視網膜是中樞神經系統中延伸自大腦的一部份，常被利用來研究視覺資訊的處理。顧名思義，“方向選擇性節細胞”是在視網膜中可以感應物體移動方向的一種神經元，在看到物體以某個方向行進時，它們會產生強烈的動作電位反應，但對相反方向的運動卻不會。目前已知這種方向性的主要產生因素是經由對抑制性傳導途徑非對稱性的作用。星狀無軸突細胞是一種聯絡神經元，它同時會釋放出神經傳導物質γ-胺基丁酸和乙醯膽鹼。雖然星狀無軸突細胞長久以來一直被視為是抑制作用的來源，不過，絕大部分的相關機制仍然存在著許多爭議。本研究旨在探究星狀無軸突細胞和方向選擇性節細胞之間相互作用的模式。實驗方法是先以胞內記錄得知方向選擇性節細胞的方向性，然後再將此細胞和其鄰近的星狀無軸突細胞先後注射入螢光染劑，接著進行免疫染色來標定A型γ-胺基丁酸受器。如此，便可以觀察它們之間樹突的關係和抑制性突觸連結。實驗結果發現星狀無軸突細胞的樹突在與方向選擇性節細胞接觸時不會偏於特定方向；再者，也沒有發現在方向選擇性節細胞上的抑制性突觸連結有任何不對稱的現象。由此結果可導出，方向性既不是來自星狀無軸突細胞和方向選擇性節細胞之間非對稱樹突的安排，也不是藉由它們之間的抑制性突觸連結所決定。因此，要完成此一複雜的方向選擇性運算，必定需要有更多層細胞的參與。

The retina is an approachable part of the brain for studying information processing. Direction selective ganglion cells (DSGCs) are retinal neurons which can sense motion direction as implied by the name. They exhibit robust spiking responses to an object moving in one direction but weak in its opposite direction. It is known that the major driving force of this directionality is the asymmetric suppression through the inhibitory pathway. An interneuron - starburst amacrine cell (SAC), which co-releases γ-amino butyric acid and acetylcholine, has long been thought as the source of inhibition. Nevertheless, much about the mechanism remains controversial. This study is aimed to resolve the pattern of interactions among SACs and DSGCs. Fluorescent tracers were filled into a physiologically identified DSGC and a neighboring SAC subsequently. Immunostaining of GABAA receptors was then performed. Therefore, the dendritic relationship and the inhibitory synaptic connection between the DSGC and the SAC can be revealed. We demonstrated that the dendrites of the SAC were found to contact the DSGC without preference for any direction. Furthermore, no asymmetry of the inhibitory synaptic inputs on the DSGC was observed. These results lead to the conclusion that neither the geometric arrangement nor the inhibitory synaptic inputs between SACs and DSGCs is likely to mediate the directionality. Multiple layer interactions are necessary to fulfill this complicate processing.

1. Ammermuller, J., J. F. Muller, et al. (1995). "The organization of the turtle inner retina. II. Analysis of color-coded and directionally selective cells." J Comp Neurol 358(1): 35-62.
2. Amthor, F. R., E. S. Takahashi, et al. (1989b). "Morphologies of rabbit retinal ganglion cells with complex receptive fields." J Comp Neurol 280(1): 97-121.
3. Amthor, F. R. and N. M. Grzywacz (1993). "Inhibition in ON-OFF directionally selective ganglion cells of the rabbit retina." J Neurophysiol 69(6): 2174-87.
4. Amthor, F. R. and C. W. Oyster (1995). "Spatial organization of retinal information about the direction of image motion." Proc Natl Acad Sci U S A 92(9): 4002-5.
5. Amthor, F. R., C. W. Oyster, et al. (1984). "Morphology of on-off direction-selective ganglion cells in the rabbit retina." Brain Res 298(1): 187-90.
6. Amthor, F. R., K. T. Keyser, et al. (2002). "Effects of the destruction of starburst-cholinergic amacrine cells by the toxin AF64A on rabbit retinal directional selectivity." Vis Neurosci 19(4): 495-509.
7. Ariel, M. and N. W. Daw (1982). "Pharmacological analysis of directionally sensitive rabbit retinal ganglion cells." J Physiol 324: 161-85.
