Investigation of preferable-and aversive-taste signal transduction machinery using model fish species

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We have identified fish taste receptor orthologs, fT1R and fT2Rand shown that their effecter, phospholipase C(plc-J(32) plays a key role to transmit taste stimuli to the central nervous system evoking favorable and aversive behavior. To analyze the neuronal circuit for this taste transduction, we generated transgenic medaka expressing a transsynaptic tracer lectin(WGA) under the control of a medaka plc-β32 gene regulatory region. The immunohistochemical analysis of the transgenic fish revealed that WGA protein can be transferred to the several sensory and motor nuclei in the brain. WGA signals were detected in the secondary gustatory nucleus and the other nuclei in the thalamic regions. In the endbrain, the regions presumably corresponding to the amygdala and the hippocampus of mammals, were also WGA positive. This is the first case of directional tracing of higher order gustatory nerve circuit connected to the specific subpopulation of peripheral sensory cells and may help us to understand the basic neuronal architecture of gustatory information processing common in vertebrates.