UC San Diego

The nervous system is designed to allow an organism to react to its changing environment in a coordinated manner. The simple nervous system of Caenorhabditis elegans has been a model for molecular studies in neurobiology for over four decades. This organism has contributed to our understanding of the molecules of neurotransmission and behavioral genetics. Here we seek to further characterize the molecules and simple circuits which lead to behaviors with hopes to generalize our knowledge from worms to higher organisms. Worms' sinusoidal locomotion is based on the coordinated contraction of body wall muscles (BWM) mediated by cholinergic signaling. Cholinergic signaling at the neuromuscular junction (NMJ) is mediated by the nicotinic acetylcholine receptors (nAChRs), this is also the site of psychotropic activity of the addictive drug nicotine. Our ultimate goal of this research was to elucidate the molecular mechanisms involved in cholinergic signaling to further understand nicotine addiction. We initiated a screen to find effectors of the cholinergic signaling system to further our understanding of the molecular elements involved in neurotransmission. We over- stimulated the BWMs with a cholinergic agonist, nicotine, causing paralysis. Loss of molecules involved with cholinergic neurotransmission ameliorates the nicotine- induced paralysis. Utilizing a RNA interference (RNAi) library to systematically knock down each predicted gene products on chromosome one, we attempt to find new molecules that play a role in cholinergic signaling. This screen produced several hits, here we analyze one, agef-1, an ADP-ribosylation factor's guanine nucleotide exchange factor (Arf-GEF). Advancements in cell physiologic techniques in C. elegans have been revolutionary in extending the capabilities of researchers of this organism. Using calcium imaging, we examine the activity of specific cells in relation to behaviors. A small circuit of neurons and muscles control the egg-laying behavior. This simple design belies its molecular complexity. Egg-laying is controlled by at least two neurotransmitters/neuromodulators, acetylcholine (ACh) and serotonin (5-HT)--as well as neuropeptides. We use calcium imaging to describe the response of the egg-laying circuit to pharmacological agents in order to understand the molecular signaling networks underpinning its control