Overweight and obesity result from an imbalance between caloric intake and energy expenditure, including expenditure from spontaneous physical activity (SPA). Changes in SPA and resulting changes in non-exercise activity thermogenesis (NEAT) likely interact with diet to influence risk for obesity. However, previous research on the relationship between diet, physical activity, and energy expenditure has been mixed. The neuropeptide orexin is a driver of SPA, and orexin neuron activity can be manipulated using DREADDs (Designer Receptors Exclusively Activated by Designer Drugs). We hypothesized that HFD decreases SPA and NEAT, and that DREADD-mediated activation of orexin neuron signaling would abolish this decrease and produce an increase in NEAT instead. To test these ideas, we characterized behaviors to determine the extent to which access to a high-fat diet (HFD) influences the proportion and probability of engaging in food intake and activity. We then measured NEAT following access to HFD and following a DREADD intervention targeting orexin neurons. Two cohorts of orexin-cre male mice were injected with an excitatory DREADD virus into the caudal hypothalamus, where orexin neurons are concentrated. Mice were then housed in continuous metabolic phenotyping cages (Sable Promethion). Food intake, indirect calorimetry, and SPA were automatically measured every second. For cohort 1 (n=8), animals were given access to chow, then switched to HFD. For cohort 2 (n=4/group), half of the animals were given access to HFD, the other access to chow. Then, among animals on HFD, orexin neurons were activated following injections of clozapine n-oxide (CNO). Mice on HFD spent significantly less time eating (p<0.01) and more time inactive compared to mice on chow (p<0.01). Following a meal, mice on HFD were significantly more likely to engage in periods of inactivity compared to those on chow (p<0.05). NEAT was decreased in animals on HFD, and was increased to the NEAT level of control animals following activation of orexin neurons with DREADDs. Food intake (kilocalories) was not significantly different between mice on chow and HFD, yet mice on chow expended more energy per unit of SPA, relative to that in mice consuming HFD. These results suggest that HFD consumption reduces SPA and NEAT, and increases inactivity following a meal. Together, the data suggest a change in the efficiency of energy expenditure based upon diet, such that SPA during HFD burns fewer calories compared to SPA on a standard chow diet.

Summary Mammals expend energy in many ways, including basic cellular maintenance and repair, digestion, thermoregulation, locomotion, growth and reproduction. These processes can vary tremendously among species and individuals, potentially leading to large variation in daily energy expenditure (DEE). Locomotor energy costs can be substantial for large-bodied species and those with high-activity lifestyles. For humans in industrialized societies, locomotion necessary for daily activities is often relatively low, so it has been presumed that activity energy expenditure and DEE are lower than in our ancestors. Whether this is true and has contributed to a rise in obesity is controversial. In humans, much attention has centered on spontaneous physical activity (SPA) or non-exercise activity thermogenesis (NEAT), the latter sometimes defined so broadly as to include all energy expended due to activity, exclusive of volitional exercise. Given that most people in Western societies engage in little voluntary exercise, increasing NEAT may be an effective way to maintain DEE and combat overweight and obesity. One way to promote NEAT is to decrease the amount of time spent on sedentary behaviours (e.g. watching television). The effects of voluntary exercise on other components of physical activity are highly variable in humans, partly as a function of age, and have rarely been studied in rodents. However, most rodent studies indicate that food consumption increases in the presence of wheels; therefore, other aspects of physical activity are not reduced enough to compensate for the energetic cost of wheel running. Most rodent studies also show negative effects of wheel access on body fat, especially in males. Sedentary behaviours per se have not been studied in rodents in relation to obesity. Several lines of evidence demonstrate the important role of dopamine, in addition to other neural signaling networks (e.g. the endocannabinoid system), in the control of voluntary exercise. A largely separate literature points to a key role for orexins in SPA and NEAT. Brain reward centers are involved in both types of physical activities and eating behaviours, likely leading to complex interactions. Moreover, voluntary exercise and, possibly, eating can be addictive. A growing body of research considers the relationships between personality traits and physical activity, appetite, obesity and other aspects of physical and mental health. Future studies should explore the neurobiology, endocrinology and genetics of physical activity and sedentary behaviour by examining key brain areas, neurotransmitters and hormones involved in motivation, reward and/or the regulation of energy balance.

