Dendritic glutamate autoreceptors modulate signal processing in rat mitral cells.
It has been shown recently that in mitral cells of the rat olfactory bulb, N-methyl-D-aspartate (NMDA) autoreceptors are activated during mitral cell firing. Here we consider in more details the mechanisms of mitral cell self-excitation and its physiological relevance. We show that both ionotropic NMDA and non-NMDA autoreceptors are activated by glutamate released from primary and secondary dendrites. In contrast to non-NMDA autoreceptors, NMDA autoreceptors are almost exclusively located on secondary dendrites and their activation generates a large and sustained self-excitation. Both intracellularly evoked and miniature NMDA-R mediated synaptic potentials are blocked by intracellular bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) and result from a calcium-dependent release of glutamate. Self-excitation can be produced by a single spike, and trains of spikes result in frequency facilitation. Thus activation of excitatory autoreceptors is a major function of action potentials backpropagating in mitral cell dendrites, which results in an immediate positive feedback counteracting recurrent inhibition and increasing the signal-to-noise ratio of olfactory inputs.
Salin
P A
PA
Laboratory of Physiology, Ecole Supérieure de Physique et Chimie, 75005 Paris, France. salin@cesg.cnrs.fr
Lledo
P M
PM
Vincent
J D
JD
Charpak
S
S
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D017660:Autoreceptors / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D003712:Dendrites / Q000378:metabolism*; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D058787:GABA-A Receptor Antagonists; D018698:Glutamic Acid / Q000378:metabolism*; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009830:Olfactory Bulb / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D012964:Sodium / Q000378:metabolism
D017660:Autoreceptors; D018691:Excitatory Amino Acid Antagonists; D058787:GABA-A Receptor Antagonists; D018091:Receptors, AMPA; D018094:Receptors, Metabotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D012964:Sodium