The economics of food choice in chicks

Growing chicks offered diets containing either surfeit or inadequate protein in the day but adequate protein at night adopted a pattern of nocturnal feeding but did not eliminate diurnal meals. Their weight gain surpassed that of corresponding dietary controls who received continuous access to surfeit or inadequate protein but was less than that of chicks with continuous access to a standard diet. Chicks receiving the standard diet at night with no food available in the light phase also grew but did so at a slower rate than the diurnally feeding control group. The shift in feeding patterns was not accompanied by a shift in body temperature, nor was nocturnal antipredator behavior, characterized by sustained motoric inhibition, disrupted by nocturnal feeding. These data demonstrate that feeding specializations which have been selected over a species' evolutionary history are not rigidly fixed but can be modified by the economic relations in the current habitat.     

Susceptibility and Resistance to Leishmania amazonensis in H-2q Syngeneic High and Low Antibody Responder Mice (Biozzi Mice)

H-2 syngeneic H and L (Biozzi) mice provide a model to study Leishmania infections in which polar resistant and susceptible phenotypes are independent from H-2 differences. High-Ab-responder (H) and low-Ab-responder (L) mice syngeneic at the H-2 locus (H-2^q) were, respectively, susceptible and highly resistant to Leishmania amazonensis infection. L-mice resistance was associated with high IFN-γ and transient IL-4 production by lymph node (LN) cells, in contrast with sustained IL-4 and decreasing IFN-γ production by susceptible H mice. IL-12 production could be detected only in LN from resistant mice. The cytokine production pattern was consistent with preferential progression to a Th1-type response in resistant L-mice, and to a Th2-type response in susceptible H-mice. We also investigated whether this shift towards Th1- or Th2-type cytokine responses was dependent upon H or L antigen presenting cells' (APC) intrinsic ability to preferentially stimulate either T-cell subset. To this end, LN-derived T-cell lines were grown from 12-day infected mice, when both strains produced IFN-γ and IL-4. L-derived T-cell lines developed a Th2 cytokine pattern whereas H-derived T-cell lines produced IFN-γ, IL-4 and IL-10 whatever the APC origin (H or L) used for their derivation. This work constitutes the first characterization of cellular immune responses to the intracellular parasite, L. amazonensis in H-2 syngeneic mice, an infection model in which polar resistant and susceptible phenotypes are determined by non-MHC genes.     

Ecological determinants of reinforcement in the guinea pig

The hypothesis that constraints on the parameters of free feeding are the source of motivation in feeding behavior was explored in Guinea pigs. The effect of effort (FR size) on meal frequency, meal size and rate of eating was investigated when reinforcement consisted of an entire meal or a small portion of a meal. Frequency of feeding decreased and the duration and rate of eating increased when an entire meal was available. Frequency of meals was unaffected and rate of lever pressing and duration of meals increased when reinforcement consisted of a single food pellet. These data were taken to argue that there is a common pattern of changes in feeding behavior across species with respect to these variables and the value of these variables can be taken to describe the properties of different ecological niches.     

Group feeding behavior of brown trout is a correlated response to selection for growth shaped by the environment

Group feeding pattern is a response correlated to selection for growth in brown trout. Previous results suggest that the feeding pattern of two lines (NL and SY), selected with the same process at two different fishfarms, differ. This study addresses the following questions: (i) are the patterns differentially fixed by the selection process and if yes (ii) is this explained by the different genetic background of the lines? In a first experiment, we tested if the group feeding behavior can be inherited. We produced and reared under the same experimental conditions selected hybrids (NLS × SYS) and pure SY selected line (SYS). We compared their behavior on self-feeders when reared single or mixed (groups of 500 fish; mean initial BW = 6 g, 90-day period). Growth rates were comparable among the groups. In the lines reared single, NLS × SYS exhibited greater morning feeding activity than SYS. Feeding activity of SYS was higher later in the day. The inter-day variation of the morning peak was less variable for the hybrid than for the SYS line. In the mixed group, the pattern was intermediate between that of the hybrid and the pure line. In a second experiment we compared the feeding pattern of control hybrids (NLC × SYC) to pure control lines (SYC and NLC) reared single or mixed (groups of 500 fish; mean initial BW = 12 g, 92-day period). Feeding activity patterns were similar among the control groups. These results show that group feeding pattern is a heritable trait that can be indirectly selected with growth, which shape is less influenced by the growth performance and the genetic background than by the environmental conditions applied during the selection process.     

