Bimodal modulation by nicotine of anxiety in the social interaction test: Role of the dorsal hippocampus

In conditions generating moderate levels of anxiety in the social interacti on test (low Light, unfamiliar arena or high light, familiar arena), parent eral administration of nicotine had bimodal actions, low doses (0.01 and 0. 1 mg/kg ip) had anxiolytic effects and high doses (0.5 and 1.0 mg/kg ip) ha d anxiogenic effects. In test conditions where anxiety was lowest (low ligh t, familiar arena) and highest (high light, unfamiliar arena), nicotine was without effect after intraperitoneal or hippocampal administration. Thus, nicotine plays a modulatory role in which the activity of other neurotransm itters is crucial to its expression. After bilateral administration to the dorsal hippocampus, nicotine (0.1-8.0 mu g) had anxiogenic effects in condi tions of moderate anxiety; mecamylamine (30 ng) was silent in these conditi ons, indicating no intrinsic tone. Our results show that the dorsal hippoca mpus is one area that can mediate anxiogenic effects in the social interact ion test, but the brain region mediating anxiolytic effects remains to be i dentified.