Abstract
An outstanding challenge in olfactory neurobiology is to explain how glomerular networks encode information about stimulus mixtures, which are typical of natural olfactory stimuli. In the moth Manduca sexta, a species-specific blend of two sex-pheromone components is required for reproductive signaling. Each component stimulates a different population of olfactory receptor cells that in turn target two identified glomeruli in the macroglomerular complex of the male’s antennal lobe. Using intracellular recording and staining, we examined how responses of projection neurons innervating these glomeruli are modulated by changes in the level and ratio of the two essential components in stimulus blends. Compared to projection neurons specific for one component, projection neurons that integrated information about the blend (received excitatory input from one component and inhibitory input from the other) showed enhanced ability to track a train of stimulus pulses. The precision of stimulus-pulse tracking was furthermore optimized at a synthetic blend ratio that mimics the physiological response to an extract of the female’s pheromone gland. Optimal responsiveness of a projection neuron to repetitive stimulus pulses therefore appears to depend not only on stimulus intensity but also on the relative strength of the two opposing synaptic inputs that are integrated by macroglomerular complex projection neurons.
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Abbreviations
- AL :
-
Antennal lobe
- BAL :
-
Bombykal
- C15 :
-
(E,Z)-11,13-pentadecadienal
- MGC :
-
Macroglomerular complex
- ORC :
-
Olfactory receptor cell
- PN :
-
Projection neuron
- T1 :
-
Toroid 1 glomerulus of the MGC
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Acknowledgements
We are grateful to Dr. Vonnie D.C. Shields for comments on the manuscript. We thank Dr. Rebecca Johnston and Dr. Vonnie D.C. Shields for advice on statistical analysis, Patricia Jansma and Wendy Pott for technical advice on confocal microscopy, Peggy Randolph for general laboratory assistance, Dr. A.A. Osman for insect rearing, and Dr. J.H. Tumlinson (USDA, Gainesville, Florida, USA) for synthetic compounds. This study was supported by a Flinn Foundation Biology Graduate Fellowship and a Sensory Science Scholarship to T.H. and NIH grants AI-23253 and DC-02751 to J.G.H. The experiments described in this study comply with the Principles of animal care, publication No. 86-23, revised 1985 of the National Institutes of Health and also with the current laws of the USA.
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Heinbockel, T., Christensen, T.A. & Hildebrand, J.G. Representation of binary pheromone blends by glomerulus-specific olfactory projection neurons. J Comp Physiol A 190, 1023–1037 (2004). https://doi.org/10.1007/s00359-004-0559-7
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DOI: https://doi.org/10.1007/s00359-004-0559-7