Can insecticide-free clean water regenerate the midgut epithelium of the freshwater shrimp after dimethoate treatment?

Insecticides such as dimethoate persist for a long time in freshwater environments, influencing the physiology of the animals inhabiting such environments. In aquatic organisms, toxic substances can enter the body through the epidermis and the digestive system. The midgut is part of this system in which intense processes constitute a barrier against the effects of toxic substances on the body. The aim of this study was to evaluate the toxic potential of dimethoate in the midgut epithelium of the freshwater shrimp Neocaridina davidi, emphasizing ultrastructural alterations. However, the additional and main purpose was to determine whether the midgut epithelium can regenerate after placing animals in insecticide-free clean water after various periods of exposure to dimethoate. N. davidi originates from Asia, but it has also been described in European rivers. This species is of particular interest among breeders worldwide due to its ease of breeding and reproduction. The animals were treated with dimethoate for 1, 2, and 3 weeks and then placed in clean water for 1, 2, and 3 weeks. The qualitative and quantitative analysis revealed different sensitivity of organs forming the midgut in freshwater crustaceans and the possibility for midgut regeneration after insecticide exposure. We concluded that different processes were triggered in the intestine and hepatopancreas to regenerate cells after damage, and mitochondria were the first organelles to respond to the appearance of a stressor in the living environment.

Autophagy and Apoptosis in the Midgut Epithelium of Millipedes.

The process of autophagy has been detected in the midgut epithelium of four millipede species: Julus scandinavius, Polyxenus lagurus, Archispirostreptus gigas, and Telodeinopus aoutii. It has been examined using transmission electron microscopy (TEM), which enabled differentiation of cells in the midgut epithelium, and some histochemical methods (light microscope and fluorescence microscope). While autophagy appeared in the cytoplasm of digestive, secretory, and regenerative cells in J. scandinavius and A. gigas, in the two other species, T. aoutii and P. lagurus, it was only detected in the digestive cells. Both types of macroautophagy, the selective and nonselective processes, are described using TEM. Phagophore formation appeared as the first step of autophagy. After its blind ends fusion, the autophagosomes were formed. The autophagosomes fused with lysosomes and were transformed into autolysosomes. As the final step of autophagy, the residual bodies were detected. Autophagic structures can be removed from the midgut epithelium via, e.g., atypical exocytosis. Additionally, in P. lagurus and J. scandinavius, it was observed as the neutralization of pathogens such as Rickettsia-like microorganisms. Autophagy and apoptosis ca be analyzed using TEM, while specific histochemical methods may confirm it.

Ultrastructure of the salivary glands in Lithobius forficatus (Myriapoda, Chilopoda, Lithobiidae) according to seasonal and circadian rhythms.

The salivary glands (mandibular epidermal glands) of adult males and females of Lithobius forficatus (Myriapoda, Chilopoda) were isolated during spring, summer and autumn. In addition, the organs were isolated at different times of the day - at about 12:00 (noon) and about 00:00 (midnight). The ultrastructure of these organs depending on seasonal and circadian rhythms was analyzed using transmission and scanning electron microscopy and histochemical methods. The paired salivary glands of L. forficatus are situated in the vicinity of the foregut and they are formed by numerous acini that are surrounded by the fat body, hemocytes and tracheolae. The salivary glands are composed of a terminal acinar component and a system of tubular ducts that are lined with a cuticle. The glandular part is composed of secretory epithelial cells that are at various stages of their secretory activity. The saliva that is produced by the secretory cells of the acini is secreted into the salivary ducts, which are lined with a simple epithelium that is based on the non-cellular basal lamina. The ultrastructural variations suggest that salivary glands function differently depending on seasonal rhythms and prepare the animal for overwintering. Therefore, the salivary glands of the centipedes that were analyzed participate in the accumulation of proteins, lipids and polysaccharides during the spring, summer and autumn. Subtle differences in the ultrastructure of the secretory cells of the salivary glands during the circadian cycle must be related to the physiological reactions of the organism. The salivary ducts showed no differences in the specimens that were analyzed during the day/night cycle or during the seasonal cycle.