Does the difference between physically active and couch potato lie in the dopamine system?

Dopamine D3 receptor status modulates sexual dimorphism in voluntary wheel running behavior in mice

Sexual dimorphism has been described in various aspects of physiological and pathophysiological processes involving dopaminergic signaling. This might account for the different disease characteristics in men and women in e.g. Parkinson's disease or ADHD. A better understanding might contribute to the future individualization of therapy. We examined spontaneous wheel running activity of male and female mice, homo- and heterozygote for dopamine D3 receptor deficiency (D3R -/- and D3R+/-), and compared them to wild type controls. We found higher wheel running activity in female mice than in their male littermates. D3-/- mice, irrespective of sex, were also hyperactive compared to both D3+/- and wild type animals. Hyperactivity of D3-/- female mice was pronounced during the first days of wheel running but then decreased while their male counterparts continued to be hyperactive. Physical activity was menstrual cycle-dependent. Activity fluctuations were also seen in D3 receptor knockout mice and are therefore presumably independent of D3 receptor activation. Our data underscore the complex interaction of dopaminergic signaling and gonadal hormones that leads to specific running behavior. Furthermore, we detected sex- and D3 receptor status-specific reactions during novel exposure to the running wheel. These findings suggest the need for adapting dopaminergic therapies to individual factors such as sex or even menstrual cycle to optimize therapeutic success.

Heritability of the affective response to exercise and its correlation to exercise behavior

OBJECTIVES

Individual differences in adolescent exercise behavior are strongly influenced by genetic factors. The affective response to exercise is a potential source of these genetic influences. To test its role in the motivation to exercise, we estimated the heritability of the affective responses during and after exercise and the overlap with the genetic factors influencing regular voluntary exercise behavior.

DESIGN

226 twin pairs and 38 siblings completed two submaximal exercise tests on a cycle ergometer and a treadmill and a maximal exercise test on a cycle ergometer. Affective responses were assessed by the Feeling Scale (FS), Borg's Rating of Perceived Exertion (RPE) and the Activation-Deactivation Adjective Checklist (AD ACL).

METHODS

Multivariate structural equation modeling was used to estimate heritability of the affective responses during and after submaximal and maximal exercise and the (genetic) correlation with self-reported regular voluntary exercise behavior over the past year.

RESULTS

Genetic factors explained 15% of the individual differences in FS responses during the cycle ergometer test, as well as 29% and 35% of the individual differences in RPE during the cycle ergometer and treadmill tests, respectively. For the AD ACL scales, heritability estimates ranged from 17% to 37% after submaximal exercise and from 12% to 37% after maximal exercise. Without exception, more positive affective responses were associated with higher amounts of regular exercise activity (.15 < r < .21) and this association was accounted for by an overlap in genetic factors influencing affective responding and exercise behavior.

CONCLUSIONS

We demonstrate low to moderate heritability estimates for the affective response during and after exercise and significant (genetic) associations with regular voluntary exercise behavior. These innate individual differences in the affective responses to exercise should be taken into account in interventions aiming to motivate adolescents to adopt and maintain regular exercise.

Running from Disease: Molecular Mechanisms Associating Dopamine and Leptin Signaling in the Brain with Physical Inactivity, Obesity, and Type 2 Diabetes

Physical inactivity is a primary contributor to diseases such as obesity, cardiovascular disease, and type 2 diabetes. Accelerometry data suggest that a majority of US adults fail to perform substantial levels of physical activity needed to improve health. Thus, understanding the molecular factors that stimulate physical activity, and physical inactivity, is imperative for the development of strategies to reduce sedentary behavior and in turn prevent chronic disease. Despite many of the well-known health benefits of physical activity being described, little is known about genetic and biological factors that may influence this complex behavior. The mesolimbic dopamine system regulates motivating and rewarding behavior as well as motor movement. Here, we present data supporting the hypothesis that obesity may mechanistically lower voluntary physical activity levels via dopamine dysregulation. In doing so, we review data that suggest mesolimbic dopamine activity is a strong contributor to voluntary physical activity behavior. We also summarize findings suggesting that obesity leads to central dopaminergic dysfunction, which in turn contributes to reductions in physical activity that often accompany obesity. Additionally, we highlight examples in which central leptin activity influences physical activity levels in a dopamine-dependent manner. Future elucidation of these mechanisms will help support strategies to increase physical activity levels in obese patients and prevent diseases caused by physical inactivity.

Early-Life Effects on Adult Physical Activity: Concepts, Relevance, and Experimental Approaches

Locomotion is a defining characteristic of animal life and plays a crucial role in most behaviors. Locomotion involves physical activity, which can have far-reaching effects on physiology and neurobiology, both acutely and chronically. In human populations and in laboratory rodents, higher levels of physical activity are generally associated with positive health outcomes, although excessive exercise can have adverse consequences. Whether and how such relationships occur in wild animals is unknown. Behavioral variation among individuals arises from genetic and environmental factors and their interactions as well as from developmental programming (persistent effects of early-life environment). Although tremendous progress has been made in identifying genetic and environmental influences on individual differences in behavior, early-life effects are not well understood. Early-life effects can in some cases persist across multiple generations following a single exposure and, in principle, may constrain or facilitate the rate of evolution at multiple levels of biological organization. Understanding the mechanisms of such transgenerational effects (e.g., exposure to stress hormones in utero, inherited epigenetic alterations) may prove crucial to explaining unexpected and/or sex-specific responses to selection as well as limits to adaptation. One area receiving increased attention is early-life effects on adult physical activity. Correlational data from epidemiological studies suggest that early-life nutritional stress can (adversely) affect adult human activity levels and associated physiological traits (e.g., body composition, metabolic health). The few existing studies of laboratory rodents demonstrate that both maternal and early-life exercise can affect adult levels of physical activity and related phenotypes. Going forward, rodents offer many opportunities for experimental studies of (multigenerational) early-life effects, including studies that use maternal exposures and cross-fostering designs.

Genetic Correlation between Body Fat Percentage and Cardiorespiratory Fitness Suggests Common Genetic Etiology

Objectives

It has long been discussed whether fitness or fatness is a more important determinant of health status. If the same genetic factors that promote body fat percentage (body fat%) are related to cardiorespiratory fitness (CRF), part of the concurrent associations with health outcomes could reflect a common genetic origin. In this study we aimed to 1) examine genetic correlations between body fat% and CRF; 2) determine whether CRF can be attributed to a genetic risk score (GRS) based on known body fat% increasing loci; and 3) examine whether the fat mass and obesity associated (FTO) locus associates with CRF.

Methods

Genetic correlations based on pedigree information were examined in a family based cohort (n = 230 from 55 families). For the genetic association analyses, we examined two Danish population-based cohorts (n_total = 3206). The body fat% GRS was created by summing the alleles of twelve independent risk variants known to associate with body fat%. We assessed CRF as maximal oxygen uptake expressed in millilitres of oxygen uptake per kg of body mass (VO₂max), per kg fat-free mass (VO₂max_FFM), or per kg fat mass (VO₂max_FM). All analyses were adjusted for age and sex, and when relevant, for body composition.

