Daichi Yamada1), Eriko Matsuo1), Yuki Ishikawa1), Hiroshi Ishimoto1), Azusa Kamikouchi1),2)

1) Graduate School of Science, Nagoya University
2) KAKENHI (25115007, 25640010, 25710001), PREST from JST, the Human Frontier Science Program

In vertebrates and insects, sound plays essential roles to detect the external environment and to communicate with each other. The fruit fly, an excellent model animal to study how hearing works, detects sound, gravity and wind with Johnston's organ (JO), the antennal ear of flies. The sensory neurons in JO (JO neurons) can anatomically be divided into five subgroups, A to E (Kamikouchi et al, 2006). Of these subgroups -A and -B neurons reportedly respond respectively to high (peak at 400 Hz) and low (< 100 Hz) frequencies of the antennal vibration, whereas the C and E neurons are activated by anterior and posterior deflection of the antennal receiver, respectively (Kamikouchi et al, 2009; Yorozu et al, 2009). The response characteristics of subgroup-D neurons, on the contrary, have not yet been clarified.
To elucidate the physiological property of subgroup-D neurons, we established a method to monitor neural activity in the axons of subgroup-D neurons distributed in the AMMC zone D in a fly brain. Calcium imaging of subgroup-D neurons while actuating the antennal receiver revealed that subgroup-D neurons respond selectively to (1) vibrations of middle-range frequencies, which peaks around 200 Hz, and (2) a static deflection of the antenna only toward the anterior side of the fly. These findings clearly showed that the AMMC zone D, the projection target of subgroup-D JO neurons, is a primary center for the antennal vibrations and deflection in the fly brain. Previous studies had shown that subgroups of JO neurons other than D neurons strongly respond to either vibrations or deflection. Subgroup-D neurons thus are a unique primary center for JO, which responds to both vibrations and static deflection of the antenna. These results suggest that subgroup-D JO neurons would be involved in the neural circuits that process (1) the wing beat, which includes the fly's courtship song, and (2) the anterior movement of the antenna.