Effect of acute and chronic caloric restriction and metabolic glucoprivation on spontaneous physical activity in obesity-prone and obesity-resistant rats

The Fidget Factor and the obesity paradox. How small movements have big impact

The hypothesis is that the Fidget Factor is the innate neurological pulse that propels humans and other species to move to support their health. Fidgets, previously thought to be spontaneous, are neurologically regulated and highly ordered (non-random). Modern societies being chair-based overwhelm Fidget Factor pulses and consequently inflict chair-based living for transportation, labor, and leisure. Despite impulses firing through the nervous system, people sit because environmental design overwhelms the biology. Urbanization and chair-based societies were designed after the industrial revolution to promote productivity; however, the consequence has been opposite. Crushing the natural urge to move—the Fidget Factor—is a public health calamity. Excess sitting is associated with a myriad of detrimental health consequences and impairs productivity. Fidgeting may reduce all-cause mortality associated with excessive sitting. The Fidget Factor offers hope; data demonstrate that workplaces and schools can be designed to promote activity and free people's Fidget Factors. Evidence shows that people are happier, healthier, wealthier, and more successful if their Fidget Factors are freed.

Resistance to obesity prevents obesity development without increasing spontaneous physical activity and not directly related to greater metabolic and oxidative capacity

There are evidence that obese-resistant animals are more physically active, due to a higher rate of lipid oxidation. Efficiency in such pathways can favor greater spontaneous physical activity and, consequently, less body fat deposition. The aim of study was characterizing the nutritional profile and spontaneous physical activity in the condition of Resistance to Obesity (OR). Wistar rats were randomized into standard diet (SD; n = 50) and high-fat diet (HFD; n = 50) groups, after obesity induction, were redistributed into Control (C), False-control (FC), Propensity to obesity (OP) and OR, and then spontaneous physical activity was evaluated. Analyzed parameters: body mass (BM), epididymal (EF), retroperitoneal (RF), visceral (VF) and respective summations (∑), adiposity index (AI), nutritional, morphological, biochemical and metabolic parameters and protein quantification. The comparison of the groups was performed by ANOVA one or two factors, with 5% significance adopted. OP and FC presented high final MC values compared to C and OR. OR had lower EF, RF, VF, ∑ and IA compared to OP. OR had similar values to C and higher HDL than FC and OP. In GTT, OR and C presented similar values and both were lower than OP in the 30 minutes. OP promoted higher values than C for glycemic AUC. OR had higher PPARγ content than C and OP, as well as levels similar to C for leptin and insulin. Spontaneous physical activity did not differ between groups. The results were not enough to show that OR animals have greater lipid oxidative capacity, as well as greater spontaneous physical activity.

Social isolation is a direct determinant of decreased home-cage activity in mice: A within-subjects study using a body-implantable actimeter

NEW FINDINGS

What is the central question of this study? It is generally recognized that social isolation is associated with physical inactivity; however, is social isolation a direct determinant of decreased physical activity? What is the main finding and its importance? We conducted a within-subjects experiment with the aid of a body-implantable actimeter. Our results clearly demonstrated that social isolation decreased home-cage activity in mice. This might have resulted from increased immobility and decreased vigorous activity, suggesting that avoiding social isolation is important to preventing physical inactivity.

ABSTRACT

An inactive lifestyle can negatively affect physiological and mental health. Social isolation is associated with physical inactivity; however, it remains uncertain whether social isolation is a direct determinant of decreased physical activity. Hence, we assessed whether social isolation decreases home-cage activity using a within-subjects design and examined the effects of social isolation on hippocampal neurogenesis in mice. This study used a body-implantable actimeter called nanotag®, which enabled us to measure home-cage activity despite housing the mice in groups. We first examined the influence of the intraperitoneal implantation of nanotag® on home-cage activity. Although nanotag® implantation decreased home-cage activity temporarily, 7 days post-implantation, it recovered to the same level as that of control (non-implanted) mice, suggesting that implantation of nanotag® does not have a negative influence on home-cage activity if mice undergo a 1-week recovery period after implantation. In the main experiment, after the 1-week baseline measurement performed while in group housing, the mice were placed in a group or in isolation. Home-cage activity was measured for an additional 4 weeks. Home-cage activity in isolated mice during the dark period decreased by 26% from pre-intervention to the last week of intervention. Furthermore, the reduction in the number of 5-minute epochs during which the activity count exceeded 301 (an index of vigorous activity) was significantly larger for isolated mice. Contrary to expectations, social isolation did not impair hippocampal neurogenesis. Our results demonstrate that social isolation is a direct determinant of decreased physical activity, possibly because of reduced vigorous physical activity. This article is protected by copyright. All rights reserved.

