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Participation of spinal norepinephrine in morphine analgesia in rats

Xie Cuiwei, Du Xiaoli, Tang Jian, Han Jisheng

Department of Physiology, Beijing Medical College. Beijing, China

Abstract

The present study was performed in an attempt to define the involvement of descending noradrenergic pathway and the spinal a-adrenoceptors in the mechanisms of morphine analgesia. It was found that acute morphine treatment (6mg/kg, sc) increased the spinal content of 3-methoxy-4-hydroxyphenylglycol sulfate (MHPG·SO_(4)), a metabolic end-product of central norepinephrine (NE),thus suggesting an increased NE turn-over. This response was no longer present in animals made tolerant to morphine analgesia by chronic morphine treatment. Different kinds of a-adrenoceptor antagonists were injected intrathecally to assess their effects on morphine analgesia. While analgesia produced by a small dose of systemic morphine was attenuated by phentolamine, as well as by selective #alpha#_(1) or #alpha#_(2)-blocker, prazosin or yohimbine, analgesia induced by intrathecal morphine was not affected by prazosin or yohimbine. These findings indicate that descending noradrenergic system from supcaspinal structures may serve as one of the important mechanisms for morpine analgesia.

Key words: Norepanephrine;MHPG·SO_(4);Morphine analgesia;Morphine tolerance;Alpha-adrenoceptor antagonist;Intrathecal injection

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Citing This Article：

Xie Cuiwei, Du Xiaoli, Tang Jian, Han Jisheng. Participation of spinal norepinephrine in morphine analgesia in rats. Acta Physiol Sin 1985; 37 (3): (in Chinese with English abstract).