8. Barlow, H. B. (1953). "Summation and inhibition in the frog's retina." J Physiol 119(1): 69-88.
9. Barlow, H. B. and R. M. Hill (1963). "Selective sensitivity to direction of movement in ganglion cells of the rabbit retina." Science 139: 412-4.
10. Barlow, H. B., R. M. Hill, et al. (1964). "Retinal Ganglion Cells Responding Selectively To Direction And Speed Of Image Motion In The Rabbit." J Physiol 173: 377-407.
11. Barlow, H. B. and W. R. Levick (1965). "The mechanism of directionally selective units in rabbit's retina." J Physiol 178(3): 477-504.
12. Borg-Graham, L. J. (2001). "The computation of directional selectivity in the retina occurs presynaptic to the ganglion cell." Nat Neurosci 4(2): 176-83.
13. Boycott, B. and H. Wassle (1999). "Parallel processing in the mammalian retina: the Proctor Lecture." Invest Ophthalmol Vis Sci 40(7): 1313-27.
14. Brandon, C. (1987). "Cholinergic neurons in the rabbit retina: immunocytochemical localization, and relationship to GABAergic and cholinesterase-containing neurons." Brain Res 401(2): 385-91.
15. Brandstatter, J. H., U. Greferath, et al. (1995). "Co-stratification of GABAA receptors with the directionally selective circuitry of the rat retina." Vis Neurosci 12(2): 345-58.
16. Brecha, N., D. Johnson, et al. (1988). "Cholinergic amacrine cells of the rabbit retina contain glutamate decarboxylase and gamma-aminobutyrate immunoreactivity." Proc Natl Acad Sci U S A 85(16): 6187-91.
17. Caldwell, J. H., N. W. Daw, et al. (1978). "Effects of picrotoxin and strychnine on rabbit retinal ganglion cells: lateral interactions for cells with more complex receptive fields." J Physiol 276: 277-98.
18. Chiao, C. C. and R. H. Masland (2002). "Starburst cells nondirectionally facilitate the responses of direction-selective retinal ganglion cells." J Neurosci 22(24): 10509-13.
19. Cronly-Dillon, J. R. (1964). "Units Sensitive To Direction Of Movement In Goldfish Optic Tectum." Nature 203: 214-5.
20. Dacheux, R. F., M. F. Chimento, et al. (2003). "Synaptic input to the on-off directionally selective ganglion cell in the rabbit retina." J Comp Neurol 456(3): 267-78.
21. Dong, W., W. Sun, et al. (2004). "Dendritic relationship between starburst amacrine cells and direction-selective ganglion cells in the rabbit retina." J Physiol 556(Pt 1): 11-7.
22. Euler, T. and H. Wassle (1998). "Different contributions of GABAA and GABAC receptors to rod and cone bipolar cells in a rat retinal slice preparation." J Neurophysiol 79(3): 1384-95.
23. Euler, T., P. B. Detwiler, et al. (2002). "Directionally selective calcium signals in dendrites of starburst amacrine cells." Nature 418(6900): 845-52.
24. Famiglietti, E. V. (1991). "Synaptic organization of starburst amacrine cells in rabbit retina: analysis of serial thin sections by electron microscopy and graphic reconstruction." J Comp Neurol 309(1): 40-70.
25. Famiglietti, E. V. (1992). "Dendritic co-stratification of ON and ON-OFF directionally selective ganglion cells with starburst amacrine cells in rabbit retina." J Comp Neurol 324(3): 322-35.
26. Famiglietti, E. V. (2002). "A structural basis for omnidirectional connections between starburst amacrine cells and directionally selective ganglion cells in rabbit retina, with associated bipolar cells." Vis Neurosci 19(2): 145-62.
27. Famiglietti, E. V., Jr. and H. Kolb (1976). "Structural basis for ON-and OFF-center responses in retinal ganglion cells." Science 194(4261): 193-5.
28. Fletcher, E. L., P. Koulen, et al. (1998). "GABAA and GABAC receptors on mammalian rod bipolar cells." J Comp Neurol 396(3): 351-65.
