Serotonin reduces synaptic excitation in the superficial medial entorhinal cortex of the rat via a presynaptic mechanism

Item Type:	Article
Title:	Serotonin reduces synaptic excitation in the superficial medial entorhinal cortex of the rat via a presynaptic mechanism
Creators Name:	Schmitz, D. and Gloveli, T. and Empson, R.M. and Draguhn, A. and Heinemann, U.
Abstract:	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 {alpha}-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 microM 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-HT1A receptor agonists (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT) and 5-carboxamido-tryptamine maleate (5-CT), and reduced by 5-HT1A 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-HT1A receptors in layers II and III of the medial entorhinal cortex by a presynaptic mechanism.
Keywords:	8-Hydroxy-2-(di-n-propylamino)tetralin/pharmacology, AMPA Receptors, Bicuculline, Entorhinal Cortex, Excitatory Postsynaptic Potentials, Guanosine Triphosphate, Hippocampus, N-Methyl-D-Aspartate Receptors, Patch-Clamp Techniques, Piperazines, Potassium Channels, Serotonin, Serotonin Antagonists, Serotonin Receptor Agonists, Serotonin Receptors, Spiperone, Synapses, Synaptic Transmission, Tetrodotoxin, Animals, Rats
Source:	Journal of Physiology
ISSN:	0022-3751
Publisher:	Cambridge University Press
Volume:	508
Number:	Pt 1
Page Range:	119-129
Date:	1 April 1998
Official Publication:	https://doi.org/10.1111/j.1469-7793.1998.119br.x
PubMed:	View item in PubMed

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