ABSTRACT
glucocorticoids. Catecholamines are released rapidly and typically r~tum to baseline levels within 10 min, but the glucocorticoid response is much slower13• The finding that plasma levels of wrticosterone, from blood collected immediately after the probe trial, were elevated in the impaired 30-min group (P < 0.01), but not in any of the other stress groups (Table Ia), suggests that increased adrenocortical function induced by the stressor may have disrupted memory retrieval. To examine this possibility, rats were given metyTapone, a drug that reduces the synthesis of corticosterone by inhibiting the 11J3-hydroxylation reaction in the adrenal glands. Meryrapone (50 mg per kg, subcutaneous (s.c.) injection; Sigma) was dissolved in a vehicle containing 40% polyethylene glycol and 60% saline. Consistent with previous findings 1", metyrapone injected 40 min before footshock had no effect on baseline corticosterone levels, but blocked the stress~induced increase in plasma corticosterone (P < 0.01; Table I b). Metyrapone also blocked the stress-induced retention impairment (P < 0.01, Fig. 2a). Other possible actions of meryrapone were excluded as meryrapone did not block the retention impairment in rats given corticosterone (3.0 mg per kg. s.c.) 30 min before testing. Neither of the treannents altered swimming pathlengths (F,_., = 0.61, P > 0.64).