Chronic intracerebral cannula can affect feeding behavior in the rat

Intracerebral cannulae were placed in the lateral ventricle of rats. It was shown that the cannulae per se can affect feeding behavior. After recovery from surgery, rats displayed an unusual eating rate which consisted of very long, slow and large meals. This slow eating rate led to a modification of the circadian pattern; it induced a decrease in night-time and increase in day-time cumulative intakes. This phenomenon appeared when cannulae crossed the cortical motor area concerned with forelimb movements. Different stereotaxic coordinates had to be used in order to place cannulae in the lateral ventricle without disturbing the feeding pattern. This observation underlines the importance of recording feeding pattern before any surgery in any study of feeding behavior.     

DNA, RNA and total protein content of leg and breast muscles of White Rock chickens selected for 56-day body weight

Pectoralis and gastrocnemius muscles from White Rock chickens divergently selected for 29 generations for high or low 56-day body weight were analyzed for DNA, RNA and protein (mg/g) content at 12 ages between hatch and 273 days of age. Dimorphism between lines was maximum at day 18 for both muscle types and then declined with age. High-line chickens generally deposited relatively more muscle tissue than those from the low line. Although nonadditive genetic variation was evident for absolute muscle weights, it was more frequent for muscle weight relative to body weight. For both muscle types, DNA unit number, as measured by DNA content (mg/g), was larger for the high line than the low immediately after hatch and smaller in the high than in the low line from day 10 to 56 after which lines were similar. RNA and protein/g muscle were similar for both lines at most ages. Between days 4 and 56, a period of rapid muscle growth, DNA unit size (protein/DNA) of both muscle types was larger in the high than in the low line. Heterosis was positive for protein, DNA unit number and size, and negative for RNA content. While weight of pectoralis muscle was similar to that of one gastrocnemius muscle on day 1, by day 273 its weight was over 3-fold greater. DNA unit number was higher in pectoralis than gastrocnemius muscle from hatch to day 4, similar on days 7 and 10 and lower for pectoralis muscle beyond day 10. RNA content was similar at all ages except 4, 7 and 10 days. DNA unit size followed the same pattern as DNA unit number; however, greater nuclei number at hatch for the high line corresponded with low DNA unit size. This pattern suggests a higher rate of cellular filling for pectoralis than gastrocnemius muscle.     

Dynamics of relative growth rate in Japanese quail lines divergently selected for growth and their control

This study was undertaken to test the hypothesis that relative growth is the same in Japanese quail divergently selected for 4-week body weight for 30 generations, and their control. Relative growth rate is the increase in body weight per unit of body weight per unit of time, and it represents the efficiency of an animal as a producer of new body mass material. The maximum relative growth rate of the divergent and control lines were observed during the first week. Selection for high 4-week body weight has resulted in higher relative growth rate for the first two weeks compared to quail from the low line, but by week 3, quail from the low line had higher relative growth rate compared to quail from the high line. Asymptotic body weight increased by about 100 and 70%, respectively in the male and female high lines and declined by about 25% in the low lines. Absolute growth rate is thought to be related to the cumulative growth already achieved whereas relative growth rate is related to the amount of growth remaining. However, selection on absolute weight basis can elicit a response in relative growth rate in the early part of the developmental period which possibly pre-determines the asymptotic body weight. Since relative growth rate depends on the amount of growth remaining, the rate of decline in relative growth is then set accordingly. Furthermore, it is thought that different sets of genes may operate between the developmental period and maturation period.     

Effect of chronic caloric restriction on physiological variables related to energy metabolism in the male Fischer 344 rat

In the present study, a number of physiological and behavioral measures that are related to metabolism were continuously monitored in 19-month-old male Fischer 344 rats that were fed ad libitum or fed a caloric restricted diet. Caloric restricted rats ate fewer meals but consumed more food during each meal and spent more time eating per meal than did rats fed ad libitum. Therefore, the timing and duration of meals as well as the total number of calories consumed may be associated with life extension. Average body temperature per day was significantly lower in restricted rats but body temperature range per day and motor activity were higher in restricted rats. Dramatic changes in respiratory quotient, indicating rapid changes in metabolic pathway and lower temperature, occurred in caloric restricted rats when carbohydrate reserves were depleted. Lower body temperature and metabolism during this time interval may result in less DNA damage, thereby increasing the survival potential of restricted rats. Nighttime feeding was found to synchronize physiological performance between ad libitum and caloric restricted rats better than daytime feeding, thereby allowing investigators to distinguish the effects of caloric restriction from those related solely to the time-of-day of feeding.     

