Food-restricted Conditions Research Articles

Life History Differences Between Lepidoptera Larvae and Blattodea Nymphs Lead to Different Energy Allocation Strategies and Cellular Qualities.

Different life histories result in different strategies to allocate energy in biosynthesis, including growth and reproduction, and somatic maintenance. One of the most notable life history differences between Lepidoptera and Blattodea species is that the former grow much faster than the latter, and during metamorphosis, a large amount of tissue in Lepidoptera species disintegrates. In this review, using Lepidoptera caterpillars and cockroach nymphs as examples, we show that, due to these differences in growth processes, cockroach nymphs spend 20 times more energy on synthesizing one unit of biomass (indirect cost of growth) than butterfly caterpillars. Because of the low indirect cost of growth in caterpillars, the fraction of metabolic energy allocated to growth is six times lower, and that for maintenance is seven times higher in caterpillars, compared to cockroach nymphs, despite caterpillar's higher growth rates. Moreover, due to the higher biosynthetic energy cost in cockroach nymphs, they have better cellular qualities, including higher proteasomal activity for protein quality control and higher resistance to oxidative stress. We also show that under food restriction conditions, the fraction of assimilated energy allocated to growth was reduced by 120% in cockroach nymphs, as they lost body weight under food restriction, while this reduction was only 14% in hornworms, and the body mass increased at a lower rate. Finaly, we discuss future research, especially the difference in adult lifespans associated with the energetic differences.

Comparison of Energy Budget of Cockroach Nymph (Hemimetabolous) and Hornworm (Holometabolous) under Food Restriction.

Animals with different life histories budget their intake energy differently when food availability is low. It has been shown previously that hornworm (larva of Manduca sexta), a holometabolous insect species with a short development stage, prioritizes growth at the price of metabolism under food restriction, but it is unclear how hemimetabolous insect species with a relatively long development period budget their intake energy under food scarcity. Here, we use orange head cockroaches (Eublaberus posticus) to investigate this question. We found that for both species under food restriction, rates of metabolism and growth were suppressed, but the degree of reduction was more severe in growth than that of metabolism for cockroaches. Under both free-feeding and food restriction conditions, hornworms allocated a larger fraction of assimilated energy to growth than to metabolism, and cockroaches were the opposite. More importantly, when food availability was low, the fraction of assimilated energy allocated to growth was reduced by 120% in cockroaches, and the energy from growth was channeled to compensate for the reduction in metabolism; but, the fraction of assimilated energy allocated to growth was only reduced by 14% in hornworms. These results suggest that, compared to hornworms, cockroaches prioritize metabolism over growth.

Circadian Rhythm and Leptin Hormone Responses to Nutritional Restriction in Gerbils (Meriones unguiculatus) with Suprachiasmatic Nucleus Lesions

Rhythmically-regulated feeding behavior is in harmony with physiologic and metabolic activities in mammals. This rhythmic regulation is orchestrated by Suprachiasmatic Nucleus (SCN). However, it is not entirely clear how the SCN, which generates endogenous (internal) rhythms, influences body weight and serum leptin profile with activity rhythms in relation to feeding timing. In this study, animals in long photoperiod (14L:10D) were divided into two groups as control (sham-SCNx) and SCN lesions (SCNx). Then, these groups were split into four separate subgroups: a) ad libitum feeding; b) feeding only during the dark phase; c) feeding only during the light phase; and d) feeding during a specific period of the day (11:00-14:00 h). Locomotor activity and leptin hormone changes were observed in animals fed in cages attached to activity wheels for one month. Under the conditions of food restriction, the locomotor activities of the groups with SCNx and sham-SCNx demonstrated a phase shift toward the time of feeding. Serum leptin level did not change with feeding conditions but decreased in lesioned groups (SCNx). In conclusion, nutritional restriction caused phase shifts in activity rhythms and it was found that the SCN in gerbils was in charge of these rhythmic changes in the presence and absence of nutrients.

Rapid, automated, and experimenter-free touchscreen testing reveals reciprocal interactions between cognitive flexibility and activity-based anorexia in female rats.

