快猫短视频

THE nicotine in a single cigarette can trigger a long-lasting chemical change
in brain cells, scientists have discovered. If they can confirm that similar
changes occur in living brains, it might lead to new treatments for nicotine
addiction.

Rats exposed to nicotine have raised levels of the neurotransmitter dopamine
in their brains. Dopamine is responsible for feelings of pleasure, and high
levels of the chemical last for hours after exposure to nicotine. 快猫短视频s
suspected that this leads to addiction.

Now neurobiologists Daniel McGehee and Hulbert Mansvelder from the University
of Chicago have uncovered how nicotine has this insidious effect. Working on
slices of rat brain, the team discovered that nicotine attaches to alpha7, a
specific sub-unit of a family of nicotinic receptors in neurons. As a result,
these neurons release glutamate. This in turn persuades other neurons to release
dopamine. Levels of this key neurotransmitter persist for 45 minutes or more
after nicotine exposure.

They say the buzz is higher the next time the same part of the brain is
exposed to nicotine. The effect, called long-term potentiation, is also linked
to memory and learning in a part of the brain called the hippocampus. 鈥淚t鈥檚 an
insidious process that is motivating us to breathe carcinogens into our lungs,鈥�
says McGehee. The team has calculated that the nicotine from just one cigarette
is enough for the brain to remember the 鈥渉igh鈥� that results.

The addictive effect of nicotine explains why so many people cannot stop
smoking, despite widespread awareness that it causes heart disease and cancer.
Experts estimate that one in two smokers will die prematurely as a direct result
of their habit.

The new finding runs counter to the traditional theory that addiction comes
when repeated exposure to a chemical weakens its effect, so that a person needs
to take more and more of the drug to get a 鈥渉it鈥�. But the results are consistent
with a newer theory of addiction, according to Ian Stolerman of the Institute of
Psychiatry at King鈥檚 College, London. This theory says that repeated exposure
increases the user鈥檚 sensitivity to a drug. And this is what makes the
experience more and more pleasurable鈥攁nd therefore harder to give up.

Now the researchers need to reproduce the results in live animals, Stolerman
says. Earlier studies in animals failed to show that blocking alpha7 receptors
affects nicotine dependence.

鈥淚f it can be verified that alpha7 receptors play a role in tobacco addiction
it opens up possibilities of new drugs that may help people to stop smoking,鈥�
says Stolerman. The drugs most often used today to block nicotine have marked
effects outside the brain. They cause low blood pressure, dizziness and blurred
vision, adds Stolerman.

He suggest that new drugs might avoid such problems. 鈥淪ince alpha7 receptors
are mainly in the brain, drugs that block only these receptors would not have
these side effects.鈥