>FOR RELEASE: 24 AUGUST 2000 AT 00:01 ET US >University of Chicago Medical Center >http://www.medcenter.uchicago.edu/ > >Brief exposure to nicotine makes lasting mark on the brain > >Brief exposure to low levels of nicotine, as little as that provided by a >single cigarette, can cause lasting changes in the brain's "reward" areas, >report two University of Chicago scientists in the August 2000 issue of the >journal Neuron [ http://www.neuron.org/ ]. The finding is a major advance in >understanding the process of nicotine addiction. > >The researchers discovered that nicotine uses a mechanism responsible for >learning and memory to enhance the connections between one set of nerve cells >that are sensitive to the drug and other nerve cells that register pleasure. >They also demonstrate that the first exposure to nicotine can induce an >enduring "memory trace," which amplifies the pleasing effects of the drug -- >and boosts the desire to repeat the exposure. > >By uncovering the precise cellular mechanisms of nicotine's effect, this study >suggests new and more precise targets for drugs designed to block this powerful >craving. > >"This appears to be the crucial first step in the process of addiction," said >neurobiologist Daniel McGehee [ >http://neurobiology.bsd.uchicago.edu/faculty/McGehee.htm ], Ph.D., assistant >professor in the department of anesthesia and critical care at the University >of Chicago and director of the study. "Now that we know how this happens, we >can begin to search for better ways to intervene." > >The reinforcing effect [ >http://www.bmjpg.com/data/tobarch/autumn98/fromama.htm ] of nicotine is the >primary reason people cannot quit smoking, despite widespread awareness that >smoking causes cancer, heart disease, stroke, emphysema, bronchitis, vascular >disease, cataracts, impotence and many other health problems. Nicotine >dependence has been estimated to cause 70 times more deaths in the United >States than all other types of drug dependence combined. Nearly 25 million >Americans alive today will die prematurely from smoking-related illnesses. > >"Nicotine addiction makes millions of people suck carcinogens into their lungs >over and over again, day after day," said McGehee. "If this knowledge leads to >new ways of helping people quit successfully, it will be an important step for >public health worldwide." > >The brain reward areas serve to acknowledge and reinforce beneficial behaviors, >for example eating when you're hungry. The system encourages the body to repeat >pleasing behaviors by releasing dopamine, the neurotransmitter associated with >the pleasant feelings, in the reward areas. "That was good," is the basic >message of increased dopamine levels. "Do it again." > >Unfortunately, drugs of abuse, such as nicotine, can usurp those pathways, >providing the same sort of encouragement for some very harmful actions, such as >smoking. They also do this by stimulating the release of dopamine. > >McGehee and his colleague, post-doctoral researcher Huibert Mansvelder, PhD, >working with brain tissue from rats, demonstrated how nicotine takes control of >the reward pathways. Nicotine alters the connections between neurons using a >process that is similar to the cellular mechanisms underlying the creation of >memory. "In this way," Mansvelder said, "the brain erroneously learns that the >intake of nicotine was good and remembers the sensations it caused." > >The ability to remember things, such as pleasant sensations, is thought to >depend on the strengthening of links between neurons. Nerve cells communicate >with each other at synapses, junction points where chemical signals mediate >communication back and forth. When a synapse is used a lot, there is a >persistent strengthening of the communication. In effect, the more that one >side of the synapse 'talks,' the better the other side 'listens,' and the more >effective the communication becomes. > >Nicotine appears to cause addiction by strengthening the excitatory connect ions >on the neurons that make dopamine, which are found in the Ventral Tegmental >Area (VTA) of the brain reward center. Thus, the neurons are more excited, >which means that more dopamine is released within the reward areas. > >This cellular locus of addiction is farther "upstream" in the reward pathway >than anticipated. McGehee and Mansvelder demonstrate that nicotine's lasting >effects result from the drug's interaction with a receptor on the synaptic >endings, the part of the cell that sends the signals. When these endings are >exposed to nicotine, there is a direct increase in the excitatory signal >transmitted onto the dopamine neurons, which then increases dopamine release. > >Nicotine stimulates neurons by attaching to a specific structure on the neuron, >known as the nicotinic acetylcholine receptor. There are many different types >of nicotinic acetylcholine receptors, performing various roles throughout the >body. The addictive process fortunately appears to involve only one subtype, >acetylcholine receptors containing the alpha7 subunit, making it a potential >target for medications that could help smokers kick the habit. > >"Anything we can do to discover even a slightly more effective method to help >people stop smoking can have a tremendous health impact," added McGehee. > > > >This study was funded by the National Institute of Neurological Disorders and >Stroke, the Brain Research Foundation and the Netherlands Organization for >Scientific Research. >http://www.ninds.nih.gov/ > > <A HREF="http://www.ctrl.org/">www.ctrl.org</A> DECLARATION & DISCLAIMER ========== CTRL is a discussion & informational exchange list. Proselytizing propagandic screeds are unwelcomed. Substance—not soap-boxing—please! 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