No abstract

Interactions among different neuronal circuits are essential for adaptable coordinated behavior. Specifically, higher motor centers and central pattern generators (CPGs) induce rhythmic leg movements that act in concert in the control of locomotion.Here we explored the relations between the subesophageal ganglion (SEG) and thoracic leg CPGs in the desert locust. Backfill staining revealed about 300 SEG descending interneurons (DINs) and some overlap with the arborization of DINs and leg motor neurons. In accordance, in in-vitro preparations, electrical stimulation applied to the SEG excited these neurons, and in some cases also induced CPGs activity. Additionally, we found that the SEG regulates the coupling pattern among the CPGs: when the CPGs were activated pharmacologically, inputs from the SEG were able to synchronize contralateral CPGs. This motor output was correlated to the firing of SEG descending and local interneurons. Altogether, these findings point to a role of the SEG in both activating leg CPGs and in coordinating their oscillations, and suggest parallels between the SEG and the brainstem of vertebrates.

The neural control of insect locomotion is distributed among various body segments. Local pattern-generating circuits at the thoracic ganglia interact with incoming sensory signals and central descending commands from the head ganglia. The evidence from different insect preparations suggests that the subesophageal ganglion (SEG) may play an important role in locomotion-related tasks. In a previous study, we demonstrated that the locust SEG modulates the coupling pattern between segmental leg CPGs in the absence of sensory feedback. Here, we investigated its role in processing and transmitting sensory information to the leg motor centers and mapped the major related neural pathways. Specifically, the intra- and inter-segmental transfer of leg-feedback were studied by simultaneously monitoring motor responses and descending signals from the SEG. Our findings reveal a crucial role of the SEG in the transfer of intersegmental, but not intrasegmental, signals. Additional lesion experiments, in which the intersegmental connectives were cut at different locations, together with double nerve staining, indicated that sensory signals are mainly transferred to the SEG via the connective contralateral to the stimulated leg. We therefore suggest that, similar to data reported for vertebrates, insect leg sensory-motor loops comprise contralateral ascending pathways to the head and ipsilateral descending ones.

Honeybees use their visual flow field to measure flight distance. It has been suggested that the experience of serial landmarks encountered on the flight toward a feeding place contributes to distance estimation. Here, we address this question by tracing the flight paths of individual bees with a harmonic radar system. Bees were trained along an array of three landmarks (tents), and the distance between these landmarks was either increased or decreased under two test conditions. We find that absolute distance estimation dominates the search for the feeding place, but serial position effects are also found. In the latter case, bees search only or additionally at locations determined by serial experience of the landmarks.

30Interactions among different neuronal circuits are essential for adaptable 31 coordinated behavior. Specifically, higher motor centers and central pattern generators 32 (CPGs) induce rhythmic leg movements that act in concert in the control of locomotion. 33Here we explored the relations between the subesophageal ganglion (SEG) and thoracic 34 leg CPGs in the desert locust. Backfill staining revealed about 300 SEG descending 35 interneurons (DINs) and some overlap with the arborization of DINs and leg motor 36 neurons. In accordance, in in-vitro preparations, electrical stimulation applied to the SEG 37 excited these neurons, and in some cases also induced CPGs activity. Additionally, we 38 found that the SEG regulates the coupling pattern among the CPGs: when the CPGs were 39 activated pharmacologically, inputs from the SEG were able to synchronize contralateral 40CPGs. This motor output was correlated to the firing of SEG descending and local 41 interneurons. Altogether, these findings point to a role of the SEG in both activating leg 42CPGs and in coordinating their oscillations, and suggest parallels between the SEG and 43 the brainstem of vertebrates. 44 45 46