Recovery of stress-induced increases in noradrenaline turnover is delayed in specific brain regions of old rats |
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Authors: | Y Ida M Tanaka A Tsuda Y Kohno Y Hoaki R Nakagawa K Iimori N Nagasaki |
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Affiliation: | Department of Pharmacology, Kurume University School of Medicine, Kurume 830, Japan |
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Abstract: | Male Wistar rats at 2 and 12 months of age were sacrificed before, immediately following, and at 6 and 24 hours after a 3-hour immobilization stress period. Levels of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), in eight brain regions and plasma corticosterone levels were fluorometrically determined. Immobilization stress caused significant increases of MHPG-SO4 levels in all brain regions examined and significant elevations in plasma corticosterone levels in both 2 and 12 month old rats. In 2 month old rats, the MHPG-SO4 levels in all brain regions returned to control levels within 6 hours after release from the stress. However, in 12 month old rats, the metabolite levels in the hypothalamus, amygdala, pons plus medulla oblongata (pons+med. obl .) and midbrain still remained at significantly increased levels at 6 and 24 hours after the stress. Moreover, in the amygdala of older rats, stress-induced decreases in NA levels persisted even 6 hours after stress. Plasma corticosterone levels also showed significant elevations at 6 and 24 hours after the stress only in 12 month old rats. These results suggest that brain NA metabolism during recovery periods from an acute exposure to a stressful situation is altered by the aging process in such a manner that NA neurons in the hypothalamus, amygdala, pons+med. obl . and midbrain in older rats remain activated by stressful stimuli for prolonged periods of time following release from stress. |
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