New Gland Type Discovered in Cestodes: Neurosecretory Neurons Release a Secret into the Fish Host.

Free endings of peripheral neurosecretory neurons (NNs) were found in the tegument of plerocercoids of five species of parasitic cestodes of fish in an ultrastructural study. The free terminals secreted vesicles on the tegument surface and into the host body. Secretion was experimentally shown to increase in response to the host fish blood serum. In the cestode body, NNs form paracrine-type contacts near the cell membranes of the frontal glands, the tegument, and muscles, functioning as endocrine glands. Simultaneously, NNs function as exocrine glands and secrete the so-called manipulative factors, which influence the physiology of the host.

Structure of the Excretory System of the Plerocercoid Pyramicocephalus phocarum (Cestoda: Diphyllobothriidea): Proof for the Existence of Independent Terminal Cells.

The excretory system ultrastructure and immunocytochemistry have been investigated in the plerocercoid Pyramicocephalus phocarum. It has been shown that P. phocarum has independent terminal cells, cyrtocytes. The entire canal system is a single undivided syncytium, which includes nephridial funnels of the terminal tubules, and peripheral and central canals. The nephridial funnel and cyrtocyte form a filtration complex of the protonephridial type. In the caudal region, several peripheral canals open into a deep fold of the tegument, the urinary bladder. The excretory pores are separated from the tegument by annular septate desmosomes. There are no cell junctions inside the excretory system. The presence of the F-actin ring and the expression of non-synaptic serotonin in the collar area have been detected in cyrtocytes by immunocytochemistry methods.

[Localization of prostaglandin E2, γ-aminobutyric acid, and other potential immunomodulators in the plerocercoid Diphyllobothrium dendriticum (Cestoda)].

For the first time, the potential immunomodulators prostaglandin E2 and γ-aminobutyric acid (GABA) have been revealed in the plerocercoid Diphyllobothrium dendriticum, which is a parasite in the tissues and abdominal cavity of the Baikal omul Coregonus migratorius. The localization of immunomodulators in parasite tissues was compared with the location of typical markers of the nervous system (serotonin (5-HT) and FMRF-amide) and a marker of microtubules (α-tubulin). Prostaglandin E2 was revealed in the cells that are immunoreactive to α-tubulin and are situated in the cortical parenchyma outside the central nervous system (CNS). It is supposed that prostaglandin E2 is produced by the frontal glands and is carried out onto the tegument surface through specialized ducts. Immunoreaction to GABA was revealed in the central and peripheral nervous systems. GABA-ergic neurosomes, the neurites of which form a net on the surface of muscle layers and in the subtegument, were revealed in the cerebral ganglion and main nerve cords. The morphological characteristics for the identification of serotoninergic neurons in the CNS were described.

[Structure of the glial cells in the nervous system of parasitic and free-living flatworms].

This study is devoted to ultrastructural and immunosytochemical investigation of the nervous system in parasitic and free-living platyhelminthes to learn if glial cells exist in the nervous system of flatworms. We described the ultrastructure of different types of glial cells and the peculiarities of myelinization of gigantic axons; immunoreactivity to the S100b protein is revealed. Comparative analysis of the glia structure of annelids and platods is given; structural, functional, and evolutionary aspects of myelinization of gigantic axons, which are revealed in cestodes, are discussed.

[Fine structure of glial cells in the central nervous system of the tapeworm Grillotia erinaceus (Cestoda: Trypanorhyncha)].

