Nicotine use is highly addictive in primates, say researchers who conducted an unusual study of squirrel monkeys.
The study by researchers from the Centre for Addiction and Mental Health in Toronto and the U.S. National Institutes of Health examined the reinforcing effects of nicotine. It found that squirrel monkeys who could give themselves nicotine by pressing a lever initially used it very little - but over time developed a "high motivation" for using it.
"The number of the lever presses that the monkey had to perform to get a single injection of nicotine progressively increased," said Dr. Bernard Le Foll, a CAMH scientist and associate professor at the University of Toronto.
"We were able to measure the motivation to take nicotine ... This revealed a high motivation to take nicotine, with monkeys pressing up to 600 times to get a single injection of nicotine."
A catheter was implanted into a vein of the animals. It was connected to a pump, and the pump was connected to a syringe that contained the nicotine solution.
Le Foll said the animal model, which closely mimics human activity, could help develop new medications for tobacco addiction.
"I was surprised to get such high level of responding by the monkeys, because previous investigators had lots of difficulties to obtain significant self-administration behaviour with nicotine in primates," he said in an interview Tuesday.
"That is an indication that nicotine is a critical component of tobacco smoke and that it is the desire to obtain nicotine that is an important drive of smoking behaviour."
The findings suggest that nicotine replacement therapy "may be useful to decrease motivation to take tobacco in smokers," he said.