The emerging obesity epidemic and accompanying health consequences led The Obesity Society (TOS) in 2008 to publish a position paper defining obesity as a disease. Since then, new information has emerged on the underlying mechanisms leading to excess adiposity and the associated structural, cardiometabolic, and functional disturbances. This report presents the updated TOS 2018 position statement on obesity as a noncommunicable chronic disease.

Brain-derived neurotrophic factor (BDNF) mediates energy metabolism and feeding behavior. As a neurotrophin, BDNF promotes neuronal differentiation, survival during early development, adult neurogenesis, and neural plasticity; thus, there is the potential that BDNF could modify circuits important to eating behavior and energy expenditure. The possibility that "faulty" circuits could be remodeled by BDNF is an exciting concept for new therapies for obesity and eating disorders. In the hypothalamus, BDNF and its receptor, tropomyosin-related kinase B (TrkB), are extensively expressed in areas associated with feeding and metabolism. Hypothalamic BDNF and TrkB appear to inhibit food intake and increase energy expenditure, leading to negative energy balance. In the hippocampus, the involvement of BDNF in neural plasticity and neurogenesis is important to learning and memory, but less is known about how BDNF participates in energy homeostasis. We review current research about BDNF in specific brain locations related to energy balance, environmental, and behavioral influences on BDNF expression and the possibility that BDNF may influence energy homeostasis via its role in neurogenesis and neural plasticity. food intake; body weight; ventromedial hypothalamus; paraventricular nucleus; brain-derived neurotrophic factor BRAIN-DERIVED NEUROTROPHIC factor (BDNF) is a member of the neurotrophin family of growth factors (151), along with nerve growth factor (152), and neurotrophin (NT) 3 (67, 163), NT 4/5 (28), and NT 6 (88). Neurotrophins are synthesized as 32-35-kDa pro-isoforms, which are later cleaved to mature forms that dimerize after translation and then act as receptor ligands (136). Whereas the precursor forms of other neurotrophins are constitutively secreted, the 32-kDa pro-BDNF is packaged into vesicles of a regulated pathway and is secreted in an activitydependent manner (87). Pro-BDNF may be secreted as is (48), cleaved by the extracellular protease plasmin (202), or interact with the pan-neurotrophin receptor p75 NTR and other receptors that cause an independent biological effect (244). Alternatively, pro-BDNF is processed to the mature form intracellularly by furin or proconvertases, where it forms C-terminal dimers (212, 226).Mature BDNF is considered the biologically active form, which has a high affinity for the tropomyosin-related kinase B (TrkB) receptor (130). Both BDNF and TrkB are present in presynaptic axon terminals and postsynaptic dendritic compartments of neurons, and they are capable of bidirectional release and activity [for review, see Tyler et al. (259)]. Typical of the neurotrophic factors, BDNF stimulates the development and differentiation of new neurons (3, 131) and promotes long-term potentiation (LTP) (139,140,205), and neuron survival (97,105,116). BDNF is abundantly expressed throughout the developing and mature CNS and in many peripheral tissues, including muscle, liver, and adipose (42,159,182,261). Regional differences between BDNF mRNA levels and protein concentrations in the CNS a...

