Accelerated rates of forgetting of spatial information during aging and long-term ethanol consumption in mice: Evidence for two distinct forms of amnesia

Abstract

In the experiments reported here, we examined the effects of aging and long-term alcohol consumption on spatial memory performance of BALB/c mice in a T-maze. The spontaneous alternation task used consisted of two forced trials (acquisition phase) followed, at varying retention intervals (from 5 min to 6 h), by a free-test trial (retention phase). Tests were conducted under different conditions by varying the intramaze contexts during the retention phase only. Thus, relative to acquisition trials, animals were submitted to test trials either involving a change of intramaze context (cue added: ON) or being run in their usual condition (no context variation: OFF). The results of the first experiment showed that in usual context conditions (OFF), both aging (17-month-old subjects) and an administration of alcohol over a 6-month period (9-month-old subjects) induced an accelerated rate of decay of spontaneous alternation as a function of delay. The results of the second experiment showed that a change in context (ON; 6-h retention interval) dramatically alleviated the deficit observed among alcohol-treated subjects, whereas aged animals were still impaired. The results of the first experiment indicate that both aged and alcohol-treated mice exhibited an accelerated rate of "forgetting" as defined operationally. However, the results of the second experiment suggest that the deficit of alcohol-treated animals under usual conditions (OFF) is probably attributable to an impairment of retrieval processes, since the deficit was reversed by the context change. In contrast, the persistence of the deficit among aged mice suggests that their deficit was more likely related to an impairment in the maintenance of information over time.