AMPK in the gut-liver-brain axis and its influence on OP rats in an HSHF intake and WTD rat model

Obesogenic diets (ODs) can affect AMPK activation in several sites as the colon, liver, and hypothalamus. OD intake can impair the hypothalamic AMPK regulation of energy homeostasis. Despite consuming ODs, not all subjects have the propensity to develop or progress to obesity. The obesity propensity is more associated with energy intake than expenditure dysregulations and may have a link with AMPK activity. While the effects of ODs are studied widely, few evaluate the short-term effects of terminating OD intake. Withdrawing from OD (WTD) is thought to improve or reverse the damages caused by the intake. Therefore, here we applied an OD intake and WTD protocol aiming to evaluate AMPK protein content and phosphorylation in the colon, liver, and hypothalamus and their relationship with obesity propensity. To this end, male Wistar rats (60 days) received control or high-sugar/high-fat (HSHF) OD for 30 days. Half of the animals were OD-withdrawn and fed the control diet for 48 h. After intake, we found a reduction in AMPK phosphorylation in the hypothalamus and colon, and after WTD, we found an increase in its hepatic and hypothalamic phosphorylation. The decrease in colon pAMPK/AMPK could be linked with hypothalamic pAMPK/AMPK after HSHF intake, while the increase in hepatic pAMPK/AMPK could have prevented the increase in hypothalamic pAMPK/AMPK. In the obesity-prone rats, we found higher levels of hypothalamic and colon pAMPK/AMPK despite the higher body mass gain. Our results highlight the relevance in multi-organ investigations and animal phenotype evaluation when studying the energy metabolism regulations.

A low-cost system to easily measure spontaneous physical activity in rodents

Spontaneous physical activity (SPA) can be responsible for variations of a lot of physiological parameters at the molecular, cellular, tissue, and systemic levels. It is increasingly recognized that good understanding of a large part of experimental results requires weighting them by SPA in order to reduce variability and thus to decrease the number of animals necessary to conduct a study. However, because of the high cost of this equipment, only a few laboratories are equipped with such equipment to measure the SPA of their animals. Here we present an effective, adaptable, and affordable system to measure SPA in rodents based on video acquisition of the animal in its own environment. We compared results obtained with our system to those collected at the same time with a commercial system of actimetry recording, and we found a high degree of correlation between these two approaches ( r = 0.93; P < 0.001). We also were able to detect small variations of SPA induced by a special environment like chronic hypoxia exposure (25% less spontaneous activity compared with animals in normoxia, P < 0.05) or during the circadian cycle (107% more activity during the nocturnal phase compared with the diurnal phase, P < 0.05).

Methodological considerations for measuring spontaneous physical activity in rodents

When exploring biological determinants of spontaneous physical activity (SPA), it is critical to consider whether methodological factors differentially affect rodents and the measured SPA. We determined whether acclimation time, sensory stimulation, vendor, or chamber size affected measures in rodents with varying propensity for SPA. We used principal component analysis to determine which SPA components (ambulatory and vertical counts, time in SPA, and distance traveled) best described the variability in SPA measurements. We compared radiotelemetry and infrared photobeams used to measure SPA and exploratory activity. Acclimation time, sensory stimulation, vendor, and chamber size independently influenced SPA, and the effect was moderated by the propensity for SPA. A 24-h acclimation period prior to SPA measurement was sufficient for habituation. Principal component analysis showed that ambulatory and vertical measurements of SPA describe different dimensions of the rodent's SPA behavior. Smaller testing chambers and a sensory attenuation cubicle around the chamber reduced SPA. SPA varies between rodents purchased from different vendors. Radiotelemetry and infrared photobeams differ in their sensitivity to detect phenotypic differences in SPA and exploratory activity. These data highlight methodological considerations in rodent SPA measurement and a need to standardize SPA methodology.

