Characteristics of the toxic effect of imidacloprid on the state of Eisenia fetida (Annelida, Clitellata, Lumbricidae)

Imidacloprid became the most sold neonicotinoid insecticide in the world in the 21st century. Due to their constant use, neonicotinoids are stored in soils, bottom deposits, and surface waters. It is known that neonicotinoids reveal toxicity for non-target species: annelid worms, insects, fish, birds, and mammals. Neonicotinoids exhibit reproductive toxicity, neuro-, hepato-, and genotoxicity for mammals. Earthworms are useful modeling organisms that are proposed to carry out toxicity tests. Eisenia fetida is considered a convenient and adequate species in toxicological studies. Analysis of available data shows that even low concentrations of imidacloprid caused protrusion of a belt, blackening, leakage of a cellar fluid, narrowing areas of the body with edema in segments, and dark body pigmentation in E. fetida. There are also biochemical changes. Low concentrations of imidacloprid (<0.2 mg/L) suppress the activity of cellulase. Imidacloprid also causes damage to DNA, production of reactive oxygen species, and alterations in antioxidant enzymes activity in E. fetida: inhibition of catalase, but activation of superoxide dismutase and glutathione-S-transferase. Imidacloprid reduces reproductive success in E. fetida, causing significant deformation of sperm, reducing the average number and size of cocoons and the success of birth. At concentrations ≥10 mg/kg of imidacloprid, the high mortality of worms makes it impossible for vermiculture. At 5 mg/kg of imidacloprid in plants remains for vermicomposting in seven weeks, the mortality rate of 25% of E. fetida individuals is fixed. The stereotypical escape reflex behavior in the worms was observed in relation to imidacloprid at a concentration of 1.32 mg/kg. At the same time, molecular and cellular mechanisms of toxic effects of imidacloprid on E. fetida are almost not studied and needed special attention with further research.

Distinct aging-vulnerable trajectories of motor circuit functions in oxidation- and temperature-stressed Drosophila

We examined several sensory-motor processing circuits in Drosophila across the lifespan and uncovered distinctive age-resilient and age-vulnerable trajectories in their established functional properties. We observed relatively little deterioration toward the end of lifespan in the giant-fiber (GF) and downstream circuit elements responsible for the jump-and-flight escape reflex. In contrast, we found substantial age-dependent modifications in the performance of GF inputs and other circuits driving flight motoneuron activities. Importantly, in high temperature (HT)-reared flies (29 °C), the characteristic age-dependent progression of these properties was largely maintained, albeit over a compressed time scale, lending support for the common practice of expediting Drosophila aging studies by HT rearing. We discovered shortened lifespans in Cu2+/Zn2+Superoxide Dismutase 1 (Sod) mutant flies were accompanied by alterations distinct from HT-reared flies, highlighting differential effects of oxidative vs temperature stressors. This work also establishes several age-vulnerable parameters that may serve as quantitative neurophysiological landmarks for aging in Drosophila.

Change from baseline as an outcome illustrates escape behaviour of rats in hot plate method

Background: The Hot Plate test is a thermal hyperalgesia model to assess the analgesic activity of many compounds. Traditional analysis compares reaction times with controls, reports only analgesic activity without considering escape reflex. Escape reflex to pain sensation also provides an indirect measure of analgesic activity. However, it requires repeated exposure of rats to hot plate. We explored the learning activities and escape behaviour of rats by calculating the change from baseline of reaction times.Methods: Male Wister strain albino rats, weighing between 150-200mg were used for assessment of hot-plate induced hyperalgesia. Author analysed the analgesic activity of aspirin (100mg/Kg) and compared with animals receiving saline. Aspirin and saline were administered 1hr orally before the commencement of the experiment. The reaction time was recorded at every 30 min up to 6hrs.Results: With traditional analysis, we can observe that the onset of action, peak action and duration of analgesic activity of aspirin was at 0.5, 2.0 and 5.0 hours respectively. Peak inhibition of reaction time was seen at 2 hours with a magnitude of 474%. When we applied a statistical procedure, absolute change from baseline statistics, we found that animals treated with aspirin also exhibited escape reflex after fading of drug response and animals treated with saline demonstrated early (0.5hr) escape behaviour from the hot plate and continued throughout the rest of the experiment.Conclusions: Change from baseline as an outcome illustrates escape behaviour of rats in hot plate method and it should be employed along with percentage inhibition during assessment of analgesic activity.