No abstract

lectively-bred obesity-resistant [diet resistant (DR)] rats weigh less than obesity-prone [diet-induced obese (DIO)] rats, despite comparable daily caloric intake, suggesting phenotypic energy expenditure differences. Human data suggest that obesity is maintained by reduced ambulatory or spontaneous physical activity (SPA). The neuropeptide orexin A robustly stimulates SPA. We hypothesized that DR rats have greater: 1) basal SPA, 2) orexin A-induced SPA, and 3) preproorexin, orexin 1 and 2 receptor (OX1R and OX2R) mRNA, compared with DIO rats. A group of age-matched out-bred Sprague-Dawley rats were used as additional controls for the behavioral studies. DIO, DR, and Sprague-Dawley rats with dorsal-rostral lateral hypothalamic (rLHa) cannulas were injected with orexin A (0, 31.25, 62.5, 125, 250, and 500 pmol/0.5 l). SPA and food intake were measured for 2 h after injection. Preproorexin, OX1R and OX2R mRNA in the rLHa, and whole hypothalamus were measured by real-time RT-PCR. Orexin A significantly stimulated feeding in all rats. Orexin A-induced SPA was significantly greater in DR and Sprague-Dawley rats than in DIO rats. Two-mo-old DR rats had significantly greater rLHa OX1R and OX2R mRNA than DIO rats but comparable preproorexin levels. Eight-moold DR rats had elevated OX1R and OX2R mRNA compared with DIO rats, although this increase was significant for OX2R only at this age. Thus DR rats show elevated basal and orexin A-induced SPA associated with increased OX1R and OX2R gene expression, suggesting that differences in orexin A signaling through OX1R and OX2R may mediate DIO and DR phenotypes.hypocretin; lateral hypothalamus; locomotor activity; diet-induced obesity.OUT-BRED MALE SPRAGUE-DAWLEY rats fed a high-energy diet display divergent body weight gain patterns. Approximately half of the rats become obese [diet induced obese (DIO)] while the other half remain lean [diet resistant (DR)]. DIO and DR rats can be prospectively identified before exposure to a highenergy diet based on sympathetic activation (32) and monoaminergic function (13,24,26), suggesting that differences in the propensity toward weight gain are due to differences in CNS function. To better understand the mechanism underlying the propensity or resistance to weight gain observed in the out-bred DIO and DR rats, Sprague-Dawley rats fed a high-fat diet were selectively bred for their weight gain. This selective breeding scheme produced two substrains of Sprague-Dawley rats that displayed divergent body weight gain patterns despite comparable caloric intake following chow feeding (29, 47), suggesting that differences in energy expenditure primarily underlie phenotypic differences in body weight gain patterns. It has been demonstrated that lean individuals spent more time standing and ambulating than obese individuals, and this amount of time remained fixed independent of body weight despite overfeeding lean or underfeeding mildly obese individuals (33). Similarly, differences in spontaneous physical activity (SPA) between lean and obese out-...

Novak, Colleen M., Catherine M. Kotz, and James A. Levine. Central orexin sensitivity, physical activity, and obesity in diet-induced obese and diet-resistant rats. Am J Physiol Endocrinol Metab 290: E396-E403, 2006. First published September 27, 2005 doi:10.1152/ajpendo.00293.2005.-Nonexercise activity thermogenesis (NEAT), the most variable component of energy expenditure, can account for differential capacities for human weight gain. Also highly variable, spontaneous physical activity (SPA) may similarly affect weight balance in animals. In the following study, we utilized the rat model of obesity, the diet-induced obese (DIO) rat, as well as the diet-resistant (DR) rat strain, to investigate how access to a high-fat diet alters SPA and the associated energy expenditure (i.e., NEAT). DIO and DR rats showed no differences in the amount of SPA before access to the high-fat diet. After 29 days on a high-fat diet, the DIO rats showed significant decreases in SPA, whereas the DR rats did not. Next, we wanted to determine whether the DIO and DR rats showed differential sensitivity to microinjections of orexin into the paraventricular nucleus of the hypothalamus (PVN). Unilateral guide cannulae were implanted, aimed at the PVN. Orexin A (0, 0.125, 0.25, and 1.0 nmol in 500 nl) was microinjected through the guide cannula into the PVN, then SPA and energy expenditure were measured for 2 h. Using the response to vehicle as a baseline, the DR rats showed significantly greater increase in NEAT compared with the DIO rats. These data indicate that diet-induced obesity is associated with decreases in SPA and a lack of increase in NEAT. A putative mechanism for changes in NEAT that accompany obesity is a decreased sensitivity to the NEAT-activating effects of neuropeptides such as orexin.nonexercise activity thermogenesis; paraventricular nucleus of the hypothalamus; high-fat diet; hypocretin OBESITY IS AN EPIDEMIC associated with the increased prevalence of many diseases, increased mortality, and decreased quality of life (1, 8, 16 -20, 23, 26, 27, 31, 32, 55, 56, 58, 62, 67, 70). One major contributor to the rise in obesity is the sedentary lifestyle of many individuals, leading to decreased energy expenditure and increased body weight, as well as decreased health quality (3,6,11,22, 29, 30, 34, 36,65,77,82). In fact, energy expended through physical activity is the single most variable component of energy expenditure, and in the majority of individuals, daily physical activity is composed primarily of nonexercise activity (47, 48, 52). Nonexercise activity thermogenesis, or NEAT, differs between obese and lean individuals: lean subjects show significantly more ambulation and less sitting compared with obese subjects (50). Moreover, this difference is not altered after weight gain in lean individuals or weight loss in obese individuals, indicating that increased sedentariness is not secondary to the increased body mass in the obese subjects (50). Last, increases in NEAT in nonobese subjects after overfeeding are correlate...

