Neuronal pathways of classical crustacean neurohormones in the central nervous system of the woodlouse, Oniscus asellus (L.)

Neuropeptide-immunoreactive neurons have been mapped by immunocytochemistry in whole-mount preparations and sections of the central nervous system of Oniscus asellus . We tested rabbit antisera against decapod crustacean hyperglycemic hormone (CHH), moult inhibiting hormone (MIH ), pigment dispersing hormone (PDH) and red pigment concentrating hormone (RPCH). four CHH- and three PDH-immunoreactive neurons localized in the superior median protocerebrum of the brain constitute neurosecretory pathways to the neurohaemal sinus gland. No immunoreactive structures have been detected with an antiserum against MIH of Carcinus maenus . Another, newly identified neurosecretory pathway is formed by a group of RPCH-immunoreactive neurons in the mandibular ganglion. These neurons project to the neurohaemal lateral cephalic nerve plexus, further PDH- and RPCH-immunoreactive neurons and fibres occur in the brain and the ventral nerve cord (VNC). Two groups of PDH-immunoreactive neurons supply brain and optic lobe neuropils, the bases of the ommatidia, and probably give rise to descending fibres innervating all VNC-neuropils. Two groups and five individuals of RPCH-immunoreactive neurons that innervate several brain neuropils or occur as ascending neurons in the VNC have been reconstructed. The CHH-immunoreactive neurons, and distinct 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 neurotransmitters or neuromodulators, which is in agreement with similar observations in the decapod central nervous system.

PARAVENTRICULAR—HYPOPHYSIAL NEUROSECRETORY PATHWAYS IN THE GUINEA-PIG

SUMMARY The neurosecretory pathways from the paraventricular (PV) nuclei have been identified in the guinea-pig and plotted according to stereotaxic coordinates for the guinea-pig brain. The magnocellular neurosecretory neurones are concentrated in the lateral tip of the PV nucleus approximately half-way between the third ventricle and the fornix. Some neurosecretory fibres pass between the cranio-ventral extension of the PV nucleus and the supraoptic (SO) nucleus. Neurosecretory fibres leave the rostral region of the main part of the PV nucleus and pass ventral to the fornix, those from the middle region pass both ventral and dorsal to the fornix and those from the caudal region pass mainly dorsal to the fornix. After passing around the fornix, these fibres merge to form a broad band, the paraventricular—hypophysial tract, which curves ventrolaterally and then ventromedially in a gentle arc around the lateral edge of the anterior hypothalamic area and the hypothalamic ventromedial nucleus before turning caudomedially to run over the dorsal surface of the optic chiasma towards the median eminence. Neurosecretory fibres were not observed in the anterior hypothalamic area or in the ventromedial nucleus. An accessory PV nucleus was found dorsolateral to the fornix. Neurosecretory fibres pass over the fornix in both directions between the PV and the accessory PV nuclei, also fibres leave the accessory PV nucleus and pass ventrally to merge with those of the main paraventricular—hypophysial tract.