Abstract
The Dexamethasone Suppression Test (DST) was applied to male rats of Koltushi high- (KHA) and low-avoidance (KLA) strains, genetically selected on the basis of divergent acquisition of a conditioned avoidance response in a two-way shuttlebox. Rats were exposed to either inescapable (IS) or escapable (ES) electroshock. IS produced escape deficit in a shuttle box only in KHA rats. ES enhanced escape failures only in KLA rats. There were no differences in plasma corticosterone levels between naive KLA and KHA rats. IS led to increase of the post-dexamethasone corticosterone levels in KHA rats, while both basal and stress-induced corticosterone levels in the KHA strain remained unchanged following IS. In KLA rats exposed to IS, both pre- and post-dexamethasone basal corticosterone levels were increased and stress-induced cortisterone levels were decreased. Thus, resistance to the DST after IS occurred only in KHA rats. ES led to enhanced basal and reduced stress-induced corticosterone levels in KLA rats compared to KHA rats before and after dexamethasone treatment. These findings suggest that the HPA axis reactivity following aversive stimuli depends on the interaction between genotype and stressor controllability.
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