The mediator of the interaction between positive energy balance and physical activity is unknown. In this study, we address the hypothesis that orexin A acts in the hypothalamic paraventricular nucleus (PVN) to increase nonfeeding-associated physical activity. PVN-cannulated rats were injected with either orexin A or vehicle during the light and dark cycle. Spontaneous physical activity (SPA) was measured using arrays of infrared activity sensors and night vision videotaped recording (VTR). O2 consumption and CO2 production were measured by indirect calorimetry. Feeding behavior was assessed by VTR. Regardless of the time point of injection, orexin A (1 nmol) was associated with dramatic increases in SPA for 2 h after injection (orexin A: 6.27 Ϯ 1.95 ϫ 10 3 beam break count, n ϭ 24; vehicle: 1.85 Ϯ 1.13 ϫ 10 3 , n ϭ 38). This increase in SPA was accompanied by compatible increase in O2 consumption. Duration of feeding was increased only when orexin A was injected in the early light phase and accounted for only 3.5 Ϯ 2.5% of the increased physical activity. In a dose-response experiment, increases in SPA were correlated with dose of orexin A linearly up to 2 nmol. PVN injections of orexin receptor antagonist SB-334867 were associated with decreases in SPA and attenuated the effects of PVN-injected orexin A. Thus orexin A can act in PVN to increase nonfeeding-associated physical activity, suggesting that this neuropeptide might be a mediator of NEAT. energy expenditure; hypothalamus; obesity; nonexercise activity thermogenesis OBESITY AFFECTS ONE-THIRD of the American population and is the second leading cause of death in the United States after smoking (1). Treatment of obesity has proven difficult, and this intractability may be due to the fact that energy balance is regulated through multiple and complex mechanisms that are not fully understood (4). Maintenance of body weight is achieved by an intricate balance between energy intake and expenditure. We found that changes in nonexercise activity thermogenesis (NEAT) mediate resistance to weight gain with overfeeding in sedentary adults (32). There is evidence that "spontaneous" physical activity (SPA) is familial (63) and shows marked interindividual differences in its contribution to daily energy expenditure (49); however, the mediator of the interaction between overfeeding and physical activity is unknown.Orexins (A and B, also known as hypocretin 1 and 2) are recently identified neuropeptides synthesized exclusively in the lateral hypothalamus, an area classically believed to be a crucial "feeding" center (25). Initial interest in these neuropeptides concentrated on their orexigenic actions, since central injection of orexins increased food intake, and prepro-orexin mRNA was shown to be upregulated with fasting (50). Apart from appetite regulation, orexins have been implicated in the central nervous system (CNS) regulation of arousal and sleep, cardiovascular function, temperature, metabolic rate, locomotor activity, pituitary secretion, glucose homeostasis, ...