillover for the whole body, and from the heart and kidneys was substantially higher than in the healthy lean volunteers. In normotensive obesity, the whole body noradrenaline spillover rate was normal, mean renal noradrenaline spillover was elevated (twice normal), and cardiac noradrenaline spillover reduced by approximately 50%. In obesity-related hypertension, there was elevation of renal noradrenaline spillover, comparable to that present in normotensive obese individuals but not accompanied by suppression of cardiac noradrenaline spillover, which was more than double that of normotensive obese individuals (P<0.05), and 25% higher than in healthy volunteers. There was a parallel elevation of heart rate in hypertensive obese individuals.

CONCLUSIONS

The sympathetic underactivity hypothesis of obesity causation now looks untenable, as based on measures of noradrenaline spillover, sympathetic nervous system activity was normal for the whole body and increased for the kidneys; the low sympathetic activity in the heart would have only a trifling impact on total energy balance. The increase in renal sympathetic activity in obesity may possibly be a necessary cause for the development of hypertension in obese individuals, although clearly not a sufficient cause, being present in both normotensive and hypertensive obese individuals. The discriminating feature of obesity-related hypertension was an absence of the suppression of the cardiac sympathetic outflow seen in normotensive obese individuals. Sympathetic nervous changes in obesity-related hypertension conformed rather closely to those expected from the Landsberg hypothesis.

Leptin is released from the human brain: influence of adiposity and gender

Leptin, a 16-kDa circulating protein primarily derived from adipocytes, is an important factor in the regulation of appetite and energy expenditure. Using simultaneous arterio-venous blood sampling, several organs were assessed with regard to their individual roles in leptin metabolism in healthy male and female subjects constituting a range of body mass indices. Plasma leptin levels were unchanged after passage through the hepatosplanchnic and forearm circulations. In contrast, concentrations in the renal vein were consistently lower than those in the renal artery (-15%; P<0.005), indicating net extraction, whereas the brain was observed to be a net leptin releaser. Concentrations in the internal jugular vein were significantly higher than arterial levels in lean females (change, 3.0+/-1.2 ng/mL; P<0.02) and in obese males (body mass index, >28 kg/m2), but not lean (change, 2.3+/-2.3 vs. 0.1+/-0.1 ng/mL, respectively; P<0.05), indicating a probable influence of both gender and adiposity on brain leptin release. An attempt to grossly localize the site of brain release by using cerebral venous scans to distinguish between jugular venous drainage from cortical and subcortical brain areas revealed no region-specific secretion. These data raise the possibility that the brain is a nonadipose source of leptin. In addition, the higher level of brain release observed in females may contribute to the well documented gender differences in overall plasma leptin levels.

Is fasting leptin associated with insulin resistance among nondiabetic individuals? The Miami Community Health Study

OBJECTIVE

Whether serum leptin levels are associated with insulin resistance independent of the effects of hyperinsulinemia and adiposity is an important unanswered question. We examined the relationship between the rate of insulin-mediated glucose uptake and serum leptin concentrations among nondiabetic men and women.

RESEARCH DESIGN AND METHODS

A cross-sectional analysis was performed among 49 young to middle-aged men and women who participated in the Miami Community Health Study. All participants had measures of insulin resistance (euglycemic-hyperinsulinemic clamp), postchallenge insulin levels, fasting serum leptin levels, and several measures of adiposity.

RESULTS

The rate of insulin-mediated glucose uptake (M in milligrams per kilogram per minute) was significantly associated with leptin concentrations in both men (r = -0.83; P < 0.001) and women (r = -0.59; P < 0.001). M was also inversely related to percent body fat and to the 2-h insulin area under the curve (AUC). After covariate adjustment for sex, percent body fat, and AUC, leptin remained a significant correlate of M (P = 0.04).

CONCLUSIONS

Cross-sectionally, leptin was significantly associated with insulin resistance in this nondiabetic sample of men and women. There may be a different physiological mechanism to explain the leptin/insulin resistance association apart from the insulin/adiposity link. Confirmatory evidence awaits the results of clinical trials.

