We found that
ckr-1 is broadly expressed in the nervous system, showing expression in a subset of ventral nerve cord motor neurons, amphid and phasmid sensory neurons, premotor interneurons, and motor neurons in the nerve ring. We identified many of these neurons, largely from analysis of
ckr-1 co-expression with previously characterized reporters. In the ventral nerve cord, we found that
ckr-1 is expressed in cholinergic, but not GABAergic, ventral cord motor neurons. Amongst head neurons, the
ckr-1 reporter is expressed in GABAergic RMEV, RMED, AVL and RIS neurons, cholinergic SMDV, SMDD, and RIV head motor neurons, the interneuron RIG, the serotonergic NSM neuron, and in the interneurons AIA and AIB. Additional studies using DiI uptake indicated that
ckr-1 is also expressed in the amphid sensory neurons ASK and ASI and the phasmid sensory neurons PHA and PHB. With the exception of the ventral cord cholinergic neurons, the
ckr-1 reporter almost exclusively labeled neurons that do not receive direct synaptic input from DVA, suggesting that NLP-12 acts at least partially through extrasynaptic mechanisms.