What Do Long Distance Running and Marijuana Have in Common?

Maybe it isn't endorphins after all.

[From time to time, I reprint earlier posts that have remained perennial favorites at Addiction Inbox. This one originally ran on August 4, 2010.]

What do long-distance running and marijuana smoking have in common? Quite possibly, more than you’d think. A growing body of research suggests that the runner’s high and the cannabis high are more similar than previously imagined.

The nature of the runner’s high is inconsistent and ephemeral, involving several key neurotransmitters and hormones, and therefore difficult to measure. Much of the evidence comes in the form of animal models. Endocannabinoids—the body’s internal cannabis—“seem to contribute to the motivational aspects of voluntary running in rodents.” Knockout mice lacking the cannabinioid CB1 receptor, it turns out, spend less time wheel running than normal mice. 

A Canadian neuroscientist who blogs as NeuroKuz suggests that “a reduction in CB1 levels could lead to less binding of endocannabinoids to receptors in brain circuits that drive motivation to exercise.” NeuroKuz speculates on why this might be the case. Physical activity and obtaining rewards are clearly linked. The fittest and fleetest obtain the most food. “A possible explanation for the runner’s high, or ‘second wind,’ a feeling of intense euphoria associated with going on a long run, is that our brains are stuck thinking that lots of exercise should be accompanied by a reward.”

In 2004, the British Journal of Sports Medicine ran a research review, “Endocannabinoids and exercise,” which seriously disputed the “endorphin hypothesis” assumed to be behind the runner’s high. To begin with, other studies have shown that exercise activates the endocannabinoid system.

“In recent years,” according to the authors, “several prominent endorphin researchers—for example, Dr Huda Akil and Dr. Solomon Snyder—have publicly criticised the hypothesis as being ‘overly simplistic,’ being ‘poorly supported by scientific evidence’, and a ‘myth perpetrated by pop culture.’” The primary problem is that the opioid system is responsible for respiratory depression, pinpoint pupils, and other effects distinctly unhelpful to runners.

The investigators wired up college students and put them to work in the gym, and found that “exercise of moderate intensity dramatically increased concentrations of anandamide in blood plasma.” The researchers break the runner’s high into four major components. Exercise, they say, “suppresses pain, induces sedation, reduces stress, and elevates mood.” Some of the parallels with the cannabis high are not hard to tease out: “Analgesia, sedation (post-exercise calm or glow), a reduction in anxiety, euphoria, and difficulties in estimating the passage of time.”

There are cannabinoid receptors in muscles, skin and the lungs. Intriguingly, the authors suggest that unlike “other rhythmic endurance activities such as swimming, running is a weight bearing sport in which the feet must absorb the ‘pounding of the pavement.’” Swimming, the authors speculate, “may not stimulate endocannabinoid release to as great an extent as running.” Moreover, “cannabinoids produce neither the respiratory depression, meiosis, or strong inhibition of gastrointestinal motility associated with opiates and opioids. This is because there are few CB1 receptors in the brainstem and, apparently, the large intestine.”

A big question remains: What about running and the “motor inhibition” characteristic of high-dose cannabis? (An inhibition that may make cannabis useful in the treatment of movement disorders like tremors or tics.) Running a marathon is not the first thing on the minds of most people after getting high on marijuana.  The paper maintains, however, that at low doses, “cannabinoids tend to produce hyperactivity,” at least in animal models. The CB1 knockout mice were abnormally inactive, due to the effect of cannabinoids on the basal ganglia. Practiced, automatic motor skills like running are controlled in part by the basal ganglia. The authors predict that “low level skills such as running, which are controlled to a higher degree by the basal ganglia than high level skills, such as basketball, hockey, or tennis, may more readily activate the endocannabinoid system.”

The authors offer other intriguing bits of evidence. Anandamide, one of the brain’s own cannabinoids, “acts as a vasodilator and products hypotension, and may thus facilitate blood flow during exercise.” In addition, “endocannabinoids and exogenous cannabinoids act as bronchodilators” and could conceivably facilitate breathing during steady exercise. The authors conclude: “Compared with the opioid analgesics, the analgesia produced by the endocannabinoid system is more consistent with exercise induced analgesia.”

Photo Credit: http://www.madetorun.com/

Cannabis Receptors and the “Runner’s High”

Maybe it isn't endorphins after all.

What do long-distance running and marijuana smoking have in common? Quite possibly, more than you’d think. A growing body of research suggests that the runner’s high and the cannabis high are more similar than previously imagined.

The nature of the runner’s high is inconsistent and ephemeral, involving several key neurotransmitters and hormones, and therefore difficult to measure. Much of the evidence comes in the form of animal models. Endocannabinoids—the body’s internal cannabis—“seem to contribute to the motivational aspects of voluntary running in rodents.” Knockout mice lacking the cannabinioid CB1 receptor, it turns out, spend less time wheel running than normal mice. 

A Canadian neuroscientist who blogs as NeuroKuz suggests that “a reduction in CB1 levels could lead to less binding of endocannabinoids to receptors in brain circuits that drive motivation to exercise.” NeuroKuz speculates on why this might be the case. Physical activity and obtaining rewards are clearly linked. The fittest and fleetest obtain the most food. “A possible explanation for the runner’s high, or ‘second wind,’ a feeling of intense euphoria associated with going on a long run, is that our brains are stuck thinking that lots of exercise should be accompanied by a reward.”

In 2004, the British Journal of Sports Medicine ran a research review, “Endocannabinoids and exercise,” which seriously disputed the “endorphin hypothesis” assumed to be behind the runner’s high. To begin with, other studies have shown that exercise activates the endocannabinoid system.