Mechanisms underlying obesity resistance associated with high spontaneous physical activity

Obesity resistance due to elevated orexin signaling is accompanied by high levels of spontaneous physical activity (SPA). The behavioral and neural mechanisms underlying this observation have not been fully worked out. We determined the contribution of hypothalamic orexin receptors (OXRs) to SPA stimulated by orexin A (OXA), whether OXA-stimulated SPA was secondary to arousal and whether voluntary wheel running led to compensations in 24-h SPA. We further tested whether orexin action on dopamine one receptors (DA1R) in the substantia nigra (SN) plays an important role in the generation of SPA. To test this, SPA response was determined in lean and obese rats with cannulae targeted toward the rostral lateral hypothalamus (rLH) or SN. Sleep/wake states were also measured in rats with rLH cannula and electroencephalogram/electromyogram radiotelemetry transmitters. SPA in lean rats was more sensitive to antagonism of the OX1R and in the early response to the orexin 2 agonist. OXA increased arousal equally in lean and obese rodents, which is discordant from the greater SPA response in lean rats. Obesity-resistant rats ran more and wheel running was directly related to 24-h SPA levels. The OX1R antagonist, SB-334867-A, and the DA1R antagonist, SCH3390, in SN more effectively reduced SPA stimulated by OXA in obesity-resistant rats. These data suggest OXA-stimulated SPA is not secondary to enhanced arousal, propensity for SPA parallels inclination to run and that orexin action on dopaminergic neurons in SN may participate in the mediation of SPA and running wheel activity.

Role of the locus coeruleus in enhanced orexin A-induced spontaneous physical activity in obesity-resistant rats

Orexin/hypocretin terminals innervate noradrenergic locus coeruleus (LC) neurons that project to the prefrontral cortex, which may influence spontaneous physical activity (SPA) and energy balance. Obesity-resistant (OR) rats have higher orexin receptors (OXR) mRNA in the LC and other brain regions, as well as lower adiposity compared with obese rats. These findings led us to hypothesize that orexin activity in the LC is relevant for the OR phenotype. We compared OR rats to Sprague-Dawley rats. We predicted that: 1) brain OXR expression pattern is sufficient to differentiate OR from non-bred Sprague-Dawley rats; 2) nonresting energy expenditure (NREE) and orexin A (OXA)-stimulated SPA after injection in LC would be greater in OR rats; and 3) the effect of OXA on SPA would be greater than its effect on feeding. OXR mRNA from 11 brain sites and the SPA and feeding responses to OXA in the LC were determined. Body composition, basal SPA, and EE were determined. Principal component analysis of the OXR expression pattern differentiates OR and Sprague-Dawley rats and suggests the OXR mRNA in the LC is important in defining the OR phenotype. Compared with Sprague-Dawley rats, OR rats had greater SPA and NREE and lower resting EE and adiposity. SPA responsivity to OXA in the LC was greater in OR rats compared with Sprague-Dawley rats. OXA in the LC did not stimulate feeding in OR or Sprague-Dawley rats. These data suggest that the LC is a prominent site modulating OXA-stimulated SPA, which promotes lower adiposity and higher nonresting EE.

