[
International Worm Meeting,
2015]
Despite the extensive work performed on C. elegans sensing a variety of physical stimuli (electrical, thermal, hyper/hypo-osmotic), little is known about their sensing of magnetic field and the effect it has on their physiology or behavior. To elucidate this area, we study worm behavior when exposed to magnetic fields both internal to the organism and external. We used two electromagnets to expose worms to magnetic fields and tracked their locomotion pattern. To track the worms we used two tracking systems, a custom made and a commercially available (WormLab). We tested a number of configurations for the relative position of the magnets and the petri dish, the distance between worms and the magnets as well as on and off time intervals of applied magnetic field. Moreover, in a second set of experiments, worms were fed with superparamagnetic nanoparticles and magnetic microparticles, so as to investigate the effect of secondary magnetic field generated by the internalized particles. Particles of diameters 40nm, 70nm, 100nm and 1um were used. Secondary magnetic field generated by magnetized microparticles was simulated to estimate their magnetic field characteristics. The presence of microparticles in the gut, intestine and fat tissue was verified by fluorescent microscopy, confocal microscopy and SEM. Our results show that 1) iron core magnetic microparticles can be introduced by having the worms feed on a mixture of particles and E. coli OP50. Particles translocate in specific tissues, based on their size and they remain inside the worm's body for a time period reversely analogous to their size, 2) our tracking system offers results comparable with the commercially available system, yet we examined only velocity and distance travelled measurements thus far, 3) the magnetic field used does not seem to have any effect on untreated animals and nematodes fed with 40, 70 and 100nm diameter particles; however, worms containing particles of 1um diameter display changes in their locomotion behavior with their velocity decreased significantly. Therefore we conclude that the magnetic field with the intensity and specification we used does not seem to have an effect, for the time period applied, on the locomotion pattern of wild type animals. Moreover, it takes relatively large particles introduced in worms to observe a significant change to their locomotion parameters. Based on these results, we continue by applying stronger magnetic fields, further analyzing worm behavior to locate other possible changes, monitoring the effects of magnetic fields on specific neuron firing and using different types of particles so as to achieve different localization patterns which may affect differently the nervous system.
[
International Worm Meeting,
2017]
C. elegans is widely used as a model system for monitoring stimulus-evoked Ca2+ transients in neurons. The ASH sensory neuron is the subject of several such studies, primarily due to its key importance as a polymodal nociceptor. However, despite the pivotal role of ASH in C. elegans, the overall biology and the characteristics of its Ca2+ transients (e.g., the "off" response), no mathematical model has been developed to describe the full mechanism of ASH Ca2+ dynamics. We propose a phenomenological computational model which captures the Ca2+ transients in the C. elegans ASH neuron upon its activation. The model is built on biophysical cascades that unfold as part of the neuron's Ca2+ signaling events and homeostatic mechanism (e.g., TRPV channels and voltage-gated channels activation, Ca2+ release from intracellular stores, IP3 dynamics, PMCA and SERCA pumps function). The state of the ion channels is described based on Hodgkin-Huxley equations and the remaining molecular states are based on kinetic equations with phenomenological adjustments. We fit the model using experimental data of osmotic stimulus-evoked ASH Ca2+ transients, detected with a FRET sensor (TN-XL), in young and aged worms, both untreated and exposed to oxidative stress. We use a multi-objective genetic algorithm to find the parameters for young untreated worms' data set. Parameters are estimated using a hybrid method that consists of a genetic algorithm and nonlinear least-squares. We use the same approach to fit the model for the other groups of experimental data. We validate the model using data from the literature, from ASH activation by stimuli of several strengths and durations. Finally, we demonstrate how our model can be used to predict the ASH Ca2+ response to stimulation pulses that are challenging to achieve experimentally (stimuli sequences of varying durations/lengths, or ramp stimuli). Our model includes for the first time the changes in ASH cytoplasmic Ca2+ flux observed both upon delivery and withdrawal of the stimulus (i.e., the "on" and "off" responses). This effort is the first to propose a quantitative dynamic model of the Ca2+ transients generating mechanism in a C. elegans neuron, based on essential biochemical pathways of the Ca2+ homeostasis machinery.