Is hyper-aggressiveness associated with physiological hypoarousal? A comparative study on mouse lines selected for high and low aggressiveness

Aggressiveness is often considered a life-long, persistent personality trait and is therefore expected to have a consistent neurobiological basis. Recent meta-analyses on physiological correlates of aggression and violence suggest that certain aggression-related psychopathologies are associated with low functioning of the hypothalamo-pituitary-adrenal (HPA) axis and autonomic nervous system (ANS). We tested this hypothesis in mice selected for high and low aggressiveness by measuring baseline plasma corticosterone levels and, via radiotelemetry, heart rate and core body temperature. The radiotelemetric recordings were made for 48 h under baseline undisturbed conditions and for 90 min after a handling stressor. Consistent with the hypoarousal hypothesis of violence, we found lower resting heart rates in two out of the three highly aggressive selection lines. In contrast, body temperature during the active phase, as another ANS-regulated physiological parameter, was higher in two out of three highly aggressive lines. The handling-induced tachycardiac and hyperthermic responses were similar across the six mouse lines except for the most docile and obese line, which showed a blunted reactivity. Besides significant differences between strains, no differences in plasma corticosterone levels were found between the high- and low-aggressive phenotypes. These results are discussed in relation to the different types of aggression (normal versus pathological) exhibited by the three highly aggressive lines. We conclude that while high trait-like aggressiveness is generally associated with a higher active phase core body temperature, only animals that express pathological forms of aggression are characterized by a low resting heart rate.     

Decreased sensitivity of Zucker obese rats to the putative satiety agent cholecystokinin

In obese rodents increased daily food intake leading to accumulation of adipose tissue is frequently accompanied by increased meal size and loss of the normal diurnal variations in feeding pattern. Increased meal size of obese rats may be due to decreased sensitivity to factors which elicit satiety. We compared Zucker obese and lean rat feeding behavior responses to octapeptide of cholecystokinin (OP-CCK), a peptide shown to decrease meal size in several species. Obese rats were less sensitive than lean rats to OP-CCK (.06, .25 and 1.0 μg/kg/meal) injected before each of four consecutive scheduled meals in the light portion of the diurnal cycle, when obese meal size was larger than lean. However, neither obese nor lean rats responded to injection of the same doses of OP-CCK during meals in the dark, when average meal size was larger than during the light and when average meal size of the obese rats was similar to that of lean rats. In both obese and lean rats injection of OP-CCK affected daily feeding pattern. Obese and lean Zucker rats are less sensitive to OP-CCK when meal size is larger, whether this is due to phase of the diurnal cycle (dark vs. light in both obese and lean rats) or phenotype (obese vs. lean rats in the light).     

Metabolic rate in female Culex tarsalis (Diptera: Culicidae): age, size, activity, and feeding effects

We used flow-through respirometry on female mosquitoes to observe individual ventilatory pattern and to measure metabolic rate at rest, during activity and after a blood-meal. At rest, young adult females of the species Culex tarsalis ventilated cyclically with an average VCO2 of 6.5 nl/min and frequency of 45 mHz. Both resting metabolic rate and body mass of females increased between emergence and 4 d, but only body mass continued to increase until 12 d. Mating status had no effect on the body mass or resting metabolic rate of the females. Both lipid and carbohydrate stores strongly increased during the first week of adult life, in particular between emergence and 4 d, in which lipid mass increased 8.3-fold and carbohydrate mass increased 3.6-fold. Hourly metabolic rate after a blood or sugar meal was measured over a 6-d period in two groups of 14 females. Sugar-fed mosquitoes remained calm during the day and had nocturnal increases in metabolic rate associated with flight activity. Blood feeding elicited a specific dynamic action lasting approximately 55 h, at the peak of which metabolic rate of the blood-fed females was twice that of the sugar-fed group. Eggs were laid on the third night. The increase in metabolic rate presumably reflected the cost of blood digestion and egg production. The females were not active during digestion, so that although their metabolic rate was increased, the overall energy expenditure of the blood-fed group was not very different from that of the sugar-fed group.     

