Why Good Resolutions About Taking Up a Physical Activity Can Be Hard to Keep

an. 4, 2013 — Physical inactivity is a major public health problem that has both social and neurobiological causes. According to the results of an Ipsos survey published on December 31, the French have put “taking up a sport” at the top of their list of good resolutions for 2013. However, Francis Chaouloff, research director at Inserm’s NeuroCentre Magendie (Inserm Joint Research Unit 862, Université Bordeaux Ségalen), Sarah Dubreucq, a PhD student and François Georges, a CNRS research leader at the Interdisciplinary Institute for Neuroscience (CNRS/Université Bordeaux Ségalen) have just discovered the key role played by a protein, the CB1 cannabinoid receptor, during physical exercise. In their mouse studies, the researchers demonstrated that the location of this receptor in a part of the brain associated with motivation and reward systems controls the time for which an individual will carry out voluntary physical exercise. These results were published in the journal Biological Psychiatry.

Longitudinal section of the mouse brain (top) and diagram of interactions between the endocannabinoid, GABAergic and dopaminergic systems during voluntary physical exercise (bottom). Left: stimulating the CB1 receptors excites the dopaminergic neurons in the ventral tegmental area involved in motivation. Right: the absence of CB1 receptors lowers performance by 20 to 30% owing to reduced motivation. (Credit: ©Inserm/F. Chaouloff)

 

The collective appraisal conducted by Inserm in 2008 highlighted the many preventive health benefits of regular physical activity. Such activity is limited, however, by our lifestyle in today’s industrial society. While varying degrees of physical inactivity may be partly explained by social causes, they are also rooted in biology.

“The inability to experience pleasure during physical activity, which is often quoted as one explanation why people partially or completely drop out of physical exercise programmes, is a clear sign that the biology of the nervous system is involved,” explains Francis Chaouloff.

But how exactly? The neurobiological mechanisms underlying physical inactivity had yet to be identified.

Francis Chaouloff (Giovanni Marsicano’s team at the NeuroCentre Magendie; Inserm joint research unit, Université Bordeaux Ségalen) and his team have now begun to decipher these mechanisms. Their work clearly identifies the endogenous cannabinoid (or endocannabinoid) system as playing a decisive role, in particular one of its brain receptors. This is by no means the first time that data has pointed to interactions between the endocannabinoid system, which is the target of delta9-tetrahydrocannabinol (the active ingredient of cannabis), and physical exercise. It was discovered ten years ago that physical exercise activated the endocannabinoid system in trained sportsmen, but its exact role remained a mystery for many years. Three years ago, the same research team in Bordeaux observed that when given the opportunity to use a running wheel, mutant mice lacking the CB1 cannabinoid receptor, which is the principal receptor of the endocannabinoid system in the brain, ran for a shorter time and over shorter distances than healthy mice. The research published in Biological Psychiatry this month seeks to understand how, where and why the lack of CB1 receptor reduces voluntary exercise performance (by 20 to 30%) in mice allowed access to a running wheel three hours per day.

The researchers used various lines of mutant mice for the CB1 receptor, together with pharmacological tools. They began by demonstrating that the CB1 receptor controlling running performance is located at the GABAergic nerve endings. They went on to show that the receptor is located in the ventral tegmental area of the brain (see diagram below), which is an area involved in motivational processes relating to reward, whether the reward is natural (food, sex) or associated with the consumption of psychoactive substances.

VTA: Ventral tegmental area/NAcc: nucleus accumbens/PFC: prefrontal cortex/DA: dopamine

Based on the results of this study and earlier work, the Bordeaux team suggests the following neurobiological explanation: at the beginning and for the duration of physical exercise, the CB1 receptor is constantly simulated by the endocannabinoids, lipid molecules that naturally activate this receptor in response to pleasant stimuli (rewards) and unpleasant stimuli (stress). Endocannabinoid stimulation of the CB1 receptor during physical exercise inhibits the release of GABA, an inhibitory neurotransmitter that controls the activity of the dopamine neurons associated with the motivation and reward processes. This stimulation of the CB1 receptor “inhibits inhibition,” in other words, it activates the dopaminergic neurons in the ventral tegmental area. The CB1 receptor must therefore be stimulated before the exercise can go on for longer and the body must receive the necessary motivation.

Conversely, without these CB1 receptors, the “GABAergic brake” continues to act on the dopaminergic neurons in the ventral tegmental area, leading to the reduced performance levels observed above.

It is already known that CB1 receptors play a regulatory role in the motivation to consume rewards, whether natural or not. What is original about this research is that it shows that physical exercise can be added to the array of natural rewards regulated by the endocannabinoid system. “If confirmed, this motivational hypothesis would imply that the role played by the CB1 receptor has more to do with ‘staying power’ in the exercise than with actual physical performance levels” explain the researchers.

This work reveals that the endocannabinoid system plays a major role in physical exercise performance through its impact on motivational processes. It thus opens up new avenues of research into the mediators of pleasure — and even addiction — associated with regular physical exercise. “After endorphins, we now need to consider endocannabinoids as another potential mediator of the positive effects that physical exercise has on our mood,” the researchers conclude.


