Time-related differences in noradrenaline turnover in rat brain regions by stress

Male Wistar rats were stressed by immobilization from 15 to 180 min and the effect on noradrenaline (NA) and 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) contents in eight discrete brain regions were determined. NA levels significantly decreased and MHPG-SO4 levels increased in the hypothalamus, amygdala, thalamus, hippocampus, pons+ med.obl. and cerebral cortex. By contrast, the basal ganglia exhibited increases in NA levels and transient decreases in MHPG-SO4 levels. The midbrain failed to show significant alterations. The most rapid and marked increase in MHPG-SO4 level was found in the hypothalamus. When rats were exposed to stress after treatment with probenecid 400 mg/kg, the hypothalamus and amygdala showed greater accumulations of MHPG-SO4 in the early phase of stress, while the pons+ med.obl. and basal ganglia in the later phase. The other regions showed virtually the same accumulations. These results suggest that NA release is enhanced by immobilization in the six regions mentioned above and that response of NA neurons occurs rapidly in the hypothalamus and amygdala but is delayed in other regions.