A new study coming out of the University of California Berkeley and published in the journal Nature Neuroscience is purporting to explain how the frontal brain is affected by cocaine and how irrational drug-seeking behavior might result.
The new conclusions about cocaine coming from the researchers indicate that cocaine quickly rewires high-level learning, memory, and decision-making centers of the brain. After examining the frontal lobes of mice on a cellular level, the team discovered it only takes one dose of cocaine to induce rapid growth of dendritic spines, which are twig-like connectors between neurons in the brain.
Linda Wilbrecht, the principal author and an assistant professor of psychology and neuroscience at UC Berkeley, said that clear evidence is showing "cocaine induces rapid gains in new spines, and the more spines the mice gain, the more they show they learned about the drug," and the more they 'learned,' the more they wanted it to the point of ignoring other needs.
The research team performed microscopic imaging using 2-photon laser scanning technology, and after taking control images, they delivered cocaine to the mice. After 2 hours, new dendritic spines were forming. Wilbrech says that "the number of new, robust spines gained correlated with how much the individual mice learned to prefer the context in which they received the drug." Many necropsies have been performed on postmortem mouse brains affected by cocaine, but until now no one had taken images of the frontal cortex before and after cocaine use.
The experiment featured a two-chambered room, with each side decorated and scented differently to make it easy for the mice to know where they are. The BBC describes the experiment: the mice could explore freely, but once they found a favorite place to hang out, they were injected with cocaine and the connecting door between the two chambers was shut. A day later, the mice were allowed to move freely; the mice predictably chose to go back to where they first received that first hit of coke.
"When given a choice, most of the mice preferred to explore the side where they had the cocaine, which indicated that they were looking for more cocaine... Their change in preference for the cocaine side correlated with gains in new persistent spines that appeared on the day they experienced cocaine." Wilbrecht said of the mice's behavior.
A researcher from the institute of Psychiatry at King's College London, Dr. Gerome Breen, told the BBC that "Dendritic spine development is particularly important in learning and memory... this study gives us a solid understanding of how addiction occurs - it shows us how addiction is learned by the brain, but it is not immediately apparent how useful this would be in developing a therapy."
Image from a Youtube video from the BBC on rats.