FMRFamide-related
peptides of insects are particularly important because of their possible function as
neurohormones and
neuromodulators on a wide variety of tissues. Part of this study was an investigation of the immunofluorescent staining of motor nerves which arise in the metathoracic
ganglion, examined in wholemount using an antiserum that recognizes extended -
RFamide peptides (generally recognized to be of the
FMRFamide family). This antiserum revealed immunochemical staining of numerous cell bodies in the metathoracic
ganglion and of axons in peripheral nerve 5, a large nerve which contains both motor and sensory fibres. Axons staining positive for
FMRFamide-related
peptides were traced in nerve 5 as far as the femur-tibia joint, and into the first (sensory-motor) and third (motor only) ramus of nerve 5. Reverse-phase HPLC with radioimmunoassay revealed a peak of
FMRFamide-related
peptide activity in nerve 5 that was coincident with a peak found when thoracic ganglia were processed in the same fashion. A physiological assay was devised to test the ability of various non-native
peptides to alter the characteristics of contraction of skeletal muscles of the legs. Using neurally evoked contractions of coxal depressor muscles of the metathoracic leg it was determined that several non-native
peptides could potentiate muscle contractions. The results of this study suggest that muscles of the legs receive innervation by identifiable,
FMRFamide-related
peptide-containing neurons and that the release of
peptide(s) at the muscle may be yet another method of modulating the mechanics of muscle contraction.