Mifepristone decreases nicotine intake in dependent and non-dependent adult rats

Addiction to tobacco and nicotine products has adverse health effects and afflicts more than a billion people worldwide. Therefore, there is an urgent need for new treatments to reduce tobacco and nicotine use. Glucocorticoid receptor blockade shows promise as a novel treatment for drug abuse and stress-related disorders. The aim of these studies was to investigate if glucocorticoid receptor blockade with mifepristone diminishes the reinforcing properties of nicotine in rats with intermittent or daily long access to nicotine. The rats self-administered 0.06 mg/kg/inf of nicotine for 6 h per day, with either intermittent (3 days per week) or daily access (7 days per week) for 4 weeks before treatment with mifepristone. Daily nicotine self-administration models regular smoking, while intermittent nicotine self-administration models occasional smoking. To determine if the rats were dependent, they were treated with the nicotinic acetylcholine receptor antagonist mecamylamine, and somatic signs were recorded. The rats with intermittent access to nicotine had a higher level of nicotine intake per session than those with daily access, but only the rats with daily access to nicotine showed signs of dependence. Furthermore, mecamylamine increased nicotine intake during the first hour of access in rats with daily access but not in those with intermittent access. Mifepristone decreased total nicotine intake in rats with intermittent and daily access to nicotine. Moreover, mifepristone decreased the total distance traveled and rearing in the open field test and operant responding for food pellets. These findings indicate that mifepristone decreases the reinforcing effects of nicotine and food, but it might also be somewhat sedative.