Differential changes in rat brain noradrenaline turnover produced by continuous and intermittent restraint stress

This experiment was performed to investigate differential effects of continuous and intermittent restraint stress on noradrenaline (NA) turnover in brain regions of male Wistar rats by measuring levels of a major metabolite of NA, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4) levels, as well as by measuring levels of plasma corticosterone and organ weights of the thymus, spleen, and adrenal glands. Rats in the 15-min and 30-min intermittently stressed groups showed significantly larger increases in MHPG-SO4 levels in most brain regions relative to those in the 90-min and 180-min continuously stressed groups, even though the total stress duration was equal or shorter. Body weight loss and loss of relative thymus weight in the 15-min intermittently stressed groups were the most marked among the five treatment groups. These findings suggest that stress-rest cyclicity is critical in determining the extent of stress-induced brain NA turnover and peripheral physiological responses.