29. Fried, S. I., T. A. Munch, et al. (2002). "Mechanisms and circuitry underlying directional selectivity in the retina." Nature 420(6914): 411-4.
30. Fried, S. I., T. A. Munch, et al. (2005). "Directional selectivity is formed at multiple levels by laterally offset inhibition in the rabbit retina." Neuron 46(1): 117-27.
31. Gavrikov, K. E., A. V. Dmitriev, et al. (2003). "Cation--chloride cotransporters mediate neural computation in the retina." Proc Natl Acad Sci U S A 100(26): 16047-52.
32. Greferath, U., U. Grunert, et al. (1995). "GABAA receptor subunits have differential distributions in the rat retina: in situ hybridization and immunohistochemistry." J Comp Neurol 353(4): 553-71.
33. Grzywacz, N. M. and F. R. Amthor (1993). "Facilitation in ON-OFF directionally selective ganglion cells of the rabbit retina." J Neurophysiol 69(6): 2188-99.
34. Grzywacz, N. M., J. S. Tootle, et al. (1997). "Is the input to a GABAergic or cholinergic synapse the sole asymmetry in rabbit's retinal directional selectivity?" Vis Neurosci 14(1): 39-54.
35. He, S. and R. H. Masland (1997). "Retinal direction selectivity after targeted laser ablation of starburst amacrine cells." Nature 389(6649): 378-82.
36. Holden, A. L. (1977). "Responses of directional ganglion cells in the pigeon retina." J Physiol 270(2): 253-69.
37. Hubel, D. H. and T. N. Wiesel (1962). "Receptive fields, binocular interaction and functional architecture in the cat's visual cortex." J Physiol 160: 106-54.
38. Jacobson, M. and R. M. Gaze (1964). "Types Of Visual Response From Single Units In The Optic Tectum And Optic Nerve Of The Goldfish." Q J Exp Physiol Cogn Med Sci 49: 199-209.
39. Jensen, R. J. and R. D. DeVoe (1983). "Comparisons of directionally selective with other ganglion cells of the turtle retina: intracellular recording and staining." J Comp Neurol 217(3): 271-87.
40. Jeon, C. J., J. H. Kong, et al. (2002). "Pattern of synaptic excitation and inhibition upon direction-selective retinal ganglion cells." J Comp Neurol 449(2): 195-205.
41. Kittila, C. A. and A. M. Granda (1994). "Functional morphologies of retinal ganglion cells in the turtle." J Comp Neurol 350(4): 623-45.
42. Kittila, C. A. and S. C. Massey (1995). "Effect of ON pathway blockade on directional selectivity in the rabbit retina." J Neurophysiol 73(2): 703-12.
43. Kittila, C. A. and S. C. Massey (1997). "Pharmacology of directionally selective ganglion cells in the rabbit retina." J Neurophysiol 77(2): 675-89.
44. Koulen, P., M. Sassoe-Pognetto, et al. (1996). "Selective clustering of GABA(A) and glycine receptors in the mammalian retina." J Neurosci 16(6): 2127-40.
45. Lettvin, J. Y., H. R. Maturana, et al. (1960). "Two remarks on the visual system of the frog." AFOSR TR United States Air Force Off Sci Res 60-77: 1-25.
46. Masland, R. H. (2001). "The fundamental plan of the retina." Nat Neurosci 4(9): 877-86.
47. Masland, R. H. (2001). "Neuronal diversity in the retina." Curr Opin Neurobiol 11(4): 431-6.
48. Masland, R. H. and J. W. Mills (1979). "Autoradiographic identification of acetylcholine in the rabbit retina." J Cell Biol 83(1): 159-78.
49. Maturana, H. R. and S. Frenk (1963). "Directional Movement And Horizontal Edge Detectors In The Pigeon Retina." Science 142: 977-9.
50. O'Malley, D. M., J. H. Sandell, et al. (1992). "Co-release of acetylcholine and GABA by the starburst amacrine cells." J Neurosci 12(4): 1394-408.
51. Oyster, C. W., F. R. Amthor, et al. (1993). "Dendritic architecture of ON-OFF direction-selective ganglion cells in the rabbit retina." Vision Res 33(5-6): 579-608.
