Mild Food Deprivation Research Articles

Expression Level Changes in Serotonin Transporter are Associated with Food Deprivation in the Pond Snail Lymnaea stagnalis.

In the pond snail Lymnaea stagnalis, serotonin (5-HT) plays an important role in feeding behavior and its associated learning (e.g., conditioned taste aversion: CTA). The 5-HT content in the central nervous system (CNS) fluctuates with changes in the nutritional status, but it is also expected to be influenced by changes in the serotonin transporter (SERT) expression level. In the present study, we identified SERT in Lymnaea and observed its localization in 5-HTergic neurons, including the cerebral giant cells (CGCs) in the cerebral ganglia and the pedal A cluster neurons and right and left pedal dorsal 1 neurons in the pedal ganglia by in situ hybridization. Real-time PCR revealed that the SERT mRNA expression level was lower under severe food deprivation than under mild food deprivation in the whole CNS as well as in a single CGC. These results inversely correlated with previous data that the 5-HT content in the CNS was higher in the severely food-deprived state than in the mildly food-deprived state. Furthermore, in single CGCs, we observed that the 5-HT level was significantly increased in the severely food-deprived state compared with the mildly food-deprived state. Our present findings suggest that changes in the SERT expression level associated with food deprivation may affect 5-HT signaling, probably contributing to learning and memory mechanisms in Lymnaea.

Rats chirp with their mouth full: During an experimental meal, adult male Wistar rats emitted flat ultrasonic vocalisations upon feeding.

Rats produce ultrasonic vocalisation (USVs) that are classified into different types, based on their average frequency. In pups 40 kHz USVs are produced upon social isolation, and in adults USVs can be associated with affective states and specific behavioural patterns (i.e., appetitive 50 kHz vocalisations of frequency range 30-100 kHz, or aversive 20 kHz vocalisations of frequency range 18-30 kHz). Generally, USVs of frequency around 50 kHz are linked to activation of brain reward pathways, during anticipation or experience of rewarding stimuli. Previous studies have described several subtypes of 50 kHz USVs, according to their acoustic properties. We asked whether USV production might be relevant to feeding behaviour. We recorded USVs from 14-week old adult rats during the satisfaction of a physiological need: refeeding following mild food deprivation (17 h overnight fast). We analysed a 10 min consummatory phase, preceded by a 10 min anticipatory phase, as a control for the experimental meal. Following identification of USV subtypes, we applied frequentist and Bayesian (Monte Carlo shuffling) statistical analyses to investigate the relationship between USV emission and rat behaviour. We found that it was not total USV quantity that varied in response to food consumption, but the subtype of USV produced. Most importantly we found that rats who feed tend to produce flat USVs of a frequency around 40 kHz. Beyond the previous reports of circumstantial association feeding-flat USVs, our observation directly correlate vocalisation and ingestive behaviour. Our study highlights that, in addition to quantification of the production rate, study of USV subtypes might inform us further on rat consummatory behaviour. Since this vocalisation behaviour can have a communicative purpose, those findings also illustrate nutrition studies might benefit from considering the possible social dimension of feeding behaviour.

Associations between Early-Life Food Deprivation and Risk of Frailty of Middle-Age and Elderly People: Evidence from the China Health and Retirement Longitudinal Study

