Ž . Brain Research 830 1999 56–71 Research report Food deprivation modulates chronic stress effects on object recognition in male rats: role of monoamines and amino acids Kevin D. Beck a,b, ) , Victoria N. Luine a,b a Department of Psychology, Hunter College, 695 Park AÕenue, New York, NY 10021, USA b Graduate Program in Psychology, Biopsychology Subprogram, CUNY Graduate School and UniÕersity Center, 33 W 42nd St., New York, NY 10036, USA Accepted 9 March 1999 Abstract Ž . An object recognition task was used to determine if chronic restraint stress 6hrday for 21 days impairs non-spatial memory, since chronic restraint is known to impair spatial memory. In addition, food deprivation was tested as a possible modulating factor of any stress effect in this non-reward-dependent task. Following 3 weeks of daily restraint, subjects were tested for open field activity and object Ž . recognition over different delay intervals during one week in two separate experiments. Experiment 1 involved testing under low Ž . Ž . demand conditions small arena while experiment 2 involved testing under higher-demand conditions large arena . Basal monoamine Ž . Ž . and amino acid levels home cage were assessed in experiment one and monoamine arousal levels following a sample trial were assessed in experiment two. We observed that chronic stress impaired object recognition when the delay was extended beyond 1 h, and that food deprivation could attenuate the degree of impairment. In addition, chronic stress was associated with increased norepinephrine Ž . levels in both the amygdala and hippocampus, and dopamine HVArDA, DOPACrDA in prefrontal cortex. These changes were not observed in stress subjects that were subsequently food deprived. Food deprived subjects had higher basal serotonin activity in prefrontal cortex and hippocampus as well as higher serum CORT levels. Results suggest that food deprivation may act as a novel stress, thereby increasing subjects’ arousal and attention toward the objects, which aids stressed subjects, especially in low-demand conditions. Both restraint and food deprivation affected select limbic areas associated with memory functioning. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Stress; Food deprivation; Memory; Object recognition; Monoamines; Amino acids 1. Introduction Regimen of stimuli that create arousal in an animal, via the sympathetic nervous system or the hypothalamic–pitui- Ž . tary–adrenal HPA -axis, lead to transitory changes in behaviors, specifically those that require an animal to learn or remember specific, adaptive responses to environmental Ž w x. stimuli. Luine as reviewed in Refs. 34,35 has shown Ž . how the duration days of 6-h restraint leads to either w x performance enhancements, after 13 days 38 , or perfor- w x mance decrements, after 21 days 40 , using the radial-arm w x maze, a spatial memory task. Conrad et al. 11 similarly showed spatial memory deficits after 21 days of restraint using the Y-maze. Others have shown that stress influ- ences performance of a number of other behavioral tasks ) Corresponding author. Fax: q1-212-772-5620; E-mail: kbeck@shiva.hunter.cuny.edu w x 15,18,43,59,62 that has led to intensive research into the underlying mechanisms of these changes. In general, stress-dependent behavioral change has been ascribed to heightened release of adrenal corticosterone Ž . CORT that is known to alter both neuroanatomy and w x w x neurochemistry 57 . Luine et al. 39 found chronic high Ž . CORT plasma levels via ingestion increased serotonin Ž . 5-HT tissue levels in dentate gyrus, but decreased 5-HT Ž . and norepinephrine NE levels in frontal cortex. Magari- w x w x nos and McEwen 41 , Magarinos et al. 42 and Saplosky w x 57,58 have continually demonstrated that the chronic release of CORT from the adrenal glands, in response to stress, causes remodeling of the CA3 dendrites in the Ž . hippocampus, through excitatory amino acids EEA via w x NMDA receptors 47,63 . The temporal relationship between the stress-dependent physiological effects and behavioral change is critical in these animal models. For instance, chronic high CORT 0006-8993r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0006-8993 99 01380-3