title: Modulation of glutamatergic transmission by presynaptic N-methyl-D-aspartate mechanisms in second-order neurons of the rat nucleus tractus solitarius.
abstract: The present study investigated the physiological function of presynaptic N-methyl-d aspartate (NMDA) mechanisms in glutamatergic transmission in the rat nucleus tractus solitarius (NTS). Membrane currents were recorded from the NTS second-order neurons by using whole-cell patch pipettes including MK-801 to block postsynaptic NMDA receptors. All experiments were performed under blockade of inhibitory synaptic transmission. Co-application of NMDA and d-serine decreased the tractus solitarius (TS)-evoked excitatory postsynaptic currents (eEPSCs) in 7/12 (58%) of neurons, and increased the paired pulse ratio. The remaining neurons were insensitive to NMDA and d-serine. Application of an NMDA antagonist D-AP5 had no effect on eEPSCs in all 8 neurons tested. Action potential-independent EPSCs (miniature EPSCs; mEPSCs) were recorded in the presence of tetrodotoxin. Co-application of NMDA and d-serine increased the mEPSC frequency but had no significant effect on the amplitude in 5/28 (18%) of neurons. D-AP5 decreased the mEPSC frequency without effect on the amplitude in 6/18 (33%) of neurons. This study demonstrated that (1) NMDA receptors were presynaptically distributed in a subset of NTS second-order neurons and that (2) the presynaptic NMDA receptors played an inhibitory role in TS-mediated release of glutamate and a facilitatory role in spontaneous release of glutamate. The present results suggest that the activation of presynaptic NMDA receptors modulates glutamatergic transmissions in the rat NTS second-order neurons.
authors.affiliation: Laboratory of Neuropharmacology, School of Pharmacy, Aichi Gakuin University, Nagoya, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Ohi
authors.affiliation: Laboratory of Neuropharmacology, School of Pharmacy, Aichi Gakuin University, Nagoya, Japan.
authors.forename: Satoko
authors.initials: S
authors.lastname: Kimura
authors.affiliation: Laboratory of Neuropharmacology, School of Pharmacy, Aichi Gakuin University, Nagoya, Japan. Electronic address: haji@dpc.agu.ac.jp.
authors.forename: Akira
authors.initials: A
authors.lastname: Haji
mesh_terms: D000200:Action Potentials; D000818:Animals; D019706:Excitatory Postsynaptic Potentials; D018698:Glutamic Acid / Q000378:metabolism*; D008297:Male; D055369:Miniature Postsynaptic Potentials; D009474:Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D017661:Receptors, Presynaptic / Q000378:metabolism*; D017552:Solitary Nucleus / Q000166:cytology / Q000378:metabolism*; D009435:Synaptic Transmission
chemical_list: D016194:Receptors, N-Methyl-D-Aspartate; D017661:Receptors, Presynaptic; D018698:Glutamic Acid
keywords: Excitatory postsynaptic currents; N-methyl-d-aspartate receptors; Nucleus tractus solitarius; Presynaptic regulation; Second-order neuron