Anorexia nervosa has among the highest mortality rates of any psychiatric disorder and is characterized by cognitive inflexibility that persists after weight recovery and contributes to the chronic nature of the condition. What remains unknown is whether cognitive inflexibility predisposes individuals to anorexia nervosa, a question that is difficult to address in human studies. Our previous work using the most well-established animal model of anorexia nervosa, known as activity-based anorexia (ABA) identified a neurobiological link between cognitive inflexibility and susceptibility to pathological weight loss in female rats. However, testing flexible learning prior to exposure to ABA in the same animals has been thus far impossible due to the length of training required and the necessity of daily handling, which can itself influence the development of ABA. Here, we describe experiments that validate and optimize the first fully-automated and experimenter-free touchscreen cognitive testing system for rats and use this novel system to examine the reciprocal links between reversal learning (an assay of cognitive flexibility) and weight loss in the ABA model. First, we show substantially reduced testing time and increased throughput compared to conventional touchscreen testing methods because animals engage in test sessions at their own direction and can complete multiple sessions per day without experimenter involvement. We also show that, contrary to expectations, cognitive inflexibility measured by this reversal learning task does not predispose rats to pathological weight loss in ABA. Instead, rats that were predisposed to weight loss in ABA were more quickly able to learn this reversal task prior to ABA exposure. Intriguingly, we show reciprocal links between ABA exposure and cognitive flexibility, with ABA-exposed (but weight-recovered) rats performing much worse than ABA naïve rats on the reversal learning task, an impairment that did not occur to the same extent in rats exposed to food restriction conditions alone. On the other hand, animals that had been trained on reversal learning were better able to resist weight loss upon subsequent exposure to the ABA model. We also uncovered some stable behavioral differences between ABA susceptible versus resistant rats during touchscreen test sessions using machine learning tools that highlight possible predictors of anorectic phenotypes. These findings shed new light on the relationship between cognitive inflexibility and pathological weight loss and provide targets for future studies using the ABA model to investigate potential novel pharmacotherapies for anorexia nervosa.

Initial Pharmacological Characterization of a Major Hydroxy Metabolite of PF-5190457: Inverse Agonist Activity of PF-6870961 at the Ghrelin Receptor.

Preclinical and clinical studies have identified the ghrelin receptor [growth hormone secretagogue receptor (GHSR)1a] as a potential target for treating alcohol use disorder. A recent phase 1a clinical trial of a GHSR1a antagonist/inverse agonist, PF-5190457, in individuals with heavy alcohol drinking identified a previously undetected major hydroxy metabolite of PF-5190457, namely PF-6870961. Here, we further characterized PF-6870961 by screening for off-target interactions in a high-throughput screen and determined its in vitro pharmacodynamic profile at GHSR1a through binding and concentration-response assays. Moreover, we determined whether the metabolite demonstrated an in vivo effect by assessing effects on food intake in male and female rats. We found that PF-6870961 had no off-target interactions and demonstrated both binding affinity and inverse agonist activity at GHSR1a. In comparison with its parent compound, PF-5190457, the metabolite PF-6870961 had lower binding affinity and potency at inhibiting GHSR1a-induced inositol phosphate accumulation. However, PF-6870961 had increased inhibitory potency at GHSR1a-induced β-arrestin recruitment relative to its parent compound. Intraperitoneal injection of PF-6870961 suppressed food intake under conditions of both food restriction and with ad libitum access to food in male and female rats, demonstrating in vivo activity. The effects of PF-6870961 on food intake were abolished in male and female rats knockout for GHSR, thus demonstrating that its effects on food intake are in fact mediated by the GHSR receptor. Our findings indicate that the newly discovered major hydroxy metabolite of PF-5190457 may contribute to the overall activity of PF-5190457 by demonstrating inhibitory activity at GHSR1a. SIGNIFICANCE STATEMENT: Antagonists or inverse agonists of the growth hormone secretagogue receptor (GHSR)1a have demonstrated substantial potential as therapeutics for alcohol use disorder. We here expand understanding of the pharmacology of one such GHSR1a inverse agonist, PF-5190457, by studying the safety and pharmacodynamics of its major hydroxy metabolite, PF-6870961. Our data demonstrate biased inverse agonism of PF-6870961 at GHSR1a and provide new structure-activity relationship insight into GHSR1a inverse agonism.

