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An antiserum raised against the peptide, culetachykinin II, immunocytochemically detected a group of neurosecretory cells in the first flagellar segment of the antennae of both males and females of the mosquito, Culex salinarius. This is the first insect species in which neurosecretory cells have been found in the antennae. The ultrastructure of these antennal neurosecretory cells (ANC) is described, as well as their relationship to other neurons in the antennae and antennal lobe of the mosquito. These tachykinin-reactive cells contain relatively small (140-220 nm) elementary neurosecretory granules. Not only do the ANC have axons that terminate on specific glomeruli of the deutocerebrum, but these neurons also have collaterals that form neurohemal terminals in the receptor lymph channels of the dendrites of the sensory neurons. Thus, the ANC not only influence higher centers of the brain that interpret signals from the antennal sensillae, but also modulate the response of the sensory receptors. To our knowledge, this is the first report of neurosecretory cells directly affecting the signal reception of sensory neurons.

Ultrastructural analysis of the corpora cardiaca of the stable fly, Stomoxys calcitrans, and the tsetse fly, Glossina morsitans, revealed the presence of elementary neurosecretory granules (ENG) unique to the intrinsic neurosecretory cells (INC) of these species. In addition to electron-dense spheres, the INC of the corpus species. In addition to electron-dense spheres, the INC of the corpus cardiacum of the stable fly contain electrondense angular granules, either square or rectangular in shape, while the INC of the tsetse fly contain electron-dense spindle-shaped ENG. The distinctive granules of these INC can be traced within nerves to their sites of storage and release, eliminating the need for labeling with artificial probes. Although the INC of the corpus cardiacum of most species have been found to be fuchsinophilic, neither the INC of the stable fly nor the tsetse fly are aldehyde-fuchsinophilic. These peptigenic cells offer neuroendocrinologists a unique opportunity to study the physiology and biochemistry of neurosecretory cells.

Three myotropic peptides belonging to the Arg-amide insect tachykinin family were isolated from whole-body extracts of the mosquito, Culex salinarius. The peptides, APSGFMGMR-NH2, APYGFTGMR-NH2 and APSGFFGMR-NH2 (designated culetachykinin I, II, and III) were isolated and purified on the basis of their ability to stimulate muscle contractions of isolated Leucophaea maderae hindgut. Biologically inactive methionine sulfoxides of two of the three peptides were isolated using an ELISA system based upon antiserum raised against APYGFTGMR-NH2 and identified with mass spectrometry. Immunocytochemistry localized these peptides in cells in the brain, antennae, subesophageal, thoracic and abdominal ganglion, proventriculus and midgut. Nerve tracts containing these peptides were found in the median nerve of the brain, central body, nervi corpus cardiaci, cervical nerve, antennal lobe and on the surface of the midgut.

Antiserum against testis ecdysiotropin isolated from the gypsy moth, Lymantria dispar, reacted with neurons in the protocerebrum, optic and antennal lobes, subesophageal, thoracic and abdominal ganglia, as well as in nerve tracts extending through the optic lobes, tritocerebrum, and interganglionic connectives of the pupal stage of these insects. Testis ecdysiotropin is a peptide required by immature moths to initiate production of testes ecdysteroid, which is necessary for the development of the male reproductive system and initiation of spermatogenesis. Antiserum against testis ecdysiotropin also detected an accumulation of testis ecdysiotripic-like material between the inner and outer testis sheaths of pupae. The localization of this peptide in the imaginal disks of the last larval stage, cells and nerve fibers in the optic and antennal lobes of the pupa of both sexes, as well as in the testes during development of the adult reproductive system indicates that testis ecdysiotropin has a much larger impact on adult metamorphosis than development of the reproductive system and initiation of gametogenesis. Although this peptide may have a modulatory role in the central nervous system (CNS), it may also initiate a cascade of activity required for the development of the adult nervous system, in addition to its role in reproduction.