Cigarette smoking, alcohol use, and physical activity in relation to serum leptin levels in a multiethnic population: The Miami Community Health Study

PURPOSE

To examine the correlates of plasma leptin, including fasting insulin, adiposity, and several health habits and behaviors among a nondiabetic multiethnic population.

METHODS

A cross-sectional study was conducted among 25-44 year old African-Americans (n = 126), Cuban-Americans (n = 107), and non-Hispanic whites (n = 189) randomly selected from Dade County Florida. Fasting leptin levels were correlated with fasting insulin, percent body fat, smoking, alcohol use, and physical activity within each sex. Multiple linear regression and analysis of covariance were used to estimate the independent determinants of plasma leptin concentration separately among men and women.

RESULTS

Stepwise linear regression analyses revealed statistically significant associations of leptin with percent body fat, fasting insulin, cigarette smoking, and physical activity (both inversely) among men (p < 0.05 for each). Among women, percent body fat, fasting insulin (both positively), cigarette smoking, and alcohol use (inversely) were independent predictors of leptin levels explaining over 70% of the variance. Analyses of covariance revealed that women had higher adjusted mean leptin levels than men (13.1 ng/ml vs. 5.9 ng/ml; p < 0.001), whereas no separate effect of ethnicity was noted.

CONCLUSIONS

Although adiposity was the strongest correlate of leptin levels, fasting insulin and several health habits and behaviors were independently associated with leptin. After adjustment for these factors, women had significantly higher mean leptin levels than men. The independent association among leptin and insulin levels is intriguing and suggests additional avenues for epidemiologic research.

Arterial compliance, blood pressure, plasma leptin, and plasma lipids in women are improved with weight reduction equally with a meat-based diet and a plant-based diet

Obesity, strongly associated with the risk for coronary heart disease (CHD), is becoming increasingly prevalent. This study was designed to establish first whether systemic arterial compliance (SAC), an index of arterial function, is improved with weight loss and second, whether cardiovascular risk factors that improve with weight loss are reduced equally with lean meat or with an equivalent amount of plant protein in the diet. Thirty-six women, mostly overweight or obese, aged 40+/-9 years, were allocated nonrandomly to a 16-week parallel-design trial of two equienergetic diets designed to lead to weight loss, with one arm of the study emphasizing red meat and the other soybeans as the major protein source. Body weight, waist and hip circumference, and plasma lipids, glucose, insulin, and leptin levels were measured, and SAC was calculated from ultrasound measurement of aortic flow velocity and aortic root driving pressure. Subjects lost weight (9% of body weight in 16 weeks) and showed decreased plasma total and low-density lipoprotein (LDL) cholesterol (12% and 14%, P < .0001, respectively), triacylglycerol (17%, P < .05), and leptin (24%, P < .01) concentrations. However, lipoprotein(a) [Lp(a)] levels did not change significantly. Mean arterial pressure (MAP) decreased 7% and SAC increased 28% (P < .001 for both). However, only the decrease in arterial pressure correlated significantly with the reduction in the waist to hip ratio (WHR), and the improvement in SAC correlated inversely with the blood pressure reduction (P < .001 for both). Further, weight loss and the metabolic benefits of weight loss occurred equally with the meat-based and plant-based diets. We conclude that moderate weight loss in women leads to a substantial reduction in the cardiovascular risk, including SAC.

Examination of the self-selected fluid intake practices by junior athletes during a simulated duathlon event

Thirty-two elite junior athletes in two age categories, older than or equal to 15 years old (O15) (8 females and 9 males) and less than 15 years old (U15) (8 females and 7 males), performed a laboratory-based duathlon (run-ride-run). At the completion of the event, significant body mass losses were recorded for all groups. Compared with the other three groups, the O15 males lost body mass at a greater absolute rate (1.26 +/- 0.06 kg.hr-1 vs. a mean of 0.62 +/- 0.11 kg.hr-1 for the other three groups) and a greater relative rate (1.95 +/- 0.10%BM.hr-1 vs. a mean of 1.23 +/- 0.19%BM.hr-1 for the other three groups) (p < .05). No differences were observed between groups for fluid consumption. Subjects consumed more fluid (p < .05) during the cycle phase and postevent than preevent or during the run phases. Results indicated that the athletes' fluid intake practices were insufficient to maintain adequate hydration during the simulated event.