Results

We found a significant negative genetic correlation between VO₂max and body fat% (ρG = -0.72 (SE ±0.13)). The body fat% GRS associated with decreased VO₂max (β = -0.15 mL/kg/min per allele, p = 0.0034, age and sex adjusted). The body fat%-increasing FTO allele was associated with a 0.42 mL/kg/min unit decrease in VO₂max per allele (p = 0.0092, age and sex adjusted). Both associations were abolished after additional adjustment for body fat%. The fat% increasing GRS and FTO risk allele were associated with decreased VO₂max_FM but not with VO₂max_FFM.

Conclusions

Our findings suggest a shared genetic etiology between whole body fat% and CRF.

Loss of Cdk5 function in the nucleus accumbens decreases wheel running and may mediate age-related declines in voluntary physical activity

KEY POINTS

Physical inactivity, which drastically increases with advancing age, is associated with numerous chronic diseases. The nucleus accumbens (the pleasure and reward 'hub' in the brain) influences wheel running behaviour in rodents. RNA-sequencing and subsequent bioinformatics analysis led us to hypothesize a potential relationship between the regulation of dendritic spine density, the molecules involved in synaptic transmission, and age-related reductions in wheel running. Upon completion of follow-up studies, we developed the working model that synaptic plasticity in the nucleus accumbens is central to age-related changes in voluntary running. Testing this hypothesis, inhibition of Cdk5 (comprising a molecule central to the processes described above) in the nucleus accumbens reduced wheel running. The results of the present study show that reductions in synaptic transmission and Cdk5 function are related to decreases in voluntary running behaviour and provide guidance for understanding the neural mechanisms that underlie age-dependent reductions in the motivation to be physically active.

ABSTRACT

Increases in age are often associated with reduced levels of physical activity, which, in turn, associates with the development of numerous chronic diseases. We aimed to assess molecular differences in the nucleus accumbens (NAc) (a specific brain nucleus postulated to influence rewarding behaviour) with respect to wheel running and sedentary female Wistar rats at 8 and 14 weeks of age. RNA-sequencing was used to interrogate transcriptomic changes between 8- and 14-week-old wheel running rats, and select transcripts were later analysed by quantitative RT-PCR in age-matched sedentary rats. Voluntary wheel running was greatest at 8 weeks and had significantly decreased by 12 weeks. From 619 differentially expressed mRNAs, bioinformatics suggested that cAMP-mediated signalling, dopamine- and cAMP-regulated neuronal phosphoprotein of 32 kDa feedback, and synaptic plasticity were greater in 8- vs. 14-week-old rats. In depth analysis of these networks showed significant (∼20-30%; P < 0.05) decreases in cell adhesion molecule (Cadm)4 and p39 mRNAs, as well as their proteins from 8 to 14 weeks of age in running and sedentary rats. Furthermore, Cadm4, cyclin-dependent kinase 5 (Cdk5) and p39 mRNAs were significantly correlated with voluntary running distance. Analysis of dendritic spine density in the NAc showed that wheel access increased spine density (P < 0.001), whereas spine density was lower in 14- vs. 8-week-old sedentary rats (P = 0.03). Intriguingly, intra-NAc injection of the Cdk5 inhibitor roscovitine, dose-dependently decreased wheel running. Collectively, these experiments suggest that an age-dependent loss in synaptic function and Cdk5/p39 activity in the NAc may be partially responsible for age-related declines in voluntary running behaviour.

Effects of swimming exercise on morphine-induced reward and behavioral sensitization in maternally-separated rat pups in the conditioned place preference procedure

This study was designed to examine the effects of swimming exercise during adolescence on morphine-induced conditioned place preference (CPP) and behavioral sensitization in maternally separated male and female rat pups. Male Wistar rats were allowed to mate with female virgin Wistar rats. Pups were separated from the dam daily for 180min during postnatal days 2-14. All pups were weaned on day 21.The exercising pups were allowed to swim (60min/d, five days per a week, for 30days) during adolescence. Then, rat pups were tested for behavioral sensitization and the CPP induced by morphine. Maternal separation produced a significant increase in morphine-induced CPP in both sexes, behavioral sensitization in male pups and tolerance to morphine-induced motor activity in female pups. Swimmer pups separated from the dam exhibited a decrease in morphine-induced CPP in both sexes and behavioral sensitization in male pups than those of their control pups. The present results have shown that swimming exercise during adolescence may exert a protective effect against morphine-induced reward and behavioral sensitization in adult male and female rats following maternal separation.

Effects of intrinsic aerobic capacity and ovariectomy on voluntary wheel running and nucleus accumbens dopamine receptor gene expression

Rats selectively bred for high (HCR) and low (LCR) aerobic capacity show a stark divergence in wheel running behavior, which may be associated with the dopamine (DA) system in the brain. HCR possess greater motivation for voluntary running along with greater brain DA activity compared to LCR. We recently demonstrated that HCR are not immune to ovariectomy (OVX)-associated reductions in spontaneous cage (i.e. locomotor) activity. Whether HCR and LCR rats differ in their OVX-mediated voluntary wheel running response is unknown.

PURPOSE

To determine whether HCR are protected from OVX-associated reduction in voluntary wheel running.

METHODS

Forty female HCR and LCR rats (age ~27weeks) had either SHM or OVX operations, and given access to a running wheel for 11weeks. Weekly wheel running distance was monitored throughout the intervention. Nucleus accumbens (NAc) was assessed for mRNA expression of DA receptors at sacrifice.

RESULTS

Compared to LCR, HCR ran greater distance and had greater ratio of excitatory/inhibitory DA mRNA expression (both line main effects, P<0.05). Wheel running distance was significantly, positively correlated with the ratio of excitatory/inhibitory DA mRNA expression across animals. In both lines, OVX reduced wheel running (P<0.05). Unexpectedly, although HCR started with significantly greater voluntary wheel running, they had greater OVX-induced reduction in wheel running than LCR such that no differences were found 11weeks after OVX between HCROVX and LCROVX (interaction, P<0.05). This significant reduction in wheel running in HCR was associated with an OVX-mediated reduction in the ratio of excitatory/inhibitory DA mRNA expression.

CONCLUSION

The DA system in the NAc region may play a significant role in motivation to run in female rats. Compared to LCR, HCR rats run significantly more, which associates with greater ratio of excitatory/inhibitory DA mRNA expression. However, despite greater inherent motivation to run and an associated brain DA mRNA expression profile, HCR rats are not protected against OVX-induced reduction in wheel running or OVX-mediated reduction in the ratio of excitatory/inhibitory DA receptor mRNA expression. OVX-mediated reduction in motivated physical activity may be partially explained by a reduced ratio of excitatory/inhibitory DA receptor mRNA expression for which intrinsic fitness does not confer protection.

