Morphine blocks the brain’s memory making mechanism

April 26 : A recent research, conducted by the Brown University, has found that analgesic drug Morphine blocks the brain’s ability to strengthen connections at inhibitory synapses.

The findings, published in Nature, may help clarify the genesis of addiction in the brain and also support a challenging new theory of addiction as a disease of learning and memory.

“We’ve added a new piece to the puzzle of how addictive drugs affect the brain. We’ve shown here that morphine makes lasting changes in the brain by blocking a mechanism that’s believed to be the key to memory making. So these findings reinforce the notion that addiction is a form of pathological learning,” lead scientist Julie Kauer said.

Kauer, a professor in the Department of Molecular Pharmacology, Physiology and Biotechnology at Brown, said that the brain stores information with the help of Long-term potentiation, or LTP.

In LTP, connections between neurons, called synapses, the major spot of information exchange in the brain, become stronger after recurring stimulation. This improved synaptic power is believed to be the cellular foundation for memory.

In her experiments, Kauer found that LTP is blocked in the brains of rats given as little as a single dose of morphine. The drug’s impact was powerful as LTP continued to be blocked 24 hours later, long after the drug was out of the animal’s system.

“The persistence of the effect was stunning,” Kauer said. “This is your brain on drugs.”

Kauer recorded the fact in the ventral tegmental area, or VTA, a small section of the midbrain that is occupied in the reward system that reinforces survival-boosting behaviors such as eating and sex, a reward system linked to addiction.

The affected synapses, Kauer found, were those between inhibitory neurons and dopamine neurons. In a healthy brain, inhibitory cells would bound the release of dopamine, the “pleasure chemical” that gets released by naturally rewarding experiences. Drugs of abuse, from alcohol to cocaine, also increase dopamine release.

So the net effect of morphine and other opioids, Kauer found, is that they enhance the brain’s reward response.

“It’s as if a brake were removed and dopamine cells start firing,” she explained. “That activity, combined with other brain changes caused by the drugs, could increase vulnerability to addiction. The brain may, in fact, be learning to crave drugs.”

Kauer and her team not only recorded cellular changes caused by morphine but also molecular ones. Indeed, the researchers located the very molecule that morphine disables, guanylate cyclase. This enzyme, or inhibitory neurons themselves, would be effective targets for drugs that prevent or treat addiction.(ANI)