Patch choice as a function of procurement cost and encounter rate

The effects of patch encounter rate on patch choice and meal patterns were studied in rats foraging in a laboratory environment offering two patch types that were encountered sequentially and randomly. The cost of procuring access to one patch was greater than the other. Patches were either encountered equally often or the high-cost patch was encountered more frequently. As expected, rats exploited the low-cost patch on almost 100% of encounters and exploited the high-cost patch on a percentage of encounters that was inversely proportional to its cost. Meal size was the same at both patches. Surprisingly, when low-cost patches were rare, the rats did not increase their use of high-cost patches. This resulted in spending more time and energy searching for patches and a higher average cost per meal. The rats responded to this increased cost by reducing the frequency and increasing the size of meals at both patches and thereby limited total daily foraging cost and conserved total intake.

Behavioral thermoregulation in chicks: the best nest

The ability of prehomeothermic chicks to thermoregulate behaviorally was studied in chicks with continuous access to heated nests, running wheels, and separate sources of high and low protein. In Experiment 1, cold-reared groups with heated or unheated transparent nests ate the same amount and selected the same dietary fractions, but chicks with heated nests ran less and grew faster. Despite this, groups maintained normal body temperatures. In Experiment 2, chicks were cold- or warm-reared with heated or unheated painted nests, or no nests. Cold-reared chicks with heated nests spent most of their time in them. They selected diets containing a higher protein:carbohydrate ratio than cold-reared chicks with unheated nests but ate less, thereby consuming less absolute protein and growing more slowly. Despite differences in growth, intake, and dietary choice, all chicks maintained normal body temperatures. These data reveal that behavioral thermoregulation has a privileged status for chicks over the first 3 weeks of life. Prehomeothermic chicks exercise complex and effective solutions to energetic challenges when offered behavioral options that simulate those available in nature.

Who is in charge? Animal vs experimenter control

In the 1920s Curt Richter (1927) stated that the central problem for psychology was to discover the determinants of the initiation and termination of bouts of behavior. Ignoring this challenge, experimentation in animal psychology has been dominated by the session paradigm in which animals work in brief sessions for a resource of which they have been deprived. In this open economy, no behavioral strategy of the animal can meet its demand, and the beginnings and ends of bouts are controlled by the experimenter; thus, Richter's problem cannot be addressed. In contrast, in a free-feeding, closed economy, the animal controls the initiation and termination of feeding and can regulate its intake, and bout patterns can be observed. If the paradigm is modified to simulate a habitat where resources are distributed discontinuously and the animal must work to discover and procure access to a commodity before it can be used, behavioral strategies allowing the animal to regulate its intake while tending to maximize the ratio of benefits to costs are revealed. We offer an answer to Richter's question based on a cost/benefit analysis of feeding behavior in this foraging paradigm. We show that the time and energy costs of resource acquisition and resource consumption are powerful determinants of the pattern of resource use, and that they have different and independent effects. The former costs are reduced by reducing the frequency of initiating bouts, and the latter costs, by altering the rate and amount of consumption. Further, the time window of these relations is much longer than expected from analyses in the session paradigm. We conclude that the recurrent nature of behavior is due to the discontinuous distribution of resources rather than to cycles of physiological depletion and repletion, and that the determinants of bout initiation and termination lie in the economics of the allocation of time and effort to different resources and activities.