Central monoaminergic systems are a site of convergence of signals conveying the experience of exercise to brain circuits involved in cognition and emotional behavior

Physical activity can enhance cognitive function and increase resistance against deleterious effects of stress on mental health. Enhanced cognitive function and stress resistance produced by exercise are conserved among vertebrates, suggesting that ubiquitous mechanisms may underlie beneficial effects of exercise. In the current review, we summarize the beneficial effects of exercise on cognitive function and stress resistance and discuss central and peripheral signaling factors that may be critical for conferring the effects of physical activity to brain circuits involved in cognitive function and stress. Additionally, it is suggested that norepinephrine and serotonin, highly conserved monoamines that are sensitive to exercise and able to modulate behavior in multiple species, could represent a convergence between peripheral and central exercise signals that mediate the beneficial effects of exercise. Finally, we offer the novel hypothesis that thermoregulation during exercise could contribute to the emotional effects of exercise by activating a subset of temperature-sensitive serotonergic neurons in the dorsal raphe nucleus that convey anxiolytic and stress-protective signals to forebrain regions. Throughout the review, we discuss limitations to current approaches and offer strategies for future research in exercise neuroscience.

A dopamine and noradrenaline reuptake inhibitor (bupropion) does not alter exercise performance of bank voles

Physical performance is determined both by biophysical and physiological limitations and behavioral characteristic, specifically motivation. We applied an experimental evolution approach combined with pharmacological manipulation to test the hypothesis that evolution of increased aerobic exercise performance can be triggered by evolution of motivation to undertake physical activity. We used a unique model system: bank voles from A lines, selected for high swim-induced aerobic metabolism (VO₂swim), which achieved a 61% higher mass-adjusted VO₂swim than those from unselected C lines. Because the voles could float on the water surface with only a minimum activity, the maximum rate of metabolism achieved in that test depended not only on their aerobic capacity, but also on motivation to undertake intensive activity. Therefore, we hypothesized that signaling of neurotransmitters putatively involved in regulating physical activity (dopamine and noradrenaline) had changed in response to selection. We measured VO₂swim after intraperitoneal injections of saline or the norepinephrine and dopamine reuptake inhibitor bupropion (20 mg/kg or 30 mg/kg). Additionally, we measured forced-exercise VO₂ (VO₂max). In C lines, VO₂swim (mass-adjusted mean ± standard error (SE): 4.0 ± 0.1 mLO₂/min) was lower than VO₂max (5.0 ± 0.1 mLO₂/min), but in A lines VO2swim (6.0 ± 0.1 mLO₂/min) was as high as VO₂max (6.0 ± 0.1 mLO₂/min). Thus, the selection effectively changed both the physiological-physical performance limit and mechanisms responsible for the willingness to undertake vigorous locomotor activity. Surprisingly, the drug had no effect on the achieved level of VO₂swim. Thus, the results did not allow firm conclusions concerning involvement of these neurotransmitters in evolution of increased aerobic exercise performance in the experimental evolution model system.

Progressive Axonal Degeneration of Nigrostriatal Dopaminergic Neurons in Calcium-Independent Phospholipase A2β Knockout Mice

Calcium-independent phospholipase A₂β (iPLA₂β, PLA2G6) is essential for the remodeling of membrane glycerophospholipids. Mutations in this gene are responsible for autosomal recessive, young onset, L-dopa-responsive parkinsonism (PARK14), suggesting a neurodegenerative condition in the nigrostriatal dopaminergic system in patients with PLA2G6 mutations. We previously observed slowly progressive motor deficits in iPLA₂β-knockout (KO) mice. To clarify whether a deficiency of iPLA₂β leads to the degeneration of nigrostriatal dopaminergic neurons, we analyzed the striatum of iPLA₂β-KO mice. At all clinical stages, nerve terminals in the striatum were immunopositive for tyrosine hydroxylase (TH) and dopamine transporter (DAT) in wild-type (WT) control mice. In iPLA₂β-KO mice, focal loss of nerve terminals positive for TH and DAT was found from 56 weeks (early clinical stage), although iPLA₂β-KO mice at 56 weeks showed no significant decrease in the number of dopaminergic neurons in the substantia nigra compared with age-matched WT mice, as reported previously. At 100 weeks (late clinical stage), greater decreases in DAT immunoreactivity were observed in the striatum of iPLA₂β-KO mice. Moreover, strongly TH-positive structures, presumed to be deformed axons, were observed in the neuropils of the striatum of iPLA₂β-KO mice starting at 15 weeks (preclinical stage) and increased with age. These results suggest that the degeneration of dopaminergic neurons occurs mainly in the distal region of axons in iPLA₂β-KO mice.

Cthrc1 controls adipose tissue formation, body composition, and physical activity

OBJECTIVE

This study investigated the effects of loss of Cthrc1 on adipogenesis, body composition, metabolism, physical activity, and muscle physiology.

METHODS

Complete metabolic and activity monitoring as well as grip strength measurements and muscle myography was performed in Cthrc1 null and wildtype mice.

RESULTS

Compared to wildtypes, Cthrc1 null mice had similar body weights but significantly reduced energy expenditure, decreased lean mass, and increased fat mass, especially visceral fat. In vitro studies demonstrated that Cthrc1 inhibited adipocyte differentiation as well as PPAR and CREB reporter activity, while preadipocytes isolated from Cthrc1 null mice exhibited enhanced adipogenic differentiation. Voluntary physical activity in Cthrc1 null mice as assessed by wheel running was reduced to approximately half the distance covered by wildtypes. Reduced grip strength was observed in Cthrc1 null mice at the age of 15 weeks or older with reduced performance and mass of hyphenate muscle. In the brain, Cthrc1 expression was most prominent in neurons of thalamic and hypothalamic nuclei with evidence for secretion into the circulation in the median eminence.

CONCLUSIONS

Our data indicate that Cthrc1 regulates body composition through inhibition of adipogenesis. In addition, central Cthrc1 may be a mediator of muscle function and physical activity.

