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Substance P immunoreactivity (SP-IR) was detected in the nervous system of the gull-tapeworm Diphyllobothrium dendriticum. The distribution of the SP-IR neurons in the plerocercoid differs from that of other peptidergic and aminergic neurons in the worm. As well as occurring in the ganglionic commissure and along the two main nerve cords, SP-IR neurons are located laterally to the main nerve cords but not dorsally or ventrally. The SP-IR neurons have projections extending to the surface. Bipolar SP-IR neurons with processes to the surface also occur in the tip of the scolex. A sensory function for the SP-IR neurons is suggested.

Basic fibroblast growth factor immunoreactivity (bFGF-IR) was detected in a specific set of nerve cells in the central nervous system of the gull-tapeworm Diphyllobothrium dendriticum (Cestoda)--an obligatory endoparasite. The long varicose processes of the bFGF-IR neurons extend along the two main nerve cords, which contain an actively growing population of nerve cells. A neurotrophic function for the bFGF-like material is proposed. The adult tapeworm lives in the intestine of a homeothermic host and has a pattern of very active and never ending growth. The larval stages live in poikilothermic hosts and grow very slowly. The bFGF-IR nerve cells occur both in II stage larvae and in adult worms. Thus, no correlation between the presence of bFGF-IR and the general growth rate of the worm was found. Western blot analysis revealed the presence of an anti-bFGF immunoreactive peptide with a molecular mass of 47 kDa in both larval and adult worms.

A new method for making whole-mount immunocytochemical preparations of thick-skinned tapeworms is described. The tough tegument of the worms, which is impermeable to primary and secondary antisera, is removed by placing live worms in distilled water for 5-8 h, during which period the tegument is shed. The worms are thereafter fixed and stained as whole specimens using fluorescence immunocytochemical techniques. Both the main nervous structures and the finest neuronal details are revealed by this technique. Several types of antisera combinations are used. Diphyllobothrium dendriticum and Eubothrium crassum served as model organisms in this study.

In the central and peripheral nervous system of larval and adult Diphyllobothrium dendriticum, catecholamines were detected using the glyoxylic acid-induced fluorescence method. High-pressure liquid chromatography (HPLC) analysis revealed the presence of dopa (about 65 ng/g fresh weight) and dopamine (5 ng/g fresh weight).

Specific antibodies against histamine were used to demonstrate the occurrence and cellular distribution of histamine-like immunoreactivity in three species of flatworms (phylum Platyhelminthes). In the parasitic cestode Diphyllobothrium dendriticum, histamine-reactivity was found in neurons of the main nerve cords, and in cells lining the central and peripheral excretory ducts. In the free-living microturbellarian Microstomum lineare and in the planarian Polycelis nigra, histamine-immunoreactivity was restricted to cells and fibres of the nervous system. The occurrence of histamine or a related substance in the nervous system of flatworms, which represent primary bilateria, indicates the importance of this neuroactive substance in the animal kingdom.

The mode of growth of the populations of cells within and immediately surrounding the main lateral nerve cords in the actively growing, immature Diphyllobothrium dendriticum was studied by the use of 3H-thymidine autoradiography. The population of nerve cells within the nerve cord grows only on account of cell migration from the surrounding parenchyma. No mitotic figures were observed in the nerve cords. The rate of growth is high. Within a period of cultivation for 2 days in hamster 34% of the nerve cells within the nerve cords have arrived from the parenchyma. These cells can be considered as cells at the starting point for differentiation into nerve cells. The protective layer of binding cells around the nerve cords also grows on a-count of cells migrating from the parenchyma. The binding cells actively move from the outer regions of the layer inwards close to t-e nerve cord. As stem cells for these types of cell differentiation serve the highly basophilic, actively dividing germinative cells.

Cytodifferentiation in the neck region of adult D. dendriticum was studied. The highly basophilic germinative cells were found to differentiate into glycogen-containing parenchyma cells and three types of muscle cells. The cytodi-ferentiation was followed with the aid of 3H-thymidine. The differentiation potential of the germinative cells is discussed.

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.

The present immunocytochemical study concerns the distribution of four neuropeptides, FMRF-amide, vasotocin, leu-enkephalin and neurotensin, and of the bioamine serotonin in the plerocercoid larva of Diphyllobothrium dendriticum. Anti-FMRF-amide and vasotocin-reactivity occurs in perikarya and nerve fibres in the CNS and PNS of this worm. The peptide-containing fibres surround and seem to innervate the musculature and to terminate beneath the basal lamina of the tegument at the inner surface of the bothridia, suggesting a neurotransmitter function. Anti-leu-enkephalin reaction occurs in perikarya and fibres in the main nerve cords and in the PNS. Anti-neurotensin reactive fibres were observed in the neuropile of the nerve cords. Serotonin immunoreactivity was found in neurons in the ganglionic commissure of the brain and along the main nerve cords. This study is the first immunocytochemical identification of neuropeptides and serotonin in a parasitic flatworm and the information gained may be of importance for the development of new antihelminthics.

In the nervous system of adult Schistosoma mansoni, neuropeptides and serotonin were demonstrated immunocytochemically. Neurons and nerve fibers immunoreactive to anti-FMRF-amide, anti-substance P, anti-leu-enkephalin, and anti-growth hormone releasing factor were found in the central and peripheral nervous system. The peptidergic nerve cell bodies in the bilobed brain are large and often multipolar; those in the peripheral nerve net are smaller and often bipolar. Sensory receptors of two morphologically different types were found along the surface of the worm. They are mainly immunoreactive to anti-substance P and anti-leu-enkephalin, and, to a lesser degree, to anti-FMRF-amide. Serotonin-immunoreactive fibers are found in the central and peripheral nervous elements as well as in sensory endings.

The release of neurosecretory material was studied in the cestode tapeworm Diphyllobothrium dendriticum. In plerocercoid larvae cultivated in vitro the neurosecretory vesicles release their content by way of protrusions extending through the axolemma into the intercellular space. The released material is directed predominantly towards the muscles. No omega figures were detected. The significance of this new type of release is discussed.

Neurons immunoreactive to small cardiac peptide B (SCPb) occur in the scolex and neck region of adult Diphyllobothrium dendriticum. The localisation of the SCPb-IR neurons in the peripheral nervous system is very pronounced; they are closely associated to the bothridial musculature in the scolex. SCPb-IR neurons were not observed in plerocercoid larvae but appeared after cultivation in vitro at 37 degrees C for 30 h. Functional and developmental aspects of the SCPb-IR neurons are discussed.

The effect of the antihelminthic substance Praziquantel on the peptidergic nervous system in the adult gull-tapeworm Diphyllobothrium dendriticum was tested. As well as increasing muscle contraction the drug provoked a fall in the amount and size of the peptidergic nerve terminals in the subtegumental region. The number of small clear vesicles in the terminals also fell.