THE INVOLVEMENT OF GLUCOCORTICOIDS IN THE ACQUIRED IMMOBILITY RESPONSE IS DEPENDENT ON THE WATER TEMPERATURE

The Porsolt swim test was used to study the role of glucocorticoids in a simple learning paradigm. Two experiments were performed. In the first experiment, the stressfulness of the situation was manipulated by testing control, sham-operated and adrenalectomized mice at different water temperatures (20-degrees-C, 25-degrees-C, 30-degrees-C and 35-degrees-C). In the second experiment, control mice were injected with the glucocorticoid antagonist RU38486 (3.2 mg/kg, 10 mg/kg, 32 mg/kg); adrenalectomized mice were injected with the glucocorticoid agonists corticosterone (0.46 mg/kg, 1.0 mg/kg, 2.2 mg/kg) and dexamethasone (0.005 mg/kg, 0.05 mg/kg, 0.1 mg/kg). The results show that water temperature is a very important factor in the Porsolt swim test. It influences the overall behaviour of the animals and changes the involvement of glucocorticoids. At a water temperature of 25-degrees-C, glucocorticoids play an important role in the retention of the immobility response; ADX mice are impaired, and this impairment can be ameliorated by corticosterone and dexamethasone injection. Furthermore, the impairment can be induced in control mice by RU38486. The effects observed at 25-degrees-C were, however, not observable at 20-degrees-C, 30-degrees-C and 35-degrees-C, which suggests, contrary to previous reports, that glucocorticoids do not play a universal role in retention processes.