In the present paper the ultrastructure of the subcuticulare zone of the tegument of Fasciola hepatica and the distribution of thimidine-H3 for establishing the localization of DNA-synthesis in the tegument was studied. There were two types of subcuticular cells: 1) non-differentiated cells with presence of incorporated labelled thimidine in nuclei presented by DNA non-stable macromolecules, and 2) differentiated or definitive subcuticular cells without aggregates of silver grains. The results showed a high level of DNA replication leading to mitotic activity of the non-differentiated cells and absence of mitotic activity in the definitive cells. There was a morphological similarity between non-differentiated cells and the cells from the medular zone, supposing a relationship in their origin.
The effects in vivo of 5, 10, and 20 mg/kg of luxabendazole (LBZ) on the tegument of Fasciola hepatica have been examined 48 h, 7 days and 14 days post-treatment of experimentally-infected rats. As early as 48 h post-treatment, the drug is shown to provoke significant damage to the tegument. The pathological phenomena characterizing LBZ damage are blebbing of the apical plasmalemma, formation of microvillus-like projections over the free surface, swelling of the basal infolds and stimulation of autophagy. The spines are often fractured; the tegument in the vicinity of spines seems more strongly altered than that in other foci. The basal layer is often changed, from increase of electron density to lack of integrity with the apical cytoplasm. The progress of the ultrastructural damage with time is not expressed. However, cytochemical data show that at longer post-treatment intervals the surface-coat structure becomes irregular and patches of ruthenium red positive material of variable thickness are focally accumulated. Only a slight dose-effect is noted 48 h after LBZ application when the alterations provoked by 5 mg/kg are less evident than those by 10 and 20 mg/kg.
The in vivo effects of the anthelmintics taenifugin, VUFB 14170 and VUFB 15269 on the tegument of Hymenolepis fraterna have been examined by SEM, TEM and cytochemistry. The drugs were given to H. fraterna-infected mice on the 14th day post-infection in a single oral dose of 150, 200 and 200 mg/kg, respectively. By 72 h post-treatment, the drug-induced pathomorphological changes in the tegument indicated that all three drugs had a significant effect. Changes were most pronounced on the brush border and in the intercellular material. On the apical surface, there was blebbing as well as accumulation of membrane fragments over the microthrix tips and erosion of the brush border. The intercellular material was changed in structure, showing increased electron density in some areas and oedema of the intercellular spaces in other areas. There were also fractures of the tegument of variable depth, sometimes reaching to the parenchyma. These results suggest altered tegumental integrity and, occasionally, complete disruption of the selective permeability barrier created by the normal tegument. This suggestion is further supported by the penetration of ruthenium red into some tegumental areas and its distribution into the intercellular spaces, down to the parenchyma. The intrategumental lysosomes also appeared to be significantly activated. There was evidence of autophagy in both distal cytoplasm and tegumental cells. Mature and gravid proglottides were more susceptible to drug damage than those in the anterior strobila and neck.
The fine–structural characteristics of the basement membrane of the tegument of F. hepaticawere examined following extraction fixations and tannic acid infiltration. The basement membrane was shown to consist of three layers: lamina lucida, lamina densa, and lamina reticularis. The lamina densa appeared amorphous and homogeneous with tannic acid impregnation. The lamina reticularis appeared as a dense network of 10–12 nm fibrils. Anchoring fibrils cross this layer and form loops. Along their length they contact hemidesmosomes of muscles, thus connecting muscle to muscle and to tegument. The tegument/basement membrane contact is enhanced by extensions of the lamina densa into infoldings of the tegumental basal membrane. Where tegumental spines reach the basement membrane, the contact is reinforced by hemidesmosomes that connect to anchoring fibrils reaching toward the underlying muscles. The basement membrane thus seems to be a complex structure integrating the distal tegumental layer with underlying tissues and transducing muscle contractions to the tegument and its spines.
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