Mice Fed with Cocaine Show Growth in Brain Areas Linked with Learning, Memory

Using cocaine even once can lead to growth in brain size linked with learning and memory. A new study conducted on mice found newer structures within two hours of cocaine use. The latest research helps explain why cocaine is so addictive.

The study, conducted by researchers at UC San Francisco found that growth was especially evident in the animals' frontal cortex where the density of dendritic spines increased. Frontal cortex is the area of the brain associated with decision-making, higher reasoning and discipline. Newer dendritic spines- structures required for signalling- in this region mean that the brain is learning about a certain experience.

The study was conducted on two sets of mice - one received cocaine while the other was given saline. Researchers used 2-photon laser scanning microscope that helped them look directly into the nerve cells within the brain of live mice.

Cocaine is a powerfully addictive central nervous system stimulant that is snorted, injected, or smoked. Users risk heart attacks, respiratory failure, strokes, seizures, abdominal pain, and nausea. In rare cases, sudden death can occur on the first use of cocaine or unexpectedly afterwards, according to National Institute of Drug Abuse (NIDA). For years, researchers have been trying to find out why the drug is so addictive.

The mice in the study that were given cocaine were more likely to choose enclosures where they knew they'd get more cocaine.

"It's been observed that long-term drug users show decreased function in the frontal cortex in connection with mundane cues or tasks, and increased function in response to drug-related activity or information. This research suggests how the brains of drug users might shift toward those drug-related associations, "said Linda Wilbrecht, PhD, from UC Berkeley, lead author of the study. Wilbrecht worked on the study when she was at UCSF.

In the first experiment, researchers gave one set of mice cocaine and the other saline and observed the changes in brain activity. In the second experiment, they looked at nerve cells in mice two hours before and two hours after cocaine injection.

In the third experiment, mice were given cocaine or saline for about a week in separate chambers. Each chamber had its distinct design and texture. After a week researchers let the mice decide which chamber they wanted to go in.

"The animals that showed the highest quantity of robust dendritic spines - the spines with the greatest likelihood of developing into synapses - showed the greatest change in preference toward the chamber where they received the cocaine," Wilbrecht said in a news release. "This suggests that the new spines might be material for the association that these mice have learned to make between the chamber and the drug."

The study is published in the journal Nature Neuroscience.