Mu opioid receptor modulation in the nucleus accumbens lowers voluntary wheel running in rats bred for high running motivation

The exact role of opioid receptor signaling in mediating voluntary wheel running is unclear. To provide additional understanding, female rats selectively bred for motivation of low (LVR) versus high voluntary running (HVR) behaviors were used. Aims of this study were 1) to identify intrinsic differences in nucleus accumbens (NAc) mRNA expression of opioid-related transcripts and 2) to determine if nightly wheel running is differently influenced by bilateral NAc injections of either the mu-opioid receptor agonist D-Ala2, NMe-Phe4, Glyo5-enkephalin (DAMGO) (0.25, 2.5 μg/side), or its antagonist, naltrexone (5, 10, 20 μg/side). In Experiment 1, intrinsic expression of Oprm1 and Pdyn mRNAs were higher in HVR compared to LVR. Thus, the data imply that line differences in opioidergic mRNA in the NAc could partially contribute to differences in wheel running behavior. In Experiment 2, a significant decrease in running distance was present in HVR rats treated with 2.5 μg DAMGO, or with 10 μg and 20 μg naltrexone between hours 0-1 of the dark cycle. Neither DAMGO nor naltrexone had a significant effect on running distance in LVR rats. Taken together, the data suggest that the high nightly voluntary running distance expressed by HVR rats is mediated by increased endogenous mu-opioid receptor signaling in the NAc, that is disturbed by either agonism or antagonism. In summary, our findings on NAc opioidergic mRNA expression and mu-opioid receptor modulations suggest HVR rats, compared to LVR rats, express higher running levels mediated by an increase in motivation driven, in part, by elevated NAc opioidergic signaling.

Genetics of Regular Exercise and Sedentary Behaviors

Studies on the determinants of physical activity have traditionally focused on social factors and environmental barriers, but recent research has shown the additional importance of biological factors, including genetic variation. Here we review the major tenets of this research to arrive at three major conclusions: First, individual differences in physical activity traits are significantly influenced by genetic factors, but genetic contribution varies strongly over age, with heritability of leisure time exercise behavior ranging from 27% to 84% and heritability of sedentary behaviors ranging from 9% to 48%. Second, candidate gene approaches based on animal or human QTLs or on biological relevance (e.g., dopaminergic or cannabinoid activity in the brain, or exercise performance influencing muscle physiology) have not yet yielded the necessary evidence to specify the genetic mechanisms underlying the heritability of physical activity traits. Third, there is significant genetic modulation of the beneficial effects of daily physical activity patterns on strength and endurance improvements and on health-related parameters like body mass index. Further increases in our understanding of the genetic determinants of sedentary and exercise behaviors as well as the genetic modulation of their effects on fitness and health will be key to meaningful future intervention on these behaviors.

Physical activity and the endocannabinoid system: an overview

Recognized as a "disease modifier", physical activity (PA) is increasingly viewed as a more holistic, cost-saving method for prevention, treatment and management of human disease conditions. The traditional view that PA engages the monoaminergic and endorphinergic systems has been challenged by the discovery of the endocannabinoid system (ECS), composed of endogenous lipids, their target receptors, and metabolic enzymes. Indeed, direct and indirect evidence suggests that the ECS might mediate some of the PA-triggered effects throughout the body. Moreover, it is now emerging that PA itself is able to modulate ECS in different ways. Against this background, in the present review we shall discuss evidence of the cross-talk between PA and the ECS, ranging from brain to peripheral districts and highlighting how ECS must be tightly regulated during PA, in order to maintain its beneficial effects on cognition, mood, and nociception, while avoiding impaired energy metabolism, oxidative stress, and inflammatory processes.

Striatal enkephalinergic differences in rats selectively bred for intrinsic running capacity

Rats selectively bred for high- and low-capacity for running on a treadmill (HCR; LCR) also differ in wheel-running behavior, but whether wheel-running can be explained by intrinsic or adaptive brain mechanisms is not as yet understood. It is established that motivation of locomotory behavior is driven by dopaminergic transmission in mesolimbic and mesostriatal systems. However, whether voluntary wheel running is associated with enkephalinergic activity in the ventral striatum is not known.

MATERIALS AND METHODS

40 male (20 HCR and 20 LCR) and 40 female (20 HCR and 20 LCR) rats were randomly assigned to 3 weeks of activity wheel exposure or sedentary conditions without wheel access. After 3 weeks of activity-wheel running, rats were decapitated and brains were extracted. Coronal sections were analyzed utilizing in situ hybridization histochemistry for enkephalin (ENK) mRNA in the ventral striatum.

RESULTS

HCR rats expressed less ENK than LCR rats in the nucleus accumbens among females (p<0.01) and in the olfactory tubercle among both females (p<0.05) and males (p<0.05). There was no effect of wheel running on ENK mRNA expression.

CONCLUSION

Line differences in ENK expression in the olfactory tubercle, and possibly the nucleus accumbens, partly explain divergent wheel-running behavior. The lower striatal ENK in the HCR line is consistent with enhanced dopaminergic tone, which may explain the increased motivation for wheel running observed in the HCR line.

Nucleus accumbens neuronal maturation differences in young rats bred for low versus high voluntary running behaviour

We compared the nucleus accumbens (NAc) transcriptomes of generation 8 (G8), 34-day-old rats selectively bred for low (LVR) versus high voluntary running (HVR) behaviours in rats that never ran (LVR(non-run) and HVR(non-run)), as well as in rats after 6 days of voluntary wheel running (LVR(run) and HVR(run)). In addition, the NAc transcriptome of wild-type Wistar rats was compared. The purpose of this transcriptomics approach was to generate testable hypotheses as to possible NAc features that may be contributing to running motivation differences between lines. Ingenuity Pathway Analysis and Gene Ontology analyses suggested that 'cell cycle'-related transcripts and the running-induced plasticity of dopamine-related transcripts were lower in LVR versus HVR rats. From these data, a hypothesis was generated that LVR rats might have less NAc neuron maturation than HVR rats. Follow-up immunohistochemistry in G9-10 LVR(non-run) rats suggested that the LVR line inherently possessed fewer mature medium spiny (Darpp-32-positive) neurons (P < 0.001) and fewer immature (Dcx-positive) neurons (P < 0.001) than their G9-10 HVR counterparts. However, voluntary running wheel access in our G9-10 LVRs uniquely increased their Darpp-32-positive and Dcx-positive neuron densities. In summary, NAc cellularity differences and/or the lack of running-induced plasticity in dopamine signalling-related transcripts may contribute to low voluntary running motivation in LVR rats.

The dopaminergic reward system and leisure time exercise behavior: a candidate allele study

PURPOSE

Twin studies provide evidence that genetic influences contribute strongly to individual differences in exercise behavior. We hypothesize that part of this heritability is explained by genetic variation in the dopaminergic reward system. Eight single nucleotide polymorphisms (SNPs in DRD1: rs265981, DRD2: rs6275, rs1800497, DRD3: rs6280, DRD4: rs1800955, DBH: rs1611115, rs2519152, and in COMT: rs4680) and three variable number of tandem repeats (VNTRs in DRD4, upstream of DRD5, and in DAT1) were investigated for an association with regular leisure time exercise behavior.

MATERIALS AND METHODS

Data on exercise activities and at least one SNP/VNTR were available for 8,768 individuals aged 7 to 50 years old that were part of the Netherlands Twin Register. Exercise behavior was quantified as weekly metabolic equivalents of task (MET) spent on exercise activities. Mixed models were fitted in SPSS with genetic relatedness as a random effect.

