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The Journal of Neuroscience, November 16, 2005, 25(46):10671-10681; doi:10.1523/JNEUROSCI.3399-05.2005
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Behavioral/Systems/Cognitive
The G-Protein-Coupled Serotonin Receptor SER-1 Regulates Egg Laying and Male Mating Behaviors in Caenorhabditis elegans
Lucinda Carnell,
Julie Illi,
Swung Woo Hong, and
Steven L. McIntire
Ernest Gallo Clinic and Research Center, Department of Neurology, Programs in Neuroscience and Biomedical Science, University of California, San Francisco, Emeryville, California 94608
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-HT2 receptor function.
Key words: C. elegans; serotonin; GPCR; SER-1; egg laying; male mating; MOD-1
Received Nov 29, 2004;
revised October 3, 2005;
accepted October 3, 2005.
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