Background: The association between childhood food deprivation (FD) and health in later life has been extensively studied; however, studies on the association between childhood food deprivation and frailty are scarce. This study assessed the associations between childhood FD and the risk of frailty at middle-age and old age. Methods: Three waves of the China Health and Retirement Longitudinal Study (CHARLS), including 11,615 individuals aged over 45 years, were used for this research. Frailty was operationalized according to the FRAIL scale as a sum of fatigue, resistance, ambulation, illness, and the loss of weight. Childhood FD experiences and levels were measured by self-reported FD and historical content. Logistic mixed-effects models and proportional odds ordered logistic regression models were used to analyse the association between childhood FD and frailty. Findings: Childhood FD increased the odds of frailty at old age (1.30, 95% CI: 1.26–1.36). Compared with subjects with mild FD, those with extreme FD experiences had increased risks of frailty (1.34, 95% CI: 1.26–1.43). Subjects exposed to hunger at different ages all had an increased risk of frailty, and subjects who had FD during ages 6–12 (1.15, 95% CI: 1.09–1.22) were more likely to have an increased risk of frailty than those who had experienced FD in younger ages. The interaction of experience of FD at ages 0–6 and the experience of FD at ages 6–12 is not statistically significant after adjusting all covariates. Conclusions: Our findings suggest that childhood FD exerts long-lasting effects on frailty among older adults in China. The prevention of childhood FD may delay or even avert the emergence of frailty in people of middle-age and old age.

Enhanced consumption of salient solutions following pedunculopontine tegmental lesions

Rats with lesions of the pedunculopontine tegmental nucleus (PPTg) reliably overconsume high concentration sucrose solution. This effect is thought to be indicative of response-perseveration or loss of behavioral control in conditions of high excitement. While these theories have anatomical and behavioral support, they have never been explicitly tested. Here, we used a contact lickometer to examine the microstructure of drinking behavior to gain insight into the behavioral changes during overconsumption. Rats received either excitotoxic (ibotenic acid) damage to all PPTg neuronal subpopulations or selective depletion of the cholinergic neuronal sub-population (diphtheria toxin–urotensin II (Dtx–UII) lesions). We offered rats a variety of pleasant, neutral and aversive tastants to assess the generalizability and specificity of the overconsumption effect. Ibotenic-lesioned rats consumed significantly more 20% sucrose than sham controls, and did so through licking significantly more times. However, the behavioral microstructure during overconsumption was unaffected by the lesion and showed no indications of response-perseveration. Furthermore, the overconsumption effect did not generalize to highly consumed saccharin. In contrast, while only consuming small amounts of quinine solution, ibotenic-lesioned rats had significantly more licks and bursts for this tastant. Selective depletion of cholinergic PPTg neurons had no effect on consumption of any tastant. We then assessed whether it is the salience of the solution which determines overconsumption by ibotenic-lesioned rats. While maintained on free-food, ibotenic-lesioned rats had normal consumption of sucrose and hypertonic saline. After mild food deprivation ibotenic PPTg-lesioned rats overconsumed 20% sucrose. Subsequently, after dietary-induced sodium deficiency, lesioned rats consumed significantly more saline than controls. These results establish that it is the salience of the solution which is the determining factor leading to overconsumption following excitotoxic PPTg lesion. They also find no support for response-perseveration contributing to this effect. Results are discussed in terms of altered dopamine (DA) and salience signaling.

Central injection of relaxin-3 receptor (RXFP3) antagonist peptides reduces motivated food seeking and consumption in C57BL/6J mice

Behavioural arousal in mammals is regulated by various interacting central monoamine- and peptide-neurotransmitter/receptor systems, which function to maintain awake, alert and active states required for performance of goal-directed activities essential for survival, including food seeking. Existing anatomical and functional evidence suggests the highly-conserved neuropeptide, relaxin-3, which signals via its cognate Gi/o-protein coupled receptor, RXFP3, contributes to behavioural arousal and feeding behaviour in rodents. In studies to investigate this possibility further, adult male C57BL/6J mice were treated with the selective RXFP3 antagonist peptides, R3(B1-22)R/I5(A) and R3(B1-22)R, and motivated food seeking and consumption was assessed as a reflective output of behavioural arousal. Compared to vehicle treatment, intracerebroventricular (icv) injection of RXFP3 antagonists reduced: (i) food anticipatory activity before meal time during food restriction; (ii) consumption of highly palatable food; (iii) consumption of regular chow during the initial dark phase, and; (iv) consumption of regular chow after mild (∼4-h) food deprivation. Effects were not due to sedation and appeared to be specifically mediated via antagonism of relaxin-3/RXFP3 signalling, as RXFP3 antagonist treatment did not alter locomotor activity in wild-type mice or reduce palatable food intake in relaxin-3 deficient (knock-out) mice. Notably, in contrast to similar studies in the rat, icv injection of RXFP3 agonists and infusion into the paraventricular hypothalamic nucleus did not increase food consumption in mice, suggesting species differences in relaxin-3/RXFP3-related signalling networks. Together, our data provide evidence that endogenous relaxin-3/RXFP3 signalling promotes motivated food seeking and consumption, and in light of the established biological and translational importance of other arousal systems, relaxin-3/RXFP3 networks warrant further experimental investigation.

