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The influence of 5‐hydroxytryptamine agonists and antagonists on identified sympathetic preganglionic neurones in the rat, in vivo
Author(s) -
Lewis D.I.,
Coote J.H.
Publication year - 1990
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1990.tb12987.x
Subject(s) - excitatory postsynaptic potential , inhibitory postsynaptic potential , agonist , ketanserin , chemistry , receptor , 5 ht receptor , medicine , endocrinology , serotonin , receptor antagonist , antagonist , neuroscience , biology , biochemistry
1 5‐Hydroxytryptamine (5‐HT) was applied by microiontophoresis in the vicinity of identified sympathetic preganglionic neurones in the upper thoracic spinal cord of the rat, in vivo . 2 Sympathetic preganglionic neurones responded in one of three ways to 5‐HT: by (a) excitation (76%), (b) inhibition (4%) or (c) in a biphasic manner (5%). 3 The excitatory responses evoked by 5‐HT were mimicked by 5‐carboxamidotryptamine (5‐CT) and α‐methyl‐5‐hydroxytryptamine (α‐Me‐5‐HT). The inhibitory and biphasic responses evoked by 5‐HT were mimicked by 2‐methyl‐5‐hydroxytryptamine (2‐Me‐5‐HT). The observed responses evoked by 5‐HT and selective agonists may be different on the same cell. In several instances a single neurone excited by one agonist was inhibited by another agonist. 4 The 5‐HT 2 ‐receptor antagonists, ketanserin and LY 53857, failed to abolish selectively the excitatory responses evoked by 5‐HT and α‐Me‐5‐HT, when applied by microiontophoresis. The antagonists non‐selectively reduced the excitatory responses evoked by 5‐HT, 5‐CT, α‐Me‐5‐HT, d , l ‐homocysteic acid (DLH) and noradrenaline (NA). A reduction in synaptically evoked activity was also observed. 5 The 5‐HT 3 ‐receptor antagonist, ICS 205–930, failed to abolish the inhibitory responses evoked by 5‐HT. 6 It was concluded that the excitatory responses evoked by 5‐HT are mediated by a receptor that is neither 5‐HT 2 or 5‐HT 3 , but shows similarities to the 5‐HT 1 ‐like receptor profile. The inhibitory actions of 5‐HT are mimicked by 2‐Me‐5‐HT, but the receptor is not 5‐HT 3 , or 5‐HT 1 ‐like or 5‐HT 2 .