Wheel running reduces high-fat diet intake, preference and mu-opioid agonist stimulated intake

Exercise modifies fatty acid perception and metabolism

AIM

Obesity is a major public health issue, which is associated with several chronic diseases. In rodents, voluntary wheel running (VWR) is a type of exercise that influences ingestive behavior. This study aims to investigate the possible function of VWR activity in the perception of fat taste and if it mitigates the immediate effects of fatty acid (FA) ingestion.

METHODS

Male C57BL/6 mice were arbitrarily assigned to either a sedentary (SED) lifestyle or free access to a running wheel after 5 weeks of dietary regimen. Later these mice groups were used in the investigations on fat preference, metabolic tolerance, and electrophysiology. Diet-induced alterations in CD36 and GPR120 expression that are related to fat perception and the capacitative calcium signaling caused by FA in taste bud cells (TBCs) were also examined.

RESULTS

In obese groups, VWR temporarily reduced body weight, demonstrated improvement in preference scores for FA, and recovered from a deterioration in glucose homeostasis. In CD36-positive TBCs, electrophysiological investigations showed alterations in [Ca2+ ]i caused by FA. Further, in the TBCs of circumvallate papillae, there are differences in the expression of the genes CD36 and GPR120 between the active and SED controls. Obese mice also show lower incentive salience for long-chain fatty acids (LCFA) and adapted to the reward system of VWR which may lead to improved incentive salience accredited to wheel running.

CONCLUSION

In conclusion, this study provides the first evidence that VWR causes orosensory adaptations to fat and appears to alter taste preference for LCFAs.

Voluntary physical activity modulates self-selection of a high-caloric choice diet in male Wistar rats

Physical exercise training has been positioned as a behavioral strategy to prevent or alleviate obesity via promotion of energy expenditure as well as modulation of energy intake resulting from changes in dietary preference. Brain adaptations underlying the latter process are incompletely understood. Voluntary wheel running (VWR) is a self-reinforcing rodent paradigm that mimics aspects of human physical exercise training. Behavioral and mechanistic insight from such fundamental studies can help optimize therapies that improve body weight and metabolic health based on physical exercise training in humans. To assess the effects of VWR on dietary self-selection, male Wistar rats were given access to a two-component "no-choice" control diet (CD; consisting of prefabricated nutritionally complete pellets and a bottle with tap water) or a four-component free-choice high-fat high-sucrose diet (fc-HFHSD; consisting of a container with prefabricated nutritionally complete pellets, a dish with beef tallow, a bottle with tap water, and a bottle with 30% sucrose solution). Metabolic parameters and baseline dietary self-selection behavior during sedentary (SED) housing were measured for 21 days, after which half of the animals were allowed to run on a vertical running wheel (VWR) for another 30 days. This resulted in four experimental groups (SED^CD, SED^fc-HFHSD, VWR^CD, and VWR^fc-HFHSD). Gene expression of opioid and dopamine neurotransmission components, which are associated with dietary self-selection, was assessed in the lateral hypothalamus (LH) and nucleus accumbens (NAc), two brain regions involved in reward-related behavior, following 51 and 30 days of diet consumption and VWR, respectively. Compared to CD controls, consumption of fc-HFHSD before and during VWR did not alter total running distances. VWR and fc-HFHSD had opposite effects on body weight gain and terminal fat mass. VWR transiently lowered caloric intake and increased and decreased terminal adrenal and thymus mass, respectively, independent of diet. VWR during fc-HFHSD consumption consistently increased CD self-selection, had an acute negative effect on fat self-selection, and a delayed negative effect on sucrose solution self-selection compared to SED controls. Gene expression of opioid and dopamine neurotransmission components in LH and NAc were unaltered by fc-HFHSD or VWR. We conclude that VWR modulates fc-HFHSD component self-selection in a time-dependent manner in male Wistar rats.

Muscle-to-Brain Signaling Via Myokines and Myometabolites

Skeletal muscle health and function are important determinants of systemic metabolic homeostasis and organism-wide responses, including disease outcome. While it is well known that exercise protects the central nervous system (CNS) from aging and disease, only recently this has been found to depend on the endocrine capacity of skeletal muscle. Here, we review muscle-secreted growth factors and cytokines (myokines), metabolites (myometabolites), and other unconventional signals (e.g. bioactive lipid species, enzymes, and exosomes) that mediate muscle-brain and muscle-retina communication and neuroprotection in response to exercise and associated processes, such as the muscle unfolded protein response and metabolic stress. In addition to impacting proteostasis, neurogenesis, and cognitive functions, muscle-brain signaling influences complex brain-dependent behaviors, such as depression, sleeping patterns, and biosynthesis of neurotransmitters. Moreover, myokine signaling adapts feeding behavior to meet the energy demands of skeletal muscle. Contrary to protective myokines induced by exercise and associated signaling pathways, inactivity and muscle wasting may derange myokine expression and secretion and in turn compromise CNS function. We propose that tailoring muscle-to-CNS signaling by modulating myokines and myometabolites may combat age-related neurodegeneration and brain diseases that are influenced by systemic signals.

