Cocaine–a stimulating alkaloid crushed out of the leaves of the coca plant–has been reported to increase euphoria and energy as well as to trigger a mind-killing addiction in humans. The appeal is not limited to our species; rats and other animals given access to the drug will pursue it with a vigor normally reserved for procreation. This vigorous drive for the drug derives from its ability to stimulate the brain’s reward pathways, altering the chemical dance of neurotransmitters that tells us what is good to do–again and again and again. Neuroscientist John Wang of the University of Missouri-Kansas City and his colleagues have now traced that effect to one of the brain’s most basic molecular mechanisms.
Previous research has shown that cocaine triggers the reward pathway by activating the mesolimbic dopamine system–a series of neurons that originate near the base of the brain and project signals to its front. Their first stop en route is a section known as the striatum, where the of signals are first received. These signals inhibit the release of the neurotransmitter glutamate and increase the amount of the neurotransmitter dopamine by blocking the latter’s normal reabsorption into the synapses that released it.