New signs of nicotine's addictiveness - nicotine boosts activity within nucleus accumbens in rats - Brief Article

Science News, July 20, 1996 by Janet Raloff

Nicotine's effects on the brain precisely mimic those produced by morphine and other major drugs of abuse, according to a study conducted on rats. The finding by Italian scientists "adds new weight to the conclusion that nicotine is indeed addictive," Leslie L. Iversen of the University of Oxford in England observes in the July 18 Nature.

Gaetano Di Chiara of the University of Cagliari in Italy and his coworkers injected nicotine into the veins of unrestrained rats, then probed what happens in a part of the animals' brains known as the nucleus accumbens. This deeply embedded region at the base of the forebrain plays a role in integrating and expressing emotions, De Chiara notes.

Last year, his team showed that within an area of the nucleus accumbens known as the shell, amphetamines, morphine, and cocaine not only increased cellular activity but also boosted concentrations of dopamine. This signaling chemical has been linked to the euphoria created by addictive drugs. In the July 18 Nature, the team reports that nicotine, too, boosts dopamine and activates cells in the nucleus accumbens shell. Indeed, this pair of observations appears to be "a kind of label of [a drug's] being addictive," Di Chiara told Science News.

Di Chiara suspects that dopamine "facilitates a learning of the association between the pleasurable effects of a drug and other stimuli," such as the smell of smoke or taste of tobacco, quickly reinforcing desire for the drug. While food and water can induce cravings, they normally do so only when a person is hungry or thirsty. Drug cravings, Di Chiara says, make users seem as if they "are always hungry or thirsty because this stimulus is so strong."

Edythe D. London of the National Institute of Drug Abuse in Baltimore has spent many years mapping brain activation by drugs of abuse. What distinguishes this study, she says, is the "elegant" way it has mapped the activation of cells and the increase in dopamine simultaneously at one site.

Roy Wise of Concordia University in Montreal adds that not only have Di Chiara and his colleagues shown that nicotine turns on "the same [brain] circuitry that heroin and cocaine activate," but the research employed lower doses than those used in the past-"what are essentially real-world doses."

"We should either downgrade heroin to habit-forming or upgrade nicotine to addicting" because the same neurobiology accounts for abuse of all these drugs, Wise concludes.