title: Modulation of glutamatergic transmission by metabotropic glutamate receptor activation in second-order neurons of the guinea pig nucleus tractus solitarius.
abstract: Activity of second-order relay neurons in the nucleus tractus solitarius (NTS) is regulated by peripheral and intrinsic synaptic inputs, and modulation of those inputs by metabotropic glutamate receptors (mGluRs) has been proposed. This study investigated effects of mGluR activation on glutamatergic transmission in the NTS second-order neurons of guinea pigs. Whole-cell patch-clamp recordings from the brainstem slices revealed that activation of mGluRs exerted its effects on the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) but not on the amplitude. The sEPSC frequency was increased by an agonist of group I mGluRs, and it was decreased by an mGluR1 antagonist but not by an mGluR5 antagonist. The agonists of group II and III mGluRs decreased the sEPSC frequency, while their antagonists alone had no effect. Perfusion of cystine or TBOA, either of which elevates extracellular glutamate concentration, resulted in an increase in the sEPSC frequency, leaving the amplitude unchanged. The increased frequency of sEPSCs was returned to control by an mGluR1 antagonist. The tractus solitarius-evoked EPSCs were not altered by an agonist of group I mGluRs, whereas they were decreased along with an increase in paired-pulse ratio by agonists of group II and III mGluRs. These results suggest that mGluRs are present at the presynaptic sites in the NTS second-order neurons in guinea pigs. The mGluR1s function to facilitate the release of glutamate from axon terminals of intrinsic interneurons and the group II and III mGluRs play an inhibitory role in glutamatergic transmission.
authors.affiliation: Laboratory of Neuropharmacology, School of Pharmacy, Aichi Gakuin University, Nagoya, Japan. Electronic address: yohi@dpc.agu.ac.jp.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Ohi
authors.affiliation: Laboratory of Neuropharmacology, School of Pharmacy, Aichi Gakuin University, Nagoya, Japan. Electronic address: s-kimura@dpc.agu.ac.jp.
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: D000818:Animals; D004304:Dosage Forms; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D006168:Guinea Pigs; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D017552:Solitary Nucleus / Q000187:drug effects / Q000502:physiology*; D046509:Tissue Culture Techniques
chemical_list: D004304:Dosage Forms; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018094:Receptors, Metabotropic Glutamate; D018698:Glutamic Acid
keywords: Excitatory postsynaptic currents; Guinea pig; Metabotropic glutamate receptors; Nucleus tractus solitaries; Presynaptic modulation