Acute and chronic effects of exercise on leptin levels in humans

The acute (single bout of exercise) and chronic (exercise training) effects of exercise on plasma leptin were investigated in 97 sedentary adult men (n = 51) and women (n = 46) participating in the HERITAGE Family Study. Exercise training consisted of a standardized 20-wk endurance training program performed in the laboratory on a computer-controlled cycle ergometer. Maximal oxygen uptake, body composition assessed by hydrostatic weighing, and fasting insulin level were also measured before and after training. Pre- and posttraining blood samples were obtained before and after completion of a maximal exercise test on the cycle ergometer. Exercise training resulted in significant changes in maximal oxygen uptake (increase in both genders) and body composition (reduction of fat mass in men and increase in fat-free mass in women). There were considerable interindividual differences in the leptin response to acute and chronic effects of exercise, some individuals showing either increase or reduction in leptin, others showing almost no change. On average, leptin levels were not acutely affected by exercise. After endurance training was completed, leptin levels decreased significantly in men (from 4.6 to 3.9 ng/ml; P = 0.004) but not in women. However, after the training-induced changes in body fat mass were accounted for, the effects of exercise training were no longer significant. Most of the variation observed in leptin levels after acute exercise or endurance training appears to be within the confidence intervals of the leptin assay. We conclude that there are no meaningful acute or chronic effects of exercise, independent of the amount of body fat, on leptin levels in humans.

Meal patterns of cats encountering variable food procurement cost

The meal patterns of 2 cats in a laboratory habitat with variable foraging costs were examined in a foraging paradigm in which subjects could initiate meals at any time by completing a predetermined number of bar presses (the procurement price) and then could eat any amount. From meal to meal, the procurement price either was fixed or varied among a geometric series of five prices. As the fixed price or the mean of the variable prices increased, meal frequency decreased and meal size increased; daily intake was unaffected. Within variable-price schedules, meal size was not related to the just-paid procurement price. These results suggest that cats respond to the global rather than to the local cost structure of their habitat. They appear to respond to an average of the prices encountered, initiating meals of a frequency and size appropriate to that average. This was true even when the average price was high, meals were infrequent, and thus price encounters were widely separated in time. Therefore, the time window over which the consequences of behavior can affect behavior is longer than often conceived, at least in economies in which the animal controls its intake and the frequency, size, and distribution of its meals.

Serum leptin concentration, obesity, and insulin resistance in Western Samoans: cross sectional study

OBJECTIVE

To measure serum leptin concentrations in the Polynesian population of Western Samoa and to examine epidemiological associations of leptin with anthropometric, demographic, behavioural, and metabolic factors in this population with a high prevalence of obesity and non-insulin dependent diabetes mellitus.

DESIGN

Cross sectional study, leptin concentration being measured in a subgroup of a population based sample.

SUBJECTS

240 Polynesian men and women aged 28-74 years were selected to cover the full range of age, body mass index, and glucose tolerance.

MAIN OUTCOME MEASUREMENTS

Serum leptin, insulin, and glucose concentrations; anthropometric measures; physical activity; and area of residence.

RESULTS

Leptin concentrations were correlated with body mass index (r = 0.80 in men, 0.79 in women) and waist circumference (r = 0.82 in men, 0.78 in women) but less so with waist to hip ratio. At any body mass index, leptin concentration was higher in women than men (geometric mean adjusted for body mass index 15.3 v 3.6 pg/l, P < 0.001). Leptin concentration also correlated with fasting insulin concentration (r = 0.63 in men, 0.64 in women) and insulin concentration 2 hours after a glucose load (r = 0.58 in men, 0.52 in women). These associations remained significant after controlling for body mass index; effects of physical activity and of rural or urban living on leptin concentration were eliminated after adjusting for obesity, except values remained high in urban men. 78% of variance in leptin was explained by a model including fasting insulin concentration, sex, body mass index, and a body mass index by sex interaction term. Similar results were obtained if waist circumference replaced body mass index.

CONCLUSIONS

The strong relation of leptin with obesity is consistent with leptin production being proportional of mass to adipose tissue. The relation with insulin independent of body mass index suggests a possible role for leptin in insulin resistance or hyperinsulinaemia.

Learning and retention of conditioned aversions by freely feeding chicks

The present experiments assessed poison-based aversion learning and retention in freely feeding and drinking domestic chicks whose drinking water was colored blue and adulterated with LiCl for a 24-hr period. The amount of LiCl self-administered by 11-day-old chicks and their subsequent avoidance of unadulterated water of the same color was examined. The results of four experiments demonstrated that chicks self-administered large and often lethal doses of the LiCl solution. Chicks subsequently avoided blue water during two-bottle preference tests administered 3 to 7 days but not 14 days after exposure. These data indicate that neophobia alone is insufficient to prevent nondeprived chicks from ingesting large quantities of a toxin during their initial encounter with it. The lack of long-term retention in the present experiments indicates that naturally occurring aversions based on visual and illness cues, while effective in the short term, may not be a major factor in the choices made by freely feeding and drinking chicks over the long term.

