2017 Fiscal Year Annual Research Report
Analysis of spectral opponent mechanism in the optic lobe of the butterfly, Papilio xuthus
| Project/Area Number |
16J07688
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| Research Institution | The Graduate University for Advanced Studies |
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Principal Investigator |
Chen PeiーJu 総合研究大学院大学, 先導科学研究科, 特別研究員(DC1)
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| Project Period (FY) |
2016-04-22 – 2019-03-31
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| Keywords | butterfly / histaminergic channel / immunohistochemistry / lamina monopolar cell / photoreceptor / spectral opponency / vision |
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| Outline of Annual Research Achievements |
Spectral opponent responses have been observed at the level of photoreceptors in butterflies. This project aims to explain its mechanism and thus “histamine hypothesis” has been proposed.
I have localized two histamine-gated chloride channels, PxHCLA and PxHCLB, in the visual system of the butterfly Papilio xuthus by using specific antisera. The anti-PxHCLA labeling was associated with the membrane of non-photoreceptor neurons that are postsynaptic to photoreceptors, while the anti-PxHCLB labeling overlapped with photoreceptor axons, indicating the PxHCLB is expressed at the inter-photoreceptor synapses. The Papilio histaminergic synapses between photoreceptors indicate a possible neuronal circuit for insect color vision. Spectral opponency probably appears much earlier in insect visual processing than previously hypothesized.
We have found the variability in the response to GABA between PxHCLA and fly HCLA, which may reflect differences of underlying visual circuits between butterflies and flies. Accordingly, pathways for color and motion visions probably are less segregated in butterflies.
Based on immunolocalization and channel properties of two histaminergic channels, we proposed that PxHCLA and PxHCLB may attribute to the hyperpolarization of lamina monopolar cells (LMCs) at photoreceptor-LMC synapses and spectral opponency of photoreceptors at inter-photoreceptor synapses, respectively. I have successfully recorded LMCs and spectrally opponent photoreceptors in the Papilio lamina under collaboration with Dr. Gregor Belusic in University of Ljubljana.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The specificity of two candidates of histamine-gated chloride channels, PxHCLA and PxHCLB was confirmed by immunoblot analysis. The double-labeling immunohistochemistry with anti-PxHCLA and anti-PxHCLB is finalized. The distribution of anti-PxHCLB stands as crucial evidence for the histamine hypothesis: at least one of the histamine channels exists in the putative inter-photoreceptor synapses. The manuscript is about to be submitted.
I have started electrophysiological experiments to record LMCs and photoreceptor axons in the Papilio lamina. To acquire the techniques for experiments, I attended the workshop of microelectrode techniques for cell physiology in Plymouth UK last summer. Now I am trying to establish a fully functional system of single electrode switch clamp in the laboratory. In addition, I I spent 3 weeks in University of Ljubljana and got abundant preliminary results with Dr. Gregor Belusic. We employed intracellular recording in the Papilio lamina using 21 monochromatic lights ranging from UV to red wavelengths. We encountered a number of hyperpolarizing cells in the Papilio lamina including several spectral types of LMCs and spectrally opponent photoreceptors. A wide variety of the LMCs and photoreceptors in the Papilio lamina, which suggests considerable complexity of the chromatic signal processing in the early stage of visual system in insects.
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| Strategy for Future Research Activity |
A paper of identification and localization of the putative histamine-gated chloride channels in the Papilio eyes is ready for submission. In addition, I will present the immunohistochemical results at International Congress of Neuroethology (ICN) in Brisbane, Australia.
The immunohistochemical results provide anatomical properties to support the photoreceptor spectral opponency may be a part of butterflies’ color vision mechanism. The in vivo properties of putative channels are worthy and urgent to be confirmed by further electrophysiological studies. I will again visit University of Ljubljana and work with Prof. Gregor Belusic to record LMCs and spectrally opponent photoreceptors in the Papilio lamina. I plan to apply a single electrode switching clamp to analyze physiological properties of these cells.
The preliminary electrophysiological results will be presented in an international postgraduate course Sensory Ecology, which is held every second year at University of Lund. To figure out the ecological adaptation and evolution of their vision system as a whole, I would like to attend the course to gain knowledge about other sensory systems, which may inspire new insights into my study.
I will start to write my doctoral thesis after I finish all experiments and data analyses. A paper about the electrophysiological analysis in the Papilio lamina will be drafted as well.
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