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.

Central projection of auditory receptors in the prothoracic ganglion of the bushcricket Psorodonotus illyricus (tettigoniidae): Computer‐aided analysis of the end branch pattern

“…For comparison, the inset shows additionally, a schematic drawing of the projection (re- vealed by circumferences of the projection areas) of seven different functional types of auditory receptor cell in Decticus verrucivorus at a position inside the neuropile, which is 30 pm to the side of the midline ofthe prothoracic ganglion. The projections of the receptor cells of the intermediate organ and cnsta acustica are arranged tonotopically in a counterclockwise manner, which strongly resembles the projection arrangement in the neuropiles of the aRT of locusts (Halex et al, 1988;Bickmeyer et al, 1992). In spite of the different location, development, and construction of the tympanal organ and the truncal vibratory (-auditory) receptors, the similarity in arrangement is obvious.…”

“…However, the auditory receptors of the forelegs in tettigoniids project only to the aRT of the ipsilateral hemiganglion. The receptor cells of the subgenual organ as well as of other vibroreceptors of the forelegs (e.g., campaniform sensillae, femural and tibia1 chordotonal organs) project, as shown for locusts, to lateral parts of the related hemiganglia (Miicke, 199 1;Bickmeyer et al, 1992).…”

“…The manifold different vibroreceptors of all six legs project to neuropiles of the related segment's ipsilateral hemiganglion, situated in the lateral region of the ganglia. From there the input is also transmitted via vibratory interneurons to the neuropiles of the aRT (Bickmeyer et al, 1992). Therefore, the neuropiles of the aRT in the thoracic ganglia of the ventral nerve would appear to be the most important processing centers of the auditory-vibratory sense in locusts.…”

Sound signalling in orthoptera

“…In the metathoracic ganglion, the high frequency afferents project posteriorly to the other three groups of lower frequency (Römer, 1985), each of which projects to a distinct but more anterior region. There appears to be a gradient of decreasing sensitivity to low frequencies both away from the midline and anteriorly (Halex et al, 1988;Bickmeyer et al, 1992). The higher-frequency afferents have a greater anterior projection into the prothoracic ganglion than most of the lower-frequency ones, many of which do not project beyond the mesothoracic ganglion, while others only reach to the metathoracic ganglion.…”

Vibratory interneurons in the non-hearing cave cricket indicate evolutionary origin of sound processing elements in Ensifera

“…On the other hand, only few studies on central processing of vibratory signals of Orthoptera exist that include both physiological and morphological identification of the neurons involved (Č okl et al 1985;Bickmeyer 1991;Bickmeyer et al 1992;Sickmann 1997;Nebeling 2000). Unfortunately, these data are only available from hearing species, which is the reason why no stringent arguments for the proposed homology of the auditory and (part of) the vibratory system are available to date.…”