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  • 1
    Electronic Resource
    Electronic Resource
    Inhibitory effects of opioids in a circular muscle-myenteric plexus preparation of guinea-pig ileum (1987)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 336 (1987), S. 419-424 
    Details
    ISSN: 1432-1912
    Keywords: Guinea-pig ileum ; Myenteric plexus ; Circular muscle ; Opioid receptors ; Naloxone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The actions of opioids were examined in a strip preparation of the external muscle and myenteric plexus of the guinea-pig ileum cut parallel to the circular muscle. Contractions of the circular muscle induced by electrical stimulation of myenteric neurons were depressed in a concentration-dependent manner by the mu agonists, morphine and DAGO, and by the kappa agonist, U-50,488H. The concentrations of morphine, DAGO and U-50,488H which depressed nerve-mediated contractions by 50% (IC50) were 86 nM, 11 nM and 5.0 nM, respectively. The equilibrium dissociation constants (K D) for naloxone as an antagonist of the inhibitory effects of DAGO and of U5-0,488H were 5.6 nM and 29.4 nM, respectively. In contrast to the potent inhibitory effects of mu and kappa agonists, the delta-selective agonist, d-Pen-l-Pen, produced only weak inhibition of nerve-mediated contractions. Even at a concentration of 3 μM, there was less than 50% inhibition, which was not antagonised by the delta receptor antagonist, ICI 174864. The experiments indicate that both mu and kappa opioid receptors are present on the myenteric neurons supplying the circular muscle and that delta receptors are either absent or ineffectively activated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00164876
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  • 2
    Electronic Resource
    Electronic Resource
    Opioid dependence in myenteric neurons innervating the circular muscle of guinea-pig ileum (1989)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 339 (1989), S. 166-172 
    Details
    ISSN: 1432-1912
    Keywords: Guinea-pig ileum ; Myenteric plexus ; Circular muscle ; Opioid dependence ; Morphine withdrawal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Guinea-pigs were treated with morphine for 6–8 days by subcutaneous implantation of pellets, each containing a mixture of morphine base (120 mg) and morphine hydrochloride (35 mg). Each guinea-pig received a single pellet. Mechanical activity of the circular muscle was recorded in vitro in preparations comprising the circular muscle and myenteric plexus. Exposure to morphine was maintained by addition of 1 μM morphine to the organ baths. After 90 min, morphine was withdrawn, either by repeatedly washing tissues in morphine-free Krebs' solution , or by addition of naloxone to reduce the occupancy of the opioid receptors by morphine. Withdrawal of morphine resulted in markedly enhanced contractile activity compared with that in circular muscle-myenteric plexus preparations from untreated control guinea-pigs. The withdrawal contractions were abolished by tetrodotoxin (600 nM) and greatly reduced by hyoscine (1 μM), indicating that they resulted from action potential discharge in myenteric neurons that release acetylcholine onto the circular muscle. Activation of the cholinergic excitatory motor neurons was not secondary to synaptic activation by cholinergic interneurons, because hexamethonium (100 μM) did not affect withdrawal contractions. The withdrawal response may therefore arise in the cholinergic excitatory motor neurons themselves, or in neurons that activate them via noncholinergic mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00165139
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  • 3
    Electronic Resource
    Electronic Resource
    Projections of specific morphological types of neurons within the myenteric plexus of the small intestine of the guinea-pig (1996)
    Springer
    Cell & tissue research 285 (1996), S. 149-156 
    Details
    ISSN: 1432-0878
    Keywords: Key words: Organotypic culture ; Myenteric plexus ; Retrograde transport ; Intestine ; small ; Guinea-pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The projections of myenteric neurons within the myenteric plexus of the guinea-pig small intestine were established using retrograde tracing in organotypic culture. Three days after applying the fluorescent dye DiI to a single internodal strand in the myenteric plexus, 500–1000 nerve cell bodies were labelled. Of these, 77% were located oral to the application site, 15% were located anally and 7% were located within 1 mm of this site. Three major morphological types of neurons could be distinguished. Dogiel type I neurons had lamellar dendrites and single axons, Dogiel type II neurons had large smooth cell bodies and several long processes, and filamentous neurons had smooth ovoid cell bodies, single axons and several filamentous dendrites. Dogiel type I, II and filamentous neurons accounted for 54.6%, 38% and 7.4% of all filled cells, respectively. Labelled nerve cell bodies were present up to 13 mm aboral to the DiI application site; all neurons more than 2 mm aboral had Dogiel type I features. On the oral side, Dogiel type I neurons were found up to 110 mm, Dogiel type II neurons up to 100 mm and filamentous neurons up to 80 mm. Neurons with 2 mm oral or aboral to the DiI application site were located up to 7 mm circumferentially and were mainly Dogiel type II cells. This work revealed remarkable polarity within the myenteric plexus, with a significant prevalence of myenteric neurons projecting anally for longer distances than those projecting orally. These long pathways are probably involved in the coordination of intestinal motility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004410050630
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  • 4
    Electronic Resource
    Electronic Resource