Food and water intake as functions of resource consumption costs in a closed economy

In two experiments, rats living in a closed economy were offered continuous, concurrent access to four resources: food, water, a nest, and a running wheel. Costs of consuming food and water were imposed with bar-press requirements, and the price of either one or both resources was raised. As the consumption cost increased, less was consumed in each bout of resource use. Bout frequency increased, but not sufficiently to compensate for the fall in bout size, and total intake fell. Food and water tended to be complementary resources, in that as intake of one fell with its price, intake of the other also decreased. This interaction was accounted for by the defense of the ratio of body water to lean body mass. As amount consumed decreased, increases in feed efficiency (weight gain per unit of food ingested) and the use of stored calories compensated for the reduced energy intake. There was evidence of competition between feeding and drinking at the higher costs: When both commodities were expensive, the decline in the intake of each one was greater than when only one commodity was expensive. Although the time spent nesting, running, and in unmonitored activity was adjusted when feeding or drinking took more of the rat's day, there was no particular activity that was sacrificed.

Diet selection by chicks

Seven experiments with 324 chicks tested their ability to select a nutritionally adequate diet from separate sources of purified casein and various supplements, including gelatin (a source of two amino acids), a gelatin-creatine mixture (a source of three amino acids), and fiber (nonnutritive bulk). Nonselecting controls consumed the basal purified-casein diet or a supplemented purified-casein diet. Chicks in all selection conditions composed diets that yielded normal intake, normal body temperature, normal activity, and the maximum growth possible for their intake. They also selected components in the same percentages as in premixed diets. In all instances, their selection was nonrandom and regulated. What chicks included in their diet depended on what else was available. Although the specific percentage taken from each dietary component varied across different selection alternatives, these differences affected neither intake nor growth. Selection, per se, incurred a caloric cost. Chicks selecting from fractions of a corn-and-soy diet offset this cost by increasing intake compensatorily, but chicks with a purified-casein fraction did not, suggesting that some unspecified property of casein placed a ceiling on its intake. These findings unequivocally demonstrate that immature chicks not only can self-select nutritionally adequate diets, but can do so with unexpected precision by exploiting different but equally successful strategies.

Feeding patterns of rats when food-access cost is alternately low and high

Rats living in a laboratory foraging paradigm began each meal by bar pressing to procure access to food and then could eat any amount. In different conditions the procurement price changed from low (10 bar presses) to high (200 or 400 bar presses) every ten days, five days, or one day, or on schedules of one-day-low/two-days-high, or one-day-low/four-days-high. In a final condition, the price alternated at every meal. Meals were less frequent and larger on high-price days. In the ten- and five-day alternations, the rats adjusted meal frequency on the first day of a price, but changed meal size gradually over the first few days; by the fifth day, daily intake was not different on low- and high-price days. In the one-day alternations, the rats ate less food, and in some cases did not eat at all, on high-price days, and lost weight. Intake was greater than normal, and body weight recovered, on low-price days. This pattern saved foraging cost at the expense of greater-than-normal daily fluctuations in food intake and body weight. When two or four days of high price alternated with one day of low price, the rats did eat on the first day of high price, suggesting they may integrate costs over a time window greater than 24 h.