Effect of combined naltrexone and bupropion therapy on the brain’s reactivity to food cues

Objective:The significant weight loss observed with combination naltrexone-sustained release (SR) 32 mg and bupropion SR 360 mg (NB32) therapy is thought to be due, in part, to bupropion stimulation of hypothalamic pro-opiomelanocortin (POMC) neurons, and naltrexone blockade of opioid receptor-mediated POMC autoinhibition, but the neurobiological mechanisms are not fully understood. We assessed changes in brain reactivity to food cues before and after NB32 treatment.Methods:Forty women (31.1±8.1 years; body mass index: 32.5±3.9) received 4 weeks of NB32 or placebo, and were instructed to maintain their dietary and exercise habits. Functional magnetic resonance imaging responses (analyzed using SPM2 and clusters (>100 pixels)) to a 5-min food video (preparation of the subject's favorite food) and a 5-min neutral video (manipulation of neutral objects) under conditions of mild food deprivation (∼14 h) were assessed before and after treatment.Results:The food cues video induced positive brain activation in visual and prefrontal cortices, insula and subcortical brain regions. The group-by-treatment interaction on regional brain activation was significant and showed that whereas NB32 attenuated the activation in the hypothalamus in response to food cues (P<0.01), it enhanced activation in regions involved in inhibitory control (anterior cingulate), internal awareness (superior frontal, insula, superior parietal) and memory (hippocampal) regions (whole-brain analysis; P<0.05).Conclusions:Blunting the hypothalamic reactivity to food cues while enhancing the activation of regions involved with self-control and internal awareness by NB32 might underlie its therapeutic benefits in obesity.

Fasting Launches CRTC to Facilitate Long-Term Memory Formation in Drosophila

Canonical aversive long-term memory (LTM) formation in Drosophila requires multiple spaced trainings, whereas appetitive LTM can be formed after a single training. Appetitive LTM requires fasting prior to training, which increases motivation for food intake. However, we found that fasting facilitated LTM formation in general; aversive LTM formation also occurred after single-cycle training when mild fasting was applied before training. Both fasting-dependent LTM (fLTM) and spaced training-dependent LTM (spLTM) required protein synthesis and cyclic adenosine monophosphate response element-binding protein (CREB) activity. However, spLTM required CREB activity in two neural populations--mushroom body and DAL neurons--whereas fLTM required CREB activity only in mushroom body neurons. fLTM uses the CREB coactivator CRTC, whereas spLTM uses the coactivator CBP. Thus, flies use distinct LTM machinery depending on their hunger state.

To Favor Survival Under Food Shortage, the Brain Disables Costly Memory

The brain regulates energy homeostasis in the organism. Under resource shortage, the brain takes priority over peripheral organs for energy supply. But can the brain also down-regulate its own consumption to favor survival? We show that the brain of Drosophila specifically disables the costly formation of aversive long-term memory (LTM) upon starvation, a physiological state required for appetitive LTM formation. At the neural circuit level, the slow oscillations normally triggered in two pairs of dopaminergic neurons to enable aversive LTM formation were abolished in starved flies. Transient artificial activation of these neurons during training restored LTM formation in starved flies but at the price of a reduced survival. LTM formation is thus subject to adaptive plasticity that helps survival under food shortage.

