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.

[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.

[Composition of leucocytes of the head kidney of the crucian carp Carassius auratus gibelio (Cypriniformes: Cyprinidae) as affected by invasion of cestode Digramma interrupta (Cestoda; Pseudophyllidea)]

The composition of leucocytes of the head kidney is studied in the crucian carps (Carassius auratus) either contaminated or uncontaminated with Digramma interrupta. The composition of leucocytes in the pronephros of the crucian carp from Lake Baikal basin has a lymphoid character. Compared to the crucian carp from the European part of Russia, in the fish from Baikal the granulocytopoetic processes are more pronounced. This is proved by the high content of young forms of granulocytes. In the fish infected with digramma, the immune suppression of proliferation of blasts and young forms of eosinophils was revealed. On the other hand, the inflammatory and humoral specific immune reactions are enhanced. Partial suppression of the immune response of C. auratus to invasion by D. interrupta facilitates development of the parasite.

[Changes in mast cell composition in the hamster duodenum in experimental diphyllobothriosis]

The morphometric investigation was performed to study the reaction of mast cells (MC) in mucosal lamina propria of hamster duodenum to experimental infection with tapeworm Diphyllobothrium dendriticum. The invasion was found to result in a significant increase of MC cells absolute content, changes in the proportions of their functional groups, increased anaphylactic MC degranulation, enhanced MC precursor migration and their accelerated differentiation.

[Structural organization of mesenteric lymph nodes in postnatal development of the Baikal seal, Pusa sibirica Gmel]

Structural organization of mesenteric lymph nodes in the Baikal seal has been studied with regard to its age-dependent changes. It has been shown that the relative area of connective tissue structures (the capsule and trabeculae) increases during postnatal development, while the areas of the cortex and medulla decrease. The proportions of secondary lymph nodes and paracortical zone in the cortex become smaller, with the corticomedullary index tending to decrease with age. These phenomena indicate that mesenteric lymph nodes undergo regression during postnatal ontogeny, with their lymphopoietic function being attenuated. Lower values of the corticomedullary index in Baikal seal pups aged 1 month to 4 years are apparently explained by a decrease in the proportion of cortex substance related to the enhancement of the motor function of lymph nodes.

[Cellular composition of the mesenteric lymph node cortex in Baikal nerpa during postnatal ontogenesis]

Cellular composition (relative cell content and cell density) of nodules' germinal centers, mantle zones and paracortical zones was evaluated morphometrically in mesenteric lymph nodes of 65 Baikal nerpas (Pusa sibirica Gmelin) aged 1 month-19 years. A significant decrease in the number of large and medium lymphocytes (3 and 1.9 times, respectively) and reticular cells (2.6 times), was found to occur with age, accompanied by an increase in the number of small lymphocytes (1,5 times) and plasma cells (4.9 times). Thus, with age, on one hand, the decline of lymphopoietic function of the lymph nodes was noted, while on the other hand, the intensification of immunocytopoiesis could be observed.