New Horizon: Exercise and a Focus on Tissue-Brain Crosstalk

The world population is aging, leading to increased rates of neurodegenerative disorders. Exercise has countless health benefits and has consistently been shown to improve brain health and cognitive function. The purpose of this review is to provide an overview of exercise-induced adaptations in the brain with a focus on crosstalk between peripheral tissues and the brain. We highlight recent investigations into exercise-induced circulating factors, or exerkines, including irisin, cathepsin B, GPLD1, and ketones and the mechanisms mediating their effects in the brain.

β-endorphin differentially contributes to food anticipatory activity in male and female mice undergoing activity-based anorexia

Anorexia nervosa (AN) has a lifetime prevalence of up to 4% and a high mortality rate (~5-10%), yet little is known regarding the etiology of this disease. In an attempt to fill the gaps in knowledge, activity-based anorexia (ABA) in rodents has been a widely used model as it mimics several key features of AN including severely restricted food intake and excessive exercise. Using this model, a role for the hypothalamic proopiomelanocortin (POMC) system has been implicated in the development of ABA as Pomc mRNA is elevated in female rats undergoing the ABA paradigm. Since the Pomc gene product α-MSH potently inhibits food intake, it could be that elevated α-MSH might promote ABA. However, the α-MSH receptor antagonist SHU9119 does not protect against the development of ABA. Interestingly, it has also been shown that female mice lacking the mu opioid receptor (MOR), the primary receptor activated by the Pomc-gene-derived opioid β-endorphin, display blunted food anticipatory behavior (FAA), a key feature of ABA. Thus, we hypothesized that the elevation in Pomc mRNA observed during ABA may lead to increased β-endorphin concentrations and MOR activation to promote ABA. Further, given the known sex differences in AN and ABA, we hypothesized that MORs may contribute differentially in male and female mice. Using wild-type and MOR knockout mice of both sexes, a MOR antagonist and careful analysis of food anticipatory behavior and β-endorphin levels, we found 1) increased Pomc mRNA levels in both female and male mice that underwent ABA, 2) increased β-endorphin in female mice that underwent ABA, and 3) blunted FAA in both sexes in response to MOR genetic deletion yet blunted FAA only in males in response to MOR antagonism. The results presented provide support for both hypotheses and suggest that it may be the β-endorphin resulting from increased Pomc transcription that supports the development of some features of ABA.

From Obesity to Hippocampal Neurodegeneration: Pathogenesis and Non-Pharmacological Interventions

High-caloric diet and physical inactivity predispose individuals to obesity and diabetes, which are risk factors of hippocampal neurodegeneration and cognitive deficits. Along with the adipose-hippocampus crosstalk, chronically inflamed adipose tissue secretes inflammatory cytokine could trigger neuroinflammatory responses in the hippocampus, and in turn, impairs hippocampal neuroplasticity under obese and diabetic conditions. Hence, caloric restriction and physical exercise are critical non-pharmacological interventions to halt the pathogenesis from obesity to hippocampal neurodegeneration. In response to physical exercise, peripheral organs, including the adipose tissue, skeletal muscles, and liver, can secret numerous exerkines, which bring beneficial effects to metabolic and brain health. In this review, we summarized how chronic inflammation in adipose tissue could trigger neuroinflammation and hippocampal impairment, which potentially contribute to cognitive deficits in obese and diabetic conditions. We also discussed the potential mechanisms underlying the neurotrophic and neuroprotective effects of caloric restriction and physical exercise by counteracting neuroinflammation, plasticity deficits, and cognitive impairments. This review provides timely insights into how chronic metabolic disorders, like obesity, could impair brain health and cognitive functions in later life.

