The antennal lobe - a functional olfactory map in neural space

The antennal lobe - a functional olfactory map in neural space

Field: Sensory systems

Authors: Carlsson, Mikael A
Hansson, Bill S

Address of presenting
author: Department of Ecology
Lund University
Sölvegatan 37
223 62 Lund

E-mail: mikael.carlsson@ekol.lu.se

Phone: 046-2223780

Fax: 0

Text of abstract: The primary centra for olfactory processing in an insect brain are the antennal lobes. In the lobes, olfactory receptor neurons converge on spherical neuropils called glomeruli where synapses are made with projection neurons that send their axons into protocerebrum. In addition there are local interneurons connecting the glomeruli in the lobes. A question of paramount interest is the function of glomeruli. Do all types of receptor neurons terminate in all glomeruli or does a certain glomerulus represent a specific receptor type, i.e. are glomeruli functional units. To answer this question we have optically measured calcium activity in vivo in the moth Spodoptera littoralis. The animals were stimulated with sex pheromones and behaviorally active environmental odorants.
Different odorants evoked different activity patterns that were consistent between individuals. Certain odorants showed response in distinct parts of the lobe but the activity patterns of many odorants were overlapping suggesting that the same glomeruli were activated by several odorants. The sex pheromone components elicited strong response in males only in the area close to the antennal nerve where the macroglomerular complex (MGC) is located. The MGC is a male-specific cluster of glomeruli where pheromone detecting receptor neurons terminate. The individual components of the pheromone activated different parts of the MGC area. Plant and flower odours did normally not activate this area.
Two extremes of information coding schemes in the antennal lobes have been proposed. In a labeled line system each glomerulus should represent a specific odorant with no overlap whereas in across-fiber coding an odour is represented by a combination of activity in a number of glomeruli. Our results suggest that both strategies are used. But all odorants tested evoked distinct, reproducable patterns which indicates that the identity of an odorant is encoded in the lobe.

Keywords: Spodoptera littoralis, optical imaging, odour-coding

	The antennal lobe - a functional olfactory map in neural space
Field:	Sensory systems
Authors:	Carlsson, Mikael A Hansson, Bill S
Address of presenting author:	Department of Ecology Lund University Sölvegatan 37 223 62 Lund
E-mail:	mikael.carlsson@ekol.lu.se
Phone:	046-2223780
Fax:	0
Text of abstract:	The primary centra for olfactory processing in an insect brain are the antennal lobes. In the lobes, olfactory receptor neurons converge on spherical neuropils called glomeruli where synapses are made with projection neurons that send their axons into protocerebrum. In addition there are local interneurons connecting the glomeruli in the lobes. A question of paramount interest is the function of glomeruli. Do all types of receptor neurons terminate in all glomeruli or does a certain glomerulus represent a specific receptor type, i.e. are glomeruli functional units. To answer this question we have optically measured calcium activity in vivo in the moth Spodoptera littoralis. The animals were stimulated with sex pheromones and behaviorally active environmental odorants. Different odorants evoked different activity patterns that were consistent between individuals. Certain odorants showed response in distinct parts of the lobe but the activity patterns of many odorants were overlapping suggesting that the same glomeruli were activated by several odorants. The sex pheromone components elicited strong response in males only in the area close to the antennal nerve where the macroglomerular complex (MGC) is located. The MGC is a male-specific cluster of glomeruli where pheromone detecting receptor neurons terminate. The individual components of the pheromone activated different parts of the MGC area. Plant and flower odours did normally not activate this area. Two extremes of information coding schemes in the antennal lobes have been proposed. In a labeled line system each glomerulus should represent a specific odorant with no overlap whereas in across-fiber coding an odour is represented by a combination of activity in a number of glomeruli. Our results suggest that both strategies are used. But all odorants tested evoked distinct, reproducable patterns which indicates that the identity of an odorant is encoded in the lobe.

Keywords:	Spodoptera littoralis, optical imaging, odour-coding

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Created 2000-03-03

Department of Physiological Sciences, Lund University

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