Transcriptional analysis of the response of C. elegans to ethanol exposure.

Ethanol-induced transcriptional changes underlie important physiological responses to ethanol that are likely to contribute to the addictive properties of the drug. We examined the transcriptional responses of Caenorhabditis elegans across a timecourse of ethanol exposure, between 30 min and 8 h, to determine what genes and genetic pathways are regulated in response to ethanol in this model. We found that short exposures to ethanol (up to 2 h) induced expression of metabolic enzymes involved in metabolizing ethanol and retinol, while longer exposure (8 h) had much more profound effects on the transcriptome. Several genes that are known to be involved in the physiological response to ethanol, including direct ethanol targets, were regulated at 8 h of exposure. This longer exposure to ethanol also resulted in the regulation of genes involved in cilia function, which is consistent with an important role for the effects of ethanol on cilia in the deleterious effects of chronic ethanol consumption in humans. Finally, we found that food deprivation for an 8-h period induced gene expression changes that were somewhat ameliorated by the presence of ethanol, supporting previous observations that worms can use ethanol as a calorie source.

C. elegans Demonstrates Distinct Behaviors within a Fixed and Uniform Electric Field.

C. elegans will orient and travel in a straight uninterrupted path directly towards the negative pole of a DC electric field. We have sought to understand the strategy worms use to navigate to the negative pole in a uniform electric field that is fixed in both direction and magnitude. We examined this behavior by quantifying three aspects of electrotaxis behavior in response to different applied field strengths: the mean approach trajectory angles of the animals' tracks, turning behavior (pirouettes) and average population speeds. We determined that C. elegans align directly to the negative pole of an electric field at sub-preferred field strength and alter approach trajectories at higher field strengths to maintain taxis within a preferred range we have calculated to be ~ 5V/cm. We sought to identify the sensory neurons responsible for the animals' tracking to a preferred field strength. eat-4 mutant animals defective in glutamatergic signaling of the amphid sensory neurons are severely electrotaxis defective and ceh-36 mutant animals, which are defective in the terminal differentiation of two types of sensory neurons, AWC and ASE, are partially defective in electrotaxis. To further elucidate the role of the AWC neurons, we examined the role of each of the pair of AWC neurons (AWCOFF and AWCON), which are functionally asymmetric and express different genes. nsy-5/inx-19 mutant animals, which express both neurons as AWCOFF, are severely impaired in electrotaxis behavior while nsy-1 mutants, which express both neurons as AWCON, are able to differentiate field strengths required for navigation to a specific field strength within an electric field. We also tested a strain with targeted genetic ablation of AWC neurons and found that these animals showed only slight disruption of directionality and turning behavior. These results suggest a role for AWC neurons in which complete loss of function is less disruptive than loss of functional asymmetry in electrotaxis behavior within a uniform fixed field.

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.

The G-protein-coupled serotonin receptor SER-1 regulates egg laying and male mating behaviors in Caenorhabditis elegans.

Serotonin (5-HT) is a neuromodulator that regulates many aspects of animal behavior, including mood, aggression, sex drive, and sleep. In vertebrates, most of the behavioral effects of 5-HT appear to be mediated by G-protein-coupled receptors (GPCRs). Here, we show that SER-1 is the 5-HT GPCR responsible for the stimulatory effects of exogenous 5-HT in two sexually dimorphic behaviors of Caenorhabditis elegans, egg laying and male ventral tail curling. Loss of ser-1 function leads to decreased egg laying in hermaphrodites and defects in the turning step of mating behavior in males. ser-1 is expressed in muscles that are postsynaptic to serotonergic neurons and are known to be required for these behaviors. Analysis of the ser-1 mutant also reveals an inhibitory effect of 5-HT on egg laying that is normally masked by SER-1-dependent stimulation. This inhibition of egg laying requires MOD-1, a 5-HT-gated chloride channel. Loss of mod-1 function in males also produces defects in ventral tail curling and enhances the turning defects in ser-1 mutant males. Sustained elevations in 5-HT levels result in behavioral adaptation to both the stimulatory and inhibitory actions of the neurotransmitter, indicating that both SER-1 and MOD-1 signaling can be modulated. Removal of wild-type animals from high levels of exogenous 5-HT produces a SER-1-dependent withdrawal response in which egg laying is significantly decreased. These studies provide insight into the role of 5-HT in behavior and the regulation of 5-HT(2) receptor function.