Sleeve gastrectomy and Roux-en-Y gastric bypass exhibit differential effects on food preferences, nutrient absorption and energy expenditure in obese rats

OBJECTIVE

All available treatments directed towards obesity and obesity-related complications are associated with suboptimal effectiveness/invasiveness ratios. Pharmacological, behavioral and lifestyle modification treatments are the least invasive, but also the least effective options, leading to modest weight loss that is difficult to maintain long-term. Gastrointestinal weight loss surgery (GIWLS) is the most effective, leading to >60-70% of excess body weight loss, but also the most invasive treatment available. Sleeve gastrectomy (SGx) and Roux-en-Y gastric bypass (RYGB) are the two most commonly performed GIWLS procedures. The fundamental anatomic difference between SGx and RYGB is that in the former procedure, only the anatomy of the stomach is altered, without surgical reconfiguration of the intestine. Therefore, comparing these two operations provides a unique opportunity to study the ways that different parts of the gastrointestinal (GI) tract contribute to the regulation of physiological processes, such as the regulation of body weight, food intake and metabolism.

DESIGN

To explore the physiologic mechanisms of the two procedures, we used rodent models of SGx and RYGB to study the effects of these procedures on body weight, food intake and metabolic function.

RESULTS

Both SGx and RYGB induced a significant weight loss that was sustained over the entire study period. SGx-induced weight loss was slightly lower compared with that observed after RYGB. SGx-induced weight loss primarily resulted from a substantial decrease in food intake and a small increase in locomotor activity. In contrast, rats that underwent RYGB exhibited a substantial increase in non-activity-related (resting) energy expenditure and a modest decrease in nutrient absorption. Additionally, while SGx-treated animals retained their preoperative food preferences, RYGB-treated rats experienced a significant alteration in their food preferences.

CONCLUSIONS

These results indicate a fundamental difference in the mechanisms of weight loss between SGx and RYGB, suggesting that the manipulation of different parts of the GI tract may lead to different physiologic effects. Understanding the differences in the physiologic mechanisms of action of these effective treatment options could help us develop less invasive new treatments against obesity and obesity-related complications.

Brain orexin promotes obesity resistance

Resistance to obesity is becoming an exception rather than the norm, and understanding mechanisms that lead some to remain lean in spite of an obesigenic environment is critical if we are to find new ways to reverse this trend. Levels of energy intake and physical activity both contribute to body weight management, but it is challenging for most to adopt major long-term changes in either factor. Physical activity outside of formal exercise, also referred to as activity of daily living, and in stricter form, spontaneous physical activity (SPA), may be an attractive modifiable variable for obesity prevention. In this review, we discuss individual variability in SPA and NEAT (nonexercise thermogenesis, or the energy expended by SPA) and its relationship to obesity resistance. The hypothalamic neuropeptide orexin (hypocretin) may play a key role in regulating SPA and NEAT. We discuss how elevated orexin signaling capacity, in the context of a brain network modulating SPA, may play a major role in defining individual variability in SPA and NEAT. Greater activation of this SPA network leads to a lower propensity for fat mass gain and therefore may be an attractive target for obesity prevention and therapy.

Reduction of high-fat diet-induced obesity after chronic administration of brain-derived neurotrophic factor in the hypothalamic ventromedial nucleus

An acute injection of brain-derived neurotrophic factor (BDNF) in the hypothalamic ventromedial nucleus (VMN) decreases body weight by reducing feeding and increasing energy expenditure (EE) in animals on standard laboratory chow. Animals have divergent responses to high-fat diet (HFD) exposure, with some developing obesity and others remaining lean. In the current study, we tested the hypothesis that BDNF in the VMN reduces HFD-induced obesity. Seventy-two 10-week old rats were allowed HFD ad libitum for 8 weeks and then prepared with bilateral VMN cannulae. Animals were then divided into tertiles based on their fat mass rank: high, intermediate, and low (H, I, and L). Each group was further divided into two subgroups: BDNF (1 μg) or control (artificial cerebrospinal fluid, aCSF); they were then injected every other day for 20 days according to subgroup. Energy intake, body weight, and body composition were measured. Other metabolic indexes were measured before and after treatment. In parallel, another 12 rats were fed control diet (CD), VMN-cannulated, and injected with aCSF. HFD exposure induced obesity in the H group, with a significant increase in energy intake, body weight, fat mass, liver size, and serum glucose, insulin, and leptin. BDNF significantly reduced body weight and fat mass in all phenotypes, while it reduced energy intake only in the I group. However, BDNF increased EE, spontaneous physical activity, and fat oxidation in the H group, suggesting that BDNF-induced EE elevation contributed to reduction of body weight and fat mass. Chronic VMN BDNF reduced insulin elevation and/or reversed hyperleptinemia. These data suggest that the VMN is an important site of action for BDNF reduction of HFD-induced obesity.

