Dani_2013_Cold.Spring.Harb.Perspect.Med_3_

The majority of people who attempt to quit smoking without some assistance relapse within the first couple of weeks, indicating the increased vulnerability during the early withdrawal period. The habenula, which projects via the fasciculus retroflexus to the interpeduncular nucleus, plays an important role in the withdrawal syndrome. Particularly the alpha2, alpha5, and beta4 subunits of the nicotinic acetylcholine receptor have critical roles in mediating the somatic manifestations of withdrawal. Furthermore, withdrawal from nicotine induces a hypodopaminergic state, but there is a relative increase in the sensitivity to phasic dopamine release that is caused by nicotine. Therefore, acute nicotine re-exposure causes a phasic DA response that more potently reinforces relapse to smoking during the withdrawal period.