title: Subthalamic stimulation evokes complex EPSCs in the rat substantia nigra pars reticulata in vitro.
abstract: The subthalamic nucleus (STN) plays an important role in movement control by exerting its excitatory influence on the substantia nigra pars reticulata (SNR), a major output structure of the basal ganglia. Moreover, excessive burst firing of SNR neurons seen in Parkinson's disease has been attributed to excessive transmission in the subthalamonigral pathway. Using the 'blind' whole-cell patch clamp recording technique in rat brain slices, we found that focal electrical stimulation of the STN evoked complex, long-duration excitatory postsynaptic currents (EPSCs) in SNR neurons. Complex EPSCs lasted 200-500 ms and consisted of an initial monosynaptic EPSC followed by a series of late EPSCs superimposed on a slow inward shift in holding current. Focal stimulation of regions outside the STN failed to evoke complex EPSCs. The late component of complex EPSCs was markedly reduced by ionotropic glutamate receptor antagonists (2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitro-quinoxalone) and by a GABAA receptor agonist (isoguvacine) when these agents were applied directly to the STN using a fast-flow microapplicator. Moreover, the complex EPSC was greatly enhanced by bath application of the GABAA receptor antagonists picrotoxin or bicuculline. These data suggest that recurrent glutamate synapses in the STN generate polysynaptic, complex EPSCs that are under tonic inhibition by GABA. Because complex EPSCs are expected to generate bursts of action potentials in SNR neurons, we suggest that complex EPSCs may contribute to the pathological burst firing that is associated with the symptoms of Parkinson's disease.
authors.affiliation: Department of Neurology, Oregon Health and Science University, Portland, OR 97239, USA.
authors.forename: Ke-Zhong
authors.initials: KZ
authors.lastname: Shen
authors.forename: Steven W
authors.initials: SW
authors.lastname: Johnson
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials; D000818:Animals; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007539:Isonicotinic Acids / Q000494:pharmacology; D009434:Neural Pathways; D009474:Neurons / Q000145:classification / Q000187:drug effects / Q000502:physiology; D010300:Parkinson Disease / Q000503:physiopathology; D018408:Patch-Clamp Techniques; D010852:Picrotoxin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013378:Substantia Nigra / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D020531:Subthalamic Nucleus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission; D013997:Time Factors
chemical_list: D015763:2-Amino-5-phosphonovalerate; D018691:Excitatory Amino Acid Antagonists; D018755:GABA Agonists; D018756:GABA Antagonists; D018698:Glutamic Acid; D007539:Isonicotinic Acids; D010852:Picrotoxin; C015300:isoguvacine