RESULTS

None of the genetic variants were associated with exercise behavior (P>.02), despite sufficient power to detect small effects.

DISCUSSION AND CONCLUSIONS

We did not confirm that allelic variants involved in dopaminergic function play a role in creating individual differences in exercise behavior. A plea is made for large genome-wide association studies to unravel the genetic pathways that affect this health-enhancing behavior.

Physical activity in adolescents with psychiatric disorders and in the general population

BACKGROUND

Adults who suffer from psychiatric disorders report low levels of physical activity and the activity levels differ between disorders. Less is known regarding physical activity across psychiatric disorders in adolescence. We investigate the frequency and type of physical activity in adolescent psychiatric patients, compared with adolescents in the general population.

METHODS

A total of 566 adolescent psychiatric patients aged 13-18 years who participated in the CAP survey, Norway, were compared to 8173 adolescents aged 13-19 years who participated in the Nord-Trøndelag Health Study, Young-HUNT 3, Norway. All adolescents completed a questionnaire, including questions about physical activity and participation in team and individual sports.

RESULTS

Approximately 50% of adolescents with psychiatric disorders and 25% of the population sample reported low levels of physical activity. Within the clinical sample, those with mood disorders (62%) and autism spectrum disorders (56%) were the most inactive and those with eating disorders (36%) the most active. This pattern was the same in individual and team sports. After multivariable adjustment, adolescents with a psychiatric disorder had a three-fold increased risk of lower levels of physical activity, and a corresponding risk of not participating in team and individual sports compared with adolescents in the general population.

CONCLUSIONS

Levels of physical activity were low in adolescent psychiatric patients compared with the general population, yet activity levels differed considerably between various disorders. The findings underscore the importance of assessing physical activity in adolescents with psychiatric disorders and providing early intervention to promote mental as well as physical health in this early stage of life.

Exercise as a novel treatment for drug addiction: a neurobiological and stage-dependent hypothesis

Physical activity, and specifically exercise, has been suggested as a potential treatment for drug addiction. In this review, we discuss clinical and preclinical evidence for the efficacy of exercise at different phases of the addiction process. Potential neurobiological mechanisms are also discussed focusing on interactions with dopaminergic and glutamatergic signaling and chromatin remodeling in the reward pathway. While exercise generally produces an efficacious response, certain exercise conditions may be either ineffective or lead to detrimental effects depending on the level/type/timing of exercise exposure, the stage of addiction, the drug involved, and the subject population. During drug use initiation and withdrawal, its efficacy may be related to its ability to facilitate dopaminergic transmission, and once addiction develops, its efficacy may be related to its ability to normalize glutamatergic and dopaminergic signaling and reverse drug-induced changes in chromatin via epigenetic interactions with brain-derived neurotrophic factor (BDNF) in the reward pathway. We conclude with future directions, including the development of exercise-based interventions alone or as an adjunct to other strategies for treating drug addiction.

Loneliness is associated with an increased risk of sedentary life in older Israelis

OBJECTIVES

Both loneliness and insufficient physical activity are common in old age. This study investigated the association between loneliness and adherence to recommended guidelines of physical activity in a national sample of Israelis, and examined whether loneliness was a risk factor for insufficient physical activity independent of other variables.

METHODS

A random sample of 1663 (799 men) older adults aged 65+ reported their physical activity routine, and based on official guidelines were categorized as sufficiently active, insufficiently active, and inactive. In addition, they were divided into lonely or not lonely based on a single question from the Center for Epidemiologic Studies Depression Scale.

RESULTS

Chi-square analyses indicated that loneliness, but not living alone, were inversely related to level of physical activity in both genders. Based on multinomial stepwise logistic regressions body mass index, being religious versus secular, self-rated health, and education were associated with engaging in physical activity in men (Cox & Snell R(2) = 0.202). Loneliness contributed significantly to explaining the level of participation in physical activity beyond these variables in women, but not in men (Cox & Snell R(2) = 0.197).

CONCLUSIONS

Loneliness is associated with an increasing risk of inactivity in advanced age in women. Further research inquiring into whether loneliness is the cause of reduced physical activity or whether physical activity acts as a protective factor against loneliness is needed. Developing and implementing tailored intervention programs that encourage social interaction in combination with a physical activity program are recommended.

Vivo-morpholinos induced transient knockdown of physical activity related proteins

Physical activity is associated with disease prevention and overall wellbeing. Additionally there has been evidence that physical activity level is a result of genetic influence. However, there has not been a reliable method to silence candidate genes in vivo to determine causal mechanisms of physical activity regulation. Vivo-morpholinos are a potential method to transiently silence specific genes. Thus, the aim of this study was to validate the use of Vivo-morpholinos in a mouse model for voluntary physical activity with several sub-objectives. We observed that Vivo-morpholinos achieved between 60–97% knockdown of Drd1-, Vmat2-, and Glut4-protein in skeletal muscle, the delivery moiety of Vivo-morpholinos (scramble) did not influence physical activity and that a cocktail of multiple Vivo-morpholinos can be given in a single treatment to achieve protein knockdown of two different targeted proteins in skeletal muscle simultaneously. Knocking down Drd1, Vmat2, or Glut4 protein in skeletal muscle did not affect physical activity. Vivo-morpholinos injected intravenously alone did not significantly knockdown Vmat2-protein expression in the brain (p = 0.28). However, the use of a bradykinin analog to increase blood-brain-barrier permeability in conjunction with the Vivo-morpholinos significantly (p = 0.0001) decreased Vmat2-protein in the brain with a corresponding later over-expression of Vmat2 coincident with a significant (p = 0.0016) increase in physical activity. We conclude that Vivo-morpholinos can be a valuable tool in determining causal gene-phenotype relationships in whole animal models.

Phenotypic and molecular differences between rats selectively bred to voluntarily run high vs. low nightly distances

The purpose of the present study was to partially phenotype male and female rats from generations 8-10 (G8-G10) that had been selectively bred to possess low (LVR) vs. high voluntary running (HVR) behavior. Over the first 6 days with wheels, 34-day-old G8 male and female LVRs ran shorter distances (P < 0.001), spent less time running (P < 0.001), and ran slower (P < 0.001) than their G8 male and female HVR counterparts, respectively. HVR and LVR lines consumed similar amounts of standard chow with or without wheels. No inherent difference existed in PGC-1α mRNA in the plantaris and soleus muscles of LVR and HVR nonrunners, although G8 LVR rats inherently possessed less NADH-positive superficial plantaris fibers compared with G8 HVR rats. While day 28 body mass tended to be greater in both sexes of G9-G10 LVR nonrunners vs. G9-G10 HVR nonrunners (P = 0.06), body fat percentage was similar between lines. G9-G10 HVRs had fat mass loss after 6 days of running compared with their prerunning values, while LVR did not lose or gain fat mass during the 6-day voluntary running period. RNA deep sequencing efforts in the nucleus accumbens showed only eight transcripts to be >1.5-fold differentially expressed between lines in HVR and LVR nonrunners. Interestingly, HVRs presented less Oprd1 mRNA, which ties in to potential differences in dopaminergic signaling between lines. This unique animal model provides further evidence as to how exercise may be mechanistically regulated.