Story Source:

The above story is reprinted from materials provided byINSERM (Institut national de la santé et de la recherche médicale).

Note: Materials may be edited for content and length. For further information, please contact the source cited above.


Journal Reference:

  1. Sarah Dubreucq, Audrey Durand, Isabelle Matias, Giovanni Bénard, Elodie Richard, Edgar Soria-Gomez, Christelle Glangetas, Laurent Groc, Aya Wadleigh, Federico Massa, Dusan Bartsch, Giovanni Marsicano, Francois Georges, Francis Chaouloff. Ventral Tegmental Area Cannabinoid Type-1 Receptors Control Voluntary Exercise PerformanceBiological Psychiatry, 2012; DOI:10.1016/j.biopsych.2012.10.025
 

 

INSERM (Institut national de la santé et de la recherche médicale) (2013, January 4). Why good resolutions about taking up a physical activity can be hard to keep. ScienceDaily. Retrieved January 10, 2013, from http://www.sciencedaily.com/releases/2013/01/130104143615.htm

Researcher Calls for Global Action On Pandemic of Physical Inactivity

ScienceDaily (July 18, 2012) — The high prevalence and consequences of physical inactivity should be recognized as a global pandemic, according to a new publication by Harold W. Kohl, III, Ph.D., professor of epidemiology at The University of Texas School of Public Health, part of The University of Texas Health Science Center at Houston (UTHealth).


 

“Physical inactivity continues to be undervalued among people who can make a difference despite evidence of its health benefits and the evident cost burden posed by present levels of physical inactivity globally,” said Kohl, who is also with the Michael & Susan Dell Center for Healthy Living at the UT School of Public Health.

The paper is the fifth and final paper in The Lancet “Series on Physical Activity” published this week and outlines key strategies and resources needed to make physical activity a global public health priority. “This series emphasizes the need to focus on population physical activity levels as an outcome, not just decreasing obesity,” said Kohl, professor of kinesiology at The University of Texas at Austin.

The health burden of physical inactivity is substantial, according to Kohl. “Although regular physical activity is critical for weight control, it is equally or more important for lowering risk of many different chronic diseases such as heart disease, some cancers, osteoporosis and diabetes.”

According to Kohl, research on physical activity needs to be its own priority within public health research of non-communicable diseases.

Globally nearly one-third of persons 15 and over were insufficiently active in 2008 and approximately 3.2 million deaths each year are attributable to insufficient physical activity, according to the World Health Organization. In 2008, the prevalence of insufficient physical activity was highest in the Americas and Eastern Mediterranean regions.

In the paper, the researchers argue for increased prioritizing of physical activity across multiple sectors of influence including health, transportation, sports, education and business. “This issue is of particular importance in countries with low-to-middle incomes, where rapid economic and social changes are likely to reduce the domestic, work and transport-related physical activity demands of daily life,” said Kohl. “Improved understanding of what works best in these nations will be key to developing national policies and action plans.

Kohl recommends a multi-sector and systems-wide approach to physical activity promotion to increase population levels of activity worldwide rather than efforts focused on individual health. “Traditional approaches, where responsibility for change has resided with the health sector, will not be sufficient,” said Kohl. “Improvements must happen at every level including planning and policy, leadership and advocacy and workforce training.”

In 2008, 25.4 percent of U.S. adults reported no leisure time physical activity, according to the Centers for Disease Control and Prevention (CDC). County estimates of leisure-time physical inactivity range from 10.1 percent to 43 percent in the United States. These rates reflect adults who report no physical activity or exercise other than at their regular job.

“The response to physical inactivity has been incomplete, unfocused, understaffed and underfunded compared with other risk factors for non-communicable diseases,” said Kohl. “This has put physical activity in reverse gear compared with population trends and advances in tobacco and alcohol control and diet.”

Kohl said Texas is one of a few states that have a plan to promote physical activity, Active Texas 2020. He led the development of the plan with the Governor’s Advisory Council on Physical Fitness. The Active Texas plan includes strategies and ideas that can be used by communities throughout the state.

“Physical education in schools is still one of the most effective means promoting physical activity, particularly among children,” said Kohl. Texas Education Code requires elementary school students to receive at least 30 minutes of daily physical activity and 225 minutes of physical activity per two weeks for four of six semesters for middle school students.

Kohl was recently appointed to lead the Institute of Medicine’s committee on Physical Activity and Physical Education in the School Environment. He is on the President’s Council of Fitness, Sports & Nutrition Science Board. Kohl also led development of the 2008 U.S. Physical Activity Guidelines.

 

Journal Reference:

  1. Harold W Kohl, Cora Lynn Craig, Estelle Victoria Lambert, Shigeru Inoue, Jasem Ramadan Alkandari, Grit Leetongin, Sonja Kahlmeier. The pandemic of physical inactivity: global action for public health. The Lancet, 2012; DOI: 10.1016/S0140-6736(12)60898-8

 

University of Texas Health Science Center at Houston (2012, July 18). Researcher calls for global action on pandemic of physical inactivity. ScienceDaily. Retrieved July 19, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120718112055.htm