Sex-Dependent Wheel Running Effects on High Fat Diet Preference, Metabolic Outcomes, and Performance on the Barnes Maze in Rats

Excessive and prolonged intake of highly palatable, high fat (HF) foods contributes to the pathogenesis of obesity, metabolic syndrome, and cognitive impairment. Exercise can restore energy homeostasis and suppress HF diet preference in rats. However, it is unclear if exercise confers similar protection against the detrimental outcomes associated with a chronic HF diet preference and feeding in both sexes. We used our wheel running (WR) and two-diet choice (chow vs. HF) paradigm to investigate the efficacy of exercise in reversing HF diet-associated metabolic and cognitive dysregulation in rats, hypothesizing that beneficial effects of exercise would be more pronounced in males. All WR rats showed HF diet avoidance upon running initiation, and males, but not females, had a prolonged reduction in HF diet preference. Moreover, exercise only improved glucose tolerance and insulin profile in males. Compared to sedentary controls, all WR rats improved learning to escape on the Barnes maze. Only WR females increased errors made during subsequent reversal learning trials, indicating a sex-dependent effect of exercise on behavioral flexibility. Taken together, our results suggest that exercise is more effective at attenuating HF-associated metabolic deficits in males, and highlights the importance of developing sex-specific treatment interventions for obesity and cognitive dysfunction.

Compensatory eating behaviors in male and female rats in response to exercise training

Exercise is often used as a strategy for weight loss maintenance. In preclinical models, we have shown that exercise may be beneficial because it counters the biological drive to regain weight. However, our studies have demonstrated sex differences in the response to exercise in this context. In the present study, we sought to better understand why females and males exhibit different compensatory food eating behaviors in response to regular exercise. Using a forced treadmill exercise paradigm, we measured weight gain, energy expenditure, food intake in real time, and the anorectic effects of leptin. The 4-wk exercise training resulted in reduced weight gain in males and sustained weight gain in females. In male rats, exercise decreased intake, whereas it increased food intake in females. Our results suggest that the anorectic effects of leptin were not responsible for these sex differences in appetite in response to exercise. If these results translate to the human condition, they may reveal important information for the use and application of regular exercise programs.

Involvement of the endogenous opioid system in the beneficial influence of physical exercise on amphetamine-induced addiction parameters

Psychostimulant drugs addiction is a chronic public health problem and individuals remain susceptible to relapses increasing public expenses even after withdrawal and treatment. Our research group has focused on finding new therapies to be employed in drug addiction treatment, suggesting the physical exercise as a promising tool. This way, it is necessary to know the mechanisms involved in the beneficial influences of physical exercise observing the pathway that could be explored in drug addiction treatment. Male Wistar rats were conditioned with amphetamine (AMPH) following the conditioned place preference (CPP) protocol and subsequently submitted to swimming for 5 weeks (1 h per day, 5 days per week). Half of the animals were injected with Naloxone (0.3 mg/mL/kg body weight, i.p.) 5 min prior each physical exercise day. After AMPH-CPP re-exposure, our outcomes showed that physical exercise, in addition to minimizing the relapse behavior in the CPP, it increased D1R, D2R and DAT in the Ventral Tegmental Area (VTA), but not in the Nucleus accumbens (NAc). Interestingly, while naloxone inhibited the partial beneficial influence of the exercise on drug-relapse behavior, exercise-induced changes in the dopaminergic system were not observed in the group administered with naloxone as well. Based on these evidences, besides reinforcing the beneficial influence of the physical exercise on AMPH-induced drug addiction, we propose the involvement of endogenous opioid system activation, not as a single one, but as a possible mechanism of action resulting from the physical activity practice, thus characterizing an important therapeutic approach, which may contribute to drug withdrawal consequently preventing relapse.

Role of glucocorticoid signaling in exercise-associated changes in high-fat diet preference in rats

The simultaneous introduction of wheel running (WR) and diet choice (high-carbohydrate chow vs. high-fat diet) results in sex-specific diet choice patterns in rats. WR induces a high-fat (HF) diet avoidance, and such avoidance persists in the majority of males, but not females, throughout a 2-wk period. Exercise is a physiological stressor that activates the hypothalamic-pituitary-adrenal (HPA) axis and stimulates glucocorticoid (GC) release, which can alter dietary preferences. Here, we examined the role of the HPA axis and GC signaling in mediating exercise-induced changes in diet preference and the associated neurobiological adaptations that may underlie sex differences in diet choice patterns. Experiment 1 revealed that adrenalectomy did not significantly alter the initiation and persistence of running-induced HF diet avoidance in male rats. Experiment 2 showed that acute WR resulted in greater neural activation than chronic WR in the medial prefrontal (mPFC) and insular cortices (IC) in male rats. Experiment 3 revealed sex differences in the molecular adaptation to exercise and diet preference. First, exercise increased gene expression of fkbp5 in the mPFC, IC, and hippocampus of WR females but had limited influence in males. Second, male and female WR rats that reversed or maintained HF diet avoidance showed distinct sex- and HF diet preference-dependent expression profiles of genes involved in cortical GC signaling (e.g., nr3c1, nr3c2, and src1). Taken together, our results suggest sex differences in region-specific neural adaptations may underlie sex differences in diet preference and the health benefits from exercise.

