Memory modulation by post-training intraperitoneal, but not intracerebroventricular, administration of ACTH or epinephrine

Post-training introparitoneal (ip) administration of ACTH1-24 (25 ng/rat) or epinephrine HCl (625 ng/rat) facilitated retention of a step-down inhibitory avoidance task acquired using a small start platform (5-cm high, 25 X 7 cm) and a low intensity training footshock (0.3 mA, 60 Hz), and caused retrograde amnesia for a similar task acquired using a large platform (5-cm high, 25 X 25 cm) and a high intensity training footshock (0.8 mA, 60 Hz). The post-training intracerebroventricular (icv) administration of 5, 25, or 125 ng/rat of ACTH or of 5, 25, 125, 625, or 1250 ng/rat of epinephrine had no effect on retention of either task. These findings suggest that memory modulation by ACTH and epinephrine is mediated by reflexes initiated at peripheral receptors that affect brain activity during the post-training period.