e-Neuro New Research:  Menthol is the most popular flavor used in all forms of tobacco products. Depending on the method used to produce the menthol, these products contain two stereoisomers ((−)-menthol and (+)-menthol) in unregulated and poorly characterized amounts. We studied how these isomers of menthol differ in their ability to alter nicotinic receptors on dopamine neurons that contribute to tobacco addiction. Long-term treatment with (−)-menthol and (+)-menthol resulted in a stereospecific effect on nicotinic receptor upregulation and dopamine neuron excitability: (+)-menthol exhibited no effect while (−)-menthol exhibited a robust effect. In acute treatments, we found only slight differences between effects of the two isomers on nicotine receptors. This suggests that long-term exposure to (−)-menthol may contribute to exacerbating tobacco addiction.  Read more