シンポジウム（Symposium）

Symposium Retinal plasticity over time scales: Hibernation, circuit reorganization, and synaptic modulation シンポジウム網膜可塑性研究ー冬眠、回路、再構成、シナプス制御まで協賛：立命館大学総合科学研究機構システム視覚科学研究センター協賛：立命館大学総合科学研究機構 R-GIRO 協賛：私立大学戦略的研究基盤形成事業

7月27日（土）14:25～14:55　第6会場（朱鷺メッセ　2F　201A） 3S06a-1 Seeing in the cold – vision and hibernation Wei Li（Li Wei） NEI, NIH The ground squirrel has a cone-dominant retina and it hibernates in winter. We exploit these two unique features to study retinal biology and adaptations during hibernation. In this seminar, I will discuss an optic feature of the ground squirrel retina, as well as several forms of adaptation during hibernation in the retina and beyond. By exploring the mechanisms of such adaptation, we hope to shed light on therapeutic tactics for retinal injury and diseases, which are often associated with metabolic stress.		7月27日（土）15:25～15:55　第6会場（朱鷺メッセ　2F　201A） 3S06a-3 Mechanisms of fast adaptation at the mammalian cone photoreceptor synapse Steven H DeVries（DeVries Steven H） Northwestern University The synapses of long-distance transmission neurons are normally quiescent at rest, releasing a synchronous burst of transmitter in response to the invasion of depolarizing action potential. In contrast, photoreceptors rest at a relatively depolarized voltage in the dark continuously releasing packets of transmitter. The stimulus, a flash of light, elicits a membrane hyperpolarization that momentarily slows or stops transmitter release. While photoreceptors and other excitatory CNS construct their synapses from analogous component--active zones, Ca²⁺ channels, a synaptic cleft, and fast excitatory glutamate receptors--the precise components and their organization differs. For example, photoreceptors use synaptic ribbons to release transmitter and sign-conserving transmission to Off bipolar cells relies predominately on kainate receptors. Intriguingly, ribbons are capable of phasic and continuous transmitter release and the kainate receptors on Off bipolar cells undergo a profound and long-lasting (i.e., ~10) desensitization when exposed to glutamate. In this talk, I will first describe our results on the ebb and flow of transmitter release at ribbon synapses in cone photoreceptors from the cone-dominant retina of the ground squirrel. The ~20 ribbons in each cone terminal dock ~400 vesicles at the membrane. The entire docked pool can be released with two time constants (&tau) by a depolarizing stimulus: 0.5 ms and 11 ms. Following release, the docked pool replenishes with a &tau = 1 s. An individual ground squirrel cone contacts 5 types of Off bipolar cells, two of which express kainate receptors (80% of the receptors vs 20% AMPA receptors) with a slow recovery (&tau = ~10 s) from desensitization following a pulse of glutamate. We use modeling and cell pair voltage clamp recording to show how the ebb and flow of both vesicle release and postsynaptic kainate receptor response interact to produce signals that change dynamically with the properties of the stimulus.

7月27日（土）15:55～16:05　第6会場（朱鷺メッセ　2F　201A） 3S06a-4 網膜回路の動的特性がもたらす正常および病変状態 Katsunori Kitano（北野勝則）立命館大情報理工 In the retina, there exists a lot of subtypes of neurons and synapses, each of which exhibit different dynamical properties. Because the variety of the subtypes, or dynamical properties, would play different roles for retinal functions, it must be important to understand how such dynamical properties would contribute to retinal functions. On the other hand, the properties could affect pathological states in the retina as mentioned below. The understanding of pathological states would be helpful to understand the neural mechanism in the normal state. The retina of the retinal degeneration rd1 mouse is known to exhibit spontaneous oscillation at a low frequency (<10 Hz) that is not observed in the normal retina. According to experimental results, two potential mechanisms for the spontaneous oscillation have been proposed so far; one arises from the property of a gap junction network between cone bipolar cells (BCs) and AII amacrine cells (AII-ACs) and between AII-ACs (Trenholm et al., 2012) whereas the other does from the intrinsic property of AII-ACs (Choi et al., 2014). In either case, the oscillation emerges when the AII-ACs are hyperpolarized. This suggests that BCs as well should be more hyperpolarized in the rd1 retina than in the normal retina. Hyperpolarization of presynaptic neuron (BC) would cause less activation of the synapse from the BC to the postsynaptic neuron, ganglion cells (GCs), consequently, less activation of GC in the rd1 retina than in the normal retina. Therefore, it should be solved why the normal retina does not show the spontaneous oscillation but the rd1 retina does. We studied the mechanism for the spontaneous oscillation using a computational model of AII-AC, BC, and GC network. In particular, to solve the paradoxical phenomenon mentioned above, we incorporated a ribbon synapse model as the BC-GC synapse. Even at a depolarized state, neurotransmitter release was not always enhanced because of short-term depression (Tsodyks and Markram, 1997). If we assume upregulation of the synapses in the inner plexiform layer of the rd1 retina (Dagar et al., 2014), the model could reproduce both the normal and abnormal neural states in the absence of light stimuli: no response in the normal retina and spontaneous rhythmic activity in the abnormal retina.		7月27日（土）16:05～16:20　第6会場（朱鷺メッセ　2F　201A） 3S06a-5 網膜神経節細胞の局所集団による広域動画像の迅速かつ協同的な処理 Masao Tachibana（立花政夫）^1,4，Akihiro Matsumoto（松本彰弘）^2,3,4 ¹立命館大学総合科学研究機構 ²立命館大学グローバル・イノベーション研究機構 ³DANDRITE, Dep Biomedicine, Aarhus Univ, Aarhus, Denmark ⁴東大院人社心理 Our visually perceived world is stable, irrespective of incessant motion of the retinal image due to the movements of eyes, head, and body. Accumulating evidence indicates that the central nervous system may play a key role for stabilization of the visual world. Fixational and saccadic eye movements cause jitter and rapid motion of the whole retinal image, respectively. However, it is not yet evident how the retina processes visual information during eye movements. Furthermore, it is not clear whether multiple subtypes of retinal ganglion cells (GCs) send visual information independently or cooperatively. We performed multi-electrode recordings and whole-cell clamp recordings from ganglion cells (GCs) of the retina isolated from goldfish. GCs were physiologically classified into six subtypes (Fast/Medium/Slow, transient/sustained) based on the temporal profile of the receptive field (RF) estimated by reverse correlation method. We found that the jitter motion of a global random-dot background induced elongation and sensitization of the spatiotemporal RF of the Fast-transient GC (Ft GC). The following rapid global motion induced synchronous firing among local Ft GCs and cooperative firing with precise latencies among adjacent specific GC subtypes. Thus, global motion images that simulated fixational and saccadic eye movements were processed in a coordinated manner by local clusters of specific GCs. Stimulus conditions (duration, area, velocity, and direction of motion) that altered the properties of the receptive field (RF) were consistent with the characteristics of in vivo goldfish eye movements. The wide-range lateral interaction, possibly mediated by electrical and GABAergic synapses, contributed to the RF alterations. These results indicate that the RF properties of retinal GCs in a natural environment are substantially different from those under simplified experimental conditions. Processing of global motion images is already started in the retina and may facilitate visual information processing in the brain.