THE EFFECTS OF 2 CHRONIC INTERMITTENT STRESSORS ON BRAIN MONOAMINES

The effects of chronic exposure (27 days) to two different stressors o n brain monoaminergic activity was studied in adult male rats. The str essors used were restraint in tubes (RES) and immobilization in wooden boards (IMO). Both chronically stressed and stress naive (control) ra ts were subjected to 0, 15, and 60 min of the same stressor to which t hey were chronically exposed. Previous chronic exposure to either RES or IMO significantly reduced ACTH response to the same stressor. Monoa minergic response to these stressors was studied by measuring the leve ls of noradrenaline (NA), serotonin (5-HT) and their metabolites: 3-me thoxy,4-hydroxyphenyletileneglycol sulfate (MHPG-SO,) and 5-hydroxyind oleacetic acid (5-HIAA), respectively. The regions studied were: pens plus medulla, midbrain, hypothalamus, hippocampus, and frontal cortex. Previous chronic exposure to the stressors induced only few changes i n the resting levels of the monoamines and their metabolites. In addit ion, monoaminergic response to the same stressor to which they were ch ronically exposed was always similar in control and chronically stress ed rats. These data indicate that brain NA and 5-HT metabolism is less sensitive than ACTH to the process of habituation to a repeated stres sor, at least in the gross areas of the brain analyzed in the present study.