CHRNA4 and nicotine dependence: No significant associations of the nAChR β2 to smoking behavior or level of nicotine dependence were found.65 Although the role of α6 subunit in the etiology of nicotine dependence remains unknown, this subunit was implicated in the stimulation effect of nicotine on habituated locomotion.66α6 subunit was suggested to be an useful tool to understand the mechanisms of nicotine dependence in mice.67 On the whole, nAChR subunits have been performed on smoking have been negative.