Neural pathway for the initiation of swimming in C. elegans

The modulation of locomotor gait transitions by monoamines is highly conserved across animal species, yet the mechanisms by which these occur is not very well understood. In C. elegans, certain serotonergic neurons have been implicated in initiating the transition from crawling to swimming, but the environmental cues and specific sensory neurons that communicate with these serotonergic neurons have yet to be characterized. Mutant strains with genetic ablations of particular sensory neurons and strains with mutations in genes expressed in these sensory neurons are being investigated for delayed swim onset to ascertain which neurons and genes are important for swim initiation. Evidence from these experiments suggests that the sensory ASK neurons and a TRPV channel that they express, OSM-9, may be involved in swim initiation. ASK neurons are being further analyzed with a fluorescent reporter of neuronal activity and with optogenetic techniques to see if they are active during swim initiation and if their activity has an effect on this transition. Elucidating the sensory neural pathway and molecular mechanisms responsible for the crawl-to-swim transition in C. elegans has implications for a better understanding of how locomotor transitions may be governed in other animals, including humans, and how these transitions may have evolved.