Cocaine and the biochemistry of memory formation

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New research indicates that taking cocaine can actually begin to alter the structure of the brain within a matter of hours. The study, published in the journal Nature Neuroscience cast new light over the murky question of addiction and the degree to which it is driven by fundamental biochemical changes.

Animal tests conducted by the team at University of California, Berkeley and UC San Francisco demonstrated that new structures tied into the mechanisms of learning and memory began to develop rapidly after the drug entered the bloodstream.

Mice with the most brain changes demonstrated a greater thirst for the drug, suggesting that those whose brains were most affected were the most affected by a nascent addiction. The scientists described this pattern as ‘learning addiction’.

The changes were centred on the tiny spikes that jut out of brain cells known as dendritic spines, which are now known to be a key player in memory formation.

In the experiments, the mice were allowed to roam through two different chambers - each with a different smell and surface texture which contributed to the sense of two very different environments in which to experience the drug. Once the mice had clearly settled on a preferred setting, they were injected with cocaine in the other chamber.

Studying their brains with laser microscopy, the scientists noted that many more dendritic spines were formed than during the control experiment (an injection of water). Within two hours of the injection, the difference in spine production was marked, suggesting new memories were being formed around drug use.

Researcher Linda Wilbrecht, assistant professor of psychology and neuroscience at UC Berkeley, said: "Our images provide clear evidence that cocaine induces rapid gains in new spines, and the more spines the mice gain, the more they show they learned about the drug. This gives us a possible mechanism for how drug use fuels further drug-seeking behaviour. These drug-induced changes in the brain may explain how drug-related cues come to dominate decision making in a human drug user."

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