A single dose of cocaine affects brain chemistry long after the high has faded, scientists report.
Researchers at the University of California at San Francisco found that mice injected with cocaine had increased neural activity in an area of the brain associated with addiction one week later.
"We believe that during this week of increased activity cocaine is opening a window of vulnerability to further drug use," said UCSF neurologist Antonello Bonci. "If this is related to craving, we might be able to understand how it happens and close the window."
The scientists' investigation of cocaine's impact on the ventral tegmental area (VTA) of the brain appears in the current issue of Nature. The VTA is swarming with dopamine, a neurotransmitter associated with pleasure as well as drug cravings.
One expert, however, questioned the study's findings.
"One use will not make you addicted," said Ashok Jain, a professor of Emergency Medicine at the University of Southern California, who argued that addiction only happens through long-term, gradually increased exposure to drugs or alcohol.
To study neural activity in the VTA, the UCSF researchers inspected thinly sliced brains from the mice under a microscope.
The study also found that cocaine accelerated molecular processes related to memories and learning, said UCSF scientist Mark Ungless.
"Cocaine introduces changes similar to what happens when you form normal memories," said Ungless. "When you learn about rewarding events, a similar change happens but on a much smaller scale."
So, how do coked-up mice act, you might ask. Hyperactive, said Ungless. In fact, many studies have shown that mice and other lab animals will eagerly get high, given a chance.
The UCSF scientists hope their discovery will provide clues to drug treatment, but aren't planning to replicate the studies in humans for obvious reasons.
"We can't slice human brains up because it's too tricky to put them back together again," Ungless joked.