Sites of action of morphine on the ascending excitatory reflex in the guinea-pig small intestine

M. Tonini, S. A. Waterman, S. M. Candura, T. Coccini, M. Costa

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    26 Citations (Scopus)


    The effect of morphine on the ascending excitatory reflex of the circular muscle elicited by radial distension of the gut wall was studied in the isolated guinea-pig small intestine. A three compartment bath, in which an intermediate compartment divided the site of intraluminal stimulation (caudal compartment) from the site of reflex contraction recording (oral compartment), was used. Morphine (0.01-10 μM) applied independently to each compartment, caused a concentration-dependent depression (up to 90%) of the amplitude of distension-evoked reflex contractions. Concentration-response curves to morphine were shifted to the right by naloxone (30 nM) with an apparent pA2 value of about 8.5, which suggests an interaction with opioid μ-receptor subtypes. Our results indicate that morphine not only depressed transmission from excitatory motor neurons to the circular muscle but also neuro-neuronal transmission along the ascending excitatory reflex pathway.

    Original languageEnglish
    Pages (from-to)195-198
    Number of pages4
    JournalNeuroscience letters
    Issue number1-2
    Publication statusPublished - 14 Sept 1992


    • Ascending excitatory reflex
    • Guinea pig ileum
    • Morphine
    • Naloxone
    • Opioid μ-receptor subtype


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