Food deprivation modulates chronic stress effects on object recognition inmale rats: role of monoamines and amino acids

An object recognition task was used to determine if chronic restraint stres s (6 h/day for 21 days) impairs non-spatial memory, since chronic restraint is known to impair spatial memory. In addition, food deprivation was teste d as a possible modulating factor of any stress effect in this non-reward-d ependent task. Following 3 weeks of daily restraint, subjects were tested f or open field activity and object recognition (over different delay interva ls) during one week in two separate experiments. Experiment 1 involved test ing under low demand conditions (small arena) while experiment 2 involved t esting under higher-demand conditions (large arena). Basal monoamine and am ino acid levels (home cage) were assessed in experiment one and monoamine a rousal levels (following a sample trial) were assessed in experiment two. W e observed that chronic stress impaired object recognition when the delay w as extended beyond 1 h, and that food deprivation could attenuate the degre e of impairment. In addition, chronic stress was associated with increased norepinephrine levels in both the amygdala and hippocampus, and dopamine (H VA/DA, DOPAC/DA) in prefrontal cortex. These changes were not observed in s tress subjects that were subsequently food deprived. Food deprived subjects had higher basal serotonin activity in prefrontal cortex and hippocampus a s well as higher serum CORT levels. Results suggest that food deprivation m ay act as a novel stress, thereby increasing subjects' arousal and attentio n toward the objects, which aids stressed subjects, especially in low-deman d conditions. Both restraint and food deprivation affected select limbic ar eas associated with memory functioning. (C) 1999 Elsevier Science B.V. All rights reserved.