Neuronal sensorimotor integration guiding salt concentration navigation in Caenorhabditis elegans.

Animals navigate their environment by manipulating their movements and adjusting their trajectory which requires a sophisticated integration of sensory data with their current motor status. Here, we utilize the nematode Caenorhabditis elegans to explore the neural mechanisms of processing the sensory and motor information for navigation. We developed a microfluidic device which allows animals to freely move their heads while receiving temporal NaCl stimuli. We found that C. elegans regulates neck bending direction in response to temporal NaCl concentration changes in a way which is consistent with a C. elegans' navigational strategy which regulates traveling direction toward preferred NaCl concentrations. Our analysis also revealed that the activity of a neck motor neuron is significantly correlated with neck bending and activated by the decrease in NaCl concentration in a phase-dependent manner. By combining the analysis of behavioral and neural response to NaCl stimuli and optogenetic perturbation experiments, we revealed that NaCl decrease during ventral bending activates the neck motor neuron which counteracts ipsilateral bending. Simulations further suggest that this phase-dependent response of neck motor neurons can facilitate curving toward preferred salt concentrations.

Antagonistic regulation of salt and sugar chemotaxis plasticity by a single chemosensory neuron in Caenorhabditis elegans.

The nematode Caenorhabditis elegans memorizes various external chemicals, such as ions and odorants, during feeding. Here we find that C. elegans is attracted to the monosaccharides glucose and fructose after exposure to these monosaccharides in the presence of food; however, it avoids them without conditioning. The attraction to glucose requires a gustatory neuron called ASEL. ASEL activity increases when glucose concentration decreases. Optogenetic ASEL stimulation promotes forward movements; however, after glucose conditioning, it promotes turning, suggesting that after glucose conditioning, the behavioral output of ASEL activation switches toward glucose. We previously reported that chemotaxis toward sodium ion (Na+), which is sensed by ASEL, increases after Na+ conditioning in the presence of food. Interestingly, glucose conditioning decreases Na+ chemotaxis, and conversely, Na+ conditioning decreases glucose chemotaxis, suggesting the reciprocal inhibition of learned chemotaxis to distinct chemicals. The activation of PKC-1, an nPKC ε/η ortholog, in ASEL promotes glucose chemotaxis and decreases Na+ chemotaxis after glucose conditioning. Furthermore, genetic screening identified ENSA-1, an ortholog of the protein phosphatase inhibitor ARPP-16/19, which functions in parallel with PKC-1 in glucose-induced chemotactic learning toward distinct chemicals. These findings suggest that kinase-phosphatase signaling regulates the balance between learned behaviors based on glucose conditioning in ASEL, which might contribute to migration toward chemical compositions where the animals were previously fed.

Ensemble dynamics and information flow deduction from whole-brain imaging data.

The recent advancements in large-scale activity imaging of neuronal ensembles offer valuable opportunities to comprehend the process involved in generating brain activity patterns and understanding how information is transmitted between neurons or neuronal ensembles. However, existing methodologies for extracting the underlying properties that generate overall dynamics are still limited. In this study, we applied previously unexplored methodologies to analyze time-lapse 3D imaging (4D imaging) data of head neurons of the nematode Caenorhabditis elegans. By combining time-delay embedding with the independent component analysis, we successfully decomposed whole-brain activities into a small number of component dynamics. Through the integration of results from multiple samples, we extracted common dynamics from neuronal activities that exhibit apparent divergence across different animals. Notably, while several components show common cooperativity across samples, some component pairs exhibited distinct relationships between individual samples. We further developed time series prediction models of synaptic communications. By combining dimension reduction using the general framework, gradient kernel dimension reduction, and probabilistic modeling, the overall relationships of neural activities were incorporated. By this approach, the stochastic but coordinated dynamics were reproduced in the simulated whole-brain neural network. We found that noise in the nervous system is crucial for generating realistic whole-brain dynamics. Furthermore, by evaluating synaptic interaction properties in the models, strong interactions within the core neural circuit, variable sensory transmission and importance of gap junctions were inferred. Virtual optogenetics can be also performed using the model. These analyses provide a solid foundation for understanding information flow in real neural networks.

The redundancy and diversity between two novel PKC isotypes that regulate learning in Caenorhabditis elegans.

The nematode Caenorhabditis elegans learns the concentration of NaCl and moves toward the previously experienced concentration. In this behavior, the history of NaCl concentration change is reflected in the level of diacylglycerol and the activity of protein kinase C, PKC-1, in the gustatory sensory neuron ASER and determines the direction of migration. Here, through a genetic screen, we found that the activation of Gq protein compensates for the behavioral defect of the loss-of-function mutant of pkc-1 We found that Gq activation results in hyperproduction of diacylglycerol in ASER sensory neuron, which leads to recruitment of TPA-1, an nPKC isotype closely related to PKC-1. Unlike the pkc-1 mutants, loss of tpa-1 did not obviously affect migration directions in the conventional learning assay. This difference was suggested to be due to cooperative functions of the C1 and C2-like domains of the nPKC isotypes. Furthermore, we investigated how the compensatory capability of tpa-1 contributes to learning and found that learning was less robust in the context of cognitive decline or environmental perturbation in tpa-1 mutants. These results highlight how two nPKC isotypes contribute to the learning system.

