A team of UCLA neuroscientists has found that nicotine causes degeneration in a region of the brain that affects emotional control, sexual arousal, REM sleep and seizures.

“Nicotine causes the most selective degeneration in the brain that I have ever seen,” said neuroscientist Gaylord Ellison, a professor of psychology and member of UCLA’s Brain Research Institute. “Only one tract of the brain is affected.”

Nicotine affects a part of the brain called fasciculus retroflexus, which has two halves. In previous research conducted over more than two decades, Ellison’s research team has shown that such drugs as amphetamines, cocaine and ecstasy damage one half of fasciculus retroflexus.

In the journal Neuropharmacology and at the Society for Neuroscience’s annual meeting in New Orleans this month, Ellison’s research team reported for the first time that nicotine causes degeneration in the other half of fasciculus retroflexus. The neuroscientists further report that the drugs that damage one half of fasciculus retroflexus do no harm to the half that nicotine affects.

“Our findings suggest that this (fasciculus retroflexus) is the brain’s weak link for stimulant addictive drugs,” Ellison said. “This tract is affected more by chronic drug use than any other tract in the brain. It seems likely that fasciculus retroflexus is linked to drug addiction and relapse. In chronic smokers, this tract may well play a major role in the addiction to nicotine.”

The researchers administered nicotine to rats for five days through a mini-pump inserted under their skin.

“We initially gave relatively high doses of nicotine, and then reduced it to a dose that induces plasma levels of nicotine in rats comparable to those of two-pack-a-day smokers,” Ellison said. “Even at this much lower dose, we still found degeneration in the tract. We measured the degeneration and found that the larger the dose, the more damage.”

Ellison’s team includes graduate students Janice Carlson and Brian Armstrong, and Robert Switzer of NeuroScience Associates. Ellison’s research is funded by the National Institute of Drug Abuse and the Tobacco Related Disease Research Program, which is funded by California’s tobacco tax.