Antidepressantlike effects of chronic nicotine on learned helplessness paradigm in rats.
BACKGROUND
The association between smoking and depression has been widely investigated. Smoking cessation is known to induce depression to a variable extent, and patients with a history of depression are more likely to experience depressive symptoms. To investigate the hypothesis that nicotine may have an antidepressantlike effect, we used learned helpless rats as an animal model of depression.


METHODS
Learned helplessness was produced according to our previous method. Learned helpless rats were implanted with nicotine and escape test was performed at 7 and 14 days after the implantation.


RESULTS
The number of escape failure in the rats receiving 1.5 mg/kg/day of nicotine was significantly reduced (p < .05) compared to control at day 14. Furthermore, this effect was blocked when the nicotinic receptor antagonist mecamylamine was coadministered.


CONCLUSIONS
These results suggest that chronic nicotine may act as an antidepressant, probably via nicotinic receptors.