“In recent years,” according to the authors, “several prominent endorphin researchers—for example, Dr Huda Akil and Dr. Solomon Snyder—have publicly criticised the hypothesis as being ‘overly simplistic,’ being ‘poorly supported by scientific evidence’, and a ‘myth perpetrated by pop culture.’” The primary problem is that the opioid system is responsible for respiratory depression, pinpoint pupils, and other effects distinctly unhelpful to runners.

The investigators wired up college students and put them to work in the gym, and found that “exercise of moderate intensity dramatically increased concentrations of anandamide in blood plasma.” The researchers break the runner’s high into four major components. Exercise, they say, “suppresses pain, induces sedation, reduces stress, and elevates mood.” Some of the parallels with the cannabis high are not hard to tease out: “Analgesia, sedation (post-exercise calm or glow), a reduction in anxiety, euphoria, and difficulties in estimating the passage of time.”

There are cannabinoid receptors in muscles, skin and the lungs. Intriguingly, the authors suggest that unlike “other rhythmic endurance activities such as swimming, running is a weight bearing sport in which the feet must absorb the ‘pounding of the pavement.’” Swimming, the authors speculate, “may not stimulate endocannabinoid release to as great an extent as running.” Moreover, “cannabinoids produce neither the respiratory depression, meiosis, or strong inhibition of gastrointestinal motility associated with opiates and opioids. This is because there are few CB1 receptors in the brainstem and, apparently, the large intestine.”

A big question remains: What about running and the “motor inhibition” characteristic of high-dose cannabis? (An inhibition that may make cannabis useful in the treatment of movement disorders like tremors or tics.) Running a marathon is not the first thing on the minds of most people after getting high on marijuana.  The paper maintains, however, that at low doses, “cannabinoids tend to produce hyperactivity,” at least in animal models. The CB1 knockout mice were abnormally inactive, due to the effect of cannabinoids on the basal ganglia. Practiced, automatic motor skills like running are controlled in part by the basal ganglia. The authors predict that “low level skills such as running, which are controlled to a higher degree by the basal ganglia than high level skills, such as basketball, hockey, or tennis, may more readily activate the endocannabinoid system.”

The authors offer other intriguing bits of evidence. Anandamide, one of the brain’s own cannabinoids, “acts as a vasodilator and products hypotension, and may thus facilitate blood flow during exercise.” In addition, “endocannabinoids and exogenous cannabinoids act as bronchodilators” and could conceivably facilitate breathing during steady exercise. The authors conclude: “Compared with the opioid analgesics, the analgesia produced by the endocannabinoid system is more consistent with exercise induced analgesia.”

Photo Credit: http://www.madetorun.com/

Consider the CB(2) Receptor

A different destination for cannabinoids.

THC and its organic cousin, anandamide, do what they do by locking into both the CB1 receptor, discovered in 1988, and the CB2 receptor (as it is commonly written in shorthand), discovered 5 years later. THC and anandamide are CB receptor agonists, meaning they activate the receptors in question. (An antagonist blocks the receptor’s action.)

CB1 is a very common receptor in the central nervous system, and, when stimulated by an agonist, is responsible for the well-known roster of alleged medical effects, such as pain relief and nausea from chemotherapy--along with the typical marijuana high. (For more on this, see the excellent 2007 post by Dr. Joan Bushwell.) Conversely, blocking CB1 activity with an antagonist like rimonabant is one controversial avenue being explored in the search for new weight loss drugs. (CB1 antagonists can also produce anxiety and depression.)

However, CB2 was long considered a “peripheral” cannabinoid receptor, meaning that scientists hadn’t managed to find CB2 receptors in the central nervous system. They were, however, plentiful in the immune system, and seemed to be involved in inflammation as well as pain responses. CB2 receptors were in fact eventually discovered in the central nervous system, and are active in the brain during certain kinds of inflammatory responses.

There is a straightforward commercial incentive for tracking the extent of CB2 expression in brain neurons. As the authors of a cannabinoid receptor study wrote in the June issue of the British Journal of Pharmacology:

“As CB(2) is an attractive therapeutic target for pain management and immune system modulation without overt psychoactivity, defining the extent of its presence in neurons will have a significant impact on drug discovery.”

Translated, this means that there are a number of new molecules that are selective for CB2 receptors. Since people don’t get a strong traditional marijuana-style buzz from CB2 receptor activation, and given the active involvement of CB2 receptors in things like immune responses and inflammatory reactions, the possibility exists of finding lucrative spinoffs like pain pills or anti-inflammatory medications.  So drug researchers would like to know exactly where those receptors are, and what they do, in the event that they end up attempting to make a medicine that stimulates or blocks  them artificially. (Credit to Vaughan Bell of Mind Hacks for highlighting this study.) 

The psychologists at Indiana University who produced the paper did their best to shed light on where the CB(2) receptor is hiding, and what, exactly, it does.  But there is still not enough known about how various substances react with this somewhat elusive receptor for cannabinoids. In 2008, scientists at the University of Madrid published research in the Journal of Biological Chemistry indicating that activation of the CB2 receptor reduced nerve cell loss in animals suffering from a disease similar to multiple sclerosis. Researchers point to the possibility that a safe drug for M.S. patients could be one of the results of CB2 research.

Atwood, B., & Mackie, K. (2010). CB2: a cannabinoid receptor with an identity crisis British Journal of Pharmacology, 160 (3), 467-479 DOI: 10.1111/j.1476-5381.2010.00729.x

Graphics Credit: www.cnsforum.com