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1 Department of Anatomy and Neurobiology, University of Tennessee College of Medicine, Memphis, Tennessee 38163, Japan 2 Division of Integrative Physiology, Department of Functional, Morphological, and Regulation Science, Faculty of Medicine, Tottori University, Yonago 683-0826, Japan
Submitted 6 March 2003; accepted in final form 9 April 2003
We examined the effect of the sweet transduction blocker gurmarin on taste
responses recorded from neurons in the rat solitary nucleus (NST) to determine
how gurmarin sensitivity is distributed across neuronal type. Initially,
responses evoked by washing the anterior tongue and palate with 0.5 M sucrose,
0.1 M NaCl, 0.01 M HCl, and 0.01 M quinine-HCl were recorded from 35 neurons.
For some cells, responses to a sucrose concentration series (0.01–1.0 M)
or an array of sweet-tasting compounds were also measured. Gurmarin (10
µg/ml, 2–4 ml) was then applied to the tongue and palate. Stimuli
were reapplied after 10–15 min. Neurons were segregated into groups
based on similarities among their initial response profiles using hierarchical
cluster analysis (HCA). Results indicated that sucrose responses recorded from
neurons representative of each HCA-defined class were suppressed by gurmarin.
However, a disproportionate percentage of cells in each group displayed
sucrose responses that were substantially attenuated after gurmarin treatment.
Postgurmarin sucrose responses recorded from neurons that composed 57% of
class S, 40% of class N, and 33% of class H were suppressed by 
50%
relative to control. On average, attenuation was statistically significant
only in class S and N neurons. Although the magnitude of gurmarin-induced
response suppression did not differ across sucrose concentration, responses to
different sweet-tasting compounds were differentially affected. Responses to
NaCl, HCl, or quinine were not suppressed by gurmarin. Results suggest that
information from gurmarin-sensitive and -insensitive receptor processes
converges onto single NST neurons.
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