Spatial memory under acute cold and restraint stress.

This study examined spatial memory as measured by radial arm maze (RAM) performance after exposure to two stress conditions and a normothermic-unrestrained control condition. Male Fischer 344 rats were trained on the win-shift RAM procedure for 7 days, by which time they achieved asymptotic performance. The next day, rats in the two stress groups were exposed to 15 min of restraint in either 37 degrees C water (normothermic-restraint) or in 20 degrees C water (cold-restraint). Rats were then allowed 40 min in a dry cage before being tested in the RAM. Performance was measured using the following dependent variables: number of correct out of the first eight choices, total number of choices, and time per choice. There were statistically significant effects of stress on all these variables; performance decrements were observed in both stress conditions relative to the normothermic-unrestrained condition. Normothermic-restrained rats displayed less impairment than cold-restrained rats on the stress day. Performance of normothermic-restrained rats returned to baseline levels the day after stress, whereas performance for the cold-restrained rats typically did not. This study demonstrates that: 1) restraint and cold stress impair performance on a memory task; and 2) impairment extent is related to stress severity. One of the mechanisms responsible for the observed behavioral deficits under cold stress may involve altered cholinergic function, because we previously demonstrated that hippocampal acetylcholine levels also decrease in relation to the severity of cold stress.