    Calretinin immunoreactivity in cholinergic motor neurones, interneurones and vasomotor neurones in the guinea-pig small intestine (1991)
    Springer
    Cell & tissue research 263 (1991), S. 471-481 
    Details
    ISSN: 1432-0878
    Keywords: Calretinin ; Enteric nervous system ; Calcium binding protein ; Small intestine ; Cholinergic neurons ; Myenteric plexus ; Guinea-pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Immunoreactivity for calretinin, a calcium-binding protein, was studied in neurones in the guinea-pig small intestine. 26±1% of myenteric neurones and 12±3% of submucous neurones were immunoreactive for calretinin. All calretinin-immunoreactive neurones were also immunoreactive for choline acetyltransferase and hence are likely to be cholinergic. In the myenteric plexus, two subtypes of Dogiel type-I calretinin-immunoreactive neurones could be distinguished from their projections and neurochemical coding. Some calretinin-immunoreactive myenteric neurones had short projections to the tertiary plexus, and hence are likely to be cholinergic motor neurones to the longitudinal muscle. Some of these cells were also immunoreactive for substance P. The remaining myenteric neurones, immunoreactive for calretinin, enkephalin, neurofilament protein triplet and substance P, are likely to be orad-projecting, cholinergic interneurones. Calretinin immunoreactivity was also found in cholinergic neurones in the submucosa, which project to the submucosal vasculature and mucosal glands, and which are likely to mediate vasodilation. Thus, calretinin immunoreactivity in the guinea-pig small intestine is confined to three functional classes of cholinergic neurones. It is possible, for the first time, to distinguish these classes of cells from other enteric neurones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00327280
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  • 5
    Electronic Resource
    Electronic Resource
    Structure of the tertiary component of the myenteric plexus in the guinea-pig small intestine (1993)
    Springer
    Cell & tissue research 272 (1993), S. 509-516 
    Details
    ISSN: 1432-0878
    Keywords: Myenteric plexus ; Enteric nervous system ; Intestine, small ; Ultrastructure ; Innervation, of intestinal muscle ; Guinea-pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The tertiary component of the myenteric plexus consists of interlacing fine nerve fibre bundles that run between its principal ganglia and connecting nerve strands. It was revealed by zinc iodide-osmium impregnation and substance P immunohistochemistry at the light-microscope level. The plexus was situated against the inner face of the longitudinal muscle and was present along the length of the small intestine at a density that did not vary markedly from proximal to distal. Nerve bundles did not appear to be present in the longitudinal muscle as judged by light microscopy, although numberous fibre bundles were encountered within the circular muscle layer. At the ultrastructural level, nerve fibre bundles of the tertiary plexus were found in grooves formed by the innermost layer of longitudinal smooth muscle cells. In the distal parts of the small intestine, some of these nerve fibre bundles occasionally penetrated the longitudinal muscle coat. Vesiculated profiles in nerve fibre bundles of the tertiary plexus contained variable proportions of small clear and large granular vesicles; they often approached to within 50–200 nm of the longitudinal smooth muscle cells. Fibroblast-like cells lay between strands of the tertiary plexus and the circular muscle but were never intercalated between nerve fibre varicosities and the longitudinal muscle. These anatomical relationships are consistent with the tertiary plexus being the major site of neurotransmission to the longitudinal muscle of the guinea-pig small intestine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318557
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  • 6
    Electronic Resource
    Electronic Resource
    Ultrastructural studies of the myenteric plexus and smooth muscle in organotypic cultures of the guinea-pig small intestine (1995)
    Springer
    Cell & tissue research 280 (1995), S. 627-637 
    Details
    ISSN: 1432-0878
    Keywords: Myenteric plexus ; Smooth muscle ; Organotypic culture ; Ultrastructure ; Intestine, small ; Guinea-pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract External muscle and myenteric plexus from the small intestine of adult guinea-pigs were maintained in vitro for 3 or 6 days. Myenteric neurons and smooth muscle cells from such organotypic cultures were examined at the electron-microscopic level. An intact basal lamina was found around the myenteric ganglia and internodal strands. Neuronal membranes, nuclei and subcellular organelles appeared to be well preserved in cultured tissues and ribosomes were abundant. Dogiel type-II neurons were distinguishable by their elongated electron-dense mitochondria, numerous lysosomes and high densities of ribosomes. Vesiculated nerve profiles contained combinations of differently shaped vesicles. Synaptic membrane specializations were found between vesiculated nerve profiles and nerve processes and cell bodies. The majority of nerve fibres were well preserved in the myenteric ganglia, in internodal strands and in bundles running between circular muscle cells. No detectable changes were found in the ultrastructure of the somata and processes of glial cells. Longitudinal and circular muscle cells from cultured tissue had clearly defined membranes with some close associations with neighbouring muscle cells. Caveolae occurred in rows that ran parallel to the long axis of the muscle cells. These results indicate that the ultrastructural features of enteric neurons and smooth muscle of the guinea-pig small intestine are well preserved in organotypic culture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318365
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