摘要
目前神經科學中最大的挑戰，來自於研究感覺訊號傳到腦中較高層級的腦區時，這些較高層級的腦區是如何處理同時進來的許多不同的訊號，以決定生物面對這些複雜訊號時的適當行為反應。在一般環境中，多數的味道都會影響果蠅做出迎趨或是逃避的反應，甚至同一種味道的濃烈多寡就會產生不同的喜歡或厭惡的反應。果蠅的嗅覺系統是由嗅覺感受神經細胞(olfactory receptor neurons)接收到氣味分子之後，將產生的訊號交由嗅覺投射細胞 (projection neurons)傳到更高層級的腦區-蕈狀體（mushroom bodies）及側角（lateral horn）。為了了解蕈狀體在訊號處理的過程中扮演的角色，我們阻斷蕈狀體不同部位的神經傳導後，給予果蠅不同濃度的MCH及OCT（兩種果蠅討厭的味道）。發現當我們在低濃度的MCH及OCT之下，阻斷蕈狀體的α’/β’ lobes神經傳導物質，會破壞果蠅正常的逃避行為 ; 但在高濃度時卻沒有觀察到此現象。另外，我們也發現當阻斷蕈狀體的α/β lobes神經傳導物質時，會破壞果蠅對蘋果醋正常的吸引行為。這此實驗發現果蠅腦內蕈狀體的不同區域分別參與嗅覺躲避和吸引的行為反應，其中α’/β’ lobes參與著果蠅嗅覺逃避行為的訊息傳遞，而α/β lobes則參與果蠅嗅覺吸引行為的訊息傳遞。

Abstract
The greatest challenge for neuroscience at present is to address how sensory coding is represented from sensory input to the higher brain centers, where neural activity and information integration is computed in order to elicit appropriate behavior responses. In Drosophila, most odorants elicit either attraction or avoidance, depending on their concentration as well as their identity. Olfactory information is received from olfactory receptor neurons (ORNs) and then transferred to the two higher brain centers - mushroom bodies (MBs) and lateral horns (LHs) - via secondary olfactory neurons - projection neurons (PNs). To figure out the function of MBs in olfactory processing, we specifically disrupted neurotransmitter outputs from different lobes of the MBs and examined the resulting avoidance and attraction behavior after exposure to two different repellents - methyl cyclohexanol (MCH) and octanol (OCT) and one attraction odorant- apple cider vinegar (ACV). We found that neurotransmitter outputs from α’/β’ lobes in MBs are necessary for avoidance behavior at low concentrations of repellents but not at high concentrations. We also demonstrated that α/β lobes in MBs is necessary for attraction behavior. These findings suggested that the avoidance and attraction olfactory information may be separately processed in the different lobes of MBs in Drosophila brain.

References
Ai, M., Min, S., Grosjean, Y., Leblanc, C., Bell, R., Benton, R., and Suh, G.S.B. (2010). Acid sensing by the Drosophila olfactory system. Nature 468, 691-U112.
Bengtsson, J.M., Khbaish, H., Reinecke, A., Wolde-Hawariat, Y., Negash, M., Seyoum, E., Hansson, B.S., Hillbur, Y., and Larsson, M.C. (2011). Conserved, highly specialized olfactory receptor neurons for food compounds in 2 congeneric scarab beetles, Pachnodainterrupta and Pachnodamarginata. Chem Senses 36, 499-513.
Boulet, M., Charpentier, M.J.E., and Drea, C.M. (2009). Decoding an olfactory mechanism of kin recognition and inbreeding avoidance in a primate. Bmc. Evol. Biol. 9.
Briscoe, B.K., Lewis, M.A., and Parrish, S.E. (2002). Home range formation in wolves due to scent marking. Bulletin of Mathematical Biology 64, 261-284.
Caron, S.J., Ruta, V., Abbott, L.F., and Axel, R. (2013). Random convergence of olfactory inputs in the Drosophila mushroom body. Nature 497, 113-117.
Caspers, B.A., and Krause, E.T. (2011). Odour-based natal nest recognition in the zebra finch (Taeniopygiaguttata), a colony-breeding songbird. Biology Letters 7, 184-186.
Chauvin, C., and Thierry, B. (2005). Tonkean macaques orient their food search from olfactory cues conveyed by conspecifics. Ethology111, 301-310.
Couto, A., Alenius, M., and Dickson, B.J. (2005). Molecular, anatomical, and functional organization of the Drosophila olfactory system. Curr. Biol. 15, 1535-1547.
DeBruyne, M., Foster, K., and Carlson, J.R. (2001). Odor coding in the Drosophila antenna. Neuron 30, 537-552.
Debelle, J.S., and Heisenberg, M. (1994). Associative odor learning in Drosophila abolished by chemical ablation of mushroom bodies. Science 263, 692-695.
Dobritsa, A.A., van der Goes van Naters, W., Warr, C.G., Steinbrecht, R.A., and Carlson, J.R. (2003). Integrating the molecular and cellular basis of odor coding in the Drosophila antenna. Neuron 37, 827-841.
Dubnau, J., Grady, L., Kitamoto, T., and Tully, T. (2001). Disruption of neurotransmission in Drosophila mushroom body blocks retrieval but not acquisition of memory. Nature 411, 476-480.
Hallem, E.A., Ho, M.G., and Carlson, J.R. (2004). The molecular basis of odor coding in the Drosophila antenna. Cell 117, 965-979.
