果蠅腦中，蕈狀體(mushroom body)為一左右對稱結構，每一邊約由2500個Kenyon cell神經細胞所構成，而每邊的蕈狀體結構又可細分為五個部份： γ, α’/β’, pioneer α/β, early α/β, 與late α/β。研究顯示，對於剛孵化的果蠅幼蟲(larvae)餵食羥基□(hydroxyurea)後可以使蕈狀體的結構消失。無蕈狀體結構的果蠅成蟲，一般行為上與正常果蠅無太大差異，但是卻無法經由古典制約來學習，因為少了蕈狀體釋放的神經傳導物質，不利於記憶的形成。果蠅的記憶形成過程可以進一步區分為記憶的獲得，記憶的儲存固化和記憶的讀取。之前的研究顯示中期記憶(MTM)與長期記憶(LTM)的讀取可能都需要來自蕈狀體神經細胞軸突端的神經傳導物質釋放。我們實驗室先前的研究已經獲知阻斷所有蕈狀體的神經傳導會影響記憶的形成。我們現在的研究是更近一步剖析蕈狀體結構中不同的突出分體，在記憶形成過程中扮演的角色。有別於先前在蕈狀體上有關記憶讀取的研究只專注在定義某一蕈狀體神經突出體所扮演的角色，我們的研究是希望能找出所有不同部位的蕈狀體於記憶形成上所扮演的角色。我們發現在中期記憶(MTM)的獲得或讀取時阻斷α’/β’蕈狀體神經的傳導，會影響中期記憶的形成，而阻斷α/β蕈狀體神經傳導只影響中期記憶的讀取。我們的結果暗示了新形成的記憶可能一開始透過蕈狀體的α’/β’突出體獲得資訊，而α’/β’與α/β突出體是記憶讀取所需要的。因此，蕈狀體不同的部份可能在記憶形成的過程中各有用。 　　

The Drosophila mushroom body (MB) contains about 2500 Kenyon cell (KC) neurons in each hemisphere, divided into five groups: the γ, α’/β’, pioneer α/β, early α/β, and late α/β MB neurons. Studies have shown, hydroxyurea, fed to newly hatched larvae, had selectively abolished the MB structure. Adult flies without MB behaved normally in most situations, but were unable to learn under the classical conditioning because the neurotransmitter output from MB is essential for memory formation. The Drosophila memory formation phases can further be dissected into acquisition, consolidation and retrieval phase. Previous studies have suggested that the retrieval of both the middle term memory (MTM) and long term memory (LTM) require the output from MB neurons. In our previous studies, we have known that blocking total MB synaptic outputs abolish memory formation. Our studies further dissect the role of different MB lobes in the memory formation processes. Unlike previous studies about memory retrieval in MB which only define the role of one of specific MB lobes, our studies figure out the roles of all different MB subsets. Blocking α’/β’ subset of MB neurons specifically disrupt MTM acquisition and retrieval, whereas blocking α/β neurons only affecting retrieval of MTM. Our results imply the main function of MB α’/β’ lobes are memory acquisition, whereas both α’/β’ and α/β lobes are essential for memory retrieval. However, different subset of MB neurons may play different role during the memory formation process.

