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Postnatal downregulation of inhibitory neuromuscular transmission to the longitudinal muscle of the guinea pig ileum
Author(s) -
Bian X.,
Burda J. E.,
Carrasquillo M.,
Galligan J. J.
Publication year - 2009
Publication title -
neurogastroenterology and motility
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.489
H-Index - 105
eISSN - 1365-2982
pISSN - 1350-1925
DOI - 10.1111/j.1365-2982.2009.01296.x
Subject(s) - neuromuscular transmission , tetrodotoxin , endocrinology , medicine , inhibitory postsynaptic potential , nicotine , guinea pig , biology , excitatory postsynaptic potential , muscarinic acetylcholine receptor , neuromuscular junction , nitric oxide synthase , neurotransmission , nitric oxide , receptor , neuroscience
Neuromuscular transmission is crucial for normal gut motility but little is known about its postnatal maturation. This study investigated excitatory/inhibitory neuromuscular transmission in vitro using ileal nerve‐muscle preparations made from neonatal (≤48 h postnatal) and adult (∼4 months postnatal) guinea pigs. In tissues from neonates and adults, nicotine (0.3–30 μmol L −1 ) contracted longitudinal muscle preparations in a tetrodotoxin (TTX) (0.3 μmol L −1 )‐sensitive manner. The muscarinic receptor antagonist, scopolamine (1 μmol L −1 ), reduced substantially nicotine‐induced contractions in neonatal tissues but not adult tissues. In the presence of N ω ‐nitro‐ l ‐arginine (NLA, 100 μmol L −1 ) to block nitric oxide (NO) mediated inhibitory neuromuscular transmission, scopolamine‐resistant nicotine‐induced contractions were revealed in neonatal tissues. NLA enhanced the nicotine‐induced contractions in neonatal but not in adult tissues. Electrical field stimulation (20 V; 0.3 ms; 5–25 Hz, scopolamine 1 μmol L −1 present) caused NLA and TTX‐sensitive longitudinal muscle relaxations. Frequency–response curves in neonatal tissues were left‐shifted compared with those obtained in adult tissues. Immunohistochemical studies revealed that NO synthase (NOS)‐immunoreactivity (ir) was present in nerve fibres supplying the longitudinal muscle in neonatal and adult tissues. However, quantitative studies demonstrated that fluorescence intensity of NOS‐ir nerve fibres was higher in neonatal than adult tissues. Nerve fibres containing substance P were abundant in longitudinal muscle in adult but not in neonatal tissues. Inhibitory neuromuscular transmission is relatively more effective in the neonatal guinea pig small intestine. Delayed maturation of excitatory motor pathways might contribute to paediatric motility disturbances.