52. Oyster, C. W. and H. B. Barlow (1967). "Direction-selective units in rabbit retina: distribution of preferred directions." Science 155(764): 841-2.
53. Perry, V. H. and M. Walker (1980). "Amacrine cells, displaced amacrine cells and interplexiform cells in the retina of the rat." Proc R Soc Lond B Biol Sci 208(1173): 415-31.
54. Rockhill, R. L., F. J. Daly, et al. (2002). "The diversity of ganglion cells in a mammalian retina." J Neurosci 22(9): 3831-43.
55. Stasheff, S. F. and R. H. Masland (2002). "Functional inhibition in direction-selective retinal ganglion cells: spatiotemporal extent and intralaminar interactions." J Neurophysiol 88(2): 1026-39.
56. Tauchi, M. and R. H. Masland (1984). "The shape and arrangement of the cholinergic neurons in the rabbit retina." Proc R Soc Lond B Biol Sci 223(1230): 101-19.
57. Tauchi, M. and R. H. Masland (1985). "Local order among the dendrites of an amacrine cell population." J Neurosci 5(9): 2494-501.
58. Taylor, W. R. and D. I. Vaney (2002). "Diverse synaptic mechanisms generate direction selectivity in the rabbit retina." J Neurosci 22(17): 7712-20.
59. Taylor, W. R. and D. I. Vaney (2003). "New directions in retinal research." Trends Neurosci 26(7): 379-85.
60. Vaney, D. I., L. Peichi, et al. (1981). "Matching populations of amacrine cells in the inner nuclear and ganglion cell layers of the rabbit retina." J Comp Neurol 199(3): 373-91.
61. Vaney, D. I. (1984). "'Coronate' amacrine cells in the rabbit retina have the 'starburst' dendritic morphology." Proc R Soc Lond B Biol Sci 220(1221): 501-8.
62. Vaney, D. I. (1994). "Territorial organization of direction-selective ganglion cells in rabbit retina." J Neurosci 14(11 Pt 1): 6301-16.
63. Vaney, D. I. (2001). " Direction–selective ganglion cells in the retina." In: Zanker JM and Zeil J (eds) Motion vision: computational, neural, and ecological constraints. Springer–Verlag, Berlin, pp 13–56.
64. Vaney, D. I., L. Peichi, et al. (1981). "Matching populations of amacrine cells in the inner nuclear and ganglion cell layers of the rabbit retina." J Comp Neurol 199(3): 373-91.
65. Vaney, D. I. and D. V. Pow (2000). "The dendritic architecture of the cholinergic plexus in the rabbit retina: selective labeling by glycine accumulation in the presence of sarcosine." J Comp Neurol 421(1): 1-13.
66. Wassle, H. (2004). "Parallel processing in the mammalian retina." Nat Rev Neurosci 5(10): 747-57.
67. Werblin, F. S. (1970). "Response of retinal cells to moving spots: intracellular recording in Necturus maculosus." J Neurophysiol 33(3): 342-50.
68. Werblin, F., B. Roska, et al. (2001). "Parallel processing in the mammalian retina: lateral and vertical interactions across stacked representations." Prog Brain Res 131: 229-38.
69. Wyatt, H. J. and N. W. Daw (1975). "Directionally sensitive ganglion cells in the rabbit retina: specificity for stimulus direction, size, and speed." J Neurophysiol 38(3): 613-26.
70. Wyatt, H. J. and N. W. Day (1976). "Specific effects of neurotransmitter antagonists on ganglion cells in rabbit retina." Science 191(4223): 204-5.
71. Yang, G. and R. H. Masland (1994). "Receptive fields and dendritic structure of directionally selective retinal ganglion cells." J Neurosci 14(9): 5267-80.
72. Yoshida, K., D. Watanabe, et al. (2001). "A key role of starburst amacrine cells in originating retinal directional selectivity and optokinetic eye movement." Neuron 30(3): 771-80.
73. Zheng, J. J., S. Lee, et al. (2004). "A developmental switch in the excitability and function of the starburst network in the mammalian retina." Neuron 44(5): 851-64.