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Serotonin reduces synaptic excitation in the superficial medial entorhinal cortex of the rat via a presynaptic mechanism
Author(s) -
Schmitz Dietmar,
Gloveli Tengis,
Empson Ruth M.,
Draguhn Andreas,
Heinemann Uwe
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.119br.x
Subject(s) - chemistry , serotonin , serotonergic , excitatory postsynaptic potential , entorhinal cortex , neurotransmission , biophysics , neuroscience , hippocampus , receptor , biology , biochemistry
1 The superficial layers II and III of the entorhinal cortex, which form the main cortical input to the hippocampus, receive a large serotonergic projection from the raphe nuclei and express 5‐HT receptors at high density. Here, we studied the effects of serotonin on the intrinsic properties and excitatory synaptic transmission of the superficial medial entorhinal cortex. 2 Intracellular and patch clamp recordings revealed that serotonin hyperpolarized only one‐third of the cells, approximately, through a potassium conductance via a GTP‐dependent process. 3 Serotonin depressed mixed as well as isolated α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐ propionic acid receptor (AMPAR)‐ and N ‐methyl‐D‐aspartic acid receptor (NMDAR)‐mediated excitatory postsynaptic potentials/currents (EPSPs/EPSCsapproximately 40 % reduction with 1 μM serotonin). 4 The effect of serotonin on EPSPs/EPSCs was similar in whole‐cell versus intracellular recordings; it did not require intracellular GTP and was not visible in glutamate applications to excised patches. Miniature EPSCs recorded in the presence of tetrodotoxin and bicuculline were reduced in frequency, but not altered in amplitude. 5 The effects of serotonin on intrinsic properties and EPSPs were partially mimicked by 5‐HT 1A receptor agonists (±)‐8‐hydroxy‐2‐(di‐ n ‐propylamino)tetralin hydrobromide (8‐OH‐DPAT) and 5‐carboxamido‐tryptamine maleate (5‐CT), and reduced by 5‐HT 1A receptor antagonists S‐ (‐)‐5‐fluoro‐8‐hydroxy‐DPAT hydrochloride (S‐UH‐301), 1‐(2‐methoxyphenyl)‐4‐[4‐(2‐phthalimido)butyl]piperazine hydrobromide (NAN‐190) and spiperone. 6 We conclude that serotonin potently suppresses excitatory synaptic transmission via 5‐HT 1A receptors in layers II and III of the medial entorhinal cortex by a presynaptic mechanism.