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Menthol acts in combination with nicotine to desensitize the receptors in lung airways that are responsible for nicotine's irritation, according to a study by neuroscientists at Georgetown University Medical Center (GUMC).

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The findings were reported by Hoai Ton, PhD, a post-doctoral researcher, at Neuroscience 2014, the Annual Meeting of the Society for Neuroscience.


"We know that a menthol cough drop soothes a scratchy, sore throat. The question we looked at is if and how it works when the irritant is nicotine," said another coauthor, Kenneth Kellar, PhD, Professor of Pharmacology. "This study supports the notion that menthol is not just a flavoring, but has a pharmacologic effect."


Ton noted in a news release that the Food and Drug Administration is considering restrictions on menthol cigarettes because it has determined that menthol in cigarettes is likely associated with increased initiation and progression to regular cigarette smoking, increased dependence, and reduced success in smoking cessation, especially among African American menthol smokers.


But the agency's review of the available research and evidence relating to menthol cigarettes, issued in July 2013, also concluded that from the available studies, "the weight of evidence supports the conclusion that menthol in cigarettes is not associated with an increase in disease risk to the user compared to non-menthol cigarette smokers."


At the same time, the use of menthol cigarettes is especially high among African-American smokers, and research has shown a higher rate of lung cancer in African American smokers compared with other smokers, he noted.


"The issue may be that menthol in the presence of nicotine may reduce the irritation enough that a smoker can inhale more deeply, bringing not just nicotine but toxic smoke products farther into the lungs," explained another of the investigators, Gerald Ahern, PhD, Associate Professor of Pharmacology.


'While beyond the scope of this study, it is possible that such deeper inhalation of menthol cigarettes, to the extent it occurs, increases the already substantial health harms from smoking."


The researchers say their study provides a better understanding of how menthol affects the function of the [alpha] 3 [beta] 4 receptor, one of the most prevalent nicotinic acetylcholine receptors expressed in the peripheral nervous system. These receptors are expressed in airway sensory nerves as well as other neurons.


"These receptors are also found in the brain, but we don't know yet what effect menthol has on those receptors, or whether they contribute, in any way, to nicotine addiction," Kellar said.