Since the dopamine transporter is not being blocked, there must be something else activating the neurotransmitter, upstream of the transporter. Dr. Howell's next step is to determine what influences dopamine activity in the brain under normal circumstances. This could provide a brand new target for treatment medications, rather than those currently used, which attempt to block the action of cocaine. But blocking its action still doesn't stop the craving for the drug. Those medications only work once cocaine has been ingested, which is rarely the most effective strategy with a population of drug abusers.
Scientists already know that the neurotransmitter serotonin somehow regulates dopamine.
After that, he'll attempt to identify the specific serotonin receptor subtypes that are involved and their functions. As a complement to looking at specific neurotransmitters in a certain region of the brain, Dr. Howell is also looking at the brain as a whole using PET imaging. PET measures the pattern of blood flow in the brain, indicating which parts of the brain are being activated for any given task. In another first, Dr. Howell has trained monkeys to perform drug self-administration while they are being imaged in a PET scanner. But we thought it was important to do the images in awake animals.