Cardiotrophin-1 contributes to metabolic adaptations through the regulation of lipid metabolism and to the fasting-induced fatty acid mobilization.

It is becoming clear that several human pathologies are caused by altered metabolic adaptations. During liver development, there are physiological changes, from the predominant utilization of glucose (fetal life) to the use of lipids (postnatal life). Fasting is another physiological stress that elicits well-known metabolic adjustments. We have reported the metabolic properties of cardiotrophin-1 (CT-1), a member of the interleukin-6 family of cytokines. Here, we aimed at analyzing the role of CT-1 in response to these metabolic changes. We used different in vivo models. Furthermore, a differential study was carried out with wild-type and CT-1 null mice in fed (ad libitum) and food-restricted conditions. We demonstrated that Ct-1 is a metabolic gene induced in the liver via PPARα in response to lipids in mice (neonates- and food-restricted adults). We found that Ct-1 mRNA expression in white adipose tissue directly involved PPARα and PPARγ. Finally, the physiological role of CT-1 in fasting is confirmed by the impaired food restriction-induced adipose tissue lipid mobilization in CT-1 null mice. Our findings support a previously unrecognized physiological role of CT-1 in metabolic adaptations, through the regulation of lipid metabolism and contributes to fasting-induced free fatty acid mobilization.

Oxytocin in the dorsal raphe nucleus antagonizes the inhibition of maternal care induced by food deprivation

Lactation is indispensable for the pup's survival, but is considered a survival burden in dams under negative energy conditions. In the present study, we tested our hypothesis that oxytocin may facilitate energy investment to pups through behavioral control as well as milk ejection. Maternal care was observed in dams at 3 h but not 8 h after food deprivation. We investigated whether oxytocin in the dorsal raphe nucleus (DRN), which is involved in energy state-dependent regulation of maternal care, regulates maternal care. For this purpose, 2-pmol L368899, an oxytocin receptor antagonist, was injected into the DRN; after treatment, maternal care was inhibited in the dams with 3-h fasting, but not in the fed dams. In contrast, recovery of maternal care was observed in the dams with 8-h fasting who underwent 100-pmol oxytocin injection at the DRN. These results indicate that oxytocin in the DRN is required for displaying maternal behavior under fasting conditions, but not under fed conditions. Next, we investigated the site of oxytocin release. Presentation of pups decreased the oxytocin immunoreactivity at the paraventricular nucleus (PVN) of the hypothalamus in the 3-h-fasted dams, but not in the fed or 8-h-fasted dams. No change of the serum oxytocin level was observed. Few oxytocin-positive neurons projecting from the PVN to the DRN were detected through labeling with the retrograde tracer fluorogold. Oxytocin secreted at the PVN, which reaches the DRN, but not released as a hormone or neurotransmitter may mediate maternal care under food-restricted conditions.

A paradigm to specifically assess the respective drives for exercise and feeding in a reward-choice test in mice: Influence of adolescent stress

Introduction Anorexia nervosa (AN), mostly observed in female adolescents, is the most fatal mental illness. Its core is a motivational imbalance between exercise and feeding in favour of the former. Although several animal models of AN have been proposed, none of them specifically assesses the motivation for exercise and/or feeding. In keeping with this issue, we recently developed an operant conditioning-based model wherein motivation for each of these two rewards can be examined singly or within a choice setting in mice [1] . By means of this model, we have recently examined whether infant-early adolescent stress (post-weaning social isolation), one precipitating factor in AN, affects in a sex-dependent manner the reinforcing values of either reward [2] . Methods Stressed and control male/female C57Bl/6 N mice were exposed, when 5-weeks old, to a cued-reward motivated instrumental task wherein wheel-running sequences and palatable food pellets, each reward provided singly, were conditioned by nose-poke responses. These responses obeyed fixed ratio (FR) reinforcement schedules for 10 sessions before being tested under a progressive ratio (PR) schedule of reinforcement for one session. Thereafter, mice underwent 10 FR sessions wherein they had the choice between either reward, the last 5 sessions being performed under food restriction conditions. Infant-adolescent stress, which began at postnatal day 22 (first postweaning day), consisted in individual housing, as compared to controls, which were all collectively housed (3/cage). Results Whether wheel-running and palatable food were provided separately or within a choice paradigm, post-weaning isolation-reared males responded to similar extents for each reward when the three other mouse groups displayed increased responding for wheel-running. The negative impact of the early stressor on male nose poke responding for wheel-running, compared to that measured in the other mouse groups, extended to the running performance during each rewarded sequence (i.e. reward consumption). When food-restricted, motivation for food overpassed progressively that for running in all groups, with females reaching higher levels than males. Conclusions Although the stress model that we used did not trigger a sex-dependent imbalance between exercise and feeding drives that would be reminiscent of what is observed in anorectic girls, we believe that the quest for other stress models, possibly combined with genetics, could prove fruitful to model some endophenotypic traits of AN.

