The frontal cortex, which Wilbrecht called the "steering wheel" of the brain, controls functions such as long-term planning, decision-making and other behaviors involving higher reasoning and discipline.
The brain cells in the frontal cortex that Wilbrecht and her team studied regulate the output of this brain region, and may play a key role in decision-making. "These neurons, which are directly affected by cocaine use, have the potential to bias decision-making," she said.
Wilbrecht said the findings could potentially advance research in human addiction "by helping us identify what is going awry in the frontal cortexes of drug-addicted humans, and by explaining how drug-related cues come to dominate the brain's decision-making processes."
In the first of a series of experiments, the scientists gave cocaine injections to one group of mice and saline injections to another. The next day, they observed the animals' brain cells using a 2-photon laser scanning microscope. They were surprised to discover that even after the first dose, the mice treated with cocaine grew more new dendritic spines than the saline-treated mice.
In another experiment, they observed the mice before cocaine or saline treatment and then two hours afterward, and discovered that the animals that received cocaine were developing new dendritic spines within two hours after receiving the drug. Furthermore, the next morning, cocaine-induced spines accounted for almost four times more connections among nerve cells than was observed in saline-treated animals.
In a third experiment, the researchers for a week gave the mice cocaine in one distinctive chamber and saline in another, using identical procedures. Each chamber had its own characteristic visual design, texture and smell to distinguish it from the other chamber. They then let the mice choose which chamber to go to.
"The animals that showed the
|Contact: Jeffrey Norris|
University of California - San Francisco