The effects of intermittent food-deprivation on growth, digestive enzyme activities and serum biochemical indices in the rice-field eel(Monopterus albus)

The experiment was carried out to investigate the effects of intermittent food-deprivation on growth,digestive enzyme activities and some serum biochemical indices in the rice-field eel,Monopterus albus.A 64-day growth trial with five feeding regimes was conducted using the live tubificid worms(Limnodrilus hoffmeisteri)as the food at(25±1)℃.Groups of fish were deprived of food for 1,2,4,8 day(s)and then followed by satiation re-feeding for the corresponding day(s),respectively(i.e.S1F1,S2F2,S4F4 and S8F8 groups).The fish fed to satiation daily throughout the experiment served as the control group(i.e.C).The results showed that,deprived fish had significantly lower specific growth rates(SGR),relative weight gains and final body weights,but significantly higher actual feeding rates,than that of the control fish(P0.05).Moreover,the fish in S1F1 group had significantly higher feed conversion efficiency(FCE)than those of any other groups(P0.05).It indicated that the partial growth compensation was elicited by various extents of intermittent food-deprivation,and that the fish of S1F1 group showed the best growth compensation.The protease activity of stomach in the S1F1 group was significantly higher than that in the S2F2 group(P0.05),and the protease activities of stomach in both of the two groups were significantly higher than those in other groups(P0.05).There was no difference in amylase activities of liver,stomach,foregut and hindgut among fish in all groups(P0.05).In the liver and hindgut,the S1F1 group had significantly higher lipase activities than other groups of the control,the S4F4 or the S8F8(P0.05).In all groups of the deprived fish,the serum total protein contents and glucose contents were slightly higher and lower than that in the control group,respectively,however,there was no significant difference among the five treatments(P0.05).There was no significant difference in serum total cholesterol level between the control group and S1F1 group(P0.05),and the serum total cholesterol levels in these two groups were significantly higher than that of any other group(P0.05).In contrast,among the groups of S2F2,S4F4 or S8F8,the serum total cholesterol level gradually descended with the more serious intermittent food-deprivation.These results suggested that the growth compensation in the rice-field eel could be achieved partially through the enhancement of the activities of some of digestive enzymes,food utilization efficiency,and the physiological adaptability of digestion,and the desirable growth compensation could be elicited through mild intermittent food-deprivation that incorporates one-day of feed-deprivation with one-day of re-feeding.

Meal parameters and vagal gastrointestinal afferents in mice that experienced early postnatal overnutrition

Early postnatal overnutrition results in a predisposition to develop obesity due in part to hypothalamic and sympathetic dysfunction. Potential involvement of another major regulatory system component — the vagus nerve — has not been examined. Moreover, feeding disturbances have rarely been investigated prior to development of obesity when confounds due to obesity are minimized. To examine these issues, litters were culled on the day of birth to create small litters (SL; overnutrition), or normal size litters (NL; normal nutrition). Body weight, fat pad weight, meal patterns, and vagal sensory duodenal innervation were compared between SL and NL adult mice prior to development of obesity. Meal patterns were studied 18 h/day for 3 weeks using a balanced diet. Then vagal mechanoreceptors were labeled using anterograde transport of wheatgerm agglutinin–horseradish peroxidase injected into the nodose ganglion and their density and morphology were examined. Between postnatal day 1 and weaning, body weight of SL mice was greater than for NL mice. By young adulthood it was similar in both groups, whereas SL fat pad weight was greater in males, suggesting postnatal overnutrition produced a predisposition to obesity. SL mice exhibited increased food intake, decreased satiety ratio, and increased first meal rate (following mild food deprivation) compared to NL mice, suggesting postnatal overnutrition disrupted satiety. The density and structure of intestinal IGLEs appeared similar in SL and NL mice. Thus, although a vagal role cannot be excluded, our meal parameter and anatomical findings provided no evidence for significant postnatal overnutrition effects on vagal gastrointestinal afferents.

