The Brookhaven group used the scanner to map the dopamine receptors throughout the entire brains of of moving rats for the first time. Other groups, including Glimcher’s, have previously used invasive probes to study dopamine levels in cubic-millimeter-sized portions of the brain in unrestrained animals, but have not been able to look at the entire brain.
Glimcher describes one of several experiments that could be done with the portable device. Researchers know that addicts who have successfully completed rehab are at great risk of relapse if they visit the places they associate with the drug, probably because their brain has been chemically rewired to respond to these associations. Glimcher imagines studies in rats that map brain chemistry when the animals are allowed to decide whether or not to take a drug, and when they wander into a location they have learned to associate with the drug.
“We don’t really understand that well how circuits in [different parts of the brain] interact in addiction,” says Glimcher. “To even get to a place where I can give you a clinical hypothesis, we have got to get more basic information. This is the breakthrough that could make that possible.”
PET is not as broadly used in studies involving people as other neuroimaging methods because of the small but significant exposure to radiation that’s necessary. Still, the Brookhaven researchers say it would be possible to make a wearable PET scanner that fits inside something resembling a football helmet. Joseph Huston, chair of the Center for Behavioral Neurosciences at the University of Düsseldorf, says the Brookhaven group has done “an incredible service” to the neuroscience community in developing the device. “The rat is the most important model for the brain—everything basic [we know] about learning, feeding, fear, sex, is based on work in the rat.”
Schlyer says his group has talked with a few companies about licensing a commercial version of the device. But for now, they are mainly planning further behavioral studies in their lab. Mapping dopamine in waking animals could provide insights into a wide range of normal and pathological conditions such as the movement problems associated with Parkinson’s disease. But dopamine is just one of the many brain chemicals the group can map. Schlyer says they will also study the sexual behavior of rats.
The group is also working on another instrument that combines PET with magnetic resonance imaging to provide richer information about tissue structure and function. They will start a clinical trial of this device in breast cancer patients next month.