Activation of presynaptic 5-HT3 receptors facilitates glutamatergic synaptic inputs to area postrema neurons in rat brain slices

Methods Find Exp Clin Pharmacol. 2004 Oct;26(8):615-22. doi: 10.1358/mf.2004.26.8.863726.

Abstract

Whole-cell voltage-clamp recordings were performed to investigate the serotonergic modulation of neurotransmitter release onto rat area postrema neurons in vitro. The bath application of serotonin (5-HT; 50 microM) or phenylbiguanide (PBA; 50 microM), a potent 5-HT3 receptor agonist, increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) or miniature EPSCs (mEPSCs) in 35 of 83 neurons (42%). These increases occurred in all electrophysiological cell classes. No cells exhibited a decrease in EPSC frequency. The majority of responding cells showed no inward currents during the application of serotonergic agonists (n = 34/35). However, the amplitude of mEPSCs was increased in 11/11 cells with 5-HT or 3/11 cells with PBA. ICS-205,930, a potent 5-HT3 receptor antagonist, markedly suppressed the 5-HT-induced facilitation of sEPSCs (n = 5) or mEPSCs (n = 5). An increase in the frequency of mEPSCs after PBA exposure was found, even with media containing Cd2+ (50 microM) or zero Ca2+. mEPSCs and evoked EPSCs were completely blocked in media containing the non-NMDA ionotropic receptor antagonist, CNQX (10 microM), indicating that EPSCs were glutamate events. These results suggest that glutamate release is increased in the area postrema by presynaptic 5-HT3 receptor activation. Furthermore, we present evidence that 5-HT3 receptor activation may be able to directly release glutamate from terminals, bypassing a requirement for voltage-dependent calcium entry into terminals. Such a mechanism may contribute to the chemosensitive function of area postrema neurons.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 6-Cyano-7-nitroquinoxaline-2,3-dione / pharmacology
  • Animals
  • Antiemetics / pharmacology
  • Area Postrema / drug effects*
  • Area Postrema / physiology
  • Biguanides / pharmacology
  • Excitatory Amino Acid Agonists / pharmacology
  • Excitatory Postsynaptic Potentials / drug effects*
  • Glutamic Acid / metabolism*
  • In Vitro Techniques
  • Indoles / pharmacology
  • Neurons / drug effects
  • Neurons / physiology
  • Patch-Clamp Techniques
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Presynaptic / agonists*
  • Receptors, Presynaptic / antagonists & inhibitors
  • Serotonin / pharmacology*
  • Serotonin 5-HT3 Receptor Agonists*
  • Serotonin 5-HT3 Receptor Antagonists
  • Serotonin Receptor Agonists / pharmacology
  • Synaptic Transmission / drug effects
  • Tropisetron

Substances

  • Antiemetics
  • Biguanides
  • Excitatory Amino Acid Agonists
  • Indoles
  • Receptors, Presynaptic
  • Serotonin 5-HT3 Receptor Agonists
  • Serotonin 5-HT3 Receptor Antagonists
  • Serotonin Receptor Agonists
  • Serotonin
  • Glutamic Acid
  • Tropisetron
  • 6-Cyano-7-nitroquinoxaline-2,3-dione
  • phenyl biguanide