Dissecting a circuit for olfactory behaviour in Caenorhabditis elegans.

Although many properties of the nervous system are shared among animals and systems, it is not known whether different neuronal circuits use common strategies to guide behaviour. Here we characterize information processing by Caenorhabditis elegans olfactory neurons (AWC) and interneurons (AIB and AIY) that control food- and odour-evoked behaviours. Using calcium imaging and mutations that affect specific neuronal connections, we show that AWC neurons are activated by odour removal and activate the AIB interneurons through AMPA-type glutamate receptors. The level of calcium in AIB interneurons is elevated for several minutes after odour removal, a neuronal correlate to the prolonged behavioural response to odour withdrawal. The AWC neuron inhibits AIY interneurons through glutamate-gated chloride channels; odour presentation relieves this inhibition and results in activation of AIY interneurons. The opposite regulation of AIY and AIB interneurons generates a coordinated behavioural response. Information processing by this circuit resembles information flow from vertebrate photoreceptors to 'OFF' bipolar and 'ON' bipolar neurons, indicating a conserved or convergent strategy for sensory information processing.

Thermotaxis is a robust mechanism for thermoregulation in Caenorhabditis elegans nematodes.

Many biochemical networks are robust to variations in network or stimulus parameters. Although robustness is considered an important design principle of such networks, it is not known whether this principle also applies to higher-level biological processes such as animal behavior. In thermal gradients, Caenorhabditis elegans uses thermotaxis to bias its movement along the direction of the gradient. Here we develop a detailed, quantitative map of C. elegans thermotaxis and use these data to derive a computational model of thermotaxis in the soil, a natural environment of C. elegans. This computational analysis indicates that thermotaxis enables animals to avoid temperatures at which they cannot reproduce, to limit excursions from their adapted temperature, and to remain relatively close to the surface of the soil, where oxygen is abundant. Furthermore, our analysis reveals that this mechanism is robust to large variations in the parameters governing both worm locomotion and temperature fluctuations in the soil. We suggest that, similar to biochemical networks, animals evolve behavioral strategies that are robust, rather than strategies that rely on fine tuning of specific behavioral parameters.

Bidirectional temperature-sensing by a single thermosensory neuron in C. elegans.

Humans and other animals can sense temperature changes as small as 0.1 degree C. How animals achieve such exquisite sensitivity is poorly understood. By recording from the C. elegans thermosensory neurons AFD in vivo, we found that cooling closes and warming opens ion channels. We found that AFD thermosensitivity, which exceeds that of most biological processes by many orders of magnitude, is achieved by nonlinear signal amplification. Mutations in genes encoding subunits of a cyclic guanosine monophosphate (cGMP)-gated ion channel (tax-4 and tax-2) and transmembrane guanylate cyclases (gcy-8, gcy-18 and gcy-23) eliminated both cooling- and warming-activated thermoreceptor currents, indicating that a cGMP-mediated pathway links variations in temperature to changes in ionic currents. The resemblance of C. elegans thermosensation to vertebrate photosensation and the sequence similarity between TAX-4 and TAX-2 and subunits of the rod phototransduction channel raise the possibility that nematode thermosensation and vertebrate vision are linked by conserved evolution.

The Parallel Worm Tracker: a platform for measuring average speed and drug-induced paralysis in nematodes.

BACKGROUND: Caenorhabditis elegans locomotion is a simple behavior that has been widely used to dissect genetic components of behavior, synaptic transmission, and muscle function. Many of the paradigms that have been created to study C. elegans locomotion rely on qualitative experimenter observation. Here we report the implementation of an automated tracking system developed to quantify the locomotion of multiple individual worms in parallel. METHODOLOGY/PRINCIPAL FINDINGS: Our tracking system generates a consistent measurement of locomotion that allows direct comparison of results across experiments and experimenters and provides a standard method to share data between laboratories. The tracker utilizes a video camera attached to a zoom lens and a software package implemented in MATLAB. We demonstrate several proof-of-principle applications for the tracker including measuring speed in the absence and presence of food and in the presence of serotonin. We further use the tracker to automatically quantify the time course of paralysis of worms exposed to aldicarb and levamisole and show that tracker performance compares favorably to data generated using a hand-scored metric. CONCLUSIONS/SIGNIFICANCE: Although this is not the first automated tracking system developed to measure C. elegans locomotion, our tracking software package is freely available and provides a simple interface that includes tools for rapid data collection and analysis. By contrast with other tools, it is not dependent on a specific set of hardware. We propose that the tracker may be used for a broad range of additional worm locomotion applications including genetic and chemical screening.