Co-selection of the rare T cell receptor-γ B haplotype in mouse lines selected for low responsiveness to red blood cell antigens

Tcell receptor (TcR)-γ haplotype was investigated in seven pairs of murine Biozzi lines selected for low and high antibody (Ab) response to different antigens (Ag). High-responder lines (H) express γA or γC haplotypes irrespective of the selecting Ag. In contrast, the γB haplotype, which is rare in laboratory mouse strains, is found in all Iow-responder lines (L) to sheep erythrocyte Ag (SE). However, the TcR-γB locus might only have a low penetrance in the control of the SE response. Moreover, investigations using L_IVA mice, which were selected for low SE response from homozygous γA founder parents, indicate that the γB haplotype is neither necessary nor sufficient to achieve a low-responder phenotype. The γB haplotype might, thus, be co-selected to confer to L mice an improved resistance to bacterial infections mediated by γδ5 T cells compensating the profound and nonspecific immune perturbation associated with the low Ab response.     

Estrogen modification of feeding behavior in the female rat: influence of metabolic state

The effects of estrogen on feeding behavior and body weight regulation of adult ovariectomized rats were observed after 48 hr of food deprivation. The depletion of body nutrient stores caused by food deprivation resulted in an attenuation of the effects of estrogen treatment on food intake, eating time, meal size, meal duration and the number of meals. Nevertheless, estrogen treatment in fasted animals did shorten the interval between meals immediately after access to food was restored. Indices of the satiating effects of individual meals and the deprivation effects of intervals between meals were calculated for selected times. These indices also indicated an influence of estrogen even in the fasted condition. Estrogen diminished the satiety produced by the first meal after food access was restored, while the deprivation effects of the interval between the first and second meals were enhanced. During the dark period on the first day of refeeding, the satiating effects of food remained reduced in the fasted condition, and estrogen did not appear to further affect satiety compared to oil treatment, but estrogen did lower the deprivation effects of intermeal intervals compared to oil treatment. Estrogen treatment in non-fasted animals lowered both satiety and deprivation effects during the dark period. The varying influence of estrogen on the deprivation effects of intermeal intervals suggests that the influence of estrogen depends upon the long-term effects of an animal's metabolic state.     

Metabolic regulation in diving birds and mammals

Ducks, fur seals, Weddell seals and probably most cetaceans seem to be able to dive and remain aerobic for durations that are consistent with their elevated stores of usable oxygen and their metabolic rate while diving being similar to that when they are resting at the surface of the water. Ducks, in fact, have a high metabolic rate while diving, mainly because of their large positive buoyancy, but other species have relatively low buoyancy, are better streamlined and use lift-based rather than drag-based propulsion. However, species such as the larger penguins, grey seals and elephant seals seem to achieve the impossible by performing a substantial proportion of their dives for periods longer than would be expected on the above assumptions, and yet remaining aerobic. The logical conclusion is that during such dives these species reduce their metabolic rate below the resting level (hypometabolism) and, in some of them, there is a regional reduction in body temperature (hypothermia) which may contribute to the reduction in metabolic rate.     

Feeding patterns in pigs: The effects of amino acid deficiency

Records of feeding behaviour were collected from 10 pigs fed diets based on maize and meat and bone meal, with or without a supplement of L tryptophan. The pigs ate between 5 and 16 meals per day in a distinct diurnal pattern. The tryptophan deficient diet decreased total food intake and average meal size. The effect on the daily number of meals and average meal duration was smaller suggesting that the influence of the tryptophan deficiency was to reduce the rate of feeding.     

Effect of long-term caloric restriction on oxygen consumption and body temperature in two different strains of mice

The hypothesis, that a decrease in metabolic rate mediates the life span prolonging effect of caloric restriction (CR), was tested using two strains of mice, one of which, C57BL/6, exhibits life span extension as a result of CR, while the other, DBA/2, shows little or no effect. Comparisons of the rate of resting oxygen consumption and body temperature were made between the strains after they were fed ad libitum (AL) or maintained under 40% CR, from 4 to 16 months of age. Ad libitum-fed mice of the two strains weighed the same when young and consumed similar amounts of food throughout the experiment; however, the C57BL/6 mice weighed 25% more than DBA/2 mice at 15 months of age. The rate of oxygen consumption was normalized as per gram body weight, lean body mass or organ weight as well as per animal. The body temperature and the rate of oxygen consumption, expressed according to all of the four criteria, were decreased in the DBA/2 mice following CR. The C57BL/6 mice also showed a CR-related decrease in body temperature and in the rate of oxygen consumption per animal and when normalized according to lean body mass or organ weight. The results of this study indicate that CR indeed lowers the rate of metabolism; however, this effect by CR does not necessarily entail the prolongation of the life span of mice.     