Drinking in a patchy environment: the effect of the price of water

Rats in a laboratory foraging paradigm searched for sequential opportunities to drink in two water patches that differed in the bar-press price of each "sip" (20 licks) of water within a bout of drinking (Experiment 1) or the price and size (10, 20, or 40 licks) of each sip (Experiment 2). Total daily water intake was not affected by these variables. The rats responded faster at the patch where water was more costly. However, they accepted fewer opportunities to drink, and thus had fewer drinking bouts, and drinking bouts were smaller at the more costly patch than at the other patch. This resulted in the rats consuming a smaller proportion of their daily water from the more costly patch. The size of the differences in bout frequency and size between the patches appears to be based on the relative cost of water at the patches. The profitability of each patch was calculated in terms of the return (in milliliters) on either effort (bar presses) or time spent there. Although both measures were correlated with the relative total intake, bout size, and acceptance of opportunities at each patch, the time-based profitability was the better predictor of these intake measures. The rats did not minimize bar-press output; however, their choice between the patches and their bout sizes within patches varied in a way that reduced costs compared to what would have been expended drinking randomly. These data accord well with similar findings for choices among patches of food, suggesting that foraging for water and food occurs on the basis of comparable benefit-cost functions: In each case, the amount consumed is related to the time spent consuming.

Surfactant replacement therapy in utero for prevention of hyaline membrane disease in the preterm baboon

OBJECTIVE

A previous study of intraamniotic administration of surfactant in preterm rabbit fetuses demonstrated that exogenous surfactant can be taken up into the lungs from amniotic fluid in quantities sufficient to alter pulmonary mechanical properties. On the basis of these findings we chose to test the hypothesis that intraamniotic administration of surfactant to the preterm baboon 24 hours before delivery will prevent the development of clinical and pathological aspects of hyaline membrane disease.

STUDY DESIGN

Characteristics of hyaline membrane disease in the preterm baboon model include atelectasis, the formation of hyaline membranes in the airways and distal air saccules, overexpansion of distal airways, and disruption of airways by barotrauma associated with neonatal intensive care practices. Nine preterm baboons were treated with either saline solution (n = 4) or surfactant (n = 5) by intraamniotic injection on 136 to 137 days' gestation. One day later fetuses were delivered by cesarean section and maintained for 24 hours with standard neonatal intensive care techniques.

RESULTS

All neonates completed the protocol, and surfactant-treated animals had better clinical courses as documented by Pao2/PAO2 (p < 0.05), FIO2 (p < 0.005), and Paco2 (p < 0.05). Significant radiographic differences (p < 0.02) were noted to be the result of surfactant treatment. No differences in ventilator pressures or neonatal cardiovascular parameters were found. Significant differences in pulmonary pathologic conditions (p < 0.01) were also found, but all animals had some degree of pathologic pulmonary changes associated with hyaline membrane disease.

CONCLUSION

Therefore a single treatment with surfactant in utero significantly improved the clinical course but did not completely prevent hyaline membrane disease in an established animal model.

Developmental consequences of diet and activity

The effect of a protein-deficient and a protein-surfeit diet and continuous access to an activity wheel on food intake, growth, and body temperatures of behaviorally thermoregulating White Leghorn chicks was assessed in two experiments. In Experiment 1, both imbalanced-protein diets depressed intake and growth and differentially affected activity relative to a control diet, but activity did not ameliorate the deleterious effect of a high-protein diet on growth. Diet groups with continuous access to a running wheel did not differ on any measure from corresponding inactive dietary control groups. In Experiment 2, these results were replicated in a lower ambient temperature, and an effect of diet on body temperature emerged. Diets that affected spontaneous activity or body temperature also affected death feigning, a predation defense behavior. The data from behaviorally thermoregulating chicks are consistent with previous findings that activity does not depress growth rate in animals who cannot convert a portion of their intake into adipose tissue.

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.

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.

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.

Behavioral thermoregulation and immobilization: conflicting demands for survival

In three studies, core temperatures of immature chicks rose during immobilization induced by simulated predation and fell rapidly when immobilization terminated. Immobilization termination was predicted by proximity of the core temperature to the daily resting core temperature of adult fowl. Although immobilization duration increased with age and was shorter in cold and hot environments, immobilization terminated at the same core temperature at all ages and ambient temperatures. The common termination temperature and pattern of temperature change across all Ss suggests that immobilization is terminated in response to the demand that the rising core temperature be behaviorally maintained within a vital range. The generality of this finding was confirmed in a fourth study with preweanling kittens during exhibition of the transport response--an immobilization reaction with a different evolutionary history. These findings reveal that when immobilization and behavioral thermoregulation present conflicting survival demands for avian and mammalian young, the control of core temperature assumes behavioral priority.

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.