視覚1 Vision 1
O1-6-5-1 網膜ニューロン間電気シナプスの細胞内開閉調節機構 Cytoplasmic Regulation of Channel Opening of Electrical Synapses between Retinal Neurons ○日高聰1 ○Soh Hidaka1 藤田保健衛生大学医学部生理学1 Dept Physiol, Fujita Health Univ School of Medicine1 Electrical synapses are present in retinal neurons expressing the specific gap junction channel subunit, connexin36 (J Neurosci, 2004). Our studies demonstrated cellular components in GABAergic amacrine cells performing lateral interactions through inhibitory synapses (J Intgra Neurosci, 2009). Electrical current spread through connections of specific amacrine cells is expected to mediate inhibitory synapses. My recent studies revealed channel opening of gap junctions is regulated by high level of intracellular cyclic AMP as well as intracellular Ca2+ concentration (Brain Res, 2012). In the present study, I investigated regulatory mechanisms of channel opening of electrical synapses by extracellular and intracellular ligands under dual whole-cell patch clamp recordings of pair of cells. I examined how passage currents through electrical synapses are modulated by specific antibodies against connexin36 proteins and by change of intracellular Ca2+ concentration. Chelating intracellular Ca2+ within both cells led us to observe large passage currents between connected cells and transjunctional conductance (Gj) between the cells (2.43 + 1.21nS, n = 7). Gj between the cells suppressed to 0.23 nS by intracellular application of cyclic AMP in pipette with 5mM concentration, compared with that of control condition. Intracellular application of an antibody against the cytoplasmic domain of connexin36 (J Neurosci, 2004) reduced Gj (0.98 + 0.23nS, n=4). The inhibition of Gj by the cytoplasmic antibody was dose-dependent manner. Cocktail of the antibody against the cytoplasmic domain and intracellular cyclic AMP leaves Gj as in the level by single involvement of the cytoplasmic antibody. Application of another antibody against the extracellular domain of connexin36 leaves Gj as in the control level (1.79 + 0.51nS, n=4). These results demonstrate that regulation of channel opening of electrical synapses between retinal neurons is performed by the cytoplasmic domains of connexin36.	O1-6-5-2 発達期における個別の神経細胞の活動を抑制する事は、視覚応答選択性の発達を阻害しない Silencing activity of individual neurons throughout development does not prevent maturation of orientation selectivity in mouse visual cortex ○萩原賢太1, 田川義晃2,3, 吉田盛史1,3, 大木研一1,3 ○Kenta M Hagihara1, Yoshiaki Tagawa2,3, Takashi Yoshida1,3, Kenichi Ohki1,3 九州大院・医・分子生理1, 京都大院・理・生物物理2 Dept Mol Physiol, Univ of Kyushu, Fukuoka1, Dept Biophys, Univ of Kyoto, Kyoto2, CREST, Japan3 Orientation selectivity is a fundamental property underlying the visual information processing in early visual cortex. However, it remains unclear whether this property is formed genetically or develops dependently on other factors such as neuronal activity during developmental stages. It was reported that total suppression of cortical activity in ferret visual cortex by application of TTX during development prevented maturation of orientation selectivity (Chapman and Stryker, 1993). However, if activity of all neurons in visual cortex was suppressed, non-cell autonomous factors also might be suppressed, which could prevent the normal development of orientation selectivity. To address whether neurons require their own activity to maturate orientation selectivity, we suppressed activity of a subset of neurons, and examined whether these neurons normally maturate orientation selectivity. Active wave-like spontaneous activity is observed in the cortex during the neonatal period. This activity starts to decrease around the time of eye opening, and visually evoked response appears (Rochefort et al., 2009). We found that expression of Kir2.1 significantly reduced wave-like spontaneous activity and totally suppressed visually evoked activity in neurons expressing Kir2.1. We then examined orientation selectivity of neurons whose activities were suppressed during developmental stages with in vivo two-photon calcium imaging. Surprisingly, neurons silenced by Kir2.1 showed normal visual response and orientation selectivity. We will discuss roles of spontaneous activity during neonatal period and visually evoked activity after eye opening for maturation of orientation selectivity.
