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Sensory Neurons Arouse C. elegans Locomotion via Both Glutamate and Neuropeptide Release.

Choi S, Taylor KP, Chatzigeorgiou M, Hu Z, Schafer WR, Kaplan JM - PLoS Genet. (2015)

Bottom Line: Lethargus and adult locomotion quiescence is dramatically reduced in mutants lacking the neuropeptide receptor NPR-1.These sensory neurons accelerate locomotion via both neuropeptide and glutamate release.Our results suggest that a broad network of sensory neurons dictates transitions between aroused and quiescent behavioral states.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts, United States of America; Department of Neurobiology, Harvard Medical School, Boston, Massachusetts, United States of America; Biological and Biomedical Sciences program, Harvard Medical School, Boston, Massachusetts, United States of America.

ABSTRACT
C. elegans undergoes periods of behavioral quiescence during larval molts (termed lethargus) and as adults. Little is known about the circuit mechanisms that establish these quiescent states. Lethargus and adult locomotion quiescence is dramatically reduced in mutants lacking the neuropeptide receptor NPR-1. Here, we show that the aroused locomotion of npr-1 mutants results from the exaggerated activity in multiple classes of sensory neurons, including nociceptive (ASH), touch sensitive (ALM and PLM), and stretch sensing (DVA) neurons. These sensory neurons accelerate locomotion via both neuropeptide and glutamate release. The relative contribution of these sensory neurons to arousal differs between larval molts and adults. Our results suggest that a broad network of sensory neurons dictates transitions between aroused and quiescent behavioral states.

No MeSH data available.


Related in: MedlinePlus

Cholinergic transmission at NMJs is enhanced by increased sensory activity in npr-1 adults.Locomotion behavior of single adult worms was analyzed for the indicated genotypes. Instantaneous locomotion velocity (A) and average locomotion velocity (B-C) are plotted. (A-C) The npr-1 adult locomotion defect was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter), and suppressed in double mutants lacking TAX-4/CNG channels. (D-F) The percentage of animals paralyzed on 1 mM aldicarb at 80 min were plotted for the indicated genotypes. The number of trials is indicated for each genotype. Full time courses of aldicarb-induced paralysis are shown in S2A–S2C Fig. (D) The npr-1 aldicarb hypersensitivity was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter) but not by those expressed in GABAergic neurons (GABA rescue, unc-25 and unc-30 promoters). (E-F) The npr-1 aldicarb hypersensitivity was blocked by mutations inactivating TAX-4/CNG channels or OCR-2/TRPV channels. (G-L) mEPSCs were recorded from body wall muscles of adult worms for the indicated genotypes. Representative traces of mEPSCs (G and J) and summary data are shown (H, I, K, and L). (G-I) The npr-1 cholinergic transmission defect was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter) but not by those expressed in GABAergic neurons (GABA rescue, unc-30 promoter). (J-L) The npr-1 cholinergic transmission defect was abolished by mutations inactivating TAX-4 or OCR-2. The number of animals analyzed is indicated for each genotype. Error bars indicate SEM. Values that differ significantly are indicated (*, p <0.05; **, p <0.01; ***, p <0.001; ns, not significant).
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pgen.1005359.g001: Cholinergic transmission at NMJs is enhanced by increased sensory activity in npr-1 adults.Locomotion behavior of single adult worms was analyzed for the indicated genotypes. Instantaneous locomotion velocity (A) and average locomotion velocity (B-C) are plotted. (A-C) The npr-1 adult locomotion defect was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter), and suppressed in double mutants lacking TAX-4/CNG channels. (D-F) The percentage of animals paralyzed on 1 mM aldicarb at 80 min were plotted for the indicated genotypes. The number of trials is indicated for each genotype. Full time courses of aldicarb-induced paralysis are shown in S2A–S2C Fig. (D) The npr-1 aldicarb hypersensitivity was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter) but not by those expressed in GABAergic neurons (GABA rescue, unc-25 and unc-30 promoters). (E-F) The npr-1 aldicarb hypersensitivity was blocked by mutations inactivating TAX-4/CNG channels or OCR-2/TRPV channels. (G-L) mEPSCs were recorded from body wall muscles of adult worms for the indicated genotypes. Representative traces of mEPSCs (G and J) and summary data are shown (H, I, K, and L). (G-I) The npr-1 cholinergic transmission defect was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter) but not by those expressed in GABAergic neurons (GABA rescue, unc-30 promoter). (J-L) The npr-1 cholinergic transmission defect was abolished by mutations inactivating TAX-4 or OCR-2. The number of animals analyzed is indicated for each genotype. Error bars indicate SEM. Values that differ significantly are indicated (*, p <0.05; **, p <0.01; ***, p <0.001; ns, not significant).