Fine-tuned modulation of competitive behaviour according to kinship in barn swallow nestlings

Kin selection theory predicts that, in species where progeny members compete for limiting parental care, individual offspring should be more prone to monopolize parental resources as their genetic relatedness to brood competitors decreases. Mixed parentage among broodmates may arise as a consequence, for example, of extra-pair fertilization or brood parasitism events. In this experimental study of barn swallows (Hirundo rustica), we reciprocally partially cross-fostered hatchlings between broods and compared the behaviour of pairs of related and unrelated broodmates in a competitive context, both under normal food provisioning regime and after mild food deprivation. We found that scramble competition for food mediated by visual and vocal solicitation displays (begging) is inversely related to relatedness among competitors, independent of their level of satiation. Nestlings may modulate their competitive behaviour according to vocal cues that vary with their origin and allow kin recognition. We also uncover direct fitness costs to both parents and offspring arising from mixed parentage in a brood, in terms of increased parental workload and reduced survival of the nestlings. Such previously neglected costs may select for reduced frequency of extra-pair fertilizations and brood parasitism in species with extensive parental care.

Oral THC produces minimal behavioral alterations in preadolescent rats

Although the oral route has traditionally been used for THC administration during the perinatal period in the rat, most studies administering THC during the postnatal period utilize intraperitoneal (ip) administration. In an effort to utilize the same route of administration in both prenatal and postnatal studies, we administered Δ-9-tetrahydrocannabinol (THC) in sesame oil by gavage during postnatal days 22–40 (equivalent to childhood to early adolescence) to male and female rats. We quantified behavior 40 min after administration in the Accuscan activity monitor on days 22, 29 and 40. In addition, we examined active and passive avoidance behaviors in treated adults. Acutely, THC had subtle effects on activity when measured during the period of drug administration and minimal effects on avoidance behaviors examined up to 140 days of age. Since several groups have found that lower doses of THC administered intraperitoneally to periadolescent rats do produce behavioral alterations, we suspect that the inordinately slow absorption of the drug via the oral route may be responsible for the paucity of significant findings in our study. Therefore, oral administration of THC, particularly under conditions of mild food deprivation, may lead to sub-psychoactive concentrations of the drug within the brain.

Age-associated sex differences in response to food deprivation in two animal tests of anxiety

The effects of mild food deprivation (7 days of food restricted to once daily feeding to maintain body weights at 85% of free-feeding weights) were examined in adult male and female and adolescent female rats tested in the elevated plus maze and social interaction tests of anxiety. In adult male rats, food deprivation appeared to have an anxiolytic effect in the plus-maze as it significantly increased the percentage of entries onto open arms and the percentage of time spent on the open arms, without changing the number of closed arm entries. There were no effects of food deprivation in adult females, although in adolescent females food deprivation significantly increased the percentage of open arm entries rats. Adolescent female rats have female brains, but do not have circulating gonadal hormones and thus these results suggest that circulating female gonadal hormones are able to suppress some of the effects of mild food deprivation in the plus-maze. In the social interaction test, there were no effects of food deprivation in any group on the time spent in social interaction. There were opposite effects on locomotor activity in the adult male and female rats, with deprivation increasing activity in males and decreasing it in females. There were no effects of food deprivation on locomotor activity in the adolescent females, suggesting that circulating gonadal hormones were responsible for the bidirectional effects in the adult rats. In both tests there were age-associated differences in the female rats, with the adolescent females being less anxious (higher percentage of open arm entries and increased social interaction) than the adults.

