Serotonin (5-HT) modulates synaptic efficacy in the nervous system of vertebrates and invertebrates. In the nematode Caenorhabditis elegans, many behaviors are regulated by 5-HT levels, which are in turn regulated by the presence or absence of food. Here, we show that both food and 5-HT signaling modulate chemosensory avoidance response of octanol in C. elegans, and that this modulation is both rapid and reversible. Sensitivity to octanol is decreased when animals are off food or when 5-HT levels are decreased; conversely, sensitivity is increased when animals are on food or have increased 5-HT signaling. Laser microsurgery and behavioral experiments reveal that sensory input from different subsets of octanol-sensing neurons is selectively used, depending on stimulus strength, feeding status, and 5-HT levels. 5-HT directly targets at least one pair of sensory neurons, and 5-HT signaling requires the G␣ protein GPA-11. Glutamatergic signaling is required for response to octanol, and the GLR-1 glutamate receptor plays an important role in behavioral response off food but not on food. Our results demonstrate that 5-HT modulation of neuronal activity via G protein signaling underlies behavioral plasticity by rapidly altering the functional circuitry of a chemosensory circuit.A t the level of individual synapses, plasticity usually refers to changes in efficacy of synaptic transmission. However, at the scale of a neural network, this plasticity translates to changes in functional circuitry. The 302 neurons of the Caenorhabditis elegans nervous system are largely invariant in their location and lineage, and the overall pattern of synaptic connections between classes of neurons is similar in multiple animals (1). With limited variability in synaptic connectivity, behavioral plasticity in C. elegans likely occurs by differential utilization of existing synaptic connections, rather than de novo synaptogenesis.The biogenic amine serotonin (5-HT) modulates synaptic efficacy in vertebrates and invertebrates. For example, 5-HT modulates both locomotor reflex and nociception in the rat spinal cord (2, 3). In cultured Aplysia neurons 5-HT is critical for both short-term and long-term changes in synaptic efficacy (4, 5). In humans, defects in 5-HT signaling are implicated in behavioral disorders, including depression, bulimia, obsessivecompulsive disorder, and alcoholism (6). Although drugs that increase synaptic 5-HT levels such as fluoxetine (i.e., Prozac) are often used to treat these conditions, very little is known about how altering 5-HT levels causes changes in functional circuitry or behavior.Several lines of evidence suggest that in C. elegans, high levels of 5-HT signal the presence of food. In the presence of food (Escherichia coli is used as a food source in the laboratory), pharyngeal pumping (7, 8), egg laying (8, 9), and male mating (10) are increased, whereas locomotion is decreased (11). Conversely, in the absence of food, the opposite behaviors are observed. The effect of food on these behaviors can largely be...

The transcriptional activator PhoP is important for survival of Yersinia pestis in macrophage phagosomes. However, the phagosomes inhabited by Y. pestis have not been well characterized, and the mechanism by which PhoP promotes bacterial survival in these vacuoles is not fully understood. Lysosomal tracers, as well as antibodies to late endosomal or lysosomal proteins, were used in conjunction with confocal or electron microscopy to study the trafficking of phagosomes containing phoP

G protein-coupled receptors (GPCRs) mediate diverse signaling processes, including olfaction. G protein-coupled receptor kinases (GRKs) are important regulators of G protein signal transduction that specifically phosphorylate activated GPCRs to terminate signaling. Despite previously described roles for GRKs in GPCR signal downregulation, animals lacking C. elegans G protein-coupled receptor kinase-2 (Ce-grk-2) function are not hypersensitive to odorants. Instead, decreased Ce-grk-2 function in adult sensory neurons profoundly disrupts chemosensation, based on both behavioral analysis and Ca(2+) imaging. Although mammalian arrestin proteins cooperate with GRKs in receptor desensitization, loss of C. elegans arrestin-1 (arr-1) does not disrupt chemosensation. Either overexpression of the C. elegans Galpha subunit odr-3 or loss of eat-16, which encodes a regulator of G protein signaling (RGS) protein, restores chemosensation in Ce-grk-2 mutants. These results demonstrate that loss of GRK function can lead to reduced GPCR signal transduction and suggest an important role for RGS proteins in the regulation of chemosensation.