The article begins:

A few years ago, I attended an open Alcoholics Anonymous meeting to support a friend in recovery. During a brief break, it was impossible not to notice how many attendees rushed outside for a cigarette. Epidemiological studies have long linked smoking to other forms of addiction—but, to date, they have been unable to establish any direct biological connections. A study published in the Nov. 2 issue of Science Translational Medicine, however, has now demonstrated how nicotine may accelerate both the cellular and epigenetic processes underlying addiction, providing the first biological explanation of a “gateway” drug. http://www.dana.org/news/features/detail.aspx?id=34582

A "gateway drug" is one “that opens the door to the use of other, harder drugs.”

Researchers thought the biological tools to examine the relationship between nicotine and cocaine addiction might finally be available.

To test nicotine’s effects as a gateway drug, the Kandels and their colleagues exposed mice alternately to nicotine and cocaine and then looked at the animal’s behavior as well as changes to synaptic plasticity in the striatum, a dopamine-rich area of the brain that has long been linked to reward processing and addiction. They found that the animals that received nicotine both just before and during cocaine administration showed not only a bigger behavioral response to the harder drug (as measured by locomotor sensitization and conditioned place preference tests), but also significant reduction in long-term potentiation in striatal neurons. These effects were only seen with the nicotine pre-treatment—and then only when cocaine was administered at the same time as the nicotine.

“What we found is that nicotine stimulates the synaptic connectors in the brain involving the dopaminergic circuitry, inhibiting it,” says Eric Kandel. “And nicotine pretreatment, having that nicotine prior to cocaine, enhances that effect dramatically.” (Eric Kandel, who won the 2000 Nobel Prize in Physiology or Medicine, is also a vice-chairman of the Dana Alliance for Brain Initiatives.)

Importantly:

While many epidemiological studies have shown that smoking and cocaine addiction are related, none had previously looked at exactly how addicts were using nicotine in relation to their cocaine abuse. After she saw the mouse test results, Denise Kandel went back to epidemiological data sets to see if addicts did smoke cigarettes and use cocaine concurrently.

“The rates of addiction to cocaine were twice as high among those who were actually smoking at the time they started using cocaine,” she says. “It was nice confirmation of the mouse experiment. It would seem exposure to nicotine while using cocaine not only increases the risk of continuing to use cocaine but of becoming addicted.”

The article is steeped in terminology difficult for those without a science background to fully understand. Albeit, the findings, if duplicated, no doubt will add to the call to stop smoking.