Intermittent but not Chronic Access to Western Diet Selectively Induced Binge‐like Eating and Risk‐taking Behavior in Rats.

Binge eating disorder (BED), the most common eating disorder in the US, has a lifetime prevalence of 2.8% and has been associated with many other psychological and metabolic disorders. Several preclinical models developed to study binge‐eating disorder and related pathologies use stress, food restriction, or limited access conditions to induce binge‐like intake. Using limited access model, Corwin and colleague, demonstrated that limited‐short (2 hr Mon, Wed and Fri) access to vegetable shortening induced a binge‐compensate feeding pattern which was not present in limited‐regular (2 hr every day) access conditions. Similar findings were reported when a nutritionally complete high‐fat diet was utilized either every day (HFD‐ED) or every‐third day (HFD‐3D). Using this model, we have recently shown that both HFD‐ED and HFD‐3D groups of rats undergo similar binge‐compensate eating patterns and display compulsive feeding/risk‐taking behavior, suggesting the frequency instead of presence/absence of binge‐like feeding episodes as a major difference between HFD‐3D and HFD‐ED. It was also unclear if the intermittent availability or the HFD itself triggered compulsive feeding. Therefore, in the present study, we evaluated the impact of ad libitum chow and western diet (WD; rich in both sugar and fat) consumed in a binge manner in relation to the same diet consumed in a non‐binge manner. Male Long Evans rats received chronic (every day) or intermittent (Mon, Wed, and Fri) 24 hr access to Western Diet for six weeks. The control group received normal rodents chow. All the animals had ad libitum access to chow and water throughout the experiment. We observed that intermittent access‐group significantly overconsumed on WD‐access days and under‐consumed on chow‐access days as compared to both chow controls and chronic access group. Chronic access group, on the other hand, significantly overconsumed every day as compared to chow controls but not in a binge/compensate manner. Only intermittent access‐group showed elevated food intake than their baseline during the first two hours of WD‐access days. Finally, only the intermittent access‐group showed risk‐taking behavior when tested in the light/dark box. These data demonstrate selective induction of risk‐taking behavior following binge‐like eating but not when the same diet was consumed in a non‐binge manner.Support or Funding InformationResearch reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under Award Number TL4GM118968 and RL5GM118966. This publication was also made possible by funding, in part, by NIMHD‐RCMI # G12MD007595‐10, NIGMS‐BUILD # UL1GM118967 and NIGMS‐SCORE # 1SC3GM127173‐01A1 to SS. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Effects of Food Restriction and Pre-Training Length on Delay Discounting in Male Wistar Rats

Impulsivity is often measured using delay discounting, a task in which individuals must select between smaller, sooner and larger, later reinforcers. The magnitude effect is the tendency for individuals to discount larger delayed reinforcers less steeply than smaller ones. In terms of food restriction, the magnitude effect predicts that restricted subjects should behave less impulsively, because restriction may increase food reinforcer value and therefore increase subjects’ propensity to select larger, later reinforcers. However, previous research examining the effects of reinforcer restriction has not demonstrated this. In the present research, 12 male Wistar rats were exposed to a delay discounting procedure under both free-feeding and food restriction conditions. Subjects selected more larger, later reinforcers when restricted to ~85% of their free-feeding weights, which is consistent with the magnitude effect. In addition, we systematically examined the effects of shortening the second training phase of a common delay discounting procedure (i.e., Evenden & Ryan, 1996, 1999), during which responses produced the immediate delivery of either one or five reinforcers. The number of sessions in the second training phase did not affect discounting once delays were imposed, indicating that future researchers may shorten this training phase without affecting impulsive responding.

