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Chemical Senses Advance Access originally published online on January 16, 2008
Chemical Senses 2008 33(3):267-281; doi:10.1093/chemse/bjm085
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© 2008 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Disruption of GABAA in the Insect Antennal Lobe Generally Increases Odor Detection and Discrimination Thresholds

Esther K. Mwilaria *, Chitrita Ghatak and Kevin C. Daly *

Department of Biology, West Virginia University, PO Box 6057, Morgantown, WV, USA

Correspondence to be sent to: Kevin C. Daly, Department of Biology, PO Box 6057, West Virginia University, Morgantown, WV 26506, USA. e-mail: kevin.daly{at}mail.wvu.edu


  Abstract

Studies of olfactory function show that disruption of GABAA receptors within the insect antennal lobe (AL) disrupts discrimination of closely related odors, suggesting that local processing within the AL specifically enhances fine odor discrimination. It remains unclear, however, how extensively AL function has been disrupted in these circumstances. Here we psychophysically characterize the effect of GABAA blockade in the AL of the moth Manduca sexta. We used 2 GABAA antagonists and 3 Pavlovian-based behavioral assays of olfactory function. In all cases, we used matched saline-injected controls in a blind study. Using a stimulus generalization assay, we found that GABAA disruption abolished the differential response to related odors, suggesting that local processing mediates fine odor discrimination. We then assessed the effect of GABAA antagonist on discrimination thresholds. Moths were differentially conditioned to respond to one odor (reinforced conditioned stimulus [CS+]) but not a second (unreinforced conditioning stimulus [CS–]) then tested for a significant differential conditioned response between them across a series of increasing concentrations. Here, GABAA blockade disrupted discrimination of both similar and dissimilar odor pairs as indicated by generally increased discrimination thresholds. Finally, using a detection threshold assay, we established that GABAA blockade also increases detection thresholds. Because detection is a prerequisite of discrimination, this later finding suggests that disrupted discrimination may be due to impairment of the ability to detect. We conclude that the loss of ability to detect and subsequently discriminate is attributable to a loss of ability of the AL to provide a clear neural signal from background.

Key words: antennal lobe, detection threshold, discrimination threshold, GABA, Manduca sexta, odor encoding, olfactory bulb

* These authors contributed equally to this work.

Accepted 23 November 2007


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