San Francisco
PATRONS of smoke-filled pubs know that spirits and cigarettes are natural
companions. But there may be a nicotine and alcohol link in the brain, as well
as in the bar. 杏吧原创s have found that both chemicals affect the same protein
in the brain, perhaps explaining why alcoholics are often heavy smokers.
Evidence of alcohol鈥檚 strong influence on the mind is not hard to find. 鈥淚t鈥檚
a very simple chemical and it has many effects on the brain,鈥� says Toshio
Narahashi, a neuroscientist at Northwestern University Medical School in
Chicago, Illinois. At concentrations that make humans drunk, alcohol interferes
with the normal activity of many of the brain鈥檚 neuronal receptors. These
protein 鈥渟witches鈥� that sit on the surface of brain cells bind to
neurotransmitter chemicals released by neighbouring cells and trigger nervous
impulses. But how this interference contributes to alcohol鈥檚 addictive and
psychological effects is unclear.
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Narahashi was especially keen to know why alcoholics are about seven times as
likely to be heavy smokers as casual drinkers. Perhaps alcohol acted on the same
receptor as nicotine, the acetylcholine receptor. 鈥淚f alcohol made the receptor
less sensitive, then you鈥檇 need to get more nicotine to get the same feeling,鈥�
he says.
To test this theory, Narahashi鈥檚 group removed nerve cells that had
acetylcholine receptors on their surface from rats. They soaked the cells in
solutions containing varying concentrations of alcohol and tested the cells鈥�
electrical properties.
The receptors were surprisingly sensitive to alcohol, the researchers found.
The receptors were already slightly impaired at concentrations of alcohol 1000
times less than the legal limit for driving in the US. At 10 per cent of the
drink-driving limit the cells were generating about half the normal current, say
the researchers in the latest issue of Neuroscience Letters (vol 217,
p1).
鈥淚t鈥檚 impressive,鈥� says Adron Harris, a neuropharmacologist at the University
of Colorado School of Medicine in Denver. 鈥淭hese receptors are much more
sensitive to alcohol than any other I know.鈥� But he questions whether such a
supersensitive alcohol receptor could be physiologically important. 鈥淭hese are
doses where even the subtle behavioural effects are maybe just beginning, a very
low dose,鈥� he says.
Narahashi says that the link between drinking and smoking may be forged well
before obvious drunkenness sets in. 鈥淵ou drink a little alcohol and you feel
better. It鈥檚 that feeling that might cause this nicotine effect.鈥� Narahashi now
plans to test whether alcohol has different effects on acetylcholine receptors
at high doses.