Addictive drugs harm brain's natural brake

A single dose of morphine was found to lower the inhibitions of rats, even after the drug had left their systems, a finding that may help scientists better understand addiction in humans, U.S. researchers said.

The painkiller blocked the brain's ability to strengthen connections, or synapses, that ratchet down reward or pleasure, researchers from Brown University reported in the journal Nature.

"What we have found is that the inhibitory synapses can no longer be strengthened 24 hours after treatment with morphine, which suggests that a natural brake has been removed,".

"This happens 24 hours after the animal had one dose of morphine. There is no morphine left in the brain. It shows that it is a persistent effect of the drug".

Kauer said the finding adds to a growing body of evidence suggesting a link between learning and addiction and may help in the development of drugs to treat addiction.

By shutting off the natural ability to strengthen connections that inhibit pleasure, the brain may be learning to crave drugs.

Kauer said the brain has two kinds of neurons - those that excite the nerve connections and those that inhibit or depress them.

"If inhibition is reduced, you get runaway excitability".

This imbalance may boost the firing of neurons that make dopamine, the brain's "pleasure chemical" activated after rewarding experiences such as eating, sex, and the use of addictive drugs.

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