Clozapine reliably increases the motivation for food: parsing the role of the 5-HT2c and H1 receptors.

Although clozapine is effective in treating schizophrenia, it is associated with adverse side effects including weight gain and metabolic syndrome. Despite this, the role of clozapine on feeding behaviour and food intake has not been thoroughly characterised. Clozapine has a broad pharmacological profile, with affinities for several neurotransmitter receptors, including serotonin (5-hydroxytriptamine, 5-HT) and histamine. Given that the serotonin 5-HT2C receptor and histaminergic H1 receptor are involved in aspects of feeding behaviour, the effect of clozapine on feeding may be linked to its action at these receptors. We assessed, in rats, the effect of acute and subchronic administration of clozapine on responding for food under a progressive ratio (PR) schedule under conditions of food restriction and satiety. We also examined the effect of antagonists of the serotonin 5-HT2C and histaminergic H1 receptors on the same schedule. Clozapine reliably increased responding for food, even when rats had ad libitum access to food. The effect of clozapine on responding for food was reproduced by combined (but not individual) antagonism of the serotonin 5-HT2C and histaminergic H1 receptors. These findings show that clozapine enhances the motivation to work for food, that this effect is stable over repeated testing, and is independent of hunger state of the animal. This effect may relate to a combined action of clozapine at the serotonin 5-HT2C and histaminergic H1 receptors.

Metabolic traits in brown trout (Salmo trutta) vary in response to food restriction and intrinsic factors.

Metabolic rates vary hugely within and between populations, yet we know relatively little about factors causing intraspecific variation. Since metabolic rate determines the energetic cost of life, uncovering these sources of variation is important to understand and forecast responses to environmental change. Moreover, few studies have examined factors causing intraspecific variation in metabolic flexibility. We explore how extrinsic environmental conditions and intrinsic factors contribute to variation in metabolic traits in brown trout, an iconic and polymorphic species that is threatened across much of its native range. We measured metabolic traits in offspring from two wild populations that naturally show life-history variation in migratory tactics (one anadromous, i.e. sea-migratory, one non-anadromous) that we reared under either optimal food or experimental conditions of long-term food restriction (lasting between 7 and 17months). Both populations showed decreased standard metabolic rates (SMR-baseline energy requirements) under low food conditions. The anadromous population had higher maximum metabolic rate (MMR) than the non-anadromous population, and marginally higher SMR. The MMR difference was greater than SMR and consequently aerobic scope (AS) was higher in the anadromous population. MMR and AS were both higher in males than females. The anadromous population also had higher AS under low food compared to optimal food conditions, consistent with population-specific effects of food restriction on AS. Our results suggest different components of metabolic rate can vary in their response to environmental conditions, and according to intrinsic (population-background/sex) effects. Populations might further differ in their flexibility of metabolic traits, potentially due to intrinsic factors related to life history (e.g. migratory tactics). More comparisons of populations/individuals with divergent life histories will help to reveal this. Overall, our study suggests that incorporating an understanding of metabolic trait variation and flexibility and linking this to life history and demography will improve our ability to conserve populations experiencing global change.

Jump Exercise and Food Restriction on Bone Parameters in Young Female Rats.

We examined the effect of jump exercise on bone parameters in young female rats under food restriction. Seven-week-old female rats were divided into four groups: a sedentary and ad libitum feeding group (n = 10), a jump exercise and ad libitum feeding group (n = 9), a sedentary and 30% food restriction group (n = 9), and a jump exercise and 30% food restriction group (n = 10). The jump groups jumped 20 times/day, 5 times/week. The experiment lasted for 13weeks. There were no interactions of jump exercise and food restriction on bone. Jump exercise under food restriction conditions induced higher bone strength, bone mineral content, bone area, bone mineral density (BMD), and cortical bone volume in young female rats, similar to rats under ad libitum feeding conditions. Bone strength parameters were not significantly different between ad libitum intake and food restriction with jump exercise training; however, BMD, bone size, and bone mass in the food restriction groups did not reach the levels of those in the ad libitum conditions group with jump exercise training. Neither jump exercise nor food restriction had a significant effect on serum estradiol or IGF-1. Our study reveals jump exercise attenuates loss of biomechanical properties and some bone sites with food restriction in young female rats.

