title: Functional organization of rat olfactory bulb glomeruli revealed by optical imaging.
abstract: The functional organization and synaptic physiology of olfactory bulb glomeruli were studied in rat in vitro slice preparations stained with the voltage-sensitive dye RH-155. Optical signals were recorded with a 100-element photodiode array at high temporal resolution. Pharmacological and ionic manipulations were used to investigate synaptic responses to stimulation of the olfactory nerve layer (ONL). ONL stimulation evoked a sodium-mediated compound action potential that propagated across the ONL and invaded individual glomeruli. This presynaptic volley evoked calcium-dependent synaptic responses the amplitudes of which were largest within the glomerular layer (GL); smaller amplitude responses were recorded in deeper layers of the olfactory bulb. Synaptic responses in the GL were attenuated by the non-NMDA ionotropic glutamate receptor antagonist CNQX; the residual component was suppressed by the NMDA glutamate receptor antagonist AP-5. The GABAA receptor antagonist bicuculline methiodide had little effect, whereas the GABAB receptor agonist baclofen dramatically attenuated ONL-evoked synaptic responses. The effects of baclofen were reversed by the GABAB receptor antagonist CGP35348. Paired-pulse depression of ONL-evoked synaptic responses in the GL was partially reversed by CGP35348. These findings suggest that olfactory nerve axons release glutamate to activate both NMDA and non-NMDA receptors on GL neurons, that GABAA receptor-mediated inhibition has little effect on these responses, and that GABAB receptor-mediated inhibition may act presynaptically on olfactory nerve axons to modulate their inputs to olfactory bulb neurons.
authors.affiliation: Department of Anatomy and Neurobiology and the Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
authors.forename: A
authors.initials: A
authors.lastname: Keller
authors.forename: S
authors.initials: S
authors.lastname: Yagodin
authors.forename: V
authors.initials: V
authors.lastname: Aroniadou-Anderjaska
authors.forename: L A
authors.initials: LA
authors.lastname: Zimmer
authors.forename: M
authors.initials: M
authors.lastname: Ennis
authors.forename: N F
authors.initials: NF
authors.lastname: Sheppard
authors.forename: M T
authors.initials: MT
authors.lastname: Shipley
mesh_terms: D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D004558:Electric Stimulation; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000502:physiology; D007091:Image Processing, Computer-Assisted; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D009830:Olfactory Bulb / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology*; D009924:Organ Culture Techniques; D009943:Organophosphorus Compounds / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000502:physiology; D013268:Stimulation, Chemical; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D018755:GABA Agonists; D018756:GABA Antagonists; D009943:Organophosphorus Compounds; D017470:Receptors, Glutamate; D018698:Glutamic Acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D016202:N-Methylaspartate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; C066430:CGP 35348; D001418:Baclofen; D002118:Calcium; D001640:Bicuculline