Suboesophageal neurons involved in head movements and feeding in locusts

Abstract

The projections of nerves 6 and 7 of the locust [Locusta migratoria] subesophageal ganglion (SOG) were stained by axonal filling with cobalt chloride. Nerve 6 contains 2 motorneurons which innervate neck muscles 50 and 51. Sensory neurons innervating hairs on the dorso-occipital region of the head also enter the ganglion through nerve 6 and terminate in a small bilateral plexus. The projections of the head hairs in nerve 6 do not overlap the arborizations of the motorneurons or the neurons of nerve 7, but lie in the same area as descending sensory neurons from wind-sensitive hairs of the front of the head. One branch of nerve 7 (7 B) contains 2 fibers which innervate the salivary gland. These salivary neurons (labeled SN1 and SN2) have their cell bodies in the ganglion. The 2nd branch, 7 A, contains sensory neurons from the submentum of the labium, which form 4 sensory plexuses, 2 dorsal and 2 ventral. The sensory plexuses from the submentum have specific regions of overlap with the salivary neurons and with the neck muscle motorneurons. These are interpreted as indicating a flow of information from labial receptors signalling head and mouthpart movement to neurons involved in salivation and head movement. The anatomical separation of the various sensory plexuses is probably indicative of functional localization within the ganglion.