The nematode C. elegans is unique in that it contains known circuits of cells which control measurable responses. The proposed research is to determine the identity and function of neurotransmitter receptors in the 20 neurons controlling pharyngeal pumping and to understand the regulation of the contraction of the pharyngeal muscle by the combination of neurotransmitter receptor -mediated reactions which control signal transmission between the 20 cells. Electropharyngeograms (EPG, similar to electrocardiogram in humans) of the contraction and relaxation of the pharyngeal muscles and the release of neurotransmitter at a specific location in C. elegans by laser photolysis of caged neurotransmitter will be used. Laser ablation of specific neurons will be used to identify the function of the specific neuron: Does the neuron contain the receptor? Or does the neuron release the neurotransmitter? From this research, we will obtain information about how neurotransmitters and drugs affect the rhythmic contraction of muscles. Information from this study may have implications to an understanding of the control of rhythmic contraction of heart muscles, by circuits of cells and may be useful in the design, synthesis, and testing of compounds that affect the rhythmical pumping. The neurotransmitters that affect C. elegans pharyngeal pumping are important in the mammalian nervous system and are known to affect the heart.