Daily increase in noradrenaline turnover in brain regions of activity-stressed rats

Changes in contents of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) in brain regions (the hypothalamus, amygdala, thalamus, hippocampus, midbrain, cerebral cortex, pons plus medulla oblongata and basal ganglia) of male Wistar rats were evaluated after 1, 3 or 5 days of exposure to the activity-stress paradigm, wherein rats were housed in a cage with a running-wheel and restricted to 1-hr of feeding per day. When compared to the non-stressed control rats, contents of MHPG-SO4 in all the brain regions except of the basal ganglia in the stressed rats increased as rapidly as 1 day and continued to increase throughout the 5-day activity-stress period. Contents of NA did not change significantly in most of these brain regions. The daily increase in regional NA turnover by continuous exposure to the activity-stress paradigm was related to the large increases in running activity and gastric ulcers, and to body weight loss at the 3-day and 5-day testing periods. These data suggest that pathological states produced by a 5-day activity-stress paradigm may reflect concomitant disturbances of noradrenergic function in various brain regions. The activity-stress paradigm is regarded as an intense and progressive stress, because it induces an increase in NA response in extended brain regions.