Molecular Medicine Israel

A simple memory circuit in the fruit fly could serve as a model for human brain disorders

Proceedings of the National Academy of Sciences USA 108, 13794–13799 (2011). Doi: 10.1073/pnas.1019483108.
Lee, P.-T., Lin, H.-W., Chang, Y.-H., Fu, T.-F., Dubnau, J., Hirsh, J., Lee, T. & Chiang, A.-S.
Serotonin–mushroom body circuit modulating the formation of anesthesia-resistant memory in Drosophila”.

A type of olfactory learning in the fruit fly Drosophila is modulated by just two neurons, a research team led by Ann-Shyn Chiang of the National Tsing-Hua University, Taiwan reports. Odors are encoded by two distinct mechanisms in Drosophila. One depends on the amnesiac gene and is blocked by anesthetics, while the other requires the radish gene and is resistant to anesthesia.

Chiang and his colleagues found that inhibiting serotonin synthesis in normal flies suppressed anesthesia-resistant, but not anesthesia-sensitive, olfactory memory. They also found that reducing serotonin synthesis produced memory deficits like those observed in radish mutant flies. In contrast, feeding the flies a serotonin precursor enhanced anesthesia-resistant memory such that they learned to associate an odor with an electric shock after they were presented together just once.

Reducing expression of specific serotonin receptors in subsets of neurons also revealed that anesthesia-resistant memory requires the actions of serotonin on α/β neurons in a structure called the mushroom body. Further experiments showed that anesthesia-resistant memory depends upon just two cells, the dorsal paired medial neurons, which release serotonin into all the lobes of the mushroom body.

This circuit could serve as a simple model of human memory disorders, and will enable researchers to better understand how memory systems interact.



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