O1-6-5-3 発生段階のマウス視覚野における同一細胞系譜神経細胞が持つ機能組織 Functional organization of clonally related neurons in mouse visual cortex during development ○大槻元1,2, 西山めぐみ1,2, 吉田盛史1,2, 村上知成1,2大木研一1,2 ○Gen Ohtsuki1,2, Megumi Nishiyama1,2, Takashi Yoshida1,2, Tomonari Murakami1,2, Mark Histed3, Carlos Lois4, Kenichi Ohki1,2 九州大学大学院 医学研究院 分子生理学1, 独立行政法人科学技術振興機構, CREST2, ハーバード大学医学部　神経生物学部門3, マサチューセッツ大学医学部　神経生物学部門4 Dept. of Molecular Physiology, Kyushu University, Grad. School of Medical Sciences, Fukuoka1, Japan Science and Technology Agency, CREST, Tokyo, Japan2, Dept. of Neurobiology, Harvard Medical School, Boston, USA3, Dept. of Neurobiology, University of Massachusetts Medical School, Worcester, USA4 Neurons in rodent visual cortex are organized in a salt-and-pepper fashion for orientation selectivity (Ohki et al, 2005), but it is still unknown how this functional architecture develops. Recent studies (Yu et al., 2009, 2012) reported that the progeny of single progenitor cells are preferentially connected to each other. Since cells with similar response selectivity also have high probabilities of synaptic connection (Ko et al., 2011), we hypothesized that sister cells may share similar response selectivity. In this study, by using the combination of in vivo two-photon Ca2+ imaging and a transgenic mouse which labels all the progeny derived from single cortical progenitor cells, we found that orientation preference among clonally related cells are more similar than among unrelated cells. However, not all clonally related cells share response selectivity in adult mice (P49-62), suggesting that cell lineage is not the only determinant of response selectivity (Ohtsuki et al., 2012, see also Li et al., 2012). Although we found that similarity of orientation selectivity among clonally related neurons is moderate in adult mice, it could be stronger just after eye opening and may be weakened in the course of maturation of the cortical circuit. To test this, we examined visual responses at time points of the eye opening, 3-10 days later and matured. We found that, while cardinal orientation bias for the horizontal and vertical axis becomes weaker with visual experience, similarity of preferred orientations among clonally related cells is moderate even from the eye opening and remains stable through development. Further, we compared direction and spatial frequency selectivity between the juvenile and matured animals. We also examined whether functional similarity among clonally related cells depends on the positional relation among those cells.	O1-6-5-4 ネコの外側膝状体および網膜における明るさの恒常性と相関する神経活動 Neural correlates of the lightness constancy in the dorsal lateral geniculate nucleus (dLGN) and the retina of the cats ○七五三木聡1,2, 原真一郎2, 木村晃大1, 相馬祥吾2, 佐藤宏道1,2 ○Satoshi Shimegi1,2, Shin'ichiro Hara2, Akihiro Kimura1, Shogo Soma2, Hiromichi Sato1,2 大阪大院・医・認知行動科学1, 大阪大院・生命機能・認知行動科学2 Grad Sch Med, Osaka Univ, Osaka1, Grad Sch Front Biosci, Osaka Univ. Osaka2 We have ability to perceive the reflectance of the surface (lightness), by which we can perceive white surface of an object as white in the sunlight as well as the moonlight (lightness constancy). To examine whether and how the lightness is represented in neuronal activity of early visual pathway, we recorded the single-unit activity from the lateral geniculate nucleus (LGN) and optic tract (OT) fibers of anesthetized cats. The classical receptive field (CRF) of each neuron was stimulated with a large uniform stimulus (center stimulus, 10 ° in radius) sufficiently covering over the CRF in combination with luminance change of the background area outside the center stimulus (background (BG) stimulus). On-center or off-center cells were always stimulated with bright or dark center stimulus to evoke spike response (center response). Forty three percent of LGN neurons showed a significant center response, called as " surface-responsive (SR) neuron" . Eighty three percent of the SR neurons showed a luminance-dependency of center response. When center stimulus was presented with BG stimulus, the center response was facilitated or suppressed by the BG stimuli, and the BG-modulated responses corresponded to the ratio of the luminance between center and BG stimuli (C/BG ratio) calculated as a reflectance of the center stimulus (lightness-related response). Moreover, the C/BG tuning was not influenced by different levels of the center luminance, suggesting a neural lightness constancy. The lightness-related activity was neither disturbed nor abolished by blockade of GABA receptors. The single OT fibers also showed the same lightness-related responses as the LGN neurons. Therefore, we concluded that a certain population of LGN neurons represents not only luminance but also lightness, and those response properties are inherited from those of RGCs.

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