  The emerging field of optogenetics allows for optical activation or
inhibition of neurons and other tissue in the nervous system. In 2005
optogenetic proteins were expressed in the nematode C. elegans for the first
time. Since then, C. elegans has served as a powerful platform upon which to
conduct optogenetic investigations of synaptic function, circuit dynamics and
the neuronal basis of behavior. The C. elegans nervous system, consisting of
302 neurons, whose connectivity and morphology has been mapped completely,
drives a rich repertoire of behaviors that are quantifiable by video
microscopy. This model organism's compact nervous system, quantifiable
behavior, genetic tractability and optical accessibility make it especially
amenable to optogenetic interrogation. Channelrhodopsin-2 (ChR2), halorhodopsin
(NpHR/Halo) and other common optogenetic proteins have all been expressed in C.
elegans. Moreover recent advances leveraging molecular genetics and patterned
light illumination have now made it possible to target photoactivation and
inhibition to single cells and to do so in worms as they behave freely. Here we
describe techniques and methods for optogenetic manipulation in C. elegans. We
review recent work using optogenetics and C. elegans for neuroscience
investigations at the level of synapses, circuits and behavior.
