Abstract
Flies can sense humidity changes and run toward dry environment. Except knowing intact third antenna segment is necessary for normal hygrosensory behavior, neural circuits orchestrating hygrosensory behaviors are largely unknown. Combining functional imaging and neurogenetic behavior manipulation, we found a group of bipolar hygrosensory neurons (HSNs) with cell bodies located at the third antenna segment. These HSNs connect three sacculus chambers (chamber I, chamber II, and chamber III) on the antenna to three ventral posterior regions (VP1, VP2 and VP3) in the brain. Each bipolar HSN gives a single dendrite within a sensillum in the sacculus at one end and gives axonal terminals in the ventral posterior (VP) region of the antennal lobe at the other end. Initial MARCM analysis suggests a stereotyped connection between sacculus chambers and VP region. Next, combining PaGFP tracing and functional imaging, we identified four types of projection neurons (PNs) connecting VP regions to higher brain centers including calyx, lateral horn, superior dorsal frontal protocerebrum, superpeduncular protocerebrum, ventral lateral protocerebrum, and caudo-ventrolateral protocerebrum. All these HSNs and VP PNs were sensitive to humidity changes. Our study revealed a hygrosensory system in Drosophila.