Metabolomic responses of mussel Mytilus galloprovincialis to fluoranthene exposure under different nutritive conditions

Biomarkers are useful tools to assess biological effects of pollutants that are extensively used in monitoring programs to assess ecosystem health. However, they are strongly affected by mussel physiological state, especially nutritive status, which has led to the search of new biological indicators of chemical pollutants exposition. Environmental metabolomics is an approach for examining the metabolic responses (measurement of low molecular weight endogenous metabolites) of an organism to both natural and anthropogenic stressors that can occur in its environment. The aim of the present work was to assess the effect of the polycyclic aromatic hydrocarbon fluoranthene (FLU) exposure on the metabolomic profiles of mussel digestive glands under different nutritive conditions. To achieve this objective, mussels were reared, for a period of 56 days, under three different food rations in order to obtain a gradient of nutritive status (negative, zero and positive energy balance), and after that, they were exposed, during 3 weeks, to a nominal concentration of 3 μg FLU L−1. A total of 43 metabolites, including aminoacids (Ala, Val, Leu, Ile, etc.), energy metabolism related metabolites (ATP, AMP, etc.), organic osmolytes (taurine, etc.), redox metabolism (GSH, NADP+) and nucleotides, were identified and quantified in the digestive glands of the mussels. Principal Component Analysis (PCA) defined two principal components (PC1 and PC2) that explained 55.6% of the total variance, although the first component explains more than 80% of this variance, this being related to the mussel nutritive condition. The effect of the toxicant, explained by the PC2, is similar to that produced under conditions of food restriction, which masks the effect of the toxicant under these conditions. As the feeding conditions are more favorable, the toxic effect becomes more apparent. Therefore, the great influence of nutritive condition on mussel metabolome implies a handicap for the use of metabolomic biomarkers, as previously demonstrated for biochemical and other molecular biomarkers, in large-scale monitoring programs in which several food conditions coexist with pollution levels.

Expression of neuropeptide Y and gonadotropin-releasing hormone gene types in the brain of female Nile tilapia (Oreochromis niloticus) during mouthbrooding and food restriction

A cichlid fish, the Nile tilapia (Oreochromis niloticus), is a maternal mouthbrooder, which exhibits minimum energy expenditure and slower ovarian cycles during mouthbrooding. The objective of this study was to observe changes in the gene expression of key neuropeptides involved in the control of appetite and reproduction, including neuropeptide Y a (NPYa), reproductive neuropeptides: gonadotropin-releasing hormone (GnRH1, GnRH2 and GnRH3) and kisspeptin (Kiss2) during mouthbrooding (4- and 12-days), 12-days of food restriction and 12-days of food restriction followed by refeeding. The food restriction regime showed a significant increase in npya mRNA levels in the telencephalon. However, there were no significant alterations in npya mRNA levels during mouthbrooding. gnrh1 mRNA levels were significantly lower in mouthbrooding female as compared with females with food restriction. gnrh3 mRNA levels were also significantly lower in female with 12-days of mouthbrooding, 12-days of food restriction followed by 12-days of refeeding when compared with controls. There were no significant differences in gnrh2 and kiss2 mRNA levels between groups under different feeding regimes. No significant changes were observed in mRNA levels of receptors for peripheral metabolic signaling molecules: ghrelin (GHS-R1a and GHS-R1b) and leptin (Lep-R). These results suggested that unaffected npya mRNA levels in the telencephalon might contribute to suppression of appetite in mouthbrooding female tilapia. Furthermore, lower gnrh1 and gnrh3 mRNA levels may influence the suppression of reproductive functions such as progression of ovarian cycle and reproductive behaviours, while GnRH2 and Kiss2 may not play a significant roles in reproduction under food restriction condition.

