Quantitative analysis of neural and behavioral responses to thermal gradients in the nematode Caenorhabditis elegans.

摘要

Understanding how external stimuli are detected, encoded by the nervous system, and ultimately transformed into a behavioral output is a fundamental goal of neurobiology. However, due to the enormous complexity of the nervous system of most organisms---consider for example the ∼7 x 107 neurons making and receiving thousands of synapses in a mouse brain---characterizing this process at the level of individual neurons and synapses has proven difficult. The nematode Caenorhabditis elegans, armed with a mere 302 neurons, offers a unique opportunity to trace such complex neural processes to the activity of single, identified nerve cells. In this study, I characterize in cellular and molecular detail the response of a pair of C. elegans neurons, AFD, to thermal stimuli. I show that AFD encodes both the direction and rate of temperature change by a cGMP-gated ion channel-dependent mechanism, and that AFD thermoreceptor currents are the result of a striking, non-linear amplification process. This mechanism bears intriguing similarities to vertebrate vision and olfaction and suggests that temperature sensation and vision are linked by conserved or convergent evolution. To complement these studies, I quantify C. elegans behavioral responses to temperature. Computational analysis of such responses reveals that they may play a critical role in thermoregulation. Together, these studies offer key insights into the input and output stages of the transformation of thermal stimuli into behavior, and provide a first step towards a complete understanding of the neural processes that underlie this transformation.