Depression by morphine of the excitability of intrinsic inhibitory neurons in the guinea-pig colon.
The mechanical responses to morphine were examined in isolated preparations of longitudinal and circular muscle of the guinea-pig colon. In the longitudinal coat, morphine induced a relaxation which was prevented by naloxone, hyoscine and tetrodotoxin. Conversely, in the circular coat morphine caused a contraction which was antagonized by naloxone, mimicked by tetrodotoxin and left unaltered by hyoscine, chlorpheniramine and methysergide. In both muscular layers, morphine depressed (and tetrodotoxin abolished) the non-adrenergic relaxation induced by field stimulation. The action of morphine in the two preparations can thus be explained in terms of inhibition of the tonic excitatory cholinergic or inhibitory non-adrenergic neural control prevailing in the longitudinal and circular muscle respectively.
D000818:Animals; D003106:Colon / Q000294:innervation* / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology*; D009474:Neurons / Q000187:drug effects*
D009020:Morphine