title: Modulation of excitatory synaptic transmission by endogenous glutamate acting on presynaptic group II mGluRs in rat substantia nigra compacta.
abstract: Excitatory synaptic inputs from the subthalamic nucleus (STN) have been proposed to underlie burst firing of substantia nigra pars compacta (SNc) dopamine (DA) neurons in Parkinson's disease. Given the potential importance of the STN-SNc synapse in health and disease, our goal was to study how transmission at this synapse is regulated. We tested the hypothesis that neurotransmission at STN-SNc synapses is tonically inhibited by endogenous glutamate acting on presynaptic group II metabotropic glutamate receptors (mGluRs). By using whole-cell recording techniques in brain slices, we examined the effect of LY341495, a mGluR antagonist that is most potent at group II mGluRs, on excitatory postsynaptic currents (EPSCs) that either were evoked in SNc DA neurons by stimulation of the STN or were spontaneously occurred in the presence of tetrodotoxin (miniature EPSCs; mEPSCs). LY341495 increased the evoked EPSC amplitude and mEPSC frequency without changing mEPSC amplitude. In contrast, the group III mGluR antagonist UBP1112 failed to increase the evoked EPSC amplitude. An elevation of extracellular glutamate concentration by a glutamate transporter inhibitor, TBOA, suppressed the evoked EPSCs. LY341495, but not UBP1112, partially reversed the TBOA action. The modulations of EPSCs by TBOA and LY341495 were associated with changes in paired-pulse facilitation ratio. Furthermore, TBOA decreased mEPSC frequency, which was partially reversed by LY341495, without affecting mEPSC amplitude. The results indicate that presynaptic group II mGluRs at STN-SNc synapses appear to be partially activated by a basal level of extracellular glutamate and able to sense the change in extracellular glutamate concentration, subsequently modulating synaptic glutamate release.
authors.affiliation: Department of Neurosurgery, Neuroscience Institute, University of Tennessee Health Science Center, Memphis, 38163, USA.
authors.forename: Lie
authors.initials: L
authors.lastname: Wang
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Kitai
authors.forename: Zixiu
authors.initials: Z
authors.lastname: Xiang
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000037:antagonists & inhibitors; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001224:Aspartic Acid / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005971:Glutamates / Q000378:metabolism*; D066298:In Vitro Techniques; D018408:Patch-Clamp Techniques / Q000379:methods; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000502:physiology*; D013378:Substantia Nigra / Q000166:cytology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D014966:Xanthenes / Q000494:pharmacology
chemical_list: D027322:Amino Acid Transport System X-AG; D000596:Amino Acids; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; C114624:LY 341495; D018091:Receptors, AMPA; D014966:Xanthenes; C120673:benzyloxyaspartate; D001224:Aspartic Acid; C104722:glutamate receptor ionotropic, AMPA 2