Muscle-derived Dpp regulates feeding initiation via endocrine modulation of brain dopamine biosynthesis

In this study, Robles-Murguia et al. set out to examine whether muscle-secreted hormones regulate feeding. Using Drosophila as a model system combined with several in vivo and in vitro experiments, the authors identify Decapentaplegic (Dpp) as a myokine that can signal from the muscle to the brain to control feeding by altering dopamine synthesis through transcriptional regulation of tyrosine hydroxylase (TH).

In animals, the brain regulates feeding behavior in response to local energy demands of peripheral tissues, which secrete orexigenic and anorexigenic hormones. Although skeletal muscle is a key peripheral tissue, it remains unknown whether muscle-secreted hormones regulate feeding. In Drosophila, we found that decapentaplegic (dpp), the homolog of human bone morphogenetic proteins BMP2 and BMP4, is a muscle-secreted factor (a myokine) that is induced by nutrient sensing and that circulates and signals to the brain. Muscle-restricted dpp RNAi promotes foraging and feeding initiation, whereas dpp overexpression reduces it. This regulation of feeding by muscle-derived Dpp stems from modulation of brain tyrosine hydroxylase (TH) expression and dopamine biosynthesis. Consistently, Dpp receptor signaling in dopaminergic neurons regulates TH expression and feeding initiation via the downstream transcriptional repressor Schnurri. Moreover, pharmacologic modulation of TH activity rescues the changes in feeding initiation due to modulation of dpp expression in muscle. These findings indicate that muscle-to-brain endocrine signaling mediated by the myokine Dpp regulates feeding behavior.

The influence of 15-week exercise training on dietary patterns among young adults

BACKGROUND/OBJECTIVES

Little is currently known about how exercise may influence dietary patterns and/or food preferences. The present study aimed to examine the effect of a 15-week exercise training program on overall dietary patterns among young adults.

SUBJECTS/METHODS

This study consisted of 2680 young adults drawn from the Training Intervention and Genetics of Exercise Response (TIGER) study. Subjects underwent 15 weeks of aerobic exercise training, and exercise duration, intensity, and dose were recorded for each session using computerized heart rate monitors. In total, 4355 dietary observations with 102 food items were collected using a self-administered food frequency questionnaire before and after exercise training (n = 2476 at baseline; n = 1859 at 15 weeks). Dietary patterns were identified using a Bayesian sparse latent factor model. Changes in dietary pattern preferences were evaluated based on the pre/post-training differences in dietary pattern scores, accounting for the effects of gender, race/ethnicity, and BMI.

RESULTS

Within each of the seven dietary patterns identified, most dietary pattern scores were decreased following exercise training, consistent with increased voluntary regulation of food intake. A longer duration of exercise was associated with decreased preferences for the western (β: -0.0793; 95% credible interval: -0.1568, -0.0017) and snacking (β: -0.1280; 95% credible interval: -0.1877, -0.0637) patterns, while a higher intensity of exercise was linked to an increased preference for the prudent pattern (β: 0.0623; 95% credible interval: 0.0159, 0.1111). Consequently, a higher dose of exercise was related to a decreased preference for the snacking pattern (β: -0.0023; 95% credible interval: -0.0042, -0.0004) and an increased preference for the prudent pattern (β: 0.0029; 95% credible interval: 0.0009, 0.0048).

CONCLUSIONS

The 15-week exercise training appeared to motivate young adults to pursue healthier dietary preferences and to regulate their food intake.