Exercise metabolism and the molecular regulation of skeletal muscle adaptation

Preservation of aerobic fitness and skeletal muscle strength through exercise training can ameliorate metabolic dysfunction and prevent chronic disease. These benefits are mediated in part by extensive metabolic and molecular remodeling of skeletal muscle by exercise. Aerobic and resistance exercise represent extremes on the exercise continuum and elicit markedly different training responses that are mediated by a complex interplay between a myriad of signaling pathways coupled to downstream regulators of transcription and translation. Here, we review the metabolic responses and molecular mechanisms that underpin the adaptatation of skeletal muscle to acute exercise and exercise training.

Pharmacological blockade and genetic absence of the dopamine D2 receptor specifically modulate voluntary locomotor activity in mice

Dopaminergic signaling influences physical activity. Notably impaired D2 receptor (D2R) function has been associated with decreased voluntary physical activity. Most animal models investigating effects of genetic or pharmacological dopaminergic modulation measure physical activity for a limited time of up to few hours. The aim of this study is to investigate the impact of chronic or acute D2R dysfunction on physical activity over several days. For this purpose, we used a highly automated running wheel system to continuously record physical activity in mice. We found that D2R-knockout status led to a permanent decrease of running wheel activity. In contrast, acute D2R blockade by raclopride (1.5-5mg/kg) resulted in an initial dose-dependent reduction of running wheel usage and a compensating increase of activity in later stages of the activity phase. This indicates that D2R dysfunction reduces physical activity. Our data indicate that this reduction to a large extent cannot be explained by motor deficits. The delayed increase of activity after D2R blockade might be due to a rebound effect.

Polymorphic variants of neurotransmitter receptor genes may affect sexual function in aging males: data from the HALS study

BACKGROUND/AIMS

Human behavior is influenced by a number of brain neurotransmitters. Central dopamine, serotonin and melanocortin systems have special importance for male sexual function. We searched for associations between male aging symptoms and polymorphic sites of serotonin (5-HTR1B), melanocortin (MC4R) and dopamine (DRD2, DRD4) receptors.

METHODS

In a population-based sample, genotyping of 5-HTR1B (polymorphism: G861C), MC4R (polymorphisms: C-2745T, Val103Ile), DRD2 (polymorphism: C313T) and DRD4 (polymorphism: 48-bp VNTR) was performed in 387 healthy men. The Aging Males' Symptoms (AMS) scale was used to evaluate specific ailments of aging men. We analyzed answers to questions from the AMS scale. Five points of the questionnaire addressed sexual symptoms of the aging male: feeling of passing one's peak, decrease in beard growth, decrease in ability/frequency to perform sexually, decrease in the number of morning erections, and decrease in sexual desire/libido (lacking pleasure in sex, lacking desire for sexual intercourse). Relations between reported symptoms and variants of the polymorphic sites of the studied genes were assessed.

RESULTS

After adjusting for confounding factors (education, arterial hypertension, physical activity, weight, waist circumference) an association between the sexual dimension of AMS and genetic variants of 5-HTR1B G861C (p = 0.04) was observed.

CONCLUSIONS

Variability of neurotransmitter receptor genes may be associated with sexual symptoms of aging in men.

Sensation-seeking genes and physical activity in youth

Many studies examining genetic influences on physical activity (PA) have evaluated the impact of single nucleotide polymorphisms (SNPs) related to the development of lifestyle-related chronic diseases, under the hypothesis that they would be associated with PA. However, PA is a multidetermined behavior and associated with a multitude of health consequences. Thus, examining a broader range of candidate genes associated with a broader range of PA correlates may provide new insights into the genetic underpinnings of PA. In this study, we focus on one such correlate - sensation-seeking behavior. Participants (N = 1130 Mexican origin youth) provided a saliva sample and data on PA and sensation-seeking tendencies in 2008-2009. Participants were genotyped for 630 functional and tagging variants in the dopamine, serotonin and cannabinoid pathways. Overall 30% of participants (males - 37.6% and females - 22.0%) reported ≥60 min of PA on 5 of 7 days. After adjusting for gender, age and population stratification, and applying the Bayesian False Discovery Probability approach for assessing noteworthiness, four gene variants were significantly associated with PA. In a multivariable model, being male, having higher sensation-seeking tendencies and at least one copy of the minor allele for SNPs in angiotensin I-converting enzyme gene [ACE; rs8066276 odds ratio (OR) = 1.44; P = 0.012] and tryptophan hydroxylase 2 gene (TPH2; rs11615016 OR = 1.73; P = 0.021) were associated with increased likelihood of meeting PA recommendations. Participants with at least one copy of the minor allele for SNPs in synaptosomal-associated protein 25 gene (SNAP25; rs363035 OR = 0.53; P = 0.005) and cannabinoid receptor 1 gene (CNR1; rs6454672 OR = 0.62; P = 0.022) have decreased likelihood of meeting PA recommendations. Our findings extend current knowledge of the complex relationship between PA and possible genetic underpinnings.

DRD2 C313T and DRD4 48-bp VNTR polymorphisms and physical activity of healthy men in Lower Silesia, Poland (HALS study)

BACKGROUND

Both animal and human studies have proved that the dopaminergic system of the brain controls many aspects of behavior, e.g. motivation, addiction, motor movement, locomotion. It has been hypothesized that dopamine signalling may regulate spontaneous physical activity as well.

AIM

Literature data suggests that an intact function of dopamine receptors (DRD2-DRD4) inhibits physical activity. This study searched for associations between a propensity to be active (or sedentary) and genetic variants of DRD2 and DRD4.

SUBJECTS AND METHODS

Invitations to participate in the study were sent to 900 randomly selected, adult men living in Lower Silesia, Poland. Genotyping of DRD2 C313T and DRD4 48-bp VNTR polymorphisms of enrolled subjects (371 (DRD2 C313T) and 397 (DRD4 48-bp VNTR)) was performed. Level of physical activity was evaluated using the International Physical Activity Questionnaire (IPAQ).

RESULTS

No associations were found between level of physical activity (low, moderate, high) and the two polymorphisms: DRD2 C313T (p = 0.49) and DRD4 48-bp VNTR (p = 0.31). Studied subjects did not differ as to the number of hours spent sitting either.

CONCLUSION

The results exclude the presence of significant relationships between polymorphic variants of the dopamine receptors genes and the level of physical activity in men.

Psychological functioning and adherence to the recommended dose of physical activity in later life: results from a national health survey

BACKGROUND

Official health organizations have established the dose of physical activity needed for preserving both physical and psychological health in old age. The objective of this study was to explore whether adherence to the recommended criterion of physical activity accounted for better psychological functioning in older adults in Israel.

