An electrophysiological study of the action of N-methyl-D-aspartate on excitatory synaptic transmission in the optic tectum of the frog in vitro.
Excitatory synaptic field potentials, induced by stimulating optic nerve fibers, were recorded from in vitro preparations of the optic tectum of the frog. Bath-applied N-methyl-D-aspartate (NMDA), glutamate or quisqualate elicited transient enhancement in these field potentials, followed by a sustained depression reversible on washout. Responses to glutamate or quisqualate and the amplitude of control synaptic potentials, were not affected by the NMDA receptor antagonists aminophosphonovalerate (APV), 3(2-carboxypiperazin-4-yl)propyl-1-phosphonate (CPP), ketamine, magnesium ions or dizocipiline (MK 801) which, on the other hand, blocked the effects of NMDA. The antagonist dinitroquinoxaline-2,3-dione (DNQX), which is preferential for non-NMDA receptors, blocked the action of glutamate and synaptic transmission. In the presence of strychnine, glycine reversed the block of NMDA-mediated responses caused by magnesium. It is suggested that in the optic tectum of the frog, glutamate is the excitatory transmitter of at least one class of optic nerve fibers and that it acts through non-NMDA receptors. Although this area of the brain contains a well-developed NMDA receptor system, its function in physiological synaptic transmission remains to be elucidated.
Nistri
A
A
Department of Pharmacology, St Bartholomew's Hospital Medical College, University of London, U.K.
Sivilotti
L
L
Welsh
D M
DM
D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D005998:Glycine / Q000494:pharmacology; D066298:In Vitro Techniques; D016202:N-Methylaspartate; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D010069:Oxadiazoles / Q000494:pharmacology; D016318:Quisqualic Acid; D011896:Rana temporaria; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000187:drug effects; D013477:Superior Colliculi / Q000187:drug effects*; D013569:Synapses / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*
D005971:Glutamates; D009467:Neuromuscular Depolarizing Agents; D010069:Oxadiazoles; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D016318:Quisqualic Acid; D005998:Glycine