On August 8, 2018, a research team led by Professor Yi Zhong from School of Life Sciences and IDG/McGovern Brain Institute at Tsinghua University published a research article entitled Fan-Shaped Body Neurons in the Drosophila Brain Regulate Both Innate and Conditioned Nociceptive Avoidance in Cell Reports, reporting an important role of Drosophila Fan-shaped Body (FB) neurons in nociceptive avoidance.
The living environment for animals is complicated and dangerous. If there is no effective escaping mechanism to avoid noxious stimuli, it is hard for animals to survive. The avoidance of noxious stimuli consists of two parts, one is the innate avoidance, such as escaping after being stabbed by a sharp object, or burning; the other is the conditioned avoidance. For example, once a mouse receives electric shocks in room A which is not a dangerous room at first, it will couple the room A with electric shock damage. Even if there is no electric shock in room A later, it will still avoid the room as it has the electric shock.
Two kinds of nociceptive avoidance behaviors also exist in fruit flies. Previous studies in fruit flies mainly focused on the peripheral nervous system, and little is known about how the central nervous system processes nociceptive information and guides avoidance behavior. The authors set up an automatic stimulation equipment and living Calcium imaging recording device based on two-photon microscopy. The living brain of the transgenic fly with the calcium ion indicator protein GCaMP3 was dissected and the response to noxious electric shock stimulation was recorded. The results showed that the Fan-shaped Body (FB) located in the middle of the brain responded strongly to such noxious stimuli. Since the FB is a complex multi-layer structure, the authors further investigated electric shock-induced response in different FB layers using multiple Gal4 lines. The data showed that different FB layers responded differently to the electric shock, and the responses of the ventral layers were higher than the dorsal layers.
Fig 1 In vivo Calcium recording
Do such shock-induced responses play a role in the nociceptive avoidance behavior of Drosophila? The authors conducted behavioral experiments to explore this question. The FB neurons were found to be necessary to avoid the noxious electrical stimulation or noxious thermal stimulation. In addition, if it is not a noxious stimulus (for example, if the fly meets a disgusting smell), the avoidance behavior was not affected by the activity of FB neurons. Flies also avoided the area where the FB neurons were artificially activated, and this "avoidance" can be conditionally learned. Moreover, the author found that the FB not only participates in the innate avoidance, but also participates in the conditioned avoidance. In such behavior experiments, the flies learn to avoid an odor coupled with noxious electrical stimulation. Activity of FB neurons were found to be required in such avoidance behavior. Interestingly, different FB layers had different roles in both innate and conditioned avoidance behaviors.
Fig 2 Different FB layers take part in different avoidance behaviors
Dr. Wantong Hu, Yiqing Peng, and Jiameng Sun at the School of Life Sciences at Tsinghua University, are the co-first authors of this article. Dr. Qian Li and Dr. Yi Zhong are correspondence authors of this article. Fang Zhang, Dr. Xuchen Zhang, Lianzhang Wang, Bohan Zhao also contributed to this study. This work was supported by grants from the National Natural Science Foundation of China, the National Basic Research Project (973 program) of the Ministry of Science and Technology of China and the Tsinghua-Peking Joint Center for Life Sciences.
Paper link: https://www.cell.com/cell-reports/fulltext/S2211-1247(18)31118-5