THE DEXAMETHASONE SUPPRESSION TEST IN GENETICALLY DIFFERENT RATS EXPOSED TO INESCAPABLE AND ESCAPABLE ELECTRIC SHOCKS

The Dexamethasone Suppression Test (DST) was applied to male rats of K oltushi high- (KHA) and low-avoidance (KLA) strains, genetically selec ted on the basis of divergent acquisition of a conditioned avoidance r esponse in a two-way shuttlebox. Rats were exposed to either inescapab le (IS) or escapable (ES) electroshock. IS produced escape deficit in a shuttle box only in KHA rats. ES enhanced escape failures only in KL A rats. There were no differences in plasma corticosterone levels betw een naive KLA and KHA rats. IS led to increase of the post-dexamethaso ne corticosterone levels in KHA rats, while both basal and stress-indu ced corticosterone levels in the KHA strain remained unchanged followi ng IS. In KLA rats exposed to IS, both pre- and post-dexamethasone bas al corticosterone levels were increased and stress-induced corticoster one levels were decreased. Thus, resistance to the DST after IS occurr ed only in KHA rats. ES led to enhanced basal and reduced stress-induc ed corticosterone levels in KLA rats compared to KHA rats before and a fter dexamethasone treatment. These findings suggest that the HPA axis reactivity following aversive stimuli depends on the interaction betw een genotype and stressor controllability.