Voluntary wheel running effects on intra-accumbens opioid driven diet preferences in male and female rats

Palatability driven feeding and voluntary physical activity are mediated by and influence similar neural mechanisms, notably through the actions of opioids within the nucleus accumbens. Recent studies suggest that access to a voluntary running wheel results in sex dependent behavioral and physiological adaptations related to opioid mediated palatability-driven feeding. To explore this relationship, male and female Wistar rats were given either access to a voluntary running wheel (RUN group) or no access (SED group) for one week prior to being stereotaxically implanted with bilateral cannulae targeting the nucleus accumbens. Following 7 days of recovery, with RUN or SED conditions continuing the duration of the experiment, all rats were assessed daily (2 h/day) for feeding behavior of concurrently accessible high-carbohydrate and high-fat diet for one week. Following this week, all rats were administered the μ-opioid receptor agonist D-Ala2, NMe-Phe4, Glyol5-enkephalin (DAMGO) (0.0025  μg, 0.025  μg, or 0.25 μg/0.5 μl/side) or the opioid antagonist naloxone (20 μg/0.5 μl/side) into the nucleus accumbens and given concurrent access (2 h) to both diets. All groups expressed a significant baseline preference for the high-carbohydrate diet. DAMGO administration, compared to saline treatment, led to significant increased consumption of the high-carbohydrate diet in all treatment groups. While high-fat diet consumption also increased following DAMGO administration, the influence of DAMGO was much more robust for the preferred high-carbohydrate diet in all groups. Compared to males, females consumed significantly more of both diets at baseline and following DAMGO treatment. Both male and female rats in the RUN condition consumed more high-carbohydrate diet compared to rats in the SED condition. While males exhibited similar increased consumption of both diets regardless of RUN or SED condition, females in the RUN condition displayed a greater sensitivity to DAMGO-driven consumption of the preferred high-carbohydrate, compared to SED females.

Voluntary wheel running effects on intra-accumbens opioid high-fat feeding and locomotor behavior in Sprague-Dawley and Wistar rat strains

The present study examined the influence of physical activity vs. sedentary home cage conditions on baseline and opioid-driven high-fat feeding behaviors in two common strains of laboratory rats. Sprague-Dawley and Wistar rats were singly housed with either access to a voluntary running wheel (RUN) or locked-wheel (SED) for 5 weeks, before being stereotaxically implanted with bilateral cannulae targeting the nucleus accumbens. Following recovery, with RUN or SED conditions continuing the duration of the experiment, all rats were given 2 h daily access to a high-fat diet for 6 consecutive days to establish a stable baseline intake. Over the next 2 weeks, all subjects were administered the μ-opioid agonist D-Ala2, NMe-Phe4, Glyol5-enkephalin (DAMGO) (multiple dose range) or saline into the nucleus accumbens, immediately followed by 2 h access to a high-fat diet. Drug treatments were separated by at least 1 day and treatment order was counterbalanced. Baseline consumption of the high-fat diet during the 1-week baseline acclimation period did not differ between RUN and SED groups in either rat strain. Higher doses of DAMGO produced increased fat consumption in both strains of rats, yet no differences were observed between RUN vs. SED treated groups. However, SED treatment produced a greater locomotor response following intra-accumbens DAMGO administration, compared to the RUN condition, during the 2 h feeding session. The data suggest that the animals housed in sedentary versus voluntary wheel running conditions may differ in behavioral tolerance to the locomotor but not the orexigenic activating properties of intra-accumbens DAMGO treatment.

Aerobic Exercise Improves Food Reward Systems in Obese Rats via Insulin Signaling Regulation of Dopamine Levels in the Nucleus Accumbens

The dopaminergic pathway, comprising projections from the ventral tegmental area to the nucleus accumbens, constitutes the core of the brain reward system. Insufficient food reward caused by dopamine signaling dysfunction in the nucleus accumbens is an important contributor to obesity and may be associated with insulin signaling. Aerobic exercise has a positive effect on both preventing and treating obesity. In addition, physical exercise is important in striatal dopamine homeostasis and improves insulin sensitivity in the peripheral and central nervous system. Therefore, we hypothesized that aerobic exercise may increase dopamine levels in the nucleus accumbens through insulin signaling, thus improving food reward in obesity. In the present study, we used a rat model of obesity, induced by high fat diet. Obese rats exhibited lower basic dopamine concentration in the nucleus accumbens induced by eating or extracellular insulin, attenuated insulin signaling, and increased fat preference. Interestingly, an 8-week aerobic exercise regimen reversed these symptoms. In addition, we noted a significant increase in insulin Akt/GSK3-β signal transduction in the nucleus accumbens. These data demonstrate that aerobic exercise promotes dopamine levels in the nucleus accumbens through insulin signal transduction, which may constitute an important neurobiological mechanism of exercise against obesity.

