Chronic Stress Increases Serotonin and Noradrenaline in Rat Brain and Sensitizes Their Responses to a Further Acute Stress

Abstract: The effects of 1 h/day restraint in plastic tubes for 24 days on the levels of serotonin (5‐HT), 5‐hydroxyindole‐acetic acid (5‐HIAA), tryptophan (TP), and noradrenaline (NA) in six regions of rat brain 20 h after the last restraint period were investigated. The levels of 5‐HT, 5‐HIAA, and NA but not TP increased in several regions. The effects of 1 h of immobilization on both control and chronically restrained rats were also studied. Immobilization per se did not alter brain 5‐HT, 5‐HIAA, and TP levels, but decreased NA in the pons plus medulla oblongata and hypothalamus. However, immobilization after chronic restraint decreased 5‐HT, increased 5‐HIAA, and decreased NA in most brain regions in comparison with values for the chronically restrained rats. We suggest that chronic restraint leads to compensatory increases of brain 5‐HT and NA synthesis and sensitizes both monoaminergic systems to an additional acute stress. These changes may affect coping with stress demands. Copyright © 1988, Wiley Blackwell. All rights reserved