"Liking" and "wanting" of sweet and oily food stimuli as affected by high-fat diet-induced obesity, weight loss, leptin, and genetic predisposition

Cross-sectional studies in both humans and animals have demonstrated associations between obesity and altered reward functions at the behavioral and neural level, but it is unclear whether these alterations are cause or consequence of the obese state. Reward behaviors were quantified in male, outbred Sprague-Dawley (SD) and selected line obesity-prone (OP) and obesity-resistant (OR) rats after induction of obesity by high-fat diet feeding and after subsequent loss of excess body weight by chronic calorie restriction. As measured by the brief access lick and taste-reactivity paradigms, both obese SD and OP rats "liked" low concentrations of sucrose and corn oil less, but "liked" the highest concentrations more, compared with lean rats, and this effect was fully reversed by weight loss in SD rats. Acute food deprivation was unable to change decreased responsiveness to low concentrations but eliminated increased responsiveness to high concentrations in obese SD rats, and leptin administration in weight-reduced SD rats shifted concentration-response curves toward that seen in the obese state in the brief access lick test. "Wanting" and reinforcement learning as assessed in the incentive runway and progressive ratio lever-pressing paradigms was paradoxically decreased in both obese (compared with lean SD rats) and OP (compared with OR rats). Thus, reversible, obesity-associated, reduced "liking" and "wanting" of low-calorie foods in SD rats suggest a role for secondary effects of the obese state on reward functions, while similar differences between select lines of OP and OR rats before induction of obesity indicate a genetic component.

Effect of the estrous cycle and surgical ovariectomy on energy balance, fuel utilization, and physical activity in lean and obese female rats

This study presents an in-depth analysis of the effects of obesity on energy balance (EB) and fuel utilization in adult female rats, over the estrous cycle and immediately after surgical ovariectomy (OVX), to model pre- and postmenopausal states, respectively. Female Wistar rats were fed a high-fat (46%) diet for 16 wk to produce mature lean and obese animals. Stage of estrous was identified by daily vaginal lavage, while energy intake (EI), total energy expenditure (TEE), and fuel utilization were monitored in a multichamber indirect calorimeter and activity was monitored by infrared beam breaks. Metabolic monitoring studies were repeated during the 3-wk period of rapid OVX-induced weight gain. Component analysis of TEE was performed to determine the nonresting and resting portions of energy expenditure. Obesity was associated with a greater fluctuation in EB across the estrous cycle. Cycling obese rats were less active, expended more energy per movement, and oxidized more carbohydrate than lean rats. The changes in EB over the cycle in lean and obese rats were driven by changes in EI. Finally, OVX induced a large positive energy imbalance in obese and lean rats. This resulted primarily from an increase in EI in both groups, with little change in TEE following OVX. These observations reveal a dominant effect of obesity on EB, fuel utilization, and activity levels in cycling rats, which has implications for studies focused on obesity and EB in female rodents.

Commonly adopted caloric restriction protocols often involve malnutrition

Undernutrition without malnutrition is an intervention that enhances laboratory animal life span, and is widely studied to uncover factors limiting longevity. In a search of the literature over a course of four years, we found that most protocols currently adopted as caloric restriction do not meet micronutrient standards set by the National Research Council for laboratory rats and mice. We provide evidence that the most commonly adopted caloric restriction protocol, a 40% restriction of the AIN-93 diet without vitamin or mineral supplementation, leads to malnutrition in both mice and rats. Furthermore, others and we find that every other day feeding, another dietary intervention often referred to as caloric restriction, does not limit the total amount of calories consumed. Altogether, we propose that the term "caloric restriction" should be used specifically to describe diets that decrease calorie intake but not micronutrient availability, and that protocols adopted should be described in detail in order to allow for comparisons and better understanding of the effects of these diets.