Mentions: Adult npr-1 mutants exhibit accelerated locomotion (Fig 1A–1C), as shown in prior studies [21]. Faster adult locomotion suggests that locomotion circuit activity has been altered. Consistent with this idea, npr-1 mutant adults have enhanced sensitivity to the paralytic effects of a cholinesterase inhibitor (aldicarb) (Fig 1D–1F and S2A Fig) [22], indicating increased excitatory transmission at neuromuscular junctions (NMJs). To more directly assess changes in synaptic transmission, we recorded miniature excitatory post-synaptic currents (mEPSCs) in body muscles, which are evoked by acetylcholine (ACh) release at NMJs. The mEPSC rate observed in npr-1 adults was significantly higher than in wild type controls while mEPSC amplitudes were unaltered (Fig 1G–1I). Faster mEPSC rates suggest that ACh release from motor neurons was increased whereas unaltered mEPSC amplitudes imply that muscle responsiveness to secreted ACh was unaffected. By contrast, neither ACh release evoked by depolarizing motor neurons with a stimulating electrode (evoked EPSCs), nor transmission at GABAergic NMJs (assessed by miniature inhibitory post-synaptic currents, mIPSCs) was altered in npr-1 mutants (S1 Fig). This constellation of electrophysiological defects suggests that tonic ACh release (assessed by mEPSC rate) was enhanced in npr-1 mutants, whereas other forms of neurotransmitter release (evoked ACh release and tonic GABA release) were unaffected. Enhanced tonic ACh release at NMJs could account for the accelerated locomotion rate observed in npr-1 adults.


Sensory Neurons Arouse C. elegans Locomotion via Both Glutamate and Neuropeptide Release.

Choi S, Taylor KP, Chatzigeorgiou M, Hu Z, Schafer WR, Kaplan JM - PLoS Genet. (2015)

Cholinergic transmission at NMJs is enhanced by increased sensory activity in npr-1 adults.Locomotion behavior of single adult worms was analyzed for the indicated genotypes. Instantaneous locomotion velocity (A) and average locomotion velocity (B-C) are plotted. (A-C) The npr-1 adult locomotion defect was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter), and suppressed in double mutants lacking TAX-4/CNG channels. (D-F) The percentage of animals paralyzed on 1 mM aldicarb at 80 min were plotted for the indicated genotypes. The number of trials is indicated for each genotype. Full time courses of aldicarb-induced paralysis are shown in S2A–S2C Fig. (D) The npr-1 aldicarb hypersensitivity was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter) but not by those expressed in GABAergic neurons (GABA rescue, unc-25 and unc-30 promoters). (E-F) The npr-1 aldicarb hypersensitivity was blocked by mutations inactivating TAX-4/CNG channels or OCR-2/TRPV channels. (G-L) mEPSCs were recorded from body wall muscles of adult worms for the indicated genotypes. Representative traces of mEPSCs (G and J) and summary data are shown (H, I, K, and L). (G-I) The npr-1 cholinergic transmission defect was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter) but not by those expressed in GABAergic neurons (GABA rescue, unc-30 promoter). (J-L) The npr-1 cholinergic transmission defect was abolished by mutations inactivating TAX-4 or OCR-2. The number of animals analyzed is indicated for each genotype. Error bars indicate SEM. Values that differ significantly are indicated (*, p <0.05; **, p <0.01; ***, p <0.001; ns, not significant).
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Related In: Results  -  Collection