WormTensor: a clustering method for time-series whole-brain activity data from C. elegans.

BACKGROUND: In the field of neuroscience, neural modules and circuits that control biological functions have been found throughout entire neural networks. Correlations in neural activity can be used to identify such neural modules. Recent technological advances enable us to measure whole-brain neural activity with single-cell resolution in several species including [Formula: see text]. Because current neural activity data in C. elegans contain many missing data points, it is necessary to merge results from as many animals as possible to obtain more reliable functional modules. RESULTS: In this work, we developed a new time-series clustering method, WormTensor, to identify functional modules using whole-brain activity data from C. elegans. WormTensor uses a distance measure, modified shape-based distance to account for the lags and the mutual inhibition of cell-cell interactions and applies the tensor decomposition algorithm multi-view clustering based on matrix integration using the higher orthogonal iteration of tensors (HOOI) algorithm (MC-MI-HOOI), which can estimate both the weight to account for the reliability of data from each animal and the clusters that are common across animals. CONCLUSION: We applied the method to 24 individual C. elegans and successfully found some known functional modules. Compared with a widely used consensus clustering method to aggregate multiple clustering results, WormTensor showed higher silhouette coefficients. Our simulation also showed that WormTensor is robust to contamination from noisy data. WormTensor is freely available as an R/CRAN package https://cran.r-project.org/web/packages/WormTensor .

DAF-16/FOXO promotes taste avoidance learning independently of axonal insulin-like signaling.

The avoidance of starvation is critical for the survival of most organisms, thus animals change behavior based on past nutritional conditions. Insulin signaling is important for nutritional state-dependent behavioral plasticity, yet the underlying regulatory mechanism at the cellular level remains unclear. Previous studies showed that insulin-like signaling is required for taste avoidance learning, in which the nematode Caenorhabditis elegans avoids salt concentrations encountered under starvation conditions. DAF-2c, a splice isoform of the DAF-2 insulin receptor, functions in the axon of the ASER sensory neuron, which senses changes in salt concentrations. In addition, mutants of a major downstream factor of DAF-2, the forkhead transcription factor O (FOXO) homolog DAF-16, show defects in taste avoidance learning. Interestingly, the defect of the daf-2 mutant is not suppressed by daf-16 mutations in the learning, unlike those in other phenomena, such as longevity and development. Here we show that multiple DAF-16 isoforms function in ASER. By epistasis analysis using a DAF-2c isoform-specific mutant and an activated form of DAF-16, we found that DAF-16 acts in the nucleus in parallel with the DAF-2c-dependent pathway in the axon, indicating that insulin-like signaling acts both in the cell body and axon of a single neuron, ASER. Starvation conditioning induces nuclear translocation of DAF-16 in ASER and degradation of DAF-16 before starvation conditioning causes defects in taste avoidance learning. Forced nuclear localization of DAF-16 in ASER biased chemotaxis towards lower salt concentrtions and this effect required the Gq/PKC pathway and neuropeptide processing enzymes. These data imply that DAF-16/FOXO transmits starvation signals and modulates neuropeptide transmission in the learning.

Multiple sensory neurons mediate starvation-dependent aversive navigation in Caenorhabditis elegans.

Animals demonstrate flexible behaviors through associative learning based on their experiences. Deciphering the neural mechanisms for sensing and integrating multiple types of sensory information is critical for understanding such behavioral controls. The soil nematode Caenorhabditis elegans avoids salt concentrations it has previously experienced under starvation conditions. Here, we identify a pair of sensory neurons, the ASG neuron pair, which in cooperation with the ASER salt-sensing neuron generate starvation-dependent salt avoidance. Animals whose sensory input is restricted to only ASER failed to show learned avoidance due to inappropriately directed navigation behaviors. However, their navigation through a salt concentration gradient was improved by allowing sensory inputs to ASG in addition to ASER. Detailed behavioral analyses of these animals revealed that input from ASG neurons is required not only for controlling the frequency of initiating a set of sharp turns (called pirouettes) based on detected ambient salt concentrations but also adjusting the migration direction during pirouettes. Optogenetic activation of ASER by ChR2 induced turning behaviors in a salt concentration-dependent manner where presence of intact ASG was important for the starvation-dependent responses. Calcium imaging of the activity of ASG neurons in freely moving worms revealed that ASG is activated upon turning behavior. Our results indicate that ASG neurons cooperate with the ASER neuron to generate destination-directed reorientation in starvation-associated salt concentration avoidance.

Structural basis for Na(+) transport mechanism by a light-driven Na