I don't think anyone would ever discount the idea that nicotine has both a "priming" effect in the pleasure centers of the brain AND a "boosting" effect once that centers have been tiggered by something else.

I mean consider when people really like to smoke - after sex, while drinking, after a good meal.

Clearly, to me at least, nicotine not only alleviates negative emotion, but positively regulates pleasure as well.

However, even coupled with the physiological data in mice, it still remains a hard sell to me that nicotine necessarily translates into a gateway drug, although it may be true for a subpopulation of individuals.