ストレスによるラット脳内ノルアドレナリンニューロンの反応性と内因性オピオイドペプタイド : Naloxoneによる検討

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A variety of stressful stimuli are well known to activate noradrenergic neurons in many brain regions in rats. The present study was undertaken to investigate the possible relationship between these stress-induced increases in noradrenaline (NA) turnover and endogenous opioid peptides, utilizing the opiate antagonist, naloxone. Male Wistar rats were injected subcutaneously with either saline or naloxone, 1 mg/kg or 5 mg/kg, 10 min before exposing to 1-hour stress. Immobilization stress was employed by enclosing the animals in a flexible wire mesh (3×3 mm). Control animals were sacrificed 70 min after respective injections. Levels of NA and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO_4) and plasma corticosterone levels were determined fluorometrically. Plasma corticosterone levels were significantly elevated by stress, but these elevations were not affected by pretreatment with naloxone. Immobilization stress caused significant increases in MHPG-SO_4 levels in the hypothalamus, amygdala and thalamus and these increases of the metabolite levels were significantly enhanced by pretreatment with naloxone at 5 mg/kg. In contrast, although in the hippocampus, cerebral cortex and pons plus medulla oblongata immobilization stress significantly increased MHPG-SO_4 levels, these increases were not affected by naloxone pretreatment. When the rats were immobilized for 2 hours and then injected with saline or naloxone at 5 mg/kg and subsequently immobilized for further 1 hour, naloxone showed no enhancement of stress-induced increases in MHPG-SO_4 levels even in the hypothalmus, amygdala and thalamus. The effect of naloxone on stress-induced reductions of NA levels was unclear, since naloxone at 5 mg/kg by itself showed significant decreases in NA levels, which seemed to have resulted from an inhibitory action of the drug on catecholamine synthesis.These results suggest, indirectly, that endogenous opiod in the hypothalamus, amygdala and thalamus are partially involved in the stress process, particularly during the first 1 hour of stress, by attenuating increases in NA turnover caused by stress and that these changes might be related to the relief of hightened emotionality by aversive stimuli, i.e., fear or anxiety in animals.
日本心身医学会の論文
1982-06-01

ストレスによるラット脳内ノルアドレナリンニューロンの反応性と内因性オピオイドペプタイド : Naloxoneによる検討

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