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Cocaine affects later learning

11th August 2008

Researchers in California have found persistent brain changes in response to cocaine in rats, which they say are lined to the brain's reward and expectation mechanisms.


The University of California, San Francisco, study found brain changes in rats trained to self-administer cocaine, versus those animals that were trained to self-administer natural rewards such as food, or sucrose for several weeks.

Their behaviour sheds light on the way in which drug addiction dramatically shifts a person’s attention, priorities, and behaviours towards a focus almost entirely on seeking out and taking drugs.

Funded by the National Institute on Drug Abuse, part of the National Institutes of Health, the research shows that long-lasting brain changes may underlie the maladaptive learning that contributes to addiction and to the propensity for relapse, even after years of abstinence from the drug.

The study was published in the journal Neuron in July.

Investigators looked at how much the "expectation" of receiving the drug influenced those brain changes by comparing rats trained to self-administer the drug versus animals who could not control their own drug taking.

Persistent drug seeking is thought by some to alter the brain’s natural reward and motivational system, affecting normal processes of learning and memory formation in which there is a well documented strengthening of communication between brain cells.

The reward system's self-strengthening capacity, known as "long-term potentiation", is stimulated by anything experienced as a reward, but the process is greatly heightened in the case of cocaine, compared with natural rewards like food or sucrose.

This reinforces drug-seeking behaviours so as to privilege them over all other seeking - and learning - behaviours.

The study showed why drug related memories are so stable, and why a relapse is so easy, because the patterns laid down at a neurological level make new learning much harder to establish itself, according to researcher Nora Volkow.

The self-reinforcing reward system is not just tied into exposure to cocaine, but also is linked to the drug’s effects and the animal’s learning to obtain the drug, added lead author Billy Chen, postdoctoral fellow at UCSF’s Ernest Gallo Clinic and Research Center.

The research could lead to a better understanding how addiction develops, and why drugs can overshadow other natural rewards and become the mainstay of an addicted person’s life, Chen said.

In 2006, six million Americans age 12 and older had abused cocaine in some form. There are currently no medications for cocaine addiction, therefore standard treatments typically rely on behavioural interventions, and relapses are common.


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Article Information

Title: Cocaine affects later learning
Author: Luisetta Mudie
Article Id: 7849
Date Added: 11th Aug 2008


National Institutes of Health

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