Dopaminergic Perturbations from Food Restriction and Exercise are Sex‐Dependently Amplified During Adolescence

Eating disorders, which are 2.5‐fold more prevalent in females than males, typically emerge during adolescence. Afflicting at least 3 percent of teenagers, eating disorders such as anorexia nervosa, bulimia nervosa, and binge eating disorder entail severe health consequences in addition to their psychological toll. Yet no effective treatments for eating disorders exist. An established regulator of both eating behaviors and physical activity, the dopaminergic system undergoes a sensitive maturation period during adolescence. However, studies into the role of the dopaminergic system in ontogeny of eating disorders are lacking, as are investigations into dopaminergic system maturation in adolescent females. Here we measured function of the dopamine transporter (DAT), a critical regulator of dopaminergic signaling, using both in vivo high‐speed chronoamperometry and locomotor assays of acute cocaine response. Employing an activity‐based anorexia paradigm for 4–5 days, we investigated how food restriction, free exercise on a running wheel, or the combination thereof impacted DAT function in adult (postnatal day 90) and adolescent (postnatal day 30) Sprague‐Dawley rats of both sexes. Food restriction alone or with exercise in adolescent rats of both sexes produced leftward shifts in the dose‐response to the locomotor‐promoting effects of cocaine, though the maximal response to cocaine was blunted in females within these two groups. In adults, only food restricted females exhibited a significant increase in maximal cocaine‐induced locomotor response. Clearance of dopamine in dorsal striatum was not significantly altered by food restriction and/or exercise in adults. In contrast, food restriction plus exercise significantly attenuated dopamine clearance in adolescent males, and food restriction alone or combined with exercise elicited pronounced dopamine clearance reductions in adolescent females. Together, these findings suggest that adolescent plasticity of the dopaminergic system confers – particularly in females – vulnerability to eating disorders and persistence of associated unhealthy behaviors (e.g., compulsive exercise). Therefore, drugs that enhance dopamine uptake or otherwise reduce dopamine signaling duration may prove efficacious in the treatment of emerging adolescent eating disorders. Ongoing experiments are evaluating striatal DAT expression in these animals, and future experiments will focus on optimizing longer term food restriction and exercise conditions in adolescents to facilitate investigation of pharmacologic interventions.Support or Funding InformationThis research was supported by R21 DA038504 to LCD. TLG is supported by T32 DA031115 to Charles P. France.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effects of food restriction on the expression of genes related to acetaminophen-induced liver toxicity in rats.

It is well known that fasting substantially affects the metabolism of drugs and chemicals. Food restriction also affects drug kinetics, such as absorption, metabolism, and excretion, and therefore, it can potentially modulate the onset of chemical toxicity or drug-induced adverse reactions. In the present study, the expression of drug-metabolizing enzyme genes and total glutathione content in the liver, which are related to toxicity induced by overdose of the hepatotoxic drug acetaminophen (N-acetyl-p-aminophenol; APAP), were examined in rats reared under different feeding conditions: ad libitum feeding, 16-h fasting, and food restriction (fed 70% of the average intake of ad libitum feeding for 10 days) conditions. The rats under food restriction conditions as well as fasted rats showed significantly higher expression of Cyp2e1, the gene encoding the enzyme that metabolizes APAP to its toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). They also had lower levels of liver total glutathione, which detoxifies NAPQI. In contrast, the gene expression of UDP-glucuronosyltransferase 1A6 (Ugt1a6), sulfotransferase 1A1 (Sult1a1), and glutathione S-transferase M1 (Gstm1) was not affected by food restriction or fasting. When APAP was administered (800 mg/kg), histopathological changes were not observed in rats fed ad libitum, while hepatocellular necrosis was observed in most of the rats treated with APAP after fasting or food restriction. Taken together, these results suggest that not only fasting but also food restriction exacerbate APAP-induced acute liver injury, probably by the induction of CYP2E1 and the reduction of liver glutathione contents, in rodents.

Food restriction reduces neurogenesis in the avian hippocampal formation.

