Effects of dexamethasone on fear conditioning in pigs

Pigs were trained either to avoid shocks in a shuttle box according to a continous avoidance schedule or to push a panel with the snout to obtain a food reward according to a VI 30 schedule. After stabilization of the response, they were submitted to Pavlovian fear conditioning. Presentation of the CS alone in a subsequent test session increased the shuttling rate but decreased the operant response rate for food. Dexamethasone (0.2 mg/kg) administered before Pavlovian conditioning enhanced the change in response rate to the CS presentation in the shuttle box and facilitated extinction of the suppressed response for food. Administration of the drug before the test session further increased the response to the CS presentation in the shuttle box only. No interaction between the two treatments was observed, indicating that dexamethasone had no cue value in the present experiments. The results are discussed with reference to current theories about the mechanisms of action of the pituitary-adrenal axis on behavior.