Roots of addiction

Main Category: Alcohol / Addiction / Illegal Drugs
Article Date: 14 Aug 2003 - 0:00 PDT

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Specific nerve cells in a brain region called the nucleus accumbens are linked to relapse in recovering drug addicts.

That's what researchers from Rutgers University discovered. Their report appears in the Aug. 13 issue of the Journal of Neuroscience.

The finding may help researchers develop new addiction therapies and intervention strategies.

Even after addicts have been drug-free for a long time, they're susceptible to relapse when exposed to simple events or circumstances associated with prior drug use. For example, walking through a particular neighborhood or hearing a certain song may reawaken memories that trigger a craving and lead to a relapse.

'We've identified a part of the brain that appears to process these memories. This might be one of the brain areas that a very skilled pharmacological approach could target,' researcher and psychology professor Mark West says in a news release.

He and his colleagues zeroed in on the nerve cells in the nucleus accumbens during experiments with laboratory rats. The rats were able to self-administer cocaine by pressing a lever. Microelectrodes were used to monitor the activity of specific nerve cells in a part of the nucleus accumbens known as the shell.

When the rats pressed the lever to receive cocaine, a tone sounded. The rats came to associate the tone with the drug and by the end of three weeks had learned to press the lever when they heard the tone.

The researchers then removed both the cocaine and lever. After a month, the lever -- but no cocaine -- was returned to the rats' cage. The rats ignored the lever until the tone was sounded.

'When we stared to play the tone that had been paired with cocaine, the animals began to press the lever at a fairly high rate. It indicated that the animals had a persistent memory -- they remembered the significance of the tone. We interpreted the resumption of the lever pressing as a behavioral relapse,' West says.

When the rats went through this relapse of drug seeking, the microelectrodes monitoring brain activity showed that the nerve cells in the accumbens shell responded almost instantaneously when the rats heard the tone.

Before the rats had been conditioned to associate the tone with cocaine, those nerve cells had not responded to the tone.