Long-term imaging of circadian locomotor rhythms of a freely crawling C-elegans population

Background: Locomotor activity is used extensively as a behavioral output to study the underpinnings of circadian rhythms. Recent studies have required a populational approach for the study of circadian rhythmicity in Caenorhabditis elegans locomotion. New method: We describe an imaging system for long-term automated recording and analysis of locomotion data of multiple free-crawling C. elegans animals on the surface of an agar plate. We devised image analysis tools for measuring specific features related to movement and shape to identify circadian patterns. Results: We demonstrate the utility of our system by quantifying circadian locomotor rhythms in wildtype and mutant animals induced by temperature cycles. We show that 13 C:18 C (12:12 h) cycles are sufficient to entrain locomotor activity of wild-type animals, which persist but are rapidly damped during 13 degrees C free-running conditions. Animals with mutations in tax-2, a cyclic nucleotide-gated (CNG) ion channel, significantly reduce locomotor activity during entrainment and free-running. Comparison with existing method(s): Current methods for measuring circadian locomotor activity is generally restricted to recording individual swimming animals of C. elegans, which is a distinct form of locomotion from crawling behavior generally observed in the laboratory. Our system works well with up to 20 crawling adult animals, and allows for a detailed analysis of locomotor activity over long periods of time. Conclusions: Our population-based approach provides a powerful tool for quantification of circadian rhythmicity of C. elegans locomotion, and could allow for a screening system of candidate circadian genes in this model organism. (C) 2015 Elsevier B.V. All rights reserved.