The new study found that teenagers with certain gene variants were three times more likely to start smoking regularly in adolescence, and two times more likely to be regular smoking in adulthood, compared to those who don’t carry the gene variants.

The variations in a set of dopamine-related genes were associated with the risk of starting to smoke, and the genes had a stronger impact on beginning to smoke in adolescents than in adults. Those with the variants were 1.3 times more likely to start smoking in their teenage years.

The other set of genes were associated with the nicotinic cholinergic receptors, which are targeted in the brain during smoking. Variations in these genes contributed to the likelihood of smokers continuing the habit into adulthood, as it more strongly influenced adults than adolescents. People with these variations were 1.3 times more likely to be heavy, persistent smokers as adults.

Dr. John Krystal, Editor of the journal Biological Psychiatry, said that the dopamine-related genes may be more closely association with the risk for addiction in the context of pleasure-seeking, and cholinergic receptors, which have been associated with mood, cognition, and addiction, could contribute to self-medication as it relates to addiction.

These findings could help scientists create tests for those who want to know about their susceptibility to nicotine addiction and tobacco-related diseases. It could also help develop medication that could target an individual’s response to nicotine.

Source: Science Daily, Different Genes Influence Smoking Risk During Adolescence and Adulthood, March 31, 2011

Published in the latest issue of Pediatrics by Chyke Doubeni, MD, MPH of the University of Massachusetts, the study found that among kids who have started smoking, "an urge to smoke or being irritable because they are not able to smoke is a sign of early dependence. But they don’t seem to recognize that symptoms such as irritability are harbingers of addiction."

"Previous studies have already shown that there is a strong correlation between symptoms of nicotine dependence and nicotine addiction. This study shows that adolescents who start smoking, don’t appear to recognize the early signs of dependence," Doubeni said. Other signs of early dependence that go unnoticed include experiencing a desire to smoke or craving for a cigarette.

The study concluded that nondaily use of tobacco can trigger any of these early signs of dependence. Early dependence promotes increased smoking. That in turn accelerates additional signs of dependence, which leads to even higher frequencies of smoking. Eventually, it leads to addiction.

The conclusions are based on a study that surveyed adolescent smokers every three to four months, over a four-year period from 2002-2006. The study found that over those four years, of the 370 subjects who had inhaled from a cigarette, 62% smoked at least once per month, 52% experienced dependence symptoms, and 40% went on to become daily smokers.

The study, "Early Course of Nicotine Dependence in Adolescent Smokers," provides additional evidence supporting the Food and Drug Administration’s (FDA) recent rules placing restrictions on tobacco marketing to youth. Tobacco companies are challenging some of the FDA’s rules in court.

Doubeni’s study was funded by the Substance Abuse Policy Research Program (SAPRP) of the Robert Wood Johnson Foundation. The research supplemented an existing SAPRP grant to Joseph DiFranza, MD, also of the University of Massachusetts.

This year, 19.4% of high school seniors said they had smoked marijuana at some point in the prior 30 days, as did 13.8% of 10th-graders and 5.8% of eighth-graders. Melissa Healy of the Los Angeles Times reports that this downward trend has stalled in the last two years, and kids’ attitudes suggest a reversal may be ahead.

In 1991, 58% of eighth graders said they thought occasional marijuana use was harmful. By last year, that number had fallen to 48%, and this year, to 45%.

In a Washington, D.C., news conference Monday, drug czar Gil Kerlikowske called such numbers "a warning sign."

"When beliefs soften, drug use worsens," said Kerlikowske, whose office is expected to release its first policy initiatives to combat and treat drug abuse in February.

University of Michigan researcher Lloyd Johnston, who oversees the annual survey, said there was "serious softening" in the perceived risks of LSD, inhalants and the party drug Ecstasy—a sign that "a new generation of kids are interested…in rediscovering these drugs, because they don’t understand why they shouldn’t be using them."

Johnston also flagged a phenomenon the survey has recently begun to track—“extreme binge drinking," or the consumption of more than 10 drinks on a single occasion. They survey’s findings suggest that such high-risk drinking is not unusual among older teens.

Binge drinking, defined as consumption of five drinks or more in a row, has declined since peaking in 1983. But Johnston said there has been "not much decline" in numbers of extreme binge drinkers.

Among high school seniors, 11% said they had drunk 10 drinks or more in a row in the two weeks prior to the survey; 6% said they’d had 15 or more.

Healy writes that the survey also showed that U.S. adolescents continue to raid their parents’ and friends’ medicine chests. Use of prescription painkillers is at an all-time high: 10% of high-school seniors reported taking Vicodin for nonmedical reasons in the last year, and 5% reported taking OxyContin.

Dr. Nora Volkow, director of the National Institute on Drug Abuse, which has commissioned the survey for 35 years, said at the news conference that teen use of prescription stimulant drugs is holding steady, with just over 7% of 10th- and 12th-graders reporting they had taken amphetamines for nonmedical reasons. Volkow said that in many cases, teens take these drugs before tests or study sessions as "cognitive enhancers." Although fewer kids reported taking Ritalin, much of that decline was because kids had merely shifted to Adderall, a newer ADHD drug.

The officials said that youths report some confidence that prescription drugs are less harmful than street drugs.

In the survey’s first accounting of where kids get drugs, it found that 66% who reported illicit drug use said they got the drugs from a friend or relative. Almost 19% said they got drugs with a doctor’s prescription.

Grunberg describes the study, published by Natividad et al. in Synapse journal, as "fascinating" and suggests that it "may have implications to help understand why adolescents are particularly prone to drug abuse."

Nicotine increases the level of dopamine in the brain, a neurotransmitter that is responsible for feelings of pleasure and wellbeing. The study looked at dopamine levels in adolescent and adult rats after nicotine withdrawal. The authors found that the withdrawal signs (physical and neurochemical) seen in adolescent rats were fewer than those observed in adults.

The study provides previously unknown mechanisms as to why there are differences in nicotine withdrawal between adolescent and adult rats. The key here, as stated by Grunberg, is that "age alters [neurological] systems and interactions relevant to nicotine."

The reason that adolescents are prone to drug abuse (in this case, nicotine) is that they have increased sensitivity to its rewarding effects and do not display the same negative withdrawal effects as adults do, due to an underdeveloped dopamine-producing system.

Since rats are not subject to cultural influences, "rat studies of nicotine…have provided valuable insights that have led to practical behavioral and pharmacological interventions," says Grunberg.

The results of this study may not stop at nicotine. Grunberg continues, "These findings might also be relevant to other addictive and abuse drugs."