在許多生理反應中都有G蛋白訊息調控的參與，在過去研究中發現一種Gβ5次單元蛋白會廣泛表現在視網膜外叢狀層、內叢狀層、節狀細胞層和膽鹼能細胞中。不同於以往常見的G蛋白複合物，Gβ5會與R7RGS蛋白家族結合，對下游GTP水解過程進行調控。若將此種Gβ5次單元從感光細胞及雙極細胞中剃除，將會影響細胞突觸發育的完整性和正常的光反應。根據美國貝勒醫學院陳景康教授於2015 ARVO年會的報告發現，如果專一性地剃除小鼠視網膜星狀無軸突細胞內Gβ5的基因表現，將會縮小星狀無軸突細胞的樹突範圍。而星狀無軸突細胞其本身具有對光刺激的方向選擇性，利用此特性得以在視網膜內處理動態視覺的訊息傳遞。在此篇研究中，我們想進一步探討這種Gβ5蛋白剔除對樹突形態上的缺陷是否會影響到星狀無軸突細胞本身的光反應及方向選擇性調控的能力。我們利用不同條件的光刺激去分析星狀無軸突細胞的光感受區域大小，以及對於光刺激的時間頻率和空間頻率調控能力的探討，最後我們利用遮蔽物針對不同樹突區域給予光刺激，以觀察哪一部分的樹突區域對於方向選擇性反應較為重要。從研究結果中我們發現專一性地剃除Gβ5次單元確實會縮小星狀無軸突細胞的樹突範圍，但此形態的缺陷並不會影響其光感受區域的大小。而關於時間頻率、空間頻率與遮蔽物的實驗結果，星狀無軸突細胞也沒有因為Gβ5次單元的剃除，而減弱對方向選擇性的反應，反而有輕微增強之趨勢。這樣的結果也與陳景康教授實驗室尚未發表的Gβ5次單元剃除不影響眼動反射行為實驗結果大致相符。因此，總結來說，本篇的實驗結果證實了專一性Gβ5次單元的剃除不會顯著地影響星狀無軸突細胞的正常光反應及方向選擇性。

Detecting a moving object and its direction is a critical task for animals. The starburst amacrine cells (SACs), an interneuron in the retina, play an important role in the processing of motion direction. Gβ5 and its obligate partners R7 regulators of G-protein signaling are necessary for normal outer retinal functions. It is known that the expression of Gβ5 is wide spread in the photoreceptor layer, outer plexiform layer, inner plexiform layer, cholinergic cellular strata, and ganglion cell layer. Although previous studies have shown that Gβ5 is essential for phototransduction and neural signal processing in photoreceptors and ON-bipolar cells, the function of Gβ5 in cholinergic SACs is unclear. However, a recent study showed that Gβ5 may be associated with SAC morphology development. Thus, this study was aimed to examine whether Gβ5 elimination in SACs would affect their receptive field size and direction selectivity. By conditional knockout Gβ5 in SACs, the light responses of SACs were characterized using patch clamp recording. Our results showed that conditional Gβ5 knockout would decrease the dendritic field size of SACs, but the Gβ5 absence would not affect the receptive field of SACs. Using expanding and contracting concentric sinusoidal waves as light stimuli, our findings also showed that eliminating Gβ5 in SACs did not dramatically change the temporal and spatial frequency dependences and the central mask effect. This is consistent with Dr. CK Chen unpublished data, in which the Gβ5 specific knockout within cholinergic SACs did not disturb the normal function of motion detection in the optokinetic response. Thus, our results suggest that conditional Gβ5 knockout in SACs only led to a morphological defect, but it did not influence the normal light response function and direction selectivity in SACs.

CONTENTS
摘要 i
ABSTRACT iii
CHAPTER 1. INTRODUCTION 1
1-1 Neural circuitry in the retina 1
1-2 Starburst amacrine cell 1
1-3 The role of Gβ5 in the retina 3
1-4 Goal and summary 5
CHAPTER 2. MATERIALS AND METHODS 7
2-1 Animals 7
2-2 Retina preparation 8
2-3 Electrophysiology 8
2-4 Light stimuli 9
2-5 Image acquisition 10
2-6 Image analysis 11
2-7 Data analysis 11
CHAPTER 3. RESULTS 13
3-1 Voltage response of SACs 13
3-2 cKO Gβ5-/- SACs have smaller dendritic field than the control group, but the receptive field of cKO Gβ5-/- SACs and the control group are similar 13
3-3 Gβ5 in SACs has a limited role in the temporal frequency dependence 14
3-4 Gβ5 in SACs does not involve in the spatial frequency dependence 15
3-5 Gβ5 in SACs has a slight influence in the central mask dependence 17
3-6 cKO Gβ5-/- SACs have normal reversal potential in the I-V plot and full width at half maximum in the temporal response 18
CHAPTER 4. DISCUSSION 19
4-1 Cell-autonomous dendritic field defect of SACs in conditional Gβ5 knockout mice 19
4-2 Responses of temporal and spatial frequency dependence of SACs does not show apparent defect in the conditional Gβ5 knockout mice 20
4-3 Specific cholinergic Gβ5 knockout would enlarge the DS preference at proximal and distal dendritic sections 22
4-4 Removing the Gβ5 subunit from SACs does not change the characteristics of membrane potential and temporal response 24
REFERENCES 25
FIGURES 28

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