| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 2005: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
To gain insight into how gustatory information is processed and integrated by the specific nuclear relays in the brain, and to address the mechanisms underlying the construction of taste neuronal circuitries, we applied a genetic approach to delineate the neuronal circuitries of bitter and sweet taste by selectively expressing the transsynaptic tracer, tWGA-DsRed, in either bitter-or sweet-responsive taste receptor cells in mice. The spatial distribution of tWGA-DsRed that was transferred from either bitter-or sweet-responsive taste receptor cells was detected in the serial coronal sections of the whole brain. Locations of tWGA-DsRed-labeled neurons were analyzed in three-dimensional images of the whole brain, which were reconstructed by assembling the brain structures extracted from the serial section images. Although the labeling density is likely to be influenced by the efficiencies of transport and degradation of the tracer, which may vary among neuronal types, the neurons labeled
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by tWGA-DsRed that was transferred from sweet-responsive taste receptor cells were located in the more anterior regions of both the solitary tract nuclei and the gustatory cortex, compared with those from bitter-responsive taste receptor cells. In the gustatory cortex of adult mice, the dispersed areas of tWGA-DsRed-labeled neurons in two strains appeared to partly overlap along the anterior-posterior axis. This genetic approach may be valuable for investigating the cellular and molecular aspects underlying the construction and refinement of taste neuronal circuitries to mediate taste discrimination. During the developmental stages of sweet taste neuronal circuitries, the neurons located in the most anterior parts of both the solitary tract nuclei and the gustatory cortex initially received tWGA-DsRed originating from sweet-responsive taste receptor cells, showing clear segregation between sweet and bitter inputs. The results suggest that the pre-specified neuron pairs may selectively construct the neuronal circuitries to process either bitter or sweet taste information. Less
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