Effects of 6‐meals‐a‐day feeding and 6‐meals‐a‐day feeding combined with adrenalectomy on daily gene expression rhythms in rat epididymal white adipose tissue

The master clock in the hypothalamic suprachiasmatic nucleus (SCN) is assumed to synchronize the tissue‐specific rhythms of the peripheral clocks with the environmental day/night changes via neural, humoral and/or behavioral connections. The feeding rhythm is considered an important Zeitgeber for peripheral clocks, as daytime feeding reverses (clock) gene rhythms in the periphery, but not in the SCN. In this study, we investigated the necessity of a daily feeding rhythm for maintaining gene expression rhythms in epididymal white adipose tissue (eWAT). We showed that 7 of 9 rhythmic metabolic/adipokine genes, but not clock genes, lost their rhythmicity upon exposure to 6‐meals‐a‐day feeding. Previously, we showed comparable effects of adrenalectomy on eWAT; therefore, subsequently we investigated the effect of simultaneous disruption of these humoral and behavioral signaling pathways, by exposing adrenalectomized animals to 6‐meals‐a‐day feeding. Interestingly, under these conditions, all the clock genes and 10 of 11 rhythmic metabolic/adipokine genes lost their rhythmicity. These data indicate that adrenal hormones and feeding rhythm are indispensable for maintaining daily rhythms in metabolic/adipokine gene, but not clock gene, expression in eWAT. In contrast, at least one of these two signals should be present in order for eWAT clock gene rhythms to be maintained.     

Response to 30 generations of selection for open-field activity in laboratory mice

High and low lines resulting from 30 generations of bidirectional selection for open-field activity have nonoverlapping distributions and more than a thirtyfold difference in mean activity. Open-field defecation scores of lowactive lines are approximately 7 times higher than those of high-active lines, substantiating earlier reports of a large, negative genetic correlation between these characters. Since the selection experiment is replicated, other variables which are found to be reliably different among the high, control, and low lines are likely to be causally related to open-field activity; thus these selected lines of mice may be of use to other investigators.This investigation was supported in part by NIMH Training Grant MH-11167.     

Influence of early dietary experience on energy regulation in rats

The environmental mechanisms that have contributed to the rapid increases in overweight and obesity in the US over the past 25-30 years have yet to be fully specified. One hypothesis that has been forwarded is that increased consumption of calories in liquid form may be a contributing factor, since some studies support the idea that caloric compensation is less adequate for liquid calories compared to calories delivered in more solid form. Work from our laboratory using rats has examined the role that differences in diet viscosity may play in altering energy intake and body weight regulation. This work has suggested that when offered diets matched on caloric density, macronutrient and micronutrient composition, and differing only in viscosity, adult rats fail to compensate for calories delivered in low-viscosity form in short-term intake tests. Further, long-term consumption of low-viscosity diets leads to enhanced weight gain in adult rats. In the present studies, we examined whether short- or long-term exposure to varying relationships between viscosity and calories led to altered food intake or body weight regulation in juvenile rats. The results demonstrated that animals given either short- or long-term experience with direct relationships between viscosity and calories (high viscosity, high calorie meals and low viscosity, low calorie meals) did not differ in food intake or body weight gain compared to animals given short- or long-term experience with indirect relationships between viscosity and calories (high viscosity, low calorie meals and low viscosity, high calorie meals). When juvenile rats were given long-term (9 weeks) exposure to a single, high or low viscosity diet supplement, matched on caloric density and differing only in viscosity, there were no effects on body weight gain. However, analysis of body composition using DEXA demonstrated that animals consuming the low viscosity supplements had significantly greater body fat than animals that consumed either the high viscosity supplement or no dietary supplement at all. These differences in body fat persisted for at least 3 months following the cessation of dietary supplements; during this 3-month period, animals previously exposed to the low viscosity supplement also gained significantly more weight than animals previously exposed to the high viscosity supplement. Taken together, the results suggest that consuming calories in low viscosity form may contribute to poor intake regulation over the short-term and to increased adiposity over the long term. When animals experience these diets as juveniles, these effects may persist into adulthood.     

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.