Auditory neurons in the ventral cord of the locust: Morphological and functional properties

Abstract

1. An extracellular recording and staining technique has been used to study the structure of individual ventral-cord elements in the auditory pathway ofLocusta migratoria. 2. Three groups of auditory ventral-cord neurons can be distinguished: (a) neurons ascending to the supraesophageal ganglion, (b) T-shaped neurons, and (c) neurons limited to the thoracic ventral cord. 3. The ventral-cord neurons ascending to the supraesophageal ganglion link the auditory centers of the thorax to those of the supraesophageal ganglion. These are, at least in part, richly arborized neurons of large diameter. 4. The ventral-cord neurons with T structure send equivalent signals along both arms of the T; they resemble the neurons of the first group in that they make synaptic connections in the supraesophageal ganglion, but they also conduct auditory information to caudal regions of the thorax via the descending trunk of the axon. 5. In the supraesophageal ganglion there are several extensive projection areas of the auditory ventral-cord neurons. No direct connections to the mushroom bodies, the central body or the protocerebral bridge could be demonstrated. 6. The thoracic ventral-cord neurons act as “short” segmental interneurons, providing a connection between the tympanal receptor fibers and the ascending and T-shaped ventral-cord neurons. They play a crucial role in auditory information processing. 7. The possible functional properties of the various morphological sections of the auditory ventral-cord neurons are discussed, with reference to their connections with motor and other neuronal systems.