Running } endocannabinoids } dopamine } motivation?The researchers also examined the role that endocannabinoids play in this process. Endocannabinoids, brain chemicals that resemble the active ingredients in marijuana, play key roles in many brain processes. Here, Dr. Cheer and his colleagues found that endocannabinoids essentially open the gate that allows the dopamine neurons to fire. When the researchers reduced the level of endocannabinoids, the animals were much less likely to move to avoid shocks.