Rostral Ganglia Are Required for Induction But Not Expression of Crayfish Escape Reflex Habituation: Role of Higher Centers in Reprogramming Low-Level Circuits

It is widely assumed that learning results from alterations in the strength of synapses within the neural pathways that mediate a learned behavioral response and that these alterations are directly caused by training-induced activity of neurons connected by the changing synapses. Initial evidence for this view came from studies of habituation of defensive reflexes in several invertebrate species. However, more recent studies of habituation of the escape reflex in one of these species, the crayfish, have shown that habituation is substantially caused by tonic inhibitory input from cephalic ganglia; this descending inhibition suppresses the activity of neurons within the escape circuit, which reside in caudal ganglia. Such control by descending inhibition indicates that animals with encephalized nervous systems do not entirely abdicate to low-level circuitry the important decision of whether to habituate to stimuli that might warn of danger. Higher centers in fact play a major role in controlling the habituation of this potentially life-saving protective response. Another way for higher centers to control lower ones would be to induce alteration of the lower center's intrinsic properties. Here, we show that, whereas descending input from higher ganglia is needed to induce habituation, once established, habituation persists even after rostral ganglia are disconnected. This provides evidence that lower-level neural circuits can be reprogrammed through transient interaction with higher ganglia to decrease their intrinsic tendency to produce escape.

Dynamics and Reproducibility of a Moderately Complex Sensory-Motor Response in the Medicinal Leech

Local bending, a motor response caused by mechanical stimulation of the leech skin, has been shown to be remarkably reproducible, in its initial phase, despite the highly variable firing of motoneurons sustaining it. In this work, the reproducibility of local bending was further analyzed by monitoring it over a longer period of time and by using more intact preparations, in which muscle activation in an entire body segment was studied. Our experiments showed that local bending is a moderately complex motor response, composed of a sequence of four different phases, which were consistently identified in all leeches. During each phase, longitudinal and circular muscles in specific areas of the body segment acted synergistically, being co-activated or co-inhibited depending on their position relative to the stimulation site. Onset and duration of the first phase were reproducible across different trials and different animals as a result of the massive co-activation of excitatory motoneurons sustaining it. The other phases were produced by the inhibition of excitatory and activation of inhibitory motoneurons, and also by the intrinsic relaxation dynamics of leech muscles. As a consequence, their duration and relative timing was variable across different preparations, whereas their order of appearance was conserved. These results suggest that, during local bending, the leech neuromuscular system 1) operates a reduction of its available degrees of freedom, by simultaneously recruiting groups of otherwise antagonistic muscles and large populations of motoneurons; and 2) ensures reliability and effectiveness of this escape reflex, by guaranteeing the reproducibility of its crucial initial phase.

Hemicentin, a conserved extracellular member of the immunoglobulin superfamily, organizes epithelial and other cell attachments into oriented line-shaped junctions

him-4 mutations cause a novel syndrome of tissue fragility, defective cell migration and chromosome instability in Caenorhabditis elegans. Null mutants have abnormal escape reflex, mispositioning of the vas deferens and uterus, and mitotic chromosome loss and multinucleate cells in the germline. The him-4 gene product, hemicentin, is a conserved extracellular matrix protein with 48 tandem immunoglobulin repeats flanked by novel terminal domains. Secreted from skeletal muscle and gonadal leader cells, hemicentin assembles into fine tracks at specific sites, where it contracts broad regions of cell contact into oriented linear junctions. Some tracks organize hemidesmosomes in the overlying epidermis. Hemicentin tracks facilitate mechanosensory neuron anchorage to the epidermis, gliding of the developing gonad along epithelial basement membranes and germline cellularization.