Voluntary wheel running reduces weight gain in mice by decreasing high-fat food consumption

We investigated whether wheel running for just 30 min on 5 days each week, an exercise routine based on recommended levels of physical activity for adults, regulates body weight and food intake in mice. Male C57BL/6 mice were divided into groups and given ad libitum access to high-fat food and standard chow or standard chow only. For 30 min on 5 days each week, mice were treated with an in-cage running wheel which was either open to allow voluntary exercise or locked and could not rotate for control. Wheel running reduced weight gain and fat mass among mice fed high-fat food and standard chow, but not mice fed standard chow only. Wheel running decreased high-fat food consumption. Standard chow intake was unchanged. Mice provided with a locked running wheel but pair-fed the same amount of food as wheel running mice also displayed reduced weight gain and fat mass. We conclude that voluntary wheel running for 30 min on 5 days each week reduced weight gain and fat mass in mice by preferentially decreasing high-fat food intake. This model of voluntary wheel running can be used to investigate mechanisms underlying the benefits of exercise on body weight and food intake, informing obesity intervention strategies for humans.

The effects of scheduled running wheel access on binge-like eating behavior and its consequences

Binge eating disorder (BED) is an eating disorder involving repeated, intermittent over consumption of food in brief periods of time, usually with no compensatory behaviors. There are few successful treatments and the underlying neural mechanisms remain unclear. In the current study, we hypothesized that voluntary running wheel (RW) activity could reduce binge-like eating behavior in a rat model. Rats were given intermittent (3 times/wk) limited (1hr) access to a high-fat food (Crisco), in addition to continuously available chow. Crisco was available every Mon, Wed, and Fri for 1hr before dark onset. Rats were divided into 2 groups: those with RW access during the first half of the experiment and sedentary during the second half (RW-SED) and those that were sedentary during the first half of the experiment and had RW access during the second half (SED-RW). Crisco intake was significantly less in both groups during the period of time with a RW present. Within the bingeing RW-SED rats, the gene expression of the orexigenic neuropeptides AgRP and NPY were similar to a non-bingeing sedentary control (CON) group, while the expression of the anorexigenic neuropeptide POMC was significantly increased relative to the SED-RW and CON groups. Despite elevated POMC, the rats continued to binge. Additionally, within both groups, the gene expression of the D2R and Oprm1 in the NAc and the VTA were altered suggesting that the reward system was stimulated by both the bingeing behavior and the running wheel activity. Overall, access to a RW and the resulting activity significantly reduced binge-like behavior as well as modulated the effects of binging on brain appetite and reward systems.

Aerobic exercise modulates anticipatory reward processing via the μ-opioid receptor system

Physical exercise modulates food reward and helps control body weight. The endogenous µ-opioid receptor (MOR) system is involved in rewarding aspects of both food and physical exercise, yet interaction between endogenous opioid release following exercise and anticipatory food reward remains unresolved. Here we tested whether exercise-induced opioid release correlates with increased anticipatory reward processing in humans. We scanned 24 healthy lean men after rest and after a 1 h session of aerobic exercise with positron emission tomography (PET) using MOR-selective radioligand [¹¹ C]carfentanil. After both PET scans, the subjects underwent a functional magnetic resonance imaging (fMRI) experiment where they viewed pictures of palatable versus nonpalatable foods to trigger anticipatory food reward responses. Exercise-induced changes in MOR binding in key regions of reward circuit (amygdala, thalamus, ventral and dorsal striatum, and orbitofrontal and cingulate cortices) were used to predict the changes in anticipatory reward responses in fMRI. Exercise-induced changes in MOR binding correlated negatively with the exercise-induced changes in neural anticipatory food reward responses in orbitofrontal and cingulate cortices, insula, ventral striatum, amygdala, and thalamus: higher exercise-induced opioid release predicted higher brain responses to palatable versus nonpalatable foods. We conclude that MOR activation following exercise may contribute to the considerable interindividual variation in food craving and consumption after exercise, which might promote compensatory eating and compromise weight control.

Ovarian hormones mediate running-induced changes in high fat diet choice patterns in female rats

