An image-free opto-mechanical system for creating virtual environments and imaging neuronal activity in freely moving Caenorhabditis elegans.

Non-invasive recording in untethered animals is arguably the ultimate step in the analysis of neuronal function, but such recordings remain elusive. To address this problem, we devised a system that tracks neuron-sized fluorescent targets in real time. The system can be used to create virtual environments by optogenetic activation of sensory neurons, or to image activity in identified neurons at high magnification. By recording activity in neurons of freely moving C. elegans, we tested the long-standing hypothesis that forward and reverse locomotion are generated by distinct neuronal circuits. Surprisingly, we found motor neurons that are active during both types of locomotion, suggesting a new model of locomotion control in C. elegans. These results emphasize the importance of recording neuronal activity in freely moving animals and significantly expand the potential of imaging techniques by providing a mean to stabilize fluorescent targets.

Microfluidic devices for analysis of spatial orientation behaviors in semi-restrained Caenorhabditis elegans.

This article describes the fabrication and use of microfluidic devices for investigating spatial orientation behaviors in nematode worms (Caenorhabditis elegans). Until now, spatial orientation has been studied in freely moving nematodes in which the frequency and nature of encounters with the gradient are uncontrolled experimental variables. In the new devices, the nematode is held in place by a restraint that aligns the longitudinal axis of the body with the border between two laminar fluid streams, leaving the animal's head and tail free to move. The content of the fluid streams can be manipulated to deliver step gradients in space or time. We demonstrate the utility of the device by identifying previously uncharacterized aspects of the behavioral mechanisms underlying chemotaxis, osmotic avoidance, and thermotaxis in this organism. The new devices are readily adaptable to behavioral and imaging studies involving fluid borne stimuli in a wide range of sensory modalities.

Lateralized gustatory behavior of C. elegans is controlled by specific receptor-type guanylyl cyclases.

BACKGROUND: Even though functional lateralization is a common feature of many nervous systems, it is poorly understood how lateralized neural function is linked to lateralized gene activity. A bilaterally symmetric pair of C. elegans gustatory neurons, ASEL and ASER, senses a number of chemicals in a left/right asymmetric manner and therefore serves as a model to study the genetic basis of functional lateralization. The extent of functional lateralization of the ASE neurons and genes responsible for the left/right asymmetric activity of ASEL and ASER is unknown. RESULTS: We show here that a substantial number of salt ions are sensed in a left/right asymmetric manner and that lateralized salt responses allow the worm to discriminate between distinct salt cues. To identify molecules that may be involved in sensing salt ions and/or transmitting such sensory information, we examined the chemotaxis behavior of animals harboring mutations in eight different receptor-type, transmembrane guanylyl cyclases (encoded by gcy genes), which are expressed in either ASEL (gcy-6, gcy-7, gcy-14), ASER (gcy-1, gcy-4, gcy-5, gcy-22), or ASEL and ASER (gcy-19). Disruption of a particular ASER-expressed gcy gene, gcy-22, results in a broad chemotaxis defect to nearly all salts sensed by ASER, as well as to a left/right asymmetrically sensed amino acid. In contrast, disruption of other gcy genes resulted in highly salt ion-specific chemosensory defects. CONCLUSIONS: Our findings broaden our understanding of lateralities in neural function, provide insights into how this laterality is molecularly encoded, and reveal an unusual multitude of molecules involved in gustatory signal transduction.