Memory consolidation in senescence: effects of CO2, amphetamine and morphine

Alterations in memory storage processes that occur in senescence were investigated by challenging young and old female "small Wistar" rats with posttraining administration of CO2, amphetamine or morphine, and measuring retention performance. Neither duration of CO2 immersion, nor the time of CO2 immersion after training had a differential amnestic effect with age on retention of a one-trial, shock-motivated inhibitory avoidance task. These results indicate that the times during which memory is susceptible to disruption for old and young rats are similar. Challenge with drugs, however, did reveal age-related alterations in memory storage processes. Amphetamine attenuated CO2-induced amnesia in young rats, but had no effect in old rats. This could not be attributed to a general decline in response to amphetamine in old rats because amphetamine increased open field activity of both young and old animals. Morphine also had a differential effect on memory with age: it caused amnesia in old rats trained in a one-trial hot plate escape task, while having no effect on retention performance of young rats. Thus, the modulatory influence of catecholamine and opioid systems on memory processes is probably altered in senescence.