Methylprednisolone as a memory enhancer in rats: Effects on aversive memory, long-term potentiation and calcium influx

It is well recognized that stress or glucocorticoids hormones treatment can modulate memory performance in both directions, either impairing or enhancing it. Despite the high number of studies aiming at explaining the effects of glucocorticoids on memory, this has not yet been completely elucidated. Here, we demonstrate that a low daily dose of methylprednisolone (MP, 5 mg/kg, i.p.) administered for 10-days favors aversive memory persistence in adult rats, without any effect on the exploring behavior, locomotor activity, anxiety levels and pain perception. Enhanced performance on the inhibitory avoidance task was correlated with long-term potentiation (LTP), a phenomenon that was strengthen in hippocampal slices of rats injected with MP (5 mg/kg) during 10 days. Additionally, in vitro incubation with MP (30-300 µM) concentration-dependently increased intracellular [Ca2+]i in cultured hippocampal neurons depolarized by KCl (35 mM). In conclusion, a low daily dose of MP for 10 days may promote aversive memory persistence in rats.