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Presynaptic modulation of cholinergic and non‐cholinergic fast synaptic transmission in the myenteric plexus of guinea pig ileum
Author(s) -
LePard K. J.,
Ren J.,
Galligan J. J.
Publication year - 2004
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.1365-2982.2004.00505.x
Subject(s) - cholinergic , hexamethonium , myenteric plexus , biology , carbachol , medicine , endocrinology , acetylcholine , stimulation , immunology , immunohistochemistry
These studies investigated receptors modulating release of mediators of fast excitatory postsynaptic potentials (fEPSPs) in guinea pig ileum myenteric plexus using electrophysiological methods. Fast EPSPs inhibited by >95% by hexamethonium (100 μmol L −1 ) were cholinergic; mixed fEPSPs were inhibited <95% by hexamethonium. Non‐cholinergic fEPSPs were studied in the presence of hexamethonium. The α2‐adrenergic receptor agonist UK 14304 inhibited cholinergic (maximum inhibition = 76%, EC 50 = 18 nmol L −1 ), mixed (81%, 21 nmol L −1 ) and non‐cholinergic (76%, 44 nmol L −1 ) fEPSPs equally. The 5‐HT 1 receptor agonist 5‐carboxamidotryptamine inhibited cholinergic, mixed and non‐cholinergic fEPSPs equally. Renzapride, increased non‐cholinergic (33%) less than mixed (97%, 13 μmol L −1 ) fEPSPs. Renzapride inhibited the purely cholinergic fEPSPs (−29%) but potentiated the cholinergic component of mixed fEPSPs (39%). Prucalopride potentiated all fEPSPs equally (30–33%). 5‐HT (0.1 μmol L −1 ) induced potentiation of cholinergic (75%), mixed (97%) and non‐cholinergic (84%) fEPSPs was not statistically different. The potentiating effects of renzapride and 5‐HT on fEPSPs were inhibited by the 5‐HT 4 receptor antagonist, SB 204070 (10 nmol L −1 ). Renzapride (0.3 μmol L −1 ) blocked 5‐HT‐induced increases in cholinergic fEPSPs. α2‐Adrenergic and 5‐HT 1 receptors mediate inhibition of transmitter release from cholinergic and mixed terminals. 5‐HT and prucalopride, acting at 5‐HT 4 receptors, facilitate all fEPSPs; renzapride facilitates the cholinergic and non‐cholinergic components of mixed fEPSPs but not purely cholinergic fEPSPs. Cholinergic synapses may express few 5‐HT 4 receptors or a renzapride‐insensitive 5‐HT 4 receptor isoform.