PMID: 9652Jun 23, 1976

Effects of humoral modulators and naloxone on morphine-induced changes in the spontaneous locomotor activity of the rat

T Oka, E Hosoya


The s.c. administration of 20 mg/kg of morphine-HCl produced a decrease in the spontaneous locomotor activity (SLMA) of rats. The decrease in SLMA was significantly antagonized by p-chlorophenylalanine (p-CPA). When rats pretreated with p-CPA were given 5-hydroxytryptophan before morphine injection, the marked sedative response to morphine was restored, suggesting that the morphine-induced decrease in SLMA of rats may depend on the release of 5-hydroxytryptamine by morphine. By contrast, the s.c. administration of 5 mg/kg of morphine-HCl produced a significant increase in SLMA of rats. The magnitude of the increase was reduced by atropine, scopolamine or alpha-methyl-p-tyrosine. It appears that both adrenergic and cholinergic mechanisms participate in the increase in SLMA of rats induced by morphine. Both the increase in SLMA produced by 5 mg/kg of morphine and the decrease in SLMA induced by 20 mg/kg of morphine were completely antagonized by the s.c. administration of naloxone-HCl, 0.0625 and 0.25 mg/kg, respectively. Thus, it appears that the receptor with which morphine interacts to produce stimulation is chemically identical with or very similar to the receptor with which morphine combines to induce depression. The former ...Continue Reading


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Related Concepts

Atropine Sulfate Anhydrous
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