METHODS

A random sample of 1,663 (799 men) Israelis reported their physical activity routine, and based on official guidelines were divided into sufficiently active, insufficiently active, and inactive groups. The General Health Questionnaire (GHQ) was used for assessing mental health and the Mini-Mental State Examination (MMSE) for assessing cognitive functioning.

RESULTS

Factor analysis performed on the GHQ yielded two factors - positive and negative. Logistic regressions for the GHQ factors and for the MMSE were conducted for explaining their variance, with demographic variables entered first, followed by health and then physical activity. The explained variance in the three steps was Cox and Snell R2 = 0.022, 0.023, 0.039 for the positive factor, 0.066, 0.093, 0.101 for the negative factor, and 0.204, 0.206, 0.209 for the MMSE.

CONCLUSIONS

Adherence to the recommended dose of physical activity accounted for better psychological functioning beyond demographic and health variables; however, the additional explained variance was small. More specific guidelines of physical activity may elucidate a stronger relationship, but only randomized controlled trials can reveal cause-effect relationship between physical activity and psychological functioning. More studies are needed focusing on the positive factor of psychological functioning.

The TaqIA RFLP is associated with attenuated intervention-induced body weight loss and increased carbohydrate intake in post-menopausal obese women

INTRODUCTION

Polymorphisms of the dopamine receptor D2 (DRD2) gene have been associated with obesity phenotypes. Our aim was to examine if the genotype of TaqIA Restriction Fragment Length Polymorphism (RFPL) was related to an attenuated weight loss response or to changes in energy expenditure (EE) and food preference before and after weight loss. methods: Obese post-menopausal women (age=57.1 ± 4.6 yr, weight=85.4 ± 15.4 kg and BMI=32.8 ± 4.5 kg/m(2)) were genotyped for TaqIA (n=127) by using PCR-RFLP analysis and categorized as possessing at least one copy of the A1 allele (A1(+)) or no copy (A1(-)). Women were randomized into two groups, caloric restriction (CR) and caloric restriction+resistance training (CRRT) and in this study were further classified as follows: A1(+)CR, A1(+)CRRT, A1-(-)CR and (-)A1(-)CRRT. Body composition, total daily EE, physical activity EE, Resting EE (REE), and energy intake were obtained at baseline and post-intervention using DXA, doubly-labeled water, indirect calorimetry, and 3-day dietary records, respectively.

RESULTS

Overall, all of the anthropometric variables and REE significantly decreased post-intervention (p<0.001). Women in the CRRT group lost significantly more fat mass (FM) than the CR women (p<0.05). There were significant time by group by allele interactions for attenuated body weight (BW), BMI, and FM loss for A1(+) (vs. A1(-)) in CRRT (p<0.05) and for increased % carbohydrate intake (p<0.01).

CONCLUSION

TaqIA genotype was associated with body weight loss post-intervention; more specifically, carriers of the A1 allele lost significantly less BW and FM than the A1(-) and had increased carbohydrate intake in the CRRT group.

Neurobiological studies of fatigue

Fatigue is a symptom associated with many disorders, is especially common in women and in older adults, and can have a huge negative influence on quality of life. Although most past research on fatigue uses human subjects instead of animal models, the use of appropriate animal models has recently begun to advance our understanding of the neurobiology of fatigue. In this review, results from animal models using immunological, developmental, or physical approaches to study fatigue are described and compared. Common across these animal models is that fatigue arises when a stimulus induces activation of microglia and/or increased cytokines and chemokines in the brain. Neurobiological studies implicate structures in the ascending arousal system, sleep executive control areas, and areas important in reward. In addition, the suprachiasmatic nucleus clearly plays an important role in homeostatic regulation of the neural network mediating fatigue. This nucleus responds to cytokines, shows decreased amplitude firing rate output in models of fatigue, and responds to exercise, one of our few treatments for fatigue. This is a young field but very important as the symptom of fatigue is common across many disorders and we do not have effective treatments.

Putting desire on a budget: dopamine and energy expenditure, reconciling reward and resources

Accumulating evidence indicates integration of dopamine function with metabolic signals, highlighting a potential role for dopamine in energy balance, frequently construed as modulating reward in response to homeostatic state. Though its precise role remains controversial, the reward perspective of dopamine has dominated investigation of motivational disorders, including obesity. In the hypothesis outlined here, we suggest instead that the primary role of dopamine in behavior is to modulate activity to adapt behavioral energy expenditure to the prevailing environmental energy conditions, with the role of dopamine in reward and motivated behaviors derived from its primary role in energy balance. Dopamine has long been known to modulate activity, exemplified by psychostimulants that act via dopamine. More recently, there has been nascent investigation into the role of dopamine in modulating voluntary activity, with some investigators suggesting that dopamine may serve as a final common pathway that couples energy sensing to regulated voluntary energy expenditure. We suggest that interposed between input from both the internal and external world, dopamine modulates behavioral energy expenditure along two axes: a conserve-expend axis that regulates generalized activity and an explore-exploit axes that regulates the degree to which reward value biases the distribution of activity. In this view, increased dopamine does not promote consumption of tasty food. Instead increased dopamine promotes energy expenditure and exploration while decreased dopamine favors energy conservation and exploitation. This hypothesis provides a mechanistic interpretation to an apparent paradox: the well-established role of dopamine in food seeking and the findings that low dopaminergic functions are associated with obesity. Our hypothesis provides an alternative perspective on the role of dopamine in obesity and reinterprets the "reward deficiency hypothesis" as a perceived energy deficit. We propose that dopamine, by facilitating energy expenditure, should be protective against obesity. We suggest the apparent failure of this protective mechanism in Western societies with high prevalence of obesity arises as a consequence of sedentary lifestyles that thwart energy expenditure.

Music listening after stroke: beneficial effects and potential neural mechanisms

Music is an enjoyable leisure activity that also engages many emotional, cognitive, and motor processes in the brain. Here, we will first review previous literature on the emotional and cognitive effects of music listening in healthy persons and various clinical groups. Then we will present findings about the short- and long-term effects of music listening on the recovery of cognitive function in stroke patients and the underlying neural mechanisms of these music effects. First, our results indicate that listening to pleasant music can have a short-term facilitating effect on visual awareness in patients with visual neglect, which is associated with functional coupling between emotional and attentional brain regions. Second, daily music listening can improve auditory and verbal memory, focused attention, and mood as well as induce structural gray matter changes in the early poststroke stage. The psychological and neural mechanisms potentially underlying the rehabilitating effect of music after stroke are discussed.

