− この都医学研セミナーは終了しました。 −
|演者||M.D. Chi-Hon Lee （Section on Neuronal Connectivity, NICHD,National Institutes of Health Senior Investigator）|
|世話人||齊藤 実 参事研究員（運動・感覚システム研究分野）|
How are visual circuits assembled during development? How do the assembled circuits process color information to guide animal behaviors? Using the Drosophila visual system as a model, we analyzed the assembly and function of the chromatic circuits in the peripheral visual system. In Drosophila, several types of medulla projection (Tm) neurons process and relay spectral information from photoreceptors to higher visual centers. Using a novel color-learning paradigm, we demonstrated that four Tm types (Tm5a/b/c and Tm20) are functionally redundant for associating green or blue color with aversive stimuli. In sharp contrast, innate spectral preference requires a dedicated neural circuit that contains a wide-field amacrine neuron, Dm8, and their synaptic partner, Tm5c neurons. Using a modified GRASP method to probe synaptic connections at the single-cell level, we found that each Dm8 neuron forms multiple synaptic contacts with Tm5c in the center of Dm8’s dendritic field but sparse connections in the periphery. By single-cell transcript profiling and RNAi-mediated knockdown, we determined that Tm5c uses the kainate receptors to receive excitatory glutamate input from Dm8. Together, we conclude that photoreceptor R7s->Dm8->Tm5c form a hard-wired glutamatergic circuit that mediates innate spectral preference by pooling ～ 16 UV-sensing R7 signals for transfer to the lobula, a higher visual center.