Paula Lindroos

Immunocytochemical localization of histamine in flatworms

SummarySpecific 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-immuno-reactivity 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 nervous system of Tricladida. IV. Neuroanatomy of Planaria torva (Paludicola, Planaridae): an immunocytochemical study

Characters of the nervous system have scarcely been used in consideration of the phylogenetic relationships of the Tricladida. In order to contribute characters toward this end, we studied the nervous system of Planaria torva with immunocytochemical methods and we compare the results with what is known of nervous system structure in other triclads. Antisera against four neuroactive substances were used: neuropeptide F (NPF), RFamide, GYIRFamide, and serotonin (5-HT). All four substances showed positive immunoreactions throughout the nervous system; and the patterns of distribution of the first three were similar, while 5-HT showed a distinct distribution. The organization of these nervous system elements in Planariidae and Dendrocoelidae resembles that of the Maricola but differs from that of the Dugesiidae. The results support the hypotheses that the Paludicola is a more advanced taxon than the Maricola and that the Planariidae and Dendrocoelidae together are a sister group of the Dugesiidae.

The excretory system ofDiphyllobothrium dendriticum (Nitzsch 1824) plerocercoids as revealed by an injection technique

The excretory system ofDiphyllobothrium dendriticum was studied morphologically and functionally. In living plerocercoids, one of the large excretory ducts was injected with latex-based stain. The excretory system was found to consist of a peripheral network of ducts, a central system of two longitudinal ducts, communicating through transverse ducts, a capillary plexus in the scolex and the excretory bladder and pore in the tail. The central and peripheral duct systems were both found to communicate with the capillary plexus in the scolex. In the peripheral network the stain was mainly spread by those contractions of the plerocercoid, which start in the neck region and are propagated through the body. The flow in the central ducts was usually independent of the contractions. Occasional reverse contractions led to a rapid flush in the central ducts. From the peripheral and central ducts the stain was transported out through the excretory bladder and pore. The distributive role of the excretory system is discussed.

Extracellular matrix in some microturbellarians

Electron microscopy was used to study the ECM (extracellular matrix) in the epidermis, brain, and parenchyma of the catenulid turbellarians Stenostomum leucops leucops (Duges) and Stenostomum leucops aquariorum Luther and of the proseriates Archiloa unipunctata (Fabricius) and Promonotus schultzei Meixner. Specimens were fixed with a tannic-acid fixation that enhances staining of extracellular proteins (TARI method) or a conventional electron microscopical method. Differences between species were found in the amount of matrix and extracellular fibrils. In S. leucops leucops the ECM was very sparse, consisting of only a thin electron-dense sheath beneath the epidermis and surrounding neuropil. These sheaths were not found in S. leucops aquariorum which had only rarely encountered extracellular spaces. In P. schultzei and A. unipunctata ECM was more abundant. A. unipunctata had a distinct sheath surrounding the neuropil and a fibrillar subepidermal membrane; the same membranes in P. schultzei appeared only as patches of ECM. In A. unipunctata hemidesmosome-like structures attached the epidermal cells to the underlying membrane, and from these attachments, fibrils projected to the underlying muscle layer. The TARI method revealed exocytotic activity in the brain. The morphology of ECM in these and other flatworms indicate that it could be an internal medium for transport and exchange of substances among cells. Variability in the structure of ECM among species probably does not reflect evolutionary relationships.

The excretory ducts ofDiphyllobothrium dendriticum (Nitzsch 1824) plerocercoids: Ultrastructure and marker distribution

An electron dense marker, lanthanum nitrate, was injected into the excretory ducts of living plerocercoids ofDiphyllobothrium dendriticum and the observations made by electron microscopy. The contractions of the plerocercoid spread the marker into the excretory system, and the distribution was found to be irregular both within the ducts and from one duct to another. Communication between the smallest ducts and the rest of the excretory system was noted. The marker was also introduced from the surrounding medium, in this case the fixative. It was found to flush into the excretory ducts through the pore in the tail and to be distributed into the ducts in the same way as the injected marker. No other pores were observed through the tegument other than the excretory pore in the tail by either method. In ultrastructure the duct wall is similar to that of other cestodes. The distributive role of the excretory system is discussed, including a comparison between the tegument and the duct wall.