Physical inactivity and increased consumption of energy dense, high fat (HF) foods often leads to a state of positive energy balance. Regular exercise can facilitate the maintenance of a healthy body weight and mediate changes in dietary selection. Past studies using a two-diet choice (chow vs. HF) and voluntary wheel running paradigm found that when a novel HF diet and wheel running are simultaneously introduced, male rats show complete and persistent HF diet avoidance whereas the majority of females show HF diet avoidance for a few days, but then revert to HF diet preference. Ovariectomy (OVX) appears to decrease preference for the HF diet bringing it closer to that of males. Given that estradiol but not progesterone mediates changes in food intake and energy balance, we hypothesized that estradiol signaling is required for the reversal of HF diet avoidance in female rats. Accordingly, Experiment 1 compared the persistency of running-induced HF diet avoidance in males, sham-operated females, and OVX rats with replacement of oil vehicle, estradiol benzoate (E), progesterone (P), or both (E + P). The number of wheel running rats that either avoided or preferred the HF diet varied with hormone treatment. The reversal of HF diet avoidance in running females and OVX E + P rats occurred more rapidly and frequently than male running rats. E + P but not E or P replaced OVX wheel running rats significantly reversed HF diet avoidance. OVX oil rats avoided HF diet to the same extent as male rats for the first 11 days of diet choice and then rapidly increased HF diet intake and began preferring it. This incomplete elimination of sex differences suggests that developmental factors or androgens might play a role in sustaining running-induced HF diet avoidance. Subsequently, Experiment 2 aimed to determine the role of androgens in the persistency of running-associated HF diet avoidance with sham-operated and orchiectomized (GDX) male rats. Both intact and GDX male running rats persistently avoided the HF diet to the same extent. Taken together, these results suggest that activational effects of ovarian hormones play a role in female specific running-induced changes in diet choice patterns. Furthermore, the activational effects of androgens are not required for the expression of HF diet avoidance in males.

Sex determines effect of physical activity on diet preference: Association of striatal opioids and gut microbiota composition

Previous studies suggest an interaction between the level of physical activity and diet preference. However, this relationship has not been well characterized for sex differences that may exist. The present study examined the influence of sex on diet preference in male and female Wistar rats that were housed under either sedentary (no wheel access) (SED) or voluntary wheel running access (RUN) conditions. Following a 1 week acclimation period to these conditions, standard chow was replaced with concurrent ad libitum access to a choice of 3 pelleted diets (high-fat, high-sucrose, and high-corn starch) in the home cage. SED and RUN conditions remained throughout the next 4 week diet preference assessment period. Body weight, running distance, and intake of each diet were measured daily. At the conclusion of the 4 week diet preference test, animals were sacrificed and brains were collected for mRNA analysis. Fecal samples were also collected before and after the 4 week diet preference phase to characterize microbiota composition. Results indicate sex dependent interactions between physical activity and both behavioral and physiological measures. Females in both RUN and SED conditions preferred the high-fat diet, consuming significantly more high-fat diet than either of the other two diets. While male SED rats also preferred the high-fat diet, male RUN rats consumed significantly less high-fat diet than the other groups, instead preferring all three diets equally. There was also a sex dependent influence of physical activity on both reward related opioid mRNA expression in the ventral striatum and the characterization of gut microbiota. The significant sex differences in response to physical activity observed through both behavioral and physiological measures suggest potential motivational or metabolic difference between males and females. The findings highlight the necessity for further exploration between male and female response to physical activity and feeding behavior.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Swimming exercise reduces preference for a high-fat diet by increasing insulin sensitivity in C57BL/6 mice

The present study examined the effect of 4-week swimming training on the preference for a high-fat diet and insulin sensitivity in mice. C57BL/6 J mice were placed on either a low-fat diet or a choice diet (with both low-fat and high-fat diets available) for 6 weeks. During this period, a group of mice on the free-choice diet were randomly selected to receive a 4-week swimming exercise intervention. Mice that received the swimming exercise intervention showed a reduced preference for the high-fat diet as well as a slower rate of weight gain. Moreover, changes in insulin sensitivity, tyrosine hydroxylase expression in the ventral tegmental area-nucleus accumbens system, and the expression of IRS2, IRS2, and high-fat diet-induced Akt phosphorylation in the nucleus accumbens were delayed in the swimming exercise intervention group. Taken together, these results suggest that swimming exercise regulates the dopaminergic reward system to decrease high-fat diet intake, thereby controlling body weight to prevent obesity, in a manner likely mediated by increased insulin signal transduction in the nucleus accumbens.

Voluntary wheel-running attenuates insulin and weight gain and affects anxiety-like behaviors in C57BL6/J mice exposed to a high-fat diet

It is widely accepted that lifestyle plays a crucial role on the quality of life in individuals, particularly in western societies where poor diet is correlated to alterations in behavior and the increased possibility of developing type-2 diabetes. While exercising is known to produce improvements to overall health, there is conflicting evidence on how much of an effect exercise has staving off the development of type-2 diabetes or counteracting the effects of diet on anxiety. Thus, this study investigated the effects of voluntary wheel-running access on the progression of diabetes-like symptoms and open field and light-dark box behaviors in C57BL/6J mice fed a high-fat diet. C57BL/6J mice were placed into either running-wheel cages or cages without a running-wheel, given either regular chow or a high-fat diet, and their body mass, food consumption, glucose tolerance, insulin and c-peptide levels were measured. Mice were also exposed to the open field and light-dark box tests for anxiety-like behaviors. Access to a running-wheel partially attenuated the obesity and hyperinsulinemia associated with high-fat diet consumption in these mice, but did not affect glucose tolerance or c-peptide levels. Wheel-running strongly increased anxiety-like and decreased explorative-like behaviors in the open field and light-dark box, while high-fat diet consumption produced smaller increases in anxiety. These results suggest that voluntary wheel-running can assuage some, but not all, of the physiological problems associated with high-fat diet consumption, and can modify anxiety-like behaviors regardless of diet consumed.

