Inhibitory motor neurones supply body wall muscles in the locust abdomen

Inhibitory motor neurones in the abdominal ganglia of the locust Locusta migratoria were identified by combining extra- and intracellular electrophysiology, labelling of motor neurones by peripheral nerve backfills, and immunocytochemistry directed against the inhibitory transmitter gamma-aminobutyric acid. The fifth and sixth abdominal ganglia were studied in particular detail, although general findings were verified in all other abdominal segments. In each abdominal ganglion half, there are two inhibitory motor neurones, CIa and CIb, which supply dorsal (CIa) and ventral (CIb) longitudinal muscles. Their cell bodies are located in the next anterior ganglion to where the axons leave the ventral nerve cord via nerve 1. Both inhibitors have contralateral somata in the posterior ventral soma cortex, looping primary neurites and bilateral dorsal arborisations. There are homonomous (segmentally homologous) motor neurones in the fused abdominal neuromeres, the thoracic ganglia, and at least the third subesophageal neuromere. These body wall inhibitors are distinctly different from the limb muscle inhibitors, CI(1-3), described previously. This is signified, for example, by the fact that both types of inhibitory motor neurones coexist in the prothoracic segment and innervate leg and body wall muscles, respectively.