Spark

by John J. Ratey

Scientists discovered the endocannabinoids in the early 1990s after realizing that THC binds to specialized receptors in the brain. These receptors didn’t evolve for us to enjoy marijuana, obviously, so there had to be some natural substance the body produces for them. What they found were the neurotransmitters anandamide and 2-arachidonoylglycerol (2-AG). It turns out that marijuana, exercise, and chocolate all activate these same receptors in the brain. Both of these endocannabinoids are produced in the body and the brain when we exercise. They travel through the bloodstream to activate receptors in the spinal cord, and this blocks pain signals from getting to the brain (not unlike morphine). They also move throughout the reward system and the prefrontal cortex, where they have a direct effect on dopamine. When the endocannabinoid receptors are strongly activated, they produce all the euphoric feelings of marijuana, and, along with endorphins, they act as the body’s extra-strength aspirin. Doctors are starting to use anandamide to treat pain syndromes such as chronic fatigue and fibromyalgia, and a number of studies have shown that gradually increasing exercise can relieve the pain and fatigue associated with these syndromes. The link between exercise and these natural pain killers makes perfect sense: they evolved to help us deal with the inevitable pain of straining muscles and joints during the hunt.