title: Neurochemical phenotype and function of endomorphin 2-immunopositive neurons in the myenteric plexus of the rat colon.
abstract: The distribution and activity of endomorphins (EMs), which are endogenous μ-opioid receptor (MOR) ligands in the gastrointestinal tract (GI), are yet to be elucidated. The current study aimed to shed light on this topic. EM2 was expressed in the enteric neurons in the myenteric plexus of the mid-colon. Of the EM2-immunoreactive (EM2-IR) neurons, 53 ± 4.6%, 26 ± 4.5%, 26 ± 2.8% and 49 ± 4.2% displayed immunopositive staining for choline acetyl transferase (ChAT), substance P (SP), vasoactive intestinal peptide (VIP) and nitric oxide synthetase (NOS), respectively. A bath application of EM2 (2 μM) enhanced spontaneous contractile amplitude and tension, which were reversed by β-FNA (an antagonist of MOR) but not NG-nitro-L-arginine methyl ether (L-NAME, a non-selective inhibitor of NOS) or VIP6-28 (an antagonist of the VIP receptor) in the colonic strips. EM2 significantly suppressed inhibitory junction potentials (IJPs) in 14 of the 17 examined circular muscle cells, and this effect was not antagonized by preincubation in L-NAME. EM2 was widely expressed in interneurons and motor neurons in the myenteric plexus and presynaptically inhibited fast IJPs, thereby enhancing spontaneous contraction and tension in the colonic smooth muscle.
authors.affiliation: Department of Anatomy, Histology and Embryology, K.K. Leung Brain Research Centre, The Fourth Military Medical University Xi'an, China ; Department of Anatomy, Histology and Embryology, Ningxia Medical University Yinchuan, China.
authors.forename: Jun-Ping
authors.initials: JP
authors.lastname: Li
authors.affiliation: Department of Physiology and Cell Biology, Medical Center, Ohio State University Columbus, OH, USA.
authors.forename: Xi-Yu
authors.initials: XY
authors.lastname: Wang
authors.affiliation: Department of Anatomy, Histology and Embryology, K.K. Leung Brain Research Centre, The Fourth Military Medical University Xi'an, China.
authors.forename: Chang-Jun
authors.initials: CJ
authors.lastname: Gao
authors.affiliation: Department of Anatomy, Histology and Embryology, K.K. Leung Brain Research Centre, The Fourth Military Medical University Xi'an, China.
authors.forename: Yong-Hui
authors.initials: YH
authors.lastname: Liao
authors.affiliation: Department of Anatomy, Histology and Embryology, K.K. Leung Brain Research Centre, The Fourth Military Medical University Xi'an, China.
authors.forename: Juan
authors.initials: J
authors.lastname: Qu
authors.affiliation: Department of Anatomy, Histology and Embryology, Ningxia Medical University Yinchuan, China.
authors.forename: Zhong-Yi
authors.initials: ZY
authors.lastname: He
authors.affiliation: Department of Anatomy, Histology and Embryology, K.K. Leung Brain Research Centre, The Fourth Military Medical University Xi'an, China.
authors.forename: Ting
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Department of Physiology and Cell Biology, Medical Center, Ohio State University Columbus, OH, USA.
authors.forename: Guo-Du
authors.initials: GD
authors.lastname: Wang
authors.affiliation: Department of Anatomy, Histology and Embryology, K.K. Leung Brain Research Centre, The Fourth Military Medical University Xi'an, China.
authors.forename: Yun-Qing
authors.initials: YQ
authors.lastname: Li
keywords: colonic motility; endomorphin-2; inhibitory neuromuscular transmission; myenteric plexus; μ-opioid receptor