Exploratory Behaviour of Rats in the Elevated Plus-maze is Differentially Sensitive to Inactivation of the Basolateral and Central Amygdaloid Nuclei

The amygdala has a crucial role in detecting motivationally significant inputs and in communicating relevant information to other limbic structures. Behavioural studies have shown that the central (CeA) and basolateral (BLA) nuclei of amygdala differentially regulate conditioned and unconditioned fear. Indeed, much evidence has accumulated suggesting that regulatory mechanisms in the BLA serve as a filter for unconditioned and conditioned aversive information that ascends to higher structures from the brainstem, whereas the CeA is the main output for the autonomic and somatic components of fear reaction through major projections to other limbic regions. It is still unclear, however, how amygdaloid nuclei function in high and open spaces so as to determine the characteristic exploratory behaviour of rats submitted to the elevated plus-maze test (EPM). In the present study, we carried out an ethopharmacological analysis of the behaviour of rats submitted to the elevated plus-maze test together with analysis of the tissue content of monoamine dopamine (DA) and serotonin (5-HT) and their metabolites in the dorsal hippocampus (DH), nucleus accumbens (NAC) and dorsal striatum (DS) of animals injected with saline or muscimol (1.0 nmol/0.2 microL) into the BLA or CeA. The data obtained show that injections of muscimol into the CeA, but not into the BLA, caused anxiolytic-like effects in the EPM. Such effects of muscimol into the CeA were accompanied by increases in 5-HT content of the DH, whereas corresponding injections into the BLA caused a reduction in the DA content of the NAC. There was no change in the turnover rates of these monoamines. These data suggest that the BLA and CeA have distinct roles in the exploratory behaviour of rodents in the EPM. While BLA appears to be related to the detection and validation of threatening stimuli, the CeA appears to be involved in the expression of fear behaviours in the EPM.