Distance running or other forms of endurance exercise can produce a feeling called “runner’s high,” which is associated with a feeling of euphoria, a reduction in anxiety (anxiolysis) and pain (analgesia), and an increased sense of relaxation (sedation).
Increased abundance of β-endorphin, an endogenous opioid, and anandamide, an endocannabinoid, are observed in the plasma of humans and mice after long distance running. However, β-endorphin cannot cross the blood-brain barrier.
Fuss et al. used mice to investigate the molecular mechanisms that could result in runner’s high
Compared with the control group, the mice in the run group spent more time in the light-aversive bright area, an indication of reduced anxiety. Mice in the run group also displayed increased latency to either jump or lick their paws when placed on a hot plate, an indication of analgesia.
The mice in the run group, but not in the control group, had increased abundance of endocannabinoids in the plasma but not in the brain or in the cerebrospinal fluid.
Mice in the run group that were injected with naloxone, which blocks endorphin activity, displayed running-induced reduction of thermal pain sensitivity. Thus, the pharmacological data suggested that endocannabinoids rather than endorphins played a role in analgesia associated with running
Thus, this study suggests that endocannabinoids mediate some of the positive effects associated with endurance exercise and the runner’s high.
Now that marijuana is becoming more available to researchers, and after the finding that we have natural endocannabinoid receptors in our bodies, there is increasing interest in the roles of these drugs for therapeutic purpose.
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