L. Rivarda*, J. Srinivasanb*, A. Stonea, S. Ochoaa, K. Cartera, C. Loera, P. W. Sternbergb
aDept. of Biology, Univ. of San Diego; bDivision of Biology, California Institute of Technology, Pasadena, CA
Previous studies have demonstrated that C. elegans changes its locomotory rate based on the presence or absence of food; this behavioral response to food is also modulated by the worm's recent experience1. Well-fed worms introduced to a new food source slow down. This behavior is known as the basal slowing response and is regulated by dopamine1. When starved worms are introduced to a new food source, a more pronounced slowing response is observed. This behavior is known as the enhanced slowing response and is regulated by serotonin1. It is hypothesized that these slowing responses ensure that in the wild, where the food supply is irregular, a worm will remain in a food source. Behaviors that confer an advantage are selected for, and consequently similar behaviors may be observed in related nematode species that live similarly to C.elegans. We have measured, or are currently studying, slowing responses in eight different nematode species representing several different genera: Caenorhabditis elegans (N2), Caenorhabiditis briggsae (AF16), Oscheius myriophila (DF5020), Pellioditis typica (DF5025), Rhabditella axei (DF5006), Caenorhabditis sp. n. (PS1010), Pristionchus pacificus (PS312), and Panagrellus redivivus (PS1163). Our results indicate that slowing behaviors are conserved across some, but not all species tested. For example, we observe a basal and enhanced slowing response in Oscheius myriophila (DF5020), but we do not observe similar behaviors in Rhabditella axei (DF5006). We have also observed that the enhanced slowing response in O. myriophila is blocked by serotonin antagonists, which suggests this behavior is regulated by serotonin. In addition, we have characterized the staining pattern of serotonin-immunoreactive neurons in the heads of several nematode species. In C. elegans, the NSMs have a clear role in regulating the enhanced slowing response as demonstrated by laser ablation1; the role of other serotonergic neurons in the head is unclear. We have observed NSMs in all the nematode species examined. However, the profile of other serotonergic neurons in the head is more varied. We are currently completing antibody studies for several additional nematode species and using exogenous serotonin in an attempt to introduce an enhanced slowing response in species that do not exhibit this behavior.
* joint first authors; 1. Sawin et al. (2000) Neuron, 26: 619.