| Animals that plume track have developed navigational strategies that optimize the ability to track an odor to its source. This movement is an active part of the olfactory experience. For vertebrates, sniffing is also an active part of the olfactory experience that controls the speed and regularity of odor interactions with the olfactory receptors. This sniffing is coincident with locomotion throughout the environment and head movement back and forth across an odor plume. Similarly, moths actively beat their wings as they encounter odor plumes. In Manduca sexta, this wing beating influences speed and regularity of olfactory input in such a way that odor processing and perception are enhanced. While it is clear that the antennal lobe (AL) of M. sexta has evolved to process these naturally encountered olfactory stimuli, there may be a source of input that optimizes processing only when odor is sampled through wing beating. In other sensory systems, corollary discharge (CD) mechanisms have evolved to enhance sensory processing when the sensory input is caused by an animal's own muscle movement, termed reafference. These CD circuits exhibit a functional neural connection, either direct or indirect, between the sensory system and the motor system that caused the reafference. In M. sexta, there is a candidate pair of histamine (HA) immunoreactive neurons that project from the mesothoracic ganglia to the ALs. The goal of this study was to functionally characterize the role of HA signaling within the AL of M. sexta using pharmacological injections and behavioral detection assays. Here we have shown that pharmacological disruption of normal histamine signaling within the AL reduces sensitivity. This provides the first functional characterization of an olfactory CD circuit that uses flight-motor information to mediate olfactory sensitivity. |
