Distribution of myomodulin‐like immunoreactivity in the adult and developing ventral nervous system of the locust Schistocerca gregaria

The distribution of myomodulin-like immunoreactivity in the ventral nervous system of an insect, the locust Schistocerca gregaria, both in the adult and during development, is described. The results suggest the presence of a novel modulatory system in insects which uses myomodulin-like neuropeptides. The study also indicates that the myomodulins, which were first identified in mollusks, may represent another interphyletic family of neuropeptides. In the suboesophageal ganglion, immunoreactive cells occur in five groups. The processes from the two anterior ventral midline groups of cells project to the corpora allata via nervi corpora allata II. Thus myomodulin-like neuropeptides may be involved in the control of the release of juvenile hormone from the corpora allata. The thoracic ganglia contain three groups of immunoreactive cells, including a bilaterally symmetrical group of 12-15 posterior lateral cells, which project to the median nerve and its neurohaemal organs, suggesting a possible neurohaemal role for myomodulin-like peptides. Each thoracic neuromere also contains a single, intensely stained, dorsal unpaired median (DUM) cell that may correspond to the so-called H cell. In the abdominal ganglia, the staining shows sexual dimorphism, both in terms of the number of dorsal and ventral midline cells stained and in terms of the distribution of their immunoreactive processes. Myomodulin-like immunoreactivity is one of the earliest neurotransmitter/neurohormone phenotypes detectable during the development of the locust nervous system. It first appears in the single DUM cells in each of the thoracic neuromeres at 50% development, and the complete adult pattern of staining is present at 85-90% of development.