Functional genomic architecture of predisposition to voluntary exercise in mice: expression QTL in the brain

The biological basis of voluntary exercise is complex and simultaneously controlled by peripheral (ability) and central (motivation) mechanisms. The accompanying natural reward, potential addiction, and the motivation associated with exercise are hypothesized to be regulated by multiple brain regions, neurotransmitters, peptides, and hormones. We generated a large (n = 815) advanced intercross line of mice (G(4)) derived from a line selectively bred for increased wheel running (high runner) and the C57BL/6J inbred strain. We previously mapped multiple quantitative trait loci (QTL) that contribute to the biological control of voluntary exercise levels, body weight, and composition, as well as changes in body weight and composition in response to short-term exercise. Currently, using a subset of the G(4) population (n = 244), we examined the transcriptional landscape relevant to neurobiological aspects of voluntary exercise by means of global mRNA expression profiles from brain tissue. We identified genome-wide expression quantitative trait loci (eQTL) regulating variation in mRNA abundance and determined the mode of gene action and the cis- and/or trans-acting nature of each eQTL. Subsets of cis-acting eQTL, colocalizing with QTL for exercise or body composition traits, were used to identify candidate genes based on both positional and functional evidence, which were further filtered by correlational and exclusion mapping analyses. Specifically, we discuss six plausible candidate genes (Insig2, Socs2, DBY, Arrdc4, Prcp, IL15) and their potential role in the regulation of voluntary activity, body composition, and their interactions. These results develop a potential initial model of the underlying functional genomic architecture of predisposition to voluntary exercise and its effects on body weight and composition within a neurophysiological framework.

High-resolution mapping of a novel genetic locus regulating voluntary physical activity in mice

Both human beings and animals exhibit substantial inter-individual variation in voluntary physical activity, and evidence indicates that a significant component of this variation is because of genetic factors. However, little is known of the genetic basis underlying central regulation of voluntary physical activity in mammals. In this study, using an F(2) intercross population and interval-specific congenic strains (ISCS) derived from the C57BL/6J strain and a chromosome 13 substitution strain, C57BL/6J-Chr13A/J/NA/J, we identified a 3.76-Mb interval on chromosome 13 containing 25 genes with a significant impact on daily voluntary wheel running activity in mice. Brain expression and polymorphisms between the C57BL/6J and A/J strains were examined to prioritize candidate genes. As the dopaminergic pathway regulates motor movement and motivational behaviors, we tested its function by examining cocaine-induced locomotor responses in ISCS with different levels of activity. The low-activity ISCS exhibited a significantly higher response to acute cocaine administration than the high-activity ISCS. Expression analysis of key dopamine-related genes (dopamine transporter and D1, D2, D3, D4 and D5 receptors) revealed that expression of D1 receptor was higher in the low-activity ISCS than in the high-activity ISCS in both the dorsal striatum and nucleus accumbens. Pathway analysis implicated Tcfap2a, a gene found within the 3.76-Mb interval, involved in the D1 receptor pathway. Using a luciferase reporter assay, we confirmed that the transcriptional factor, Tcfap2a, regulates the promoter activity of the D1 receptor gene. Thus, Tcfap2a is proposed as a candidate genetic regulator of the level of voluntary physical activity through its influence on a dopaminergic pathway.

Dopamine D1 receptor modulation in nucleus accumbens lowers voluntary wheel running in rats bred to run high distances

Dopamine signaling in the nucleus accumbens (NAc) has been postulated to influence reward development towards drugs of abuse and exercise. Herein, we used generation 4-5 rats that were selectively bred to voluntary run high (HVR) versus low (LVR) distances in order to examine if dopamine-like 1 (D1) receptor modulation in the NAc differentially affects nightly voluntary wheel running between these lines. A subset of generation 5-6 HVR and LVR rats were also used to study the mRNA expression of key genes related to reward and addiction in the NAc (i.e., DRD1, DRD5, DRD2, Nr4a2, FosB, and BDNF). In a crossover fashion, a D1-like agonist SKF 82958 (2 μg per side) or D1-like full antagonist SCH 23390 (4 μg per side) was bilaterally injected into the NAc of HVR and LVR female Wistar rats prior to their high running nights. Notably, during hours 2-4 (between 2000 and 2300) of the dark cycle there was a significant decrement in running distances in the HVR rats treated with the D1 agonist (p=0.025) and antagonist (p=0.017) whereas the running distances in LVR rats were not affected. Interestingly, HVR and LVR rats possessed similar NAc concentrations of the studied mRNAs. These data suggest that: a) animals predisposed to run high distances on a nightly basis may quickly develop a rewarding response to exercise due to an optimal D1-like receptor signaling pathway in the NAc that can be perturbed by either activation or blocking, b) D1-like agonist or antagonist injections do not increase running distances in rats that are bred to run low nightly distances, and c) running differences between HVR and LVR animals are seemingly not due to the expression of the studied mRNAs. Given the societal prevalence of obesity and extraneous physical inactivity, future studies should be performed in order to further determine the culprit for the low running phenotype observed in LVR animals.

Promoting exercise in Parkinson's disease through community-based participatory research

Parkinson's disease (PD) is a chronic, progressive, as-of-yet incurable, neurodegenerative condition affecting the nigro-striatal dopaminergic system. Emerging evidence suggests the importance of exercise in improving the trajectory of PD. Yet few people with PD are physically active. One challenge that healthcare professionals face in the 21st century is how to deliver physical activity programs to the population of individuals living with PD. A novel approach to delivering physical activity to people with PD is introduced - termed community-based participatory research (CBPR) - which engages people with PD and patient advocates as co-researchers in the development and implementation of community-based exercise programs. The authors describe the CBPR approach and provide several recent examples of community exercise programs that are steps in the direction of developing the CBPR model. This is followed by a discussion of what a more fully realized CBPR model might look like. Finally, the authors describe some obstacles to conducting CBPR and suggest strategies for overcoming them. It is argued that people with PD are an integral component of delivering the exercise intervention.

Can we modulate physical activity in children? No

Intuition tells us that physical activity is central to weight reduction in obese children. Evidence, on the other hand, suggests that increases in physical activity are difficult to achieve in the short term, and may not be possible in the long term. One explanation could be an 'activitystat', a feedback loop in the child's brain that controls physical activity according to a set point. This brief article, which argues that it may not be possible to modulate the activity of children, reviews the principles of feedback control as they apply to physical activity, discusses evidence for its central control, and demonstrates how a physical activity control loop might operate to defend the set point. Studies restricted to objective measurement suggest that the physical activity of children varies in a systematic, rather than random manner. It varies little from environment to environment, from year to year or from place to place. Where children undertake more activity at one time of day, they appear to compensate at another. Systematic variation of this kind implies control, and the control of physical activity appears to lie with the child, not with his environment. Perturbation (temporary change in response to disturbance) during short-term physical activity interventions may be mistaken for modulation (permanent change in set point), a fundamentally different response. Perturbation lasts no longer than the disturbance that causes it, and there is little evidence that interventions raise activity long term, if at all.