Nicotine and 17β-estradiol produce an antidepressant-like effect in female ovariectomized rats

Nicotine and estrogen may influence depressive behavior in women. In this study, we sought to determine whether nicotine (NIC), alone and in combination with 17β-estradiol (E2), might influence depressive characteristics of female rats in the forced swim test (FST). Ovariectomized adult female Sprague–Dawley rats (n = 8/group) received subcutaneous (s.c.) injections of nicotine, E2 or the combination (NIC: 0.2 mg/kg, bw and E2: 10 μg) before the FST. Controls received saline and/or corn oil. Locomotor activity was also assessed. Acute administration of nicotine significantly reduced immobility in the FST. Acute administration of E2 also decreased immobility. The combination of nicotine (0.2 mg/kg) and E2 (10 μg) significantly reduced immobility; however, this reduction was not greater than either agent administered alone. No differences in locomotor activity were detected among the treatment groups. Acute administration of nicotine and E2, alone and in combination, significantly decreased immobility of ovx rats in the FST, suggesting an antidepressant-like effect of these two agents in this model. However, the combination of E2 and nicotine did not have any further reduction, indicating a lack of an additive or synergistic effect. Results from this study suggest that agents that target nicotinic acetylcholine receptors and estrogen receptors may be beneficial in alleviating depressive symptoms in women during periods of low estrogen levels.