Effects of mild food deprivation on the estrous cycle of rats

It has long been known that severe food deprivation disrupts the estrous cycle. One of the main problems with behavioral tasks that use food for reinforcement is the requirement that the animal be food deprived. This manipulation could be problematic in studies using female animals, since it may interfere with the estrous cycle of the animals. The purpose of the present study was to investigate: (1) the effect of mild food deprivation on four different strains of rats, (2) factors in the food deprivation procedure that could affect the estrous cycle, and (3) the possible effect of enriched diets during food deprivation on the estrous cycle. A comparison of the estrous cycle in four different rat strains revealed differences in the reliability of the estrous cycle even before the onset of food deprivation. Fischer, Long–Evans, and Sprague–Dawley rats all showed reliable cycle patterns. This was not the case for Brown Norway rats. During food deprivation, the cycle of the Fischer rats was disrupted, whereas the Long–Evans and Sprague–Dawley animals continued to cycle. Both the rate of weight loss and the percent of ad libitum body weight were related to cessation of the estrous cycle. However, enriching an animal's diet with sugar or oil additives delayed the disruption of the estrous cycle. Additionally, animals resumed cycling when returned to ad libitum weight levels. The present findings suggest that when animals need to be food deprived, preference should be given to using Long–Evans or Sprague–Dawley rats. If Fischer rats must be used, they should not be deprived below 90–95% of their ad libitum body weight. Strategies for future food deprivation studies are discussed, as well as a comparison of the effects of mild and severe food deprivation.

The Effects of Experimentally Elevated Testosterone and Food Deprivation on Food Consumption and Prey Size Preferences in Male Dark‐Eyed Juncos (Junco hyemalis, Emberizidae: Passeriformes)

Numerous studies have shown that the experimental elevation of circulating levels of testosterone reduces parental behaviour in male birds, particularly the provisioning of young. The mechanisms responsible for this change in behaviour are not fully understood. In this study, we examine the effects of elevated testosterone on food consumption and prey selection, both of which have potential consequences for nestling provisioning behaviour. We manipulated testosterone and performed two experiments on a captive, non‐breeding population of male dark‐eyed juncos (Junco hyemalis) on long day‐lengths. In the first experiment, we subjected juncos to 3 h of food deprivation and compared food consumption and prey size selection by males with elevated testosterone (testosterone males) to that of control males. Testosterone males consumed more food than control males and showed a preference for larger prey. In a second experiment in which small prey were more abundant than large prey, food consumption and prey size preferences did not differ between testosterone and control males. We also manipulated the duration of food deprivation in the second experiment. Males of both treatments consumed more small prey under conditions of mild (1 h) or moderate (5 h) food deprivation and consumed more large prey under conditions of intermediate (3 h) food deprivation. We discuss our results and the effects that testosterone has on self‐maintenance behaviour and male parental effort.

Behavioral effects of long-term administration of an anabolic steroid in intact and castrated male Wistar rats

Once a week, intact and castrated male Wistar rats were intramuscularly injected with a 0.2 ml suspension of either 0, 10, or 50 mg nandrolone decanoate in cottonseed oil, for 8 consecutive weeks. After the sixth injection, locomotor activity was measured in an open-field and the acquisition of lever press behavior was assessed in an autoshaping procedure. Subsequently, all subjects were exposed to four sessions of continuous reinforcement prior to one session in which the effects of steroid administration on extinction were assessed. Locomotor activity decreased for all groups of rats with continued exposure to the open-field, differences between groups were not observed. Rats treated with the highest dose of nandrolone decanoate spent more time in the margin of the open-field. There were no significant differences between groups on any of the learning measures. Long-term, high-dose steroid administration in conjunction with mild food deprivation inhibited growth in intact and castrated rats, while low dose administration affected body weight in intact rats only. Steroid administration resulted in heavier and enlarge kidneys and lighter testes as well. These results suggest that the administration of anabolic steroids not only produces observable physiological changes, but that it may also affect spontaneous behavior. The failure to find differences in learning indices may have been a function of the particular paradigms used in the present experiment.