References

1. A. H. Brand, N. Perrimon, Development 118, 401 (1993). Targeted gene expression as a means of altering cell fates and generating dominant phenotypes.
2. de Belle, J.S., and Heisenberg, M. (1994). Associative odor learning in Drosophila abolished by chemical ablation of mushroom bodies. Science New York, NY 263, 692-695. .
3. Dubnau, J., L. Grady, et al. (2001). Disruption of neurotransmission in Drosophila mushroom body blocks retrieval but not acquisition of memory. Nature 411(6836): 476-80. .
4. Isabel, G., A. Pascual, et al. (2004). Exclusive consolidated memory phases in Drosophila. Science 304(5673): 1024-7. .
5. Ito, K., Awano, W., Suzuki, K., Hiromi, Y., and Yamamoto, D. (1997). The Drosophila mushroom body is a quadruple structure of clonal units each of which contains a virtually identical set of neurones and glial cells. Development 124, 761–771. .
6. Joiner, W.J., Crocker, A., White, B.H., and Sehgal, A. (2006). Sleep in Drosophila is regulated by adult mushroom bodies. Nature 441, 757–760. .
7. Kawasaki, F., M. Hazen, et al. (2000). Fast synaptic fatigue in shibire mutants reveals a rapid requirement for dynamin in synaptic vesicle membrane trafficking. Nat Neurosci 3(9): 859-60. .
8. Keene, A. C., M. Stratmann, et al. (2004). Diverse odor-conditioned memories require uniquely timed dorsal paired medial neuron output. Neuron 44(3): 521-33. .
9. Keene, A. C. and S. Waddell (2007). Drosophila olfactory memory: single genes to complex neural circuits. Nat Rev Neurosci 8(5): 341-54. .
10. Kitamoto, T. (2001). Conditional modification of behavior in Drosophila by targeted expression of a temperature-sensitive shibire allele in defined neurons. J Neurobiol 47(2): 81-92. .
11. Krashes, M. J., A. C. Keene, et al. (2007). Sequential use of mushroom body neuron subsets during Drosophila odor memory processing. Neuron 53(1): 103-15. .
12. Lee, T., Lee, A., and Luo, L. (1999). Development of the Drosophila mushroom bodies: sequential generation of three distinct types of neurons from a neuroblast. Development 126, 4065–4076. .
13. Lin, H. H., J. S. Lai, et al. (2007). A map of olfactory representation in the Drosophila mushroom body. Cell 128(6): 1205-17. .
14. Liu, L., Wolf, R., Ernst, R., and Heisenberg, M. (1999). Context generalization in Drosophila visual learning requires the mushroom bodies. Nature 400, 753–756. .
15. McBride, S.M., Giuliani, G., Choi, C., Krause, P., Correale, D., Watson, K., Baker, G., and Siwicki, K.K. (1999). Mushroom body ablation impairs short-term memory and long-term memory of courtship conditioning in Drosophila melanogaster. Neuron 24, 967–977. .
16. McGuire, S. E., P. T. Le, et al. (2001). The role of Drosophila mushroom body signaling in olfactory memory. Science 293(5533): 1330-3. .
17. Pitman, J.L., McGill, J.J., Keegan, K.P., and Allada, R. (2006). A dynamic role for the mushroom bodies in promoting sleep in Drosophila. Nature 441, 753–756. .
18. Sokal, R. R, and Rohlf, F. J. (1981). Biometry, Second Edition (New York: W.H. Freeman and Company). .
19. Tang, S., and Guo, A. (2001). Choice behavior of Drosophila facing contradictory visual cues. Science 294, 1543–1547. .
20. Technau, G., and Heisenberg, M. (1982). Neural reorganization during metamorphosis of the corpora pedunculata in Drosophila melanogaster. Nature 295, 405–407. .
21. Tully, T. and W. G. Quinn (1985). Classical conditioning and retention in normal and mutant Drosophila melanogaster. J Comp Physiol 157(2): 263-77. .
22. Tully, T., T. Preat, et al. (1994). Genetic dissection of consolidated memory in Drosophila. Cell 79(1): 35-47. .
23. Vanderbliek AM, Meyerowitz EM (1991) Dynamin-like protein encoded by the Drosophila shibire gene associated with vesicular traffic. Nature 351:411–414.
24. Waddell, S., J. D. Armstrong, et al. (2000). The amnesiac gene product is expressed in two neurons in the Drosophila brain that are critical for memory. Cell 103(5): 805-13. .
25. Yu, D., D. B. Akalal, et al. (2006). Drosophila alpha/beta mushroom body neurons form a branch-specific, long-term cellular memory trace after spaced olfactory conditioning. Neuron 52(5): 845-55. .
26. Zhu, S., Chiang, A.S., and Lee, T. (2003). Development of the Drosophila mushroom bodies: elaboration, remodeling and spatial organization of dendrites in the calyx. Development 130, 2603–2610.