Changes in hypothalamic noradrenaline turnover in rats produced by controllable and uncontrollable shocks.

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The levels of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in the hypothalamus of male Wistar rats were evaluated after 3, 6 or 21 hr of exposure to controllable and uncontrollable shocks. After 3 and 6 hr in the discriminated Sidman avoidance/escape stress-session, experimental rats which could avoid or escape shock (i, e., controllable shock) had lower NA levels and higher levels of MHPG-SO4 than did yoked rats which were given the same shock but could not avoid or escape the shock (i. e., uncontrollable shock). After 21 hr of stress, however, the enhancement of NA turnover in the experimental rats were much smaller than in the matched yoked rats which had elevated levels of MHPG-SO4 in the 6-hr and 21-hr stress-sessions. Responses of noradrenergic neurons in the control rats were negligible when compared with the experimental and yoked rats at each stress duration. These results suggest that hypothalamic NA turnover is increased before the experimental animals have learned the effective coping responses, and that the NA turnover is reduced when the rats learn to cope with the shock. The yoked rats had no opportunity to learn to cope with the shock, and hence were helpless. The turnover of NA in these rats remained enhanced at all stress durations and there was also a greater increase in hypothalamic MHPG-SO4 content, relative to the experimental rats at 21-hr stress duration. It is suggested that coping with stress involves activity of noradrenergic neurons in the brain.
久留米大学医学部 The Kurume Medical Journal 編集部の論文

Changes in hypothalamic noradrenaline turnover in rats produced by controllable and uncontrollable shocks.

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