RECEIVED 1 APRIL; ACCEPTED 9 JULY; PUBLISHED ONLINE

The nematode C. elegans is an excellent model organism for studying behavior at the neuronal level. Because of the organism's small size, it is challenging to deliver stimuli to C. elegans and monitor neuronal activity in a controlled environment. To address this problem, we developed two microfluidic chips, the 'behavior' chip and the 'olfactory' chip for imaging of neuronal and behavioral responses in C. elegans. We used the behavior chip to correlate the activity of AVA command interneurons with the worm locomotion pattern. We used the olfactory chip to record responses from ASH sensory neurons exposed to high-osmotic-strength stimulus. Observation of neuronal responses in these devices revealed previously unknown properties of AVA and ASH neurons. The use of these chips can be extended to correlate the activity of sensory neurons, interneurons and motor neurons with the worm's behavior. How neural circuits process information to generate behavior is a fundamental question in neuroscience. To address this question, one should observe an animal in a well-controlled environment, in which a specific behavior can be generated and corresponding neuronal activity monitored. Ideally such an environment should not disturb normal neuronal function and should be able to reveal the specific neuronal circuit under study. C. elegans, with its optically accessible, stereotyped and compact nervous system, has drawn great scientific attention because of its diverse repertoire of behavioral outputs and its genetic conservation with vertebrates. Initial efforts to measure activity in the C. elegans nervous system relied on electrophysiological recordings from single neurons in dissected worms 1 . The recent development of genetically encoded fluorescent calcium indicators 2 has spawned an increasing interest in optical imaging approaches that permit the tracking of calcium transients in individual neurons in vivo in intact worms 3 . Although transgenic worms that express neuron-specific indicators can now routinely be generated, the present methods for confining and stimulating the worm during imaging are not ideal. The typical experimental setup involves application of glue onto specific segments of the worm to achieve permanent immobilization on a hydrated agar pad. Fluid-filled pipettes, temperature-controlled plates and sharp electrodes have been used in the past to deliver chemical, thermal and mechanical stimuli, respectively 4,5 . Whether the organic glue is toxic to the worm and how it influences neuronal activity are difficult to determine. Moreover, the delivery of chemical stimuli to the glued worm cannot be precisely controlled or separated from mechanical stimuli associated with fluid flow. More concerns arise when the circuit controlling locomotion is under study. The glue immobilizes the worm, not allowing muscles and stretch-receptor neurons, if any, to contract and relax normally. This mechanically restricted microenvironment might affect the function of the proprioceptive sensory neurons as well as motor neurons. Most importantly, the glue setup does not permit most behaviors to be generated, visualized, quantified or correlated to neuronal activity in real time. A system with two objectives 6 has been a welcome step toward simultaneous neuronal-behavior analysis, as has been a new system for tracking thermosensory neurons (albeit at low optical resolution) in freely moving worms 7 . Recent advances in microfabrication technology permit the construction of well-controllable microenvironments with applications ranging from cell analysis to tissue engineering RESULTS The behavior chip The first microfluidic device, the behavior chi

Three C-elegans Rac proteins and several alternative Rac regulators control axon guidance, cell migration and apoptotic cell phagocytosis

The Caenorhabditis elegans genome contains three rac-like genes, ced-10, mig-2, and rac-2. We report that ced-10, mig-2 and rac-2 act redundantly in axon pathfinding: inactivating one gene had little effect, but inactivating two or more genes perturbed both axon outgrowth and guidance. mig-2 and ced-10 also have redundant functions in some cell migrations. By contrast, ced-10 is uniquely required for cell-corpse phagocytosis, and mig-2 and rac-2 have only subtle roles in this process. Rac activators are also used differentially. The UNC-73 Trio Rac GTP exchange factor affected all Rac pathways in axon pathfinding and cell migration but did not affect cell-corpse phagocytosis. CED-5 DOCK180, which acts with CED-10 Rac in cell-corpse phagocytosis, acted with MIG-2 but not CED-10 in axon pathfinding. Thus, distinct regulatory proteins modulate Rac activation and function in different developmental processes

Left-right olfactory asymmetry results from antagonistic functions of voltage-activated calcium channels and the Raw repeat protein OLRN-1 in C. elegans

<p>Abstract</p> <p>Background</p> <p>The left and right AWC olfactory neurons in <it>Caenorhabditis elegans </it>differ in their functions and in their expression of chemosensory receptor genes; in each animal, one AWC randomly takes on one identity, designated AWC^OFF, and the contralateral AWC becomes AWC^ON. Signaling between AWC neurons induces left-right asymmetry through a gap junction network and a claudin-related protein, which inhibit a calcium-regulated MAP kinase pathway in the neuron that becomes AWC^ON.</p> <p>Results</p> <p>We show here that the asymmetry gene <it>olrn-1 </it>acts downstream of the gap junction and claudin genes to inhibit the calcium-MAP kinase pathway in AWC^ON. OLRN-1, a protein with potential membrane-association domains, is related to the <it>Drosophila </it>Raw protein, a negative regulator of JNK mitogen-activated protein (MAP) kinase signaling. <it>olrn-1 </it>opposes the action of two voltage-activated calcium channel homologs, <it>unc-2 </it>(CaV2) and <it>egl-19 </it>(CaV1), which act together to stimulate the calcium/calmodulin-dependent kinase CaMKII and the MAP kinase pathway. Calcium channel activity is essential in AWC^OFF, and the two AWC neurons coordinate left-right asymmetry using signals from the calcium channels and signals from <it>olrn-1</it>.</p> <p>Conclusion</p> <p><it>olrn-1 </it>and voltage-activated calcium channels are mediators and targets of AWC signaling that act at the transition between a multicellular signaling network and cell-autonomous execution of the decision. We suggest that the asymmetry decision in AWC results from the intercellular coupling of voltage-regulated channels, whose cross-regulation generates distinct calcium signals in the left and right AWC neurons. The interpretation of these signals by the kinase cascade initiates the sustained difference between the two cells.</p

The effect of activity and novelty on response frequency in a two-choice learning situation.

Originally published in Optics Express on 23 March 2015 (oe-23-6-7734