| The nematode C. elegans, with its 302 neurons and abundance of genetic, laser ablation, electrophysiological and imaging tools, is a compact and attractive system for neural circuit analysis. An understanding of the functional dynamics of neural computation requires physiological analyses. We undertook the first characterization of transfer at central synapses in C. elegans. To achieve this we employed optical stimulation techniques using channelrhodopsin-2, and combined this with whole-cell patch clamp electrophysiological recording techniques. We show that the synapse between AFD and AIY, the first stage in the thermotactic circuit, exhibits excitatory, tonic and graded release. The gain at the synapse was low (<0.1), and release was frequency independent, showing no signs of facilitation or depression. The AFD-AIY synapse thus seems designed for robust and reliable transmission of a scaled-down temperature signal from AFD to AIY, enabling AIY to continuously monitor temperature information and integrate it with other incoming sensory information. We also investigated the synapse between ASER, a chemosensory neuron, and AIY, and found that the synaptic response was small and inconsistent. The combination of optical stimulation tools with neural recording techniques is a powerful way to analyze neural circuitry, and will be a significant aid in achieving the goal of understanding how information is processed in the compact yet densely interconnected nervous system of the worm. |
