Immunocytochemical evidence for the presence of "mammalian" neurohormonal peptides in neurones of the tapeworm Diphyllobothrium dendriticum.

In the nervous system of the obligatory endoparasite Diphyllobothrium dendriticum immunoreactivity (IR) to growth hormone-releasing factor (GRF), peptide histidine isoleucine (PHI), bovine pancreatic polypeptide (BPP), gastrin, gastrin-releasing peptide (GRP), oxytocin, FMRFamide (FMRF) and serotonin (5HT) was demonstrated by immunocytochemical methods. A very strong GRF-IR was observed in the CNS and PNS of larvae and of the constantly growing adult worms. GRF-IR axon terminals occur beneath the basal lamina of the tegument along the inside of the bothridia, the holdfast organ of the worm. GRF-IR fibres surround the yolk producing vitelline glands and occur in the wall of the vagina. PHI-IR was observed in the CNS and PNS of larvae and adult worms. PHI-IR terminals occur beneath the basal lamina of the tegument along the strobila, the nutrient absorbing surface of the worm. PHI-IR fibres seem to innervate the testicular follicles. FMRF-IR fibres and perikarya occur close to the vitelline glands and the uterine pore and in the male copulatory organ. Numerous large 5HT-IR perikarya with long varicose fibres were observed in the nervous system of the worm. 5HT-IR perikarya occur close to the genital atrium. D. dendriticum is the phylogenetically lowest organism in which IR to PHI has been demonstrated.