Short-term, high-dose administration of corticosterone by injection facilitates trace eyeblink conditioning in young male rats.

Glucocorticoids released as part of the physiological response to stress are known to affect cognitive function, presumably via effects on the hippocampus. Trace classical eyeblink conditioning is an associative learning task which depends on the hippocampus and has been used to examine the development of learning processes in young mammals. Previously, we demonstrated deficits in trace eyeblink conditioning associated with postnatal administration of the glucocorticoid corticosterone by creating a sustained elevation with methods such as subcutaneous timed-release pellets and osmotic mini-pumps which were active over several days. In the present study, we examined the effects of an oscillating pattern of corticosterone elevation on subsequent trace eyeblink conditioning. Twice daily corticosterone injections (high, low, or vehicle) were administered over a 3-day period, starting at postnatal day 15. Then, on postnatal day 28, animals underwent trace classical eyeblink conditioning to examine the possible influence of earlier corticosterone elevations on the development of learning and memory. Eyeblink conditioning was affected by corticosterone treatments, but only for males, and only very early in acquisition; Males receiving the high dose of corticosterone exhibited facilitation of learning relative to controls. These data demonstrate that oscillating corticosterone elevations produce opposite effects on this associative learning task than do sustained elevations.