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

    Research output: Contribution to journalArticle

    23 Citations (Scopus)

    Abstract

    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
    Volume144
    Issue number1-2
    DOIs
    Publication statusPublished - 14 Sep 1992

    Keywords

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

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