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Serotonin reduces polysynaptic inhibition via 5-HT1A receptors in the superficial entorhinal cortex

Item Type:Article
Title:Serotonin reduces polysynaptic inhibition via 5-HT1A receptors in the superficial entorhinal cortex
Creators Name:Schmitz, D. and Gloveli, T. and Empson, R.M. and Heinemann, U.
Abstract:The superficial cells of the entorhinal cortex (EC), main input to the hippocampus, receive a serotonergic input from the raphe nuclei and express 5-hydroxytryptamine creatine sulfate complex (5-HT) receptors at high density. With the use of intracellular recordings, we investigated the effects of serotonin on synaptic inhibition of layer II and III neurons of the EC. Serotonin reduced both polysynaptic fast and slow inhibitory postsynaptic potentials (IPSPs) in projection neurons of the superficial EC. Polysynaptic fast and slow IPSPs were depressed by serotonin in a dose-dependent manner (0.1-100 microM). Serotonin in a concentration of 1 microM reduced the amplitudes of polysynaptic fast and slow IPSPs by approximately 40 and 50%, respectively. To identify the subtype of the 5-HT-receptor mediating the effects on polysynaptic IPSPs, we applied various 5-HT-receptor agonists and antagonists. Although the serotonin agonists for the 5-HT1B,2C,3 receptors were ineffective, the effects were mimicked by the 5-HT1A-receptor agonists (8-OH-DPAT, 5-CT) and prevented by the 5-HT1A-receptor antagonist NAN-190. To look at the direct effects of 5-HT on inhibitory interneurons, we elicited monosynaptic IPSPs in the absence of excitatory synaptic transmission. In contrast to the polysynaptic IPSPs, monosynaptic IPSPs were not significantly affected by serotonin. Recordings from putative inhibitory interneurons revealed that their excitatory postsynaptic potentials (EPSPs) were reversibly reduced by serotonin. We conclude that serotonin suppresses polysynaptic inhibition in projection neurons of layers II and III of the EC by depression of EPSPs on inhibitory interneurons via 5-HT1A receptors.
Keywords:2-Amino-5-phosphonovalerate, 5-HT1 Serotonin Receptors, 8-Hydroxy-2-(di-n-propylamino)tetralin, Entorhinal Cortex, Excitatory Amino Acid Antagonists, Excitatory Postsynaptic Potentials, Free Radical Scavengers, Membrane Potentials, Neural Inhibition, Organ Culture Techniques, Piperazines, Quinoxalines, Ritanserin, Serotonin, Serotonin Antagonists, Serotonin Receptor Agonists, Serotonin Receptors, Synapses, Animals, Rats, Wistar Rats
Source:Journal of Neurophysiology
Publisher:American Physiological Society
Page Range:1116-1121
Date:September 1998
Official Publication:http://jn.physiology.org/content/80/3/1116.long
PubMed:View item in PubMed

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