NEURONAL PATHWAYS OF CLASSICAL CRUSTACEAN NEUROHORMONES IN THE CENTRAL-NERVOUS-SYSTEM OF THE WOODLOUSE, ONISCUS-ASELLUS (L)

Neuropeptide-immunoreactive neurons have been mapped by immunocytochem istry in whole-mount preparations and sections of the central nervous system of Oniscus asellus. We tested rabbit antisera against decapod c rustacean hyperglycemic hormone (CHH), moult inhibiting hormone (MIH), pigment dispersing hormone (PDH) and red pigment concentrating hormon e (RPCH). Four CHH- and three PDH-immunoreactive neurons localized in the superior median protocerebrum of the brain constitute neurosecreto ry pathways to the neurohaemal sinus gland. No immunoreactive structur es have been detected with an antiserum against MIH of Carcinus maenus . Another, newly identified neurosecretory pathway is formed by a grou p of RPCH-immunoreactive neurons in the mandibular ganglion. These neu rons project to the neurohaemal lateral cephalic nerve plexus. Further PDH- and RPCH-immunoreactive neurons and fibres occur in the brain an d the ventral nerve cord (VNC). Two groups of PDH-immunoreactive neuro ns supply brain and optic lobe neuropils, the bases of the ommatidia, and probably give rise to descending fibres innervating all VNC-neurop ils. Two groups and five individuals of RPCH-immunoreactive neurons th at innervate several brain neuropils or occur as ascending neurons in the VNC have been reconstructed. The CHH-immunoreactive neurons, and d istinct types of PDH- and RPCH-immunoreactive neurons obviously belong to classical hormone-producing neurosecretory pathways. At least the CHH-immunoreactive cells seem to be part of an isopod homologue of the decapod X-organ. The existence of other PDH- and RPCH-immunoreactive interneurons suggests additional functions of these peptides as neurot ransmitters or neuromodulators, which is in agreement with similar obs ervations in the decapod central nervous system.