The bimodal auditory-vibratory system of the thoracic ventral nerve cord in Locusta migratoria (Acrididae, Locustinae, Oedipodini)

Abstract

In locusts the auditory receptors of the tympanal organs and many of the vibratory receptors of all 6 legs converge at the level of the thoracic ventral nerve cord, forming a combined auditory-vibratory sensory system; it is represented by the VS-, S-, and V-neurons ascending to the supraesophageal ganglion. The connections between vibratory receptors of the different legs and the dendritic inputs of the bimodal ascending neurons are investigated in this report. As an example, the dendritic branches of the G- and V3-neurons for auditory and vibratory input could be localized by simultaneous recording at 2 different positions of the axon. The vibratory input from the receptors of the different legs was determined. Segmental and/or intersegmental thoracic interneurons are intercalated between the receptors and the ascending auditory-vibratory neurons (G- and V3-neurons). The morphology and function of 2 intersegmental vibratory interneurons (VI1- and VI2-neurons) are described. They probably connect the vibratory receptors of 1 (or 2) leg(s) of 1 thoracic segment with the different bimodal auditory-vibratory neurons. The importance of the anterior Ring Tract for synaptic connection between receptor cells, first order interneurons, and bimodal auditory-vibratory neurons is discussed on the basis of morphological and physiological data.