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Dendritic glutamate autoreceptors modulate signal processing in rat mitral cells
P A Salin1, P M Lledo, J D Vincent
1Laboratory of Physiology, Ecole Supérieure de Physique et Chimie, 75005 Paris, France. salin@cesg.cnrs.fr
Abstract:
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.
Insights
Mitral cells in the rat olfactory bulb utilize N-methyl-D-aspartate (NMDA) and non-NMDA autoreceptors for self-excitation. This mechanism enhances olfactory signal processing by counteracting inhibition and improving the signal-to-noise ratio.
Area of Science:
- Neuroscience
- Olfactory System Research
- Cellular Electrophysiology
Background:
- Mitral cells in the rat olfactory bulb exhibit N-methyl-D-aspartate (NMDA) autoreceptor activation during firing.
- Understanding the mechanisms and physiological significance of mitral cell self-excitation is crucial for olfactory processing.
Purpose of the Study:
- To investigate the detailed mechanisms underlying mitral cell self-excitation.
- To explore the physiological relevance of excitatory autoreceptor activation in mitral cells.
Main Methods:
- Electrophysiological recordings in rat olfactory bulb mitral cells.
- Application of bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) to block NMDA receptor-mediated potentials.
- Analysis of calcium-dependent glutamate release and action potential backpropagation effects.
Main Results:
- Both NMDA and non-NMDA autoreceptors are activated by glutamate released from mitral cell dendrites.
- NMDA autoreceptors, located on secondary dendrites, mediate a significant and sustained self-excitation.
- Self-excitation is triggered by single spikes and shows frequency facilitation with spike trains, linked to calcium-dependent glutamate release.
Conclusions:
- Activation of excitatory autoreceptors by backpropagating action potentials is a key function in mitral cells.
- This self-excitation provides immediate positive feedback, counteracting recurrent inhibition.
- The process enhances the signal-to-noise ratio of olfactory inputs.