Primary commissure pioneer neurons in the brain of the grasshopper Schistocerca gregaria: Development, ultrastructure, and neuropeptide expression

The bilaterally paired primary commissure pioneer neurons in the median dom ain of the grasshopper brain are large, descending interneurons that unique ly express the TERM-1 antigen, even in the adult. After pioneering the prim ary interhemispheric brain commissure, these neurons extend TERM-1-immunore active collaterals into most parts of the brain except the mushroom bodies. In this report, the authors show that the TERM-1 antigen is located in the cell body cytoplasm of these neurons and not on the membranes. Screening w ith antisera to insect neuropeptides reveals that an antiserum recognizing peptides of the leucokinin family labels the cell body cytoplasm of the pri mary commissure neurons. Leucokinin-related peptides are known to modulate motility of visceral muscle, play a role in diuresis, and are likely to be neuromodulators in the insect nervous system. The primary commissure neuron s differ ultrastructurally from median neurosecretory cells in that their c ell body cytoplasm is more extensive, contains high numbers of mitochondria and extensive endoplasmic reticulum, but does not contain neurosecretory g ranules. In the adult, the cell somata are enveloped by multiple glia membr anes and associated trophospongia. According to these ultrastructural chara cteristics, the primary commissure pioneers are not classical neurosecretor y cells. J. Comp. Neurol. 430:118-130, 2001. (C) 2001 Wiley-Liss, Inc.