Corazonin and corazonin-like substances in the central nervous system of the Pterygote and Apterygote insects

Antisera against corazonin were used to investigate distribution of immunoreactive cells in the central nervous system (CNS) of representatives of six insect orders: Ctenolepisma lineata (Zygentoma), Locusta migratoria (Orthoptera), Oxya yezoensis (Orthoptera), Gryllus bimaculatus (Orthoptera), Pyrrhocoris apterus (Hemiptera), Arge nigrinodosa (Hymenoptera), Athalia rosae (Hymenoptera), Bombyx mori (Lepidoptera) and Anomala cuprea (Coleoptera). Corazonin-like immunoreactive (CLI) cells were detected in the brain and ventral ganglia of all insects studied except for the albino strain of L. migratoria and the beetle A. cuprea. Implantation of the brain or different ganglia from insects with detected immunoreactivity induced dark coloration in the albino locust, providing further evidence for the presence of authentic corazonins His(7)- and Arg(7)-isoforms] in these insects. The protocerebral lateral neurosecretory cells projecting into the ipsilateral retrocerebral neurohemal organs and bilateral longitudinal tracts extending and branching throughout the entire CNS seem to be a well-conserved part of the corazonin system in insects. The bilateral longitudinal tracts were formed by species-specific numbers of bilateral interneurons segmentally distributed in the ventral ganglia. Additional immunoreactive somata, mostly interneurons, were detected in the CNS of various insects. The distribution of corazonin in the cephalic neurosecretory system and in the bilateral interneurons suggests that corazonin acts as a hormone as well as a neurotransmitter or a neuromodulator. An ancient origin of corazonin is suggested by the presence of a corazonin-like substance in the primitive insect, C. lineata. These results support previous findings on the common occurrence of corazonin among insects, except for the albino strain of L. migratoria and the Coleoptera.