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

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 cryophilic movement. We establish that femtosecond laser ablation can exhibit submicrometer precision, severing individual sensory dendrites without causing collateral damage. We show that severing the dendrites of sensory neurons in young adult worms permanently abolishes their sensory contribution without functional regeneration. We show that the AFD neuron regulates 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 laser killing the AIZ interneuron causes thermophilic bias at any temperature.We conclude that laser surgical analysis of the neural circuit for thermotaxis does not support a model in which AFD opposes cryophilic bias by generating thermophilic bias. Our data supports a model in which the AFD neuron gates a mechanism for generating cryophilic bias.A major challenge in understanding the neural basis of complex behavior is determining the functional organization of underlying neural circuits. An advantage of studying simple animals like the nematode C. elegans is that quantitative analysis of their movements in response to defined sensory inputs can reveal functions that must be implemented in a nervous system with only 302 neurons. C. elegans thermotaxis is particularly interesting as it reveals an interplay of multiple neural functions [1]. Worms adjust a stored set-point of thermotactic memory to their cultivation temperature (Tcult). When navigating thermal gradients at temperatures above the thermotactic set-point (T > Tcult), C. elegans crawls down thermal gradients, displaying what is called cryophilic movement. When navigating thermal gradien