The nematode Caenorhabditis elegans is a powerful experimental system whose potential for computational neuroscience is largely untapped. The simplicity of its nervous system, with exactly 302 neurons in the adult hermaphrodite, and the existence of a complete anatomical wiring diagram, raise the prospect of a biophysically accurate model of the entire nervous system. Although detailed genetic analyses and laser ablation studies have delineated the circuits necessary for most C. elegans behaviors, it has not been possible to record from the nervous system. Thus, how these circuits function is not known. The main objective of this project, therefore, is to expand upon pilot studies indicating the feasibility of making intracellular recordings from C. elegans muscles and neurons. One of the main obstacles to recording from C. elegans is the thick external cuticle that breaks conventional microelectrodes. Initial experiments show, however, that the cuticle can be penetrated with electrodes pulled from quartz glass and that dye-fills can be made of a variety of muscles. The fills are long-lasting and reflect the morphology of anatomically defined muscles in the body wall and other structures. This sets the stage for attempts to refine this technique for making intracellular recordings from muscles. The small size of C. elegans neurons (2 mm in diameter) make it unlikely that sharp electrodes can be used to make intracellular recordings. A physiological preparation has been developed, therefore, in which neurons are exposed by a microdissection technique in which a small slit is made in the cuticle. Gigaohm seals (5-20 G) can readily be obtained on the cell bodies of exposed neurons and a variety of single channel currents observed in cell-attached patches. This study will attempt to make intracellular recordings from C. elegans neurons in the whole-cell patch configuration. Whole-cell recordings will be established by mechanical disruption of the membrane patch or by the perforated patch technique. Data from the recordings will form the basis of detailed biophysical models of the circuits underlying locomotion and chemotaxis. Measurement of intrinsic properties such as resting potential, input resistance, and active currents will be used to construct biophysically realistic single-neuron models. Single- neuron models will be assembled into circuits as defined by previous studies and the models tested by comparing the effects of "ablating" neurons in the model and actual circuits. These models constitute the initial phase of a long-term effort to understand the neural basis of behavior of a single organism in its entirety.***//
