The Journal of Neuroscience, August 15, 2002, 22(16):7281-7287
Contribution of Different Taste Cells and Signaling Pathways to
the Discrimination of "Bitter" Taste Stimuli by an Insect
John I.
Glendinning,
Adrienne
Davis, and
Sudha
Ramaswamy
Department of Biological Science, Barnard College, Columbia
University, New York, New York 10027
Animals can discriminate among many different types of foods. This
discrimination process involves multiple sensory systems, but the sense
of taste is known to play a central role. We asked how the taste system
contributes to the discrimination of different "bitter" taste
stimuli in Manduca sexta caterpillars. This insect has
approximately eight bilateral pairs of taste cells that respond selectively to bitter taste stimuli. Each bilateral pair of
bitter-sensitive taste cells has a different molecular receptive range
(MRR); some of these taste cells also contain two signaling
pathways with distinctive MRRs and temporal patterns of spiking. To
test for discrimination, we habituated the caterpillar's
taste-mediated aversive response to one bitter taste stimulus (salicin)
and then asked whether this habituation phenomenon generalized to four other bitter taste stimuli (caffeine, aristolochic acid,
Grindelia extract, and Canna extract). We
inferred that the two compounds were discriminable if the habituation
phenomenon failed to generalize (e.g., from salicin to aristolochic
acid). We found that M. sexta could discriminate between
salicin and those bitter taste stimuli that activate (1) different
populations of bitter-sensitive taste cells (Grindelia
extract and Canna extract) or (2) different signaling pathways within the same bitter-sensitive taste cell (aristolochic acid). M. sexta could not discriminate between salicin
and a bitter taste stimulus that activates the same signaling pathway
within the same bitter-sensitive taste cell (caffeine). We propose that the heterogeneous population of bitter-sensitive taste cells and signaling pathways within this insect facilitates the discrimination of
bitter taste stimuli.
Key words:
discrimination; bitter taste; taste cell; habituation-generalization paradigm; insect; Manduca sexta
Copyright © 2002 Society for Neuroscience 0270-6474/02/22167281-07$05.00/0
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