Your brain on exercise: rewarded with dopamine by cannabinoid receptors.

Lack of enough physical activity is a huge problem in the obesity-plagued modern world. With much of physical activity removed from work and daily life, to be fit and not obese, we have to exercise for extended periods of time, in activities like jogging, fast walking, bike riding and other aerobic exercise. Our willingness to exercise in this way is really a cornerstone of our health, and our society’s health. Probably more than anything single factor, our health care system would benefit from people getting more exercise. New research now reports the crucial role of cannabinoid receptors and our endocannabinoid regulatory system in our motivation to keep moving.

Research out of France, reported in Biological Psychiatry shows how small protein cannabinoid receptors operating in the walls of nerve cells in the  brain reward exercise. This unlocks a key to voluntary exercise, and perhaps ways to promote it.  Also reported in ScienceDaily, the research reported that the endocannabinoid system, especially CB1 receptors in certain parts of the brain, reward our bodies and minds with pleasurable sensations. This research was with mice, not humans, but the physiology and responses are very similar. Lack (or blockage) of these receptors caused a sharp drop in the amount of exercise control mice were willing to do.

For us to continue to exercise, rather than stopping, depends a lot on how we feel. If tired and uncomfortable we might well stop; if exhilarated and “in the zone,” we continue. How we feel during exercise, it turns out, depends much on how much of the feel-good substance, dopamine, our brains produce and receive.  Our dopamine levels, this research shows, are controlled in part by our endocannabinoid systems and CB1 receptors in certain parts of the brain. CB1 receptors are activated by our natural endocannabinoids such as anandamide. They also fit like lock and key and are activated by plant cannabinoids, especially THC, from cannabis.

Dopamine is an organic chemical produced in several areas of the brain. Many brain functions involve dopamine, especially learning, voluntary movement, reward and motivation. We feel higher dopamine levels as enjoyment and are rewarded by the experience, making us want to continue or repeat. Drugs like cocaine increase and prolong dopamine levels. The Bordeaux, France researchers studied dopamine producing nerve cells in the brain’s ventral tegmental area (VTA) known to play an important role in motivation. By working with mice with CB1 receptors present or absent or blocked, they found marked difference in how much running wheel time the rodents would spend.

The researchers had previously found “that the endogenous stimulation of cannabinoid type-1 (CB1) receptors is a prerequisite for voluntary running in mice,” but did not understand the mechanisms. In experiments involving “in vivo electrophysiology, the consequences of wheel running on VTA dopamine (DA) neuronal activity” on mice with combinations of CB1 blockage and GABA blockage. GABA is an inhibitory neurotransmitter that reduces levels of dopamine produced by other neurons. Cannabinoid receptor activation in GABA neurons inhibits this inhibitory effect on dopamine. This “inhibition of inhibition” results in an increased level of dopamine produced in this motivation area of the brain.

Exercise promotes endocannabinoid activation of CB1 receptors and this activation encourages continued exercise. If we exercise enough to allow them, our bodies reward us for the physical activities that are so good for us.

Not mentioned in this research, the “runner’s high” is likely a function of endocannabinoids, along with the endorphins. For earlier evidence of the runner’s high association with the endocannabinoid system check Runner’s high – your body rewarding exercise.