Effect of intra-amygdala injection of nicotine and GABA receptor agents on anxiety-like behaviour in rats.

There is evidence that both cholinergic and GABAergic systems are involved in the neurobiology of anxiety. In the present study, we investigated the effects and interaction of nicotinic and GABAergic systems in the central amygdala of rats, using the elevated plus maze test of anxiety. Bilateral administration of nicotine (1 and 2 microg/rat; 1 microl/rat; 0.5 microl/rat in each side) into the central amygdala (intra-CeA) induced an anxiogenic-like effect, shown by specific decreases in the percentage of open-arm time (%OAT) and percentage of open arm entries (%OAE). Intra-CeA injection of mecamylamine, a selective nicotine acetylcholine receptor antagonist (20, 30 and 50 ng/rat; 1 microl/rat; 0.5 microl/rat in each side) produced significant anxiolytic-like behaviour. The intra-CeA injection of the GABAA receptor agonist muscimol (0.25, 0.5 and 0.75 microg/rat; 1 microl/rat; 0.5 microl/rat in each side) decreased %OAT and %OAE, indicating anxiogenic-like behaviour. However, intra-CeA administration of the GABAA receptor antagonist bicuculline (0.25, 0.5 and 1 microg/rat; 1 microl/rat; 0.5 microl/rat in each side) produced significant anxiolytic-like behaviour. Nicotine in a subeffective dose (0.25 microg/rat) when co-administered with muscimol did not significantly increase the anxiety behaviour. An effective dose of nicotine (2 microg/rat) in combination with bicuculline (0.25, 0.5 and 1 microg/rat) had no interaction on %OAT, %OAE and locomotor activity. It can be concluded that in the central amygdala, the GABAergic system is not involved in the anxiogenic response to nicotine. Copyright 2008 S. Karger AG, Basel.