Effects of post-training ethanol and group housing upon memory of an appetitive task in mice

It has been shown that post-training ethanol's facilitating effects upon memory disappeared if the mice were kept isolated after training. Since ethanol-treated mice were attacked by their cagemates, it has been hypothesized that the improved retention induced by ethanol resulted from an interaction between ethanol and group housing which added aversive information to training. To investigate the correctness of this interpretation, ethanol effects upon memory of an appetitive task were studied. C57BL/6J mice (isolated the day before training) were individually trained to find a cheese pellet placed in a corner of an open-field. Mice were injected intraperitoneally immediately after training with saline, 0.5, 1.5, or 2.0 g/kg of ethanol. They were then returned to their home cage and left alone, with another mouse, or with five other mice for 2 h after training. All mice were tested 24 h later for retention. Reductions in the number of pellet approaches or in the latency to eat the pellet were taken as measures of learning. Post-training ethanol disrupted retention of the appetitive task in a dose-related manner. Moreover disruption was greater in mice group housed after training. The results support the hypothesis that ethanol's post-training facilitating effects upon aversive memory may be due to added aversive information to the stimulus complex, rather than, or in addition, to enhanced storage of memory traces.     

Effects of posttraining ethanol on an appetitive task

The present study examined the effects of posttraining ethanol administration upon retention of an appetitive task using a variety of retention behaviors associated with the task. Male C57BL/6J mice were individually trained to find a cheese pellet placed in the corner of an open field. Five behavioral measures were used including locomotor activity counts, rearings, grooming episodes, approaches to the cheese pellet, and latency to consume the cheese pellet. Immediately after training, mice were injected intraperitoneally with saline or 2.0 g/kg of ethanol and then returned to their home cage in which four "intruder" mice were added for 2 h after training. On subsequent testing days (1, 6, 14, and 51 days posttraining), mice were returned to the original training environment and the five behaviors were measured. Both saline- and ethanol-treated mice habituated to the initially novel test environment at similar rates as indicated by decreased exploratory behavior (locomotor activity and rearings). In contrast, a divergence in the latency to consume the cheese pellet was observed: Saline-treated mice behaved as though the cheese was rewarding (decreased latency to eat the pellet), while the ethanol group behaved as though the cheese was aversive (increased latency to eat the pellet). Taken with previous studies, these results demonstrate that posttraining ethanol can have strikingly different effects on retention depending on the task, the measure of retention used, and the underlying neural structures involved.