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Effects of 5‐HT receptor agonists on depolarization‐induced [ 3 H]‐noradrenaline release in rabbit hippocampus and human neocortex
Author(s) -
Allgaier C.,
Warnke P.,
Stangl A.P.,
Feuerstein T.J.
Publication year - 1995
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.1476-5381.1995.tb16661.x
Subject(s) - rauwolscine , neocortex , endocrinology , medicine , stimulation , hippocampus , 5 ht receptor , agonist , postsynaptic potential , receptor antagonist , receptor , antagonist , chemistry , neurotransmitter , prazosin , serotonin , biology , neuroscience
1 The present study attempted to determine whether noradrenaline (NA) release in rabbit hippocampus and human neocortex is modulated by presynaptic 5‐hydroxytryptamine (5‐HT) receptors 2 Slices of rabbit hippocampus and human neocortex, loaded with [ 3 H]‐noradrenaline ([ 3 H]‐NA) were superfused and the effects of 5‐hydroxytryptamine (5‐HT) receptor ligands on electrically evoked [ 3 H]‐NA release were investigated 3 In rabbit hippocampus, 5‐HT, 5‐carboxamidotryptamine (5‐CT; 32 μ m ) and 2‐CH 3 ‐5‐HT (32 μ m ) increased [ 3 H]‐NA release elicited with 360 pulses/3 Hz. Facilitation of transmitter release was not influenced by the 5‐HT 3 receptor antagonist, tropisetron but was prevented by the α 2 ‐adrenoceptor antagonist, rauwolscine. When autoinhibition was avoided by stimulating the tissue with 4 pulses/100 Hz (pseudo‐one pulse‐(POP) stimulation), 2‐CH 3 ‐5‐HT decreased evoked transmitter release, whereas 5‐HT and 5‐CT had no effect. Inhibition caused by 2‐CH 3 ‐5‐HT was not affected by tropisetron but counteracted by the α 2 ‐adrenoceptor ligands, clonidine and rauwolscine. Inhibition caused by clonidine was diminished in the presence of 5‐CT or 2‐CH 3 ‐5‐HT 4 In human neocortex, [ 3 H]‐NA release elicited with 360 pulses/3 Hz was increased by 10 μ m 5‐HT and 32 μ m 5‐CT, whereas 2‐CH 3 ‐5‐HT was ineffective. [ 3 H]‐NA release evoked with a modified POP stimulation (2 bursts of 4 pulses/100 Hz, 3.5 min apart) was not affected by 2‐CH 3 ‐5‐HT or 5‐CT 5 The present results indicate that 5‐HT, 2‐CH 3 ‐5‐HT and 5‐CT can act on presynaptic a 2 ‐autoreceptors as partial agonists (2‐CH 3 ‐5‐HT; in rabbit hippocampal tissue) or antagonists (5‐HT and 5‐CT; in tissue of rabbit hippocampus and human neocortex). Furthermore the existence of autoinhibition dictates whether these drugs cause facilitation of release, inhibition or have no effect.