Nicotine for the nerves

The days when cigarettes were held up in advertising as healthy products are long gone, but new research suggests there may be some substance to this - at least for some disorders affecting the brain.

A number of presentations at the Society of Neuroscience annual meeting in New Orleans, US, have provided insight into how nicotine can have a protective effect on nerve cells in the brain.

One study, conducted by researchers at the University of Houston in the US, has established that nicotine has a beneficial effect and, in many cases, can even reverse the memory impairment caused by stress on the brain.

The team, headed by Karim Alkadhi of UH School of Pharmacy, studied the effect of nicotine on stress-induced memory impairment in rats. They found that when stressed animals were given nicotine, they performed significantly better at short-term memory tests than stressed animals not given the chemical. In fact, the nicotine-treated stressed animals performed the same as unstressed control animals.

During times of stress, smokers tend to increase the number of cigarettes they light up, and this may be a form of self-medication to counteract the harmful effects of stress on the brain, suggest the researchers.

In another experiment presented at the meeting, scientists from the Medical College of Georgia in the US reported that cotinine, a metabolite of nicotine that has long been thought to be inactive with regard to activity on nicotine receptors in the brain, can have a protective effect on neurons. Importantly, cotinine lacks a number of side effects of nicotine, including the latter's addictive properties.

This suggests that cotinine itself, or drugs which share its mechanism of action, may be a means of treating neurodegenerative diseases such as Alzheimer's as well as schizophrenia.

In the study, the researchers evaluated cotinine's effects on performance in a computer-based memory test in monkeys and also compared the effects of cotinine to nicotine in protecting isolated nerve cells from degenerating.

They found that monkeys which were given cotinine did better on the memory tasks than control animals who did not receive supplementation, and that the improvement with cotinine went up as the dose was raised. Cotinine was also found to be as potent as nicotine in its ability to act as a protective agent in vitro​.

In further studies involving rats, Buccafusco and his colleagues discovered that cotinine was as effective as standard anti-schizophrenic drugs in reducing the startle response - the natural reaction to a loud noise. Normally, rats - just like people - are startled by loud noises. If a less intense noise consistently precedes the loud one, however, the startle response tends to weaken - but not in people with schizophrenia or in laboratory animals given schizophrenic-producing drugs.

In much the same way as smokers who are under stress tend to increase their cigarette consumption, it has been established that individuals with schizophrenia also tend to be heavy smokers. And this may also represent a form of self-medication.

"Many people have thought that cotinine was an essentially inactive metabolite, but we have shown that at appropriate doses, it enhances memory and protects brain cells from dying, as well as having antipsychotic properties," said Jerry Buccafusco, who directed the research project at MCG.​

No smoking​​

"These findings don't mean people should smoke," commented neuroscientist Michael Kuhar of Emory University. "Any benefits from the nicotine in cigarettes or other tobacco products are far outweighed by the proven harm of using those products. But pure nicotine-like compounds as medications do show promise for treating human disorders."​