Synaptic input from serial chordotonal organs onto segmentally homologous interneurons in the grasshopper Schistocerca gregaria

We investigated the synaptic inputs from the serially homologous pleural, tympanal and wing-hinge chordotonal organs onto a set of identified homologous interneurons (714, 539, 529) in the ventral nerve cord of the grasshopper Schistocerca gregaria. Cobalt backfills show that afferents from all chordotonal organs project into stereotypic tracts in the central nervous system in which intracellular staining reveals the interneurons to have dendritic arborizations. Neuron 714 was found to receive excitatory bilateral synaptic input from all the serial chordotonal organs tested, from the second thoracic segment down to the seventh abdominal segment. Neuron 531, by contrast, only receives input from the chordotonal afferents on the first abdominal segment; those on the axon side are excitatory, while those on the soma side are inhibitory. The pattern of chordotonal input onto neuron 529 is similar to that seen for neuron 714, with the exception that neuron 529 receives no input from the forewing chordotonal organs. The pattern of afferent connectivities onto neurons 714, 531 and 529 differs with respect to those afferents which synapse directly or indirectly with the respective neuron. The synaptic inputs demonstrate a segmental specialization in the chordotonal system and thereby offer an insight into information processing in a modular sensory system.