Evidence for neuropeptide Y mediation of eating produced by food deprivation and for a variant of the Y 1 receptor mediating this peptide's effect

Neuropeptide Y (NPY) elicits eating when injected directly into the paraventricular nucleus (PVN) or perifornical hypothalamus (PFH). To identify the essential regions of the NPY molecule and the relative contributions of Y 1 and Y 2 receptors, the eating stimulatory potency of NPY was compared to that of its fragments, analogues, and agonists when injected into the PVN or PFH of satiated rats. Additionally, antisera to NPY was injected into the cerebral ventricles (ICV) to determine whether passive immunization suppresses the eating produced by mild food deprivation. Tests with NPY fragments revealed that NPY(2–36) was surprisingly potent, nearly three times more so than intact NPY. In contrast, fragments with further N- terminal deletions were progressively less effective or ineffective, as was the free acid form of NPY. Collectively, this suggests that both N- and C- terminal regions of NPY participate in the stimulation of eating. Tests with agonists revealed that the putative Y 1 agonist [Pro 34]NPY elicited a strong dose-dependent feeding response, while the putative Y 2 agonist, C2-NPY, had only a small effect at the highest doses. Although this suggests mediation by Y 1 receptors, the uncharacteristically high potency of NPY(2–36) may additionally suggest that the receptor subtype underlying feeding is distinct from that mediating other responses. Additional results revealed that ICV injection of antisera to NPY, which should inactivate endogenous NPY, produced a concentration-dependent suppression of eating induced by mild food deprivation. This finding, along with published work demonstrating enhanced levels of hypothalamic NPY in food-deprived rats, suggests that endogenous NPY mediates the eating produced by deprivation.

Genuinely olfactory preferences conditioned by protein repletion

Effects of protein on mild food deprivation in the rat conditioned a relative preference for an intense, insoluble and tasteless odorant. This learned preference for the protein-paired odorant over a non-nutritive-paired odorant was temporarily obliterated by insertion of tubes in the nares to bypass the olfactory mucosa. This demonstrates truly olfactory conditioning, contrary to assertions that gustatory conditioning had not been excluded.

The thermogenic effect of a sucrose gavage on the fa/fa rat

The heat production of homozygous fa/fa and +/+ Zucker rats as well as that of Wistar control adult female rats was estimated with a direct chamber calorimeter, after a gavage of 5.2 mmoles of sucrose given with a stomach cannula. The effects of mild food deprivation (12 hours) affected the thermic response to the gavage. Obese fa/fa rats had very low basal metabolic rates, increasing very little with dietary state or gavage. Lean +/+ rats had basal rates comparable to those of Wistar rats and showed a higher effect of gavage in the food deprived state. Wistar rats had a comparable, albeit magnified, pattern. Zucker rats increased their thermogenesis with gavage with a deep decrease following suit. It is postulated that the deficient thermogenic apparatus of fa/fa rats prevented them showing a diet induced thermogenesis after forced sucrose feeding. Both lean Zucker (+/+) and Wistar rats showed a marked thermogenic response to the sucrose gavage, which was somewhat less pronounced in the Zucker lean rats.

Nocturnal patterns of macronutrient intake in freely feeding and food-deprived rats.

Analyses of rats' feeding behavior at the start and the end of the nocturnal cycle have revealed dramatic alterations in macronutrient intake over time. At dark onset, rats displayed a preference for carbohydrate, with the first meal of the night consisting of approximately 60% of this nutrient. This carbohydrate intake was soon followed by a shift toward protein-predominant meals. Superimposed on this pattern of meal-to-meal shifts in nutrient selection appears to be an additional rhythm in which carbohydrate ingestion was favored at dark onset and protein and fat ingestion were favored during the late dark hours. Differential feeding patterns were also apparent following mild food deprivation. A 2-h period of deprivation at dark onset produced a strong compensatory feeding response, particularly of fat and carbohydrate. This pattern was not observed at the end of the dark, when little compensatory feeding was demonstrated. It is suggested that these feeding patterns may be related to the activity of certain hypothalamic neurotransmitters, e.g., norepinephrine and serotonin, known to be important in modulating temporal feeding patterns and nutrient intake.