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pgen.1005359.g001: Cholinergic transmission at NMJs is enhanced by increased sensory activity in npr-1 adults.Locomotion behavior of single adult worms was analyzed for the indicated genotypes. Instantaneous locomotion velocity (A) and average locomotion velocity (B-C) are plotted. (A-C) The npr-1 adult locomotion defect was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter), and suppressed in double mutants lacking TAX-4/CNG channels. (D-F) The percentage of animals paralyzed on 1 mM aldicarb at 80 min were plotted for the indicated genotypes. The number of trials is indicated for each genotype. Full time courses of aldicarb-induced paralysis are shown in S2A–S2C Fig. (D) The npr-1 aldicarb hypersensitivity was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter) but not by those expressed in GABAergic neurons (GABA rescue, unc-25 and unc-30 promoters). (E-F) The npr-1 aldicarb hypersensitivity was blocked by mutations inactivating TAX-4/CNG channels or OCR-2/TRPV channels. (G-L) mEPSCs were recorded from body wall muscles of adult worms for the indicated genotypes. Representative traces of mEPSCs (G and J) and summary data are shown (H, I, K, and L). (G-I) The npr-1 cholinergic transmission defect was rescued by transgenes expressing NPR-1 in the RMG circuit (RMG rescue, flp-21 promoter) but not by those expressed in GABAergic neurons (GABA rescue, unc-30 promoter). (J-L) The npr-1 cholinergic transmission defect was abolished by mutations inactivating TAX-4 or OCR-2. The number of animals analyzed is indicated for each genotype. Error bars indicate SEM. Values that differ significantly are indicated (*, p <0.05; **, p <0.01; ***, p <0.001; ns, not significant).
Mentions: Adult npr-1 mutants exhibit accelerated locomotion (Fig 1A–1C), as shown in prior studies [21]. Faster adult locomotion suggests that locomotion circuit activity has been altered. Consistent with this idea, npr-1 mutant adults have enhanced sensitivity to the paralytic effects of a cholinesterase inhibitor (aldicarb) (Fig 1D–1F and S2A Fig) [22], indicating increased excitatory transmission at neuromuscular junctions (NMJs). To more directly assess changes in synaptic transmission, we recorded miniature excitatory post-synaptic currents (mEPSCs) in body muscles, which are evoked by acetylcholine (ACh) release at NMJs. The mEPSC rate observed in npr-1 adults was significantly higher than in wild type controls while mEPSC amplitudes were unaltered (Fig 1G–1I). Faster mEPSC rates suggest that ACh release from motor neurons was increased whereas unaltered mEPSC amplitudes imply that muscle responsiveness to secreted ACh was unaffected. By contrast, neither ACh release evoked by depolarizing motor neurons with a stimulating electrode (evoked EPSCs), nor transmission at GABAergic NMJs (assessed by miniature inhibitory post-synaptic currents, mIPSCs) was altered in npr-1 mutants (S1 Fig). This constellation of electrophysiological defects suggests that tonic ACh release (assessed by mEPSC rate) was enhanced in npr-1 mutants, whereas other forms of neurotransmitter release (evoked ACh release and tonic GABA release) were unaffected. Enhanced tonic ACh release at NMJs could account for the accelerated locomotion rate observed in npr-1 adults.

Bottom Line: Lethargus and adult locomotion quiescence is dramatically reduced in mutants lacking the neuropeptide receptor NPR-1.These sensory neurons accelerate locomotion via both neuropeptide and glutamate release.Our results suggest that a broad network of sensory neurons dictates transitions between aroused and quiescent behavioral states.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts, United States of America; Department of Neurobiology, Harvard Medical School, Boston, Massachusetts, United States of America; Biological and Biomedical Sciences program, Harvard Medical School, Boston, Massachusetts, United States of America.

ABSTRACT
C. elegans undergoes periods of behavioral quiescence during larval molts (termed lethargus) and as adults. Little is known about the circuit mechanisms that establish these quiescent states. Lethargus and adult locomotion quiescence is dramatically reduced in mutants lacking the neuropeptide receptor NPR-1. Here, we show that the aroused locomotion of npr-1 mutants results from the exaggerated activity in multiple classes of sensory neurons, including nociceptive (ASH), touch sensitive (ALM and PLM), and stretch sensing (DVA) neurons. These sensory neurons accelerate locomotion via both neuropeptide and glutamate release. The relative contribution of these sensory neurons to arousal differs between larval molts and adults. Our results suggest that a broad network of sensory neurons dictates transitions between aroused and quiescent behavioral states.

No MeSH data available.


Related in: MedlinePlus