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PARIS, May 31 (AFP) - The earlier the age at which smoking starts the greater the degree of nicotine dependency in later life, a French research team reported Saturday.
The study was carried out on rats but the researchers, led by Pier Vincenzo Piazza and based in Bordeaux in southwest France, said that the findings were "relevant for extrapolation to humans."
They introduced groups of rats to nicotine at two different ages; around adolescence (from about a week before puberty to a few days after it) and in post-adolescence.
When the rats reached adult age they were enabled to choose for themselves the amount of nicotine they wanted by sticking their snouts into a special hole in their cage.
The rodents that had been initiated at the earliest age showed more interest in the nicotine, made more effort to get it and helped themselves to substantially stronger doses than those that had been introduced to the drug when they were more mature.
The team found changes in some genes of the rats exposed to nicotine pre-puberty and suggest these changes accounted for the extra sensitivity to the drug.
In the same journal the same team said it had discovered the role played by a brain stress receptor in craving for cocaine. They disactivated this receptor (called GR) in a group of rats and mice and then repeated the earlier experiment, replacing the nicotine with cocaine.
A control group with "GR" were addicted: they took regular doses of the drug and their behaviour showed clear signs of its effect. The animals without "GR" were much less interested in the drug.
"These results are a first therapeutic lead for (treating) cocaine dependency," the researchers say.
The findings appear in the June issue of the Journal of Neuroscience and are the work of INSERM unit 588 (physiopathology of behaviour).
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