Age and Stress History Effects on Spatial Performance in a Swim Task in Fischer-344 Rats

Abstract

This study determined whether prior habituation to water immersion would ameliorate age-related deficits in learning and memory in a swim task. Aged (22 months) and young adult (3 months) rats were immersed in water (30°C) for 15 min on each of 28 consecutive days before training in the swim task. Additional groups of age-matched animals served as handled controls. Training on a spatial discrimination version of the water task was conducted over 5 days with two trials per day (1-h intertrial interval). A probe trial was substituted for the last trial on the fifth day to assess the rats’ use of spatial information. Three days later, rats received cue discrimination training to find a visible platform. In the spatial task, prior habituation to water immersion ameliorated deficits in acquisition within each day (i.e., at a 1-h intertrial interval) but not across days (at 24 h). The results obtained with the 24-h interval confirm the rapid forgetting characteristic of aged rats in many tasks. The stress-habituation procedures reduced age-related deficits seen on the probe trial and on cue discrimination training. These findings indicate that several aspects of age-related impairments in the swim task, often attributed to primary age-related deficits in learning and memory processes per se, may instead be secondary to age-related differences in stress responses to water immersion.