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This Article Full Text Full Text (PDF) All Versions of this Article: 90/3/1737    most recent 00180.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (14) Citing Articles via Google Scholar Google Scholar Articles by Lowe, G. Search for Related Content PubMed PubMed Citation Articles by Lowe, G.

Flash Photolysis Reveals a Diversity of Ionotropic Glutamate Receptors on the Mitral Cell Somatodendritic Membrane

Monell Chemical Senses Center, Philadelphia, Pennsylvania 19104-3308

Submitted 26 February 2003; accepted in final form 24 April 2003

It is widely held that the soma and basal dendrites of olfactory bulb mitral cells receive exclusively inhibitory synaptic input from local interneurons. However, the mitral somatodendritic membrane exhibits immunoreactivity for a variety of glutamate receptors, and blocking GABA receptors unmasks mitral cell self-excitation. This excitation is proposed to be mediated either by diffuse spillover of the mitral cells' own released glutamate, or by punctate transmission from glutamate-releasing granule cells. This study examined the pharmacology and kinetics of glutamate sensitivity of mitral cells by flash photolysis of nitroindoline caged glutamates, which facilitate reliable activation of receptors in the synaptic cleft. Wide-field laser uncaging (3.5-ms flash) of approximately 0.5–1 mM glutamate onto the soma activated large currents with fast (3.4-ms rise, 7.5-ms decay) and slow (64-ms rise, >10-s decay) components. In 100 µM APV, slow currents were reduced to 53% of control (257-ms rise, 2-s decay), displayed outward rectification in 1.3 mM Mg²⁺, and blocked by 15 µM 5,7-dichlorokynurenate. Responses to 100 µM glutamate were fully antagonized by 100 µM APV, consistent with competitive inhibition at high-affinity NMDA receptors. An APV-resistant NMDA receptor was not observed, refuting the punctate transmission model. Fast currents were blocked by 10 µM NBQX, boosted 3.28-fold by 100 µM cyclothiazide, and resolved into AMPA (40%) and kainate (60%) receptor components by 100 µM SYM2206. The results suggest that self-excitation depends on AMPA, kainite, and conventional NMDA autoreceptors on the mitral cell.

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