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Amygdaloid serotonin and endogenous opioid substances (ols) are important for mediating electroacupuncture analgesia and morphine analgesia in the rabbit

Xu Deyi, Zhou Zhongfu, Han Jisheng

Department of Physiology, Beijing Medical College. Beijing, China

Abstract

The purpose of this study was to determine whether serotonin (5-HT) and endogenous opioid substances (OLS) contained and released in amygdala play a rolein mediating the analgesic effect elicited by morphine or electroacupuncture (EA) stimulation. Rabbits were equipped with bilateral stainless steel guide cannulae (o. d. 0.7 mm) with the cannula tip placed dorsal to the amygdala. Microinjection was performed through an injection tube (o. d. 0.3 mm) protruding 2 mm beyond the cannula tip to reach the nucleus, at a speed of 2 #mu#l/8 min. Pain threshold was assessed by the latency of radiant heat head jerk response. (1) Pain threshold was significantly increased by bilateral intra-amygdaloid injection of morphine (10 #mu#g/site), but not by normal saline, naloxone (2 #mu#g/site), cinanserin (4 #mu#g/site), D-phenylalanine (DPA, 10 #mu#g/site)or 5-hydroxytryptophan (5-HTP, 2.5 #mu#g/site). (2) The analgesic effect induced by EA stimulation was significantly attenuated by the intra-amygdaloid injection of opiate receptor blocker naloxone or 5-HT receptor blocker cinanserin. Maximal blocking effect was obtained by bilateral intra-amygdaloid injection, especially to the central nucleus of amygdala. Unilateral injection elicited a weaker action. Injection to the vicinity of amygdala was not effective (3) EA analgesia was significantly augmented by intra-amygdaloid injection of 5-HTP (a precursor of 5-HT) or of DPA (a putative blocking agent for enkephalin degradating enzymes). (4) Chemical agents exerting a potentiating or antagonizing effect on EA analgesia showed a similar effect on morphine analgesia in the same site of injection. The results suggest that morphine and EA may stimulate the release of 5-HT and OLS (most probably enkephalins) in the amygdala thereby producing an analgesic effect.

Key words: Amygdala;Serotonin;Endogenous opioid substances;Electroacupuncture analgesia;Morphine analgesia;Rabbit

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Citing This Article：

Xu Deyi, Zhou Zhongfu, Han Jisheng. Amygdaloid serotonin and endogenous opioid substances (ols) are important for mediating electroacupuncture analgesia and morphine analgesia in the rabbit. Acta Physiol Sin 1985; 37 (2): (in Chinese with English abstract).