Age-dependent effects of moderate chronic ethanol administration on different forms of memory expression in mice

A large number of studies have investigated the effects of chronic ethanol administration (CEA) on performance in different types of learning and memory tasks in adult rodents. As a general rule, CEA has been reported to impair performance, although this depends both on the condition of administration (e.g. duration, presence or not of a withdrawn period) and on task demands (e.g. spatial versus non-spatial). Indeed, either no impairment or even a facilitation of performance have been reported following CEA. However, no study has directly addressed the issue as to whether the effect of CEA depends on the age of subjects. In this study, C57Bl/6 mice of two age ranges (i.e. 2-3- and 16-18-month-old) were given either a solution of ethanol (12% v/v) as their only source of fluid for 5 months (experimental groups) or were pair-fed with an isocaloric solution of dextri-maltose (control groups). Then, they were submitted to a place discrimination task in an 8-arm radial maze. Additionally, mice were tested for long-term retention following a 21-day interval. Confirming our previous findings, the results showed that, with respect to adults (7-8-month-old at the time of testing), aged mice (21-23-month-old) of the control group displayed impaired relational memory but not procedural memory performance. Further they exhibited a higher level of forgetting than adults over the 21-day interval. In the same paradigm, CEA resulted in an overall attenuation of both type of deficit in aged subjects without altering their procedural memory. Furthermore these ethanol-consuming aged mice displayed significantly less levels of forgetting than their age-matched controls. Conversely, in the adult group, CEA resulted in an overall, although, somewhat less selective impairment of relational memory with respect to procedural memory but had no effect on long-term forgetting. While confirming the deleterious effect of CEA on learning and memory processes in adults, our present findings provide evidence that CEA can selectively ameliorate certain cognitive deficits normally associated with ageing.