Heimbeck, G., Bugnon, V., Gendre, N., Keller, A., and Stocker, R.F. (2001). A central neural circuit for experience-independent olfactory and courtship behavior in Drosophila melanogaster. Proc. Natl. Acad. Sci. 98, 15336-15341.
Howard, J.D., Plailly, J., Grueschow, M., Haynes, J.D., and Gottfried, J.A. (2009). Odor quality coding and categorization in human posterior piriform cortex. Nat. Neurosci. 12, 932-940
Igarashi, K.M., and Mori, K. (2005). Spatial representation of hydrocarbon odorants in the ventrolateral zones of the rat olfactory bulb. Journal of Neurophysiology 93, 1007-1019.
Jacob, S., McClintock, M.K., Zelano, B., and Ober, C. (2002). Paternally inherited HLA alleles are associated with women's choice of male odor. Nature Genetics 30, 175-179.
Jefferis, G.S., Potter, C.J., Chan, A.M., Marin, E.C., Rohlfing, T., Maurer, C.R., Jr., and Luo, L. (2007). Comprehensive maps of Drosophila higher olfactory centers: spatially segregated fruit and pheromone representation. Cell 128, 1187-1203.
Kasuya, J., Ishimoto, H., and Kitamoto, T. (2009). Neuronal mechanisms of learning and memory revealed by spatial and temporal suppression of neurotransmission using shibire, a temperature-sensitive dynamin mutant gene in Drosophila melanogaster. Frontiers in Molecular Neuroscience 2, 11.
Keene, A.C., and Waddell, S. (2007). Drosophila olfactory memory: single genes to complex neural circuits. Nat. Rev. Neurosci. 8, 341-354.
Krashes, M.J., Keene, A.C., Leung, B., Armstrong, J.D., and Waddell, S. (2007). Sequential use of mushroom body neuron subsets during Drosophila odor memory processing. Neuron 53, 103-115.
Krause, E.T., Kruger, O., Kohlmeier, P., and Caspers, B.A. (2012). Olfactory kin recognition in a songbird. Biology Letters 8, 327-329.
Lin, H.H., Lai, J.S.Y., Chin, A.L., Chen, Y.C., and Chiang, A.S. (2007). A map of olfactory representation in the Drosophila mushroom body. Cell 128, 1205-1217.
Lin, H.H., Chu, L.A., Fu, T.F., Dickson, B.J., and Chiang, A.S. (2013). Parallel neural pathways mediate CO2 avoidance responses in Drosophila. Science 340, 1338-1341.
Masse, N.Y., Turner, G.C., and Jefferis, G.S. (2009). Olfactory information processing in Drosophila. Curr. Biol. 19, R700-713.
Mennerat, A., Bonadonna, F., Perret, P., and Lambrechts, M.M. (2005). Olfactory conditioning experiments in a food-searching passerine bird in semi-natural conditions. Behavioural Processes 70, 264-270.
Onoda, N., Sugai, T., and Yoshimura, H. (2005). Odor-intensity coding in the anterior piriform cortex. Chem Senses 30, I162-I163.
Peters, R.P., and Mech, L.D. (1975). Scent-marking in wolves. American Scientist 63, 628-637.
Plenderleith, M., van Oosterhout, C., Robinson, R.L., and Turner, G.F. (2005). Female preference for conspecific males based on olfactory cues in a Lake Malawi cichlid fish. Biology Letters 1, 411-414.
Rosell, F., and Sanda, J. (2006). Potential risks of olfactory signaling: the effect of predators on scent marking by beavers. Behav Ecol17, 897-904.
Semmelhack, J.L., and Wang, J.W. (2009). Select Drosophila glomeruli mediate innate olfactory attraction and aversion. Nature 459, 218-223.
Silbering, A.F., Okada, R., Ito, K., and Galizia, C.G. (2008). Olfactory information processing in the Drosophila antennal lobe: anything goes? J. Neurosci. 28, 13075-13087.
Takahashi, Y.K., Kurosaki, M., Hirono, S., and Mori, K. (2004). Topographic representation of odorant molecular features in the rat olfactory bulb. Journal of Neurophysiology 92, 2413-2427.
Tanaka, N.K., Awasaki, T., Shimada, T., and Ito, K. (2004). Integration of chemosensory pathways in the Drosophila second-order olfactory centers. Curr. Biol. 14, 449-457.
Uchida, N., Takahashi, Y.K., Tanifuji, M., and Mori, K. (2000). Odor maps in the mammalian olfactory bulb: domain organization and odorant structural features. Nat Neurosci 3, 1035-1043.
Wang, Y.L., Chiang, A.S., Xia, S.Z., Kitamoto, T., Tully, T., and Zhong, Y. (2003). Blockade of neurotransmission in Drosophila mushroom bodies impairs odor attraction, but not repulsion. Curr. Biol. 13, 1900-1904.
Wang, Y.L., Wright, N.J.D., Guo, H.F., Xie, Z.P., Svoboda, K., Malinow, R., Smith, D.P., and Zhong, Y. (2001). Genetic manipulation of the odor-evoked distributed neural activity in the Drosophila mushroom body. Neuron 29, 267-276.
Yu, D.H., Akalal, D.B.G., and Davis, R.L. (2006). Drosophila alpha/beta mushroom body neurons form a branch-specific, long-term cellular memory trace after spaced olfactory conditioning. Neuron 52, 845-855.