Circular muscle contraction in the mice rectum plays a key role in morphine-induced constipation.
Ono H, Nakamura A, Matsumoto K, Horie S, Sakaguchi G, Kanemasa T.
Neurogastroenterol Motil., 26(10): 1396-1407(2014)
doi: 10.1111/nmo.12387