Figure 1.
The AFD and FLP sensory neurons mediate Tav response in the head.
(A) Laser ablation of AFD, FLP and AIB led to severe defects in the head Tav response compared to mock-ablated animals (n>8). Individual neurons were identified by GFP-labeling and the success of the ablations was visualized by the disappearance of the GFP label in these neurons. Tav responses of the mock-ablated animals slightly differed, which is perhaps due to different GFP transgenes (see Methods). (B) AFD-laser-ablated and two transgenic lines [expressing Diphtheria Toxin A (DT-A) under the control of the gcy-8 promoter] in which AFD was genetically ablated showed defective head Tav response, whereas DT-A killing of five pairs of sensory neurons (from the odr-3 promoter), but not AFD, behaved like wild-type (n>80). (**P<0.001). Error bars indicate SD.
Figure 2.
The PHC sensory neurons mediate Tav response in the tail of C. elegans.
(A) sem-4 and unc-86 mutants showed strongly reduced tail Tav response (n>100). (B) Laser-ablation of the PHC neurons almost abrogated the tail Tav response, while ablation of PHA, PHB, PVD and the six touch neurons had no significant defects. (**P<0.001, n>8). Error bars indicate SD.
Table 1.
The PVC and DVA interneurons mediate thermonociception in the tail of C. elegans.
Figure 3.
AFD, FLP, and PHC function as primary sensory neurons in the Tav response.
(A) Average ratio changes in AFD, PLM, PVD and ALM upon noxious heat. (**P<0.001 different from ratio changes in AFD in wild-type). (B), (C) Average ratio changes in FLP and PHC upon heat stimuli in wild-type, unc-13 and unc-31 mutant backgrounds. Data are shown in box plot (n>4). Error bars indicate SD.
Table 2.
YFP/CFP ratio change (calcium influx) after noxious heat stimuli in different sensory neurons.
Figure 4.
OCR-2 and OSM-9 contribute to the Tav response in the FLP neurons in the head and in the PHC neurons in the tail of C. elegans.
(A), (B) The head and tail Tav of osm-9 and ocr single and double mutants are shown. (C) The defective Tav response in the head of the ocr-2 osm-9 double mutant was rescued by the expression of ocr-2 and/or osm-9 full length genomic DNA as well as by expression of their respective cDNAs under the control of the mec-3 promoter. (D) The expression of either ocr-2 or osm-9 full-length genomic DNA was sufficient for at least partial rescue of the defective Tav response in the tail of the ocr-2 osm-9 double mutant. (*P<0.01; **P<0.001, n>80). Error bars indicate SD.
Figure 5.
A cGMP signaling contributes to the Tav response in the AFD neurons.
(A) The head Tav responses of mutants in CNG channel genes are shown. (B) Genetic-ablation of AFD did not further decrease the head Tav response in tax-2;tax-4 double mutant. (C), (D) The defective Tav phenotype of both tax-2 and tax-4 single mutant was rescued by expressing a wild-type copy of the respective gene (tax-2 or tax-4). Expression of tax-4 or tax-2 cDNA under the control of the AFD-specific gcy-8 promoter rescued the respective mutant phenotype. No rescue was obtained when the tax-4 or tax-2 cDNA was expressed from the odr-4 promoter (expressed in 12 neurons, but not in AFD). (E) The head Tav responses of the gcy mutants are shown. (*P<0.01; **P<0.001, n>50). Error bars indicate SD.
Figure 6.
Models of noxious heat sensory neuron function.
(A) Circuit diagram of head Tav response. AFD forms gap junction with AIB. (B) Circuit diagram of tail Tav response. (C) Genetic pathways contributing to Tav response. Head Tav response is mediated by a cGMP signaling pathway within the AFD neurons and a TRPV1 pathway in FLP, whereas the tail Tav response is mediated via TRPV1 in the PHC neurons.