The role of the AFD neuron in C. elegans thermotaxis analyzed using femtosecond laser ablation


S. H. Chung, D. A. Clark, C. V. Gabel, E. Mazur, and A. Samuel. 2006. “The role of the AFD neuron in C. elegans thermotaxis analyzed using femtosecond laser ablation.” BMC Neuroscience, 7, Pp. 30–. Publisher's Version


Background: Caenorhabditis elegans actively crawls down thermal gradients until it reaches the temperature of its cultivation, exhibiting what is called cryophilic movement. Implicit in the worms ability to actively bias its movements down thermal gradients is an ability to detect thermal gradients, and implicit in regulating the display of cryophilic bias is the ability to compare current ambient temperature with a stored memory of cultivation temperature. Several lines of evidence link the AFD sensory neuron to thermotactic behavior, but its exact role is not yet known. A current model contends that AFD is part of a thermophilic mechanism which biases movement up thermal gradients that counterbalances a cryophilic mechanism which biases movement down thermal gradients. Results: We used tightly-focused femtosecond laser pulses to dissect the AFD neuronal cell bodies and the AFD sensory dendrites in C. elegans to investigate their contribution to biased cryophilic movement. We establish that femtosecond laser ablation can exhibit submicrometer precision allowing the severing of individual AFD nerve fibers without causing collateral damage. Severing AFD dendrites in young adult worms permanently abolishes their sensory contribution without functional regeneration. We show that thermosensory input to the AFD neuron is required to activate a mechanism for generating cryophilic bias, but we find no evidence that AFD laser surgery reduces a putative ability to generate thermophilic bias. In addition, although disruption of the AIY interneuron causes worms to exhibit cryophilic bias at all temperatures, we find no evidence that disruption of the AIZ interneuron causes thermophilic bias at any temperature. Conclusions: We conclude that laser surgical analysis of the thermotactic circuit does not support a current model in which AFD opposes cryophilic bias by generating thermophilic bias. Our data supports a model in which a mechanism for generating cryophilic bias is gated by the AFD neurons.
Last updated on 07/24/2019