The mammalian hippocampus is particularly vulnerable to chronic stress. Adult neurogenesis in the dentate gyrus is suppressed by chronic stress and by administration of glucocorticoid hormones. Post-natal and adult neurogenesis are present in the avian hippocampal formation as well, but much less is known about its sensitivity to chronic stressors. In this study, we investigate this question in a commercial bird model: the broiler breeder chicken. Commercial broiler breeders are food restricted during development to manipulate their growth curve and to avoid negative health outcomes, including obesity and poor reproductive performance. Beyond knowing that these chickens are healthier than fully-fed birds and that they have a high motivation to eat, little is known about how food restriction impacts the animals' physiology. Chickens were kept on a commercial food-restricted diet during the first 12 weeks of life, or released from this restriction by feeding them ad libitum from weeks 7–12 of life. To test the hypothesis that chronic food restriction decreases the production of new neurons (neurogenesis) in the hippocampal formation, the cell proliferation marker bromodeoxyuridine was injected one week prior to tissue collection. Corticosterone levels in blood plasma were elevated during food restriction, even though molecular markers of hypothalamic-pituitary-adrenal axis activation did not differ between the treatments. The density of new hippocampal neurons was significantly reduced in the food-restricted condition, as compared to chickens fed ad libitum, similar to findings in rats at a similar developmental stage. Food restriction did not affect hippocampal volume or the total number of neurons. These findings indicate that in birds, like in mammals, reduction in hippocampal neurogenesis is associated with chronically elevated corticosterone levels, and therefore potentially with chronic stress in general. This finding is consistent with the hypothesis that the response to stressors in the avian hippocampal formation is homologous to that of the mammalian hippocampus.

Enzootic calcinosis in horses grazing Solanum glaucophyllum in Argentina

Solanum glaucophyllum, a toxic plant known for its calcinogenic effects, causes enzootic calcinosis in ruminant and monogastric animals. We describe an outbreak of enzootic calcinosis that occurred in a herd of 110 horses grazing pastureland heavily contaminated with S. glaucophyllum in Buenos Aires province, Argentina. Ten horses developed clinical signs, and 6 horses died. Clinical signs included abnormal gait (stiff-legged action, short strides), stiffness, thoracolumbar kyphosis, reluctance to move, wide stance, chronic weight loss, weakness, recumbency, and difficulty standing. Autopsy of 2 horses revealed severe mineralization of the aorta, pulmonary arteries, heart, and lungs, consistent with enzootic calcinosis. Although horses usually have very selective grazing behavior, under food restriction conditions, they can ingest the toxic plants and can develop the disease. Enzootic calcinosis should be considered as a differential diagnosis in horses grazing S. glaucophyllum-invaded pasturelands with compatible clinical signs and lesions.

Effects of bilateral anterior agranular insula lesions on food anticipatory activity in rats.

Food anticipatory activity (FAA) refers to a daily rhythm of locomotor activity that emerges under conditions of food restriction, whereby animals develop an intense, predictable period of activity in the few hours leading up to a predictable, daily delivery of food. The neural mechanisms by which FAA is regulated are not yet fully understood. Although a number of brain regions appear to be involved in regulating the development and expression of FAA, there is little evidence to date concerning the role of the anterior agranular insular cortex (AICa). The AICa plays a critical role in integrating the perception of visceral states with motivational behaviour such as feeding. We assessed the effect of bilateral electrolytic or ibotenic acid lesions of the AICa on FAA in male Wistar rats receiving food for varying lengths of time (2 h, 3 h, or 5 h) during the middle of the light phase (starting at either ZT4 or ZT6). Contrary to our initial expectations, we found that both electrolytic and ibotenic acid lesions significantly increased, rather than decreased, the amount of FAA expressed in lesioned rats. Despite increased FAA, lesioned rats did not eat significantly more during restricted feeding (RF) periods than control rats. Similar to controls, AlCa-lesioned rats showed negligible anticipatory activity to a restricted treat suggesting that the increased anticipatory activity in lesioned rats is associated with food restriction, rather than the appetitive value of the meal. Monitoring behaviour in an open field indicated that increased FAA in AlCa-lesioned rats was not explained by a general increase in locomotor activity. Together, these findings suggest that the AICa contributes to the network of brain regions involved in FAA.