Development of tolerance to nicotine's anxiogenic effect in the social interaction test.

The purpose of the present experiment was to explore the role of the dorsal hippocampus in mediating the development of tolerance to the anxiogenic effect of nicotine in the social interaction test of anxiety, and to determine whether tolerance develops to the effects of nicotine on [3H]-5-HT release in this area. Nicotine (1 microg) administered bilaterally into the dorsal hippocampus significantly reduced the time spent in social interaction in vehicle pre-treated rats, indicating an anxiogenic effect, but tolerance to this effect was seen in the rats pre-treated for 6 days with s.c. nicotine (0.1 mg/kg/day). In rats that had been pre-treated with vehicle for 6 days, nicotine (50-200 microM), significantly stimulated [3H]-5-HT release from dorsal hippocampal slices. This stimulation was significantly reduced in rats pre-treated with nicotine (0.1 mg/kg/day) for 6 days, indicating the development of tolerance to the effects of nicotine on 5-HT release. This suggests that tolerance to the anxiogenic effect of nicotine administered into the dorsal hippocampus could be mediated by a reduction in the nicotine enhancement of 5-HT release in this area.