The antidepressant-like activity of nicotine, but not of 3-furan-2-yl-N-p-tolyl-acrylamide, is regulated by the nicotinic receptor β4 subunit.

The current study compares the antidepressant-like effect elicited by nicotine between wild-type (β4+/+) and knockout (β4-/-) mice, and subsequently, the effect of 3-furan-2-yl-N-p-tolyl-acrylamide (PAM-2), a positive allosteric modulator of α7 nicotinic receptors, on the previously determined activity of nicotine. Mice from each sex were injected daily with nicotine base (0.2 mg/kg; s.c.) or co-administered with PAM-2 (1.0 mg/kg; i.p.) for 3 weeks. Forced swim tests were performed to determine the acute (day 1), subchronic (day 7), and chronic (days 14 and 21) effects of the drugs, as well as their residual effects after treatment cessation (days 28 and 35). Our results indicate that nicotine mediates antidepressant-like activity after acute, subchronic, and chronic treatments in β4+/+, but not β4-/-, mice, and that these effects are not mediated by unspecific locomotor stimulation. Nicotine co-administered with PAM-2 produces antidepressant-like activity in both β4+/+ and β4-/- mice, except after the acute treatment of β4-/- mice, and decreases locomotor activity. This suggests that although the β4 subunit regulates the antidepressant-like activity of nicotine it does not affect the activity elicited by PAM-2 when is co-administered with nicotine. The residual antidepressant-like activity of PAM-2 + nicotine was observed only in female mice, suggesting gender-specific differences. Our findings clearly indicate that β4-containing nAChRs play an important role in the antidepressant-like activity elicited by nicotine but they are not essential for the modulatory activity of PAM-2. In fact, PAM-2 inhibits α4β4 and α3β4 AChRs at higher concentration ranges compared to that for the PAM activity previously found at the α7 AChR.
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