The problem of glial cells existing in parasitic and free living flatworms is correlated with organization of parenchyma in platyhelmintes. In the contrary to the widespread opinion that myelin-like envelopes and glial cells do not exist in the nervous system of parasitic flatworms, it has been shown by ultrastructural researches that Amphilina foliacea (Cestoda, Amphilinidea) has well developed glial cells and myelin-like envelopes in the ganglia and main cords, which include both glial cells and intercellular components. The aim of our research was to reveal and investigate in details structural components corresponding to the concept of the glial cell in the CNS of Grillotia erinaceus (Cestoda: Trypanorhyncha). Three types of glial cells have been found. The first type is the fibroblast-like glial cells; cells locate in the cerebral ganglion, contain in cytoplasm and extract out fibrillar matrix, form desmosomes and have supporting function. The glial cells of the second type form myeline-like envelope of the giant axons and bulbar nerves in scolex and have laminar cytoplasm. These cells are numerous and exceed in number the neurons bodies into the nerve. The glial cells of the third type form multilayer envelopes in the main nerve cords; extra cellular fibers and gap-junctions take place between the layers. There are contacts between the glial cells of the third type and excretory epithelium but specialized contacts with neurons have been not found. The existing of glial cells in free living and parasitic flatworms is discussed.

[Ultrathin structure of the main lateral nerve cords and accompanying elements of Triaenophorus nodulosus (Cestoda: Pseudophyllidea)]. / Ul'tratonkoe stroenie glavnykh lateral'nykh nervnykh stvolov i soputstvuiushchikh élementov Triaenophorus nodulosus (Cestoda: Pseudophyllidea).

The ultrastructure of lateral nerve cords (LNC) of Triaenophorus nodulosus has been studied. 4 of the 6 types of neurones earlier reported for cerebral ganglia are present in LNC: multipolars, bipolars, unipolars and "light"; neurosecretory cells of the 7th type lie in transverse commissures. The growth and formation of LNC occur at the expense of undifferentiated cells found on the cord periphery among mature neurones. LNC are surrounded with specialized envelopes made of cell processes of excretory vessels and a fibrillar matrix formed at early stages of cestode development. In large axons, cisternae of the cross reticulum are detected, which can serve as ultrastructural marker of the synapse. Two types of muscle innervation are determined. The direct innervation of muscular fibres is realized by peripheral neurosecretory neurones, which form contacts of the paracrine type. The central or sarco-neural innervation of muscular fibers occurs in LNC via the entering muscular processes.

The nervous system of Amphilina foliacea (Platyhelminthes, Amphilinidea). an immunocytochemical, ultrastructural and spectrofluorometrical study.

The nervous system of young and adult Amphilina foliacea was studied with immunocytochemical, electron microscopical and spectrofluorometrical methods. The general neuroanatomy is described in detail. New data on the structure and development of the brain were obtained. The 5-HT and GYIRFamide-immunoreactivities occur in separate sets of neurones. The innervation of the reproductive organs is described. The fine structure of 2 types of neurones in the CNS, a sensory neurone, a 'glial' cell type, the neuropile and the synapses are described. The level of 5-HT varies between 0.074 and 0.461 microg/g wet weight. This is the first detailed study of the nervous system of A. foliacea. Earlier data on the structure of the nervous system in A. foliacea published in Russian are introduced into the discussion. The study provides data that can be used when considering the phylogenetic position of Amphilinidea.

Sensory organs of adult Amphilina foliacea (Amphilinida).

The distribution and morphological diversity of the sensory structures on the body surface, proboscis and caudal cavity of adult Amphilina foliacea have been investigated. Fifteen different types of receptors are described. Along with nonciliated and uniciated receptors bi- and multiciliated receptors have been found for the first time. The zonal distribution of the sensory structures and their coincidence within the same areas of the body surface have been revealed. The concentration of sensory structures at the posterior end may indirectly confirm a hypothesis of the unavailability of developed attachment disk in ancestors of amphilinids.

The ultrastructure of glia-like cells in lateral nerve cords of adult Amphilina foliacea (Amphilinida).

The ultrastructure of main lateral nerve cords (MCs) of adult A. foliacea was studied. By examination of the serial sections it has been found that some glia-like cells are located on a periphery of MC. The processes of glia-like cells surround MCs and penetrate into the cord and surround the group of adjacent axons and pairs of neurones. There is a fine extracellular matrix between processes of glia-like cells. The numerous tight junctions occur between processes. The difference between the perykaryon's cytoplasm of glia-like cells in anterior, posterior and central part of MCs was found.