Getting a grip on how we may age healthily is a central interest of biogerontological research. To this end, a number of academic teams developed platforms for life-and healthspan assessment in Caenorhabditis elegans. These are very appealing for medium-to high throughput screens, but a broader implementation is lacking due to many systems relying on custom scripts for data analysis that others struggle to adopt. Hence, user-friendly recommendations would help to translate raw data into interpretable results. The aim of this communication is to streamline the analysis of data obtained by the WorMotel, an economically and practically appealing screening platform, in order to facilitate the use of this system by interested researchers. We here detail recommendations for the stepwise conversion of raw image data into activity values and explain criteria for assessment of health in C. elegans based on locomotion. Our analysis protocol can easily be adopted by researchers, and all needed scripts and a tutorial are available in S1 and S2 Files. OPEN ACCESS Citation: Jushaj A, Churgin M, Yao B, De La Torre M, Fang-Yen C, Temmerman L (2020) Optimized criteria for locomotion-based healthspan evaluation in C. elegans using the WorMotel system. PLoS ONE 15(3): e0229583. https://doi.org/10.
Neural circuits coordinate with muscles and sensory feedback to generate motor behaviors appropriate to an animal’s environment. In C. elegans, the mechanisms by which the motor circuit generates undulations and modulates them based on the environment are largely unclear. We quantitatively analyzed C. elegans locomotion during free movement and during transient optogenetic muscle inhibition. Undulatory movements were highly asymmetrical with respect to the duration of bending and unbending during each cycle. Phase response curves induced by brief optogenetic inhibition of head muscles showed gradual increases and rapid decreases as a function of phase at which the perturbation was applied. A relaxation oscillator model based on proprioceptive thresholds that switch the active muscle moment was developed and is shown to quantitatively agree with data from free movement, phase responses, and previous results for gait adaptation to mechanical loadings. Our results suggest a neuromuscular mechanism underlying C. elegans motor pattern generation within a compact circuit.
Neural circuits work together with muscles and sensory feedback to generate motor behaviors appropriate to an animal's environment. In C. elegans, forward locomotion consists of dorsoventral undulations that propagate from anterior to posterior. How the worm's motor circuit generates these undulations and modulates them based on external loading is largely unclear. To address this question, we performed quantitative behavioral analysis of C. elegans during free movement and during transient optogenetic muscle inhibition. Undulatory movements in the head were found to be highly asymmetric, with bending toward the ventral or dorsal directions occurring slower than straightening toward a straight posture during the locomotory cycle. Phase shifts induced by brief optogenetic inhibition of head muscles showed a sawtooth-shaped dependence on phase of inhibition. We developed a computational model based on proprioceptive postural thresholds that switch the active moment of body wall muscles. We show that our model, a type of relaxation oscillator, is in quantitative agreement with data from free movement, phase responses, and previous results for frequency and amplitude dependence on the viscosity of the external medium. Our results suggest a neuromuscular mechanism that enables C. elegans to coordinate rhythmic motor patterns within a compact circuit.
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