Corticosterone administration in drinking water decreases high-fat diet intake but not preference in male rats

One of the mechanisms through which regular exercise contributes to weight maintenance could be by reducing intake and preference for high-fat (HF) diets. Indeed, we previously demonstrated that wheel-running rats robustly reduced HF diet intake and preference. The reduced HF diet preference by wheel running can be so profound that the rats consumed only the chow diet and completely avoided the HF diet. Because previous research indicates that exercise activates the hypothalamic-pituitary-adrenal axis and increases circulating levels of corticosterone, this study tested the hypothesis that elevation of circulating corticosterone is involved in wheel running-induced reduction in HF diet preference in rats.Experiment 1 measured plasma corticosterone levels under sedentary and wheel-running conditions in the two-diet-choice (high-carbohydrate chow vs. HF) feeding regimen. The results revealed that plasma corticosterone is significantly increased and positively correlated with the levels of running in wheel-running rats with two-diet choice.Experiments 2 and 3 determined whether elevated corticosterone without wheel running is sufficient to reduce HF diet intake and preference. Corticosterone was elevated by adding it to the drinking water. Compared with controls, corticosterone-drinking rats had reduced HF diet intake and body weight, but the HF diet preference between groups did not differ. The results of this study support a role for elevated corticosterone on the reduced HF diet intake during wheel running. The elevation of corticosterone alone, however, is not sufficient to produce a robust reduction in HF diet preference.

Exendin-4 reduces tau hyperphosphorylation in type 2 diabetic rats via increasing brain insulin level

Type 2 diabetes (T2D) is a high risk factor for Alzheimer's disease (AD). Our previous study identified that hyperphosphorylation of tau protein, which is one of the pathophysiologic hallmarks of AD, also occurred in T2D rats' brain; while glucagon-like peptide-1 (GLP-1) mimetics, a type of drug used in T2D, could decrease the phosphorylation of tau, probably via augmenting insulin signaling pathway. The purpose of this study was to further explore the mechanisms that underlie the effect of exendin-4 (ex-4, a GLP-1 receptor agonist) in reducing tau phosphorylation. We found that peripheral ex-4 injection in T2D rats reduced hyperphosphorylation of tau protein in rat hippocampus, probably via increasing hippocampal insulin which activated insulin signaling. Furthermore, we found that ex-4 could neither activate insulin signaling, nor reduce tau phosphorylation in HT22 neuronal cells in the absence of insulin. These results suggested that insulin is required in reduction of tau hyperphosphorylation by ex-4 in brain rats with T2D.

Wheel running decreases palatable diet preference in Sprague-Dawley rats

Physical activity has beneficial effects on not only improving some disease conditions but also by preventing the development of multiple disorders. Experiments in this study examined the effects of wheel running on intakes of chow and palatable diet e.g. high fat (HF) or high sucrose (HS) diet in male and female Sprague-Dawley rats. Experiment 1 demonstrated that acute wheel running results in robust HF or HS diet avoidance in male rats. Although female rats with running wheel access initially showed complete avoidance of the two palatable diets, the avoidance of the HS diet was transient. Experiment 2 demonstrated that male rats developed decreased HF diet preferences regardless of the order of diet and wheel running access presentation. Running associated changes in HF diet preference in females, on the other hand, depended on the testing schedule. In female rats, simultaneous presentation of the HF diet and running access resulted in transient complete HF diet avoidance whereas running experience prior to HF diet access did not affect the high preference for the HF diet. Ovariectomy in females resulted in HF diet preference patterns that were similar to those in male rats during simultaneous exposure of HF and wheel running access but similar to intact females when running occurred before HF exposure. Overall, the results demonstrated wheel running associated changes in palatable diet preferences that were in part sex dependent. Furthermore, ovarian hormones play a role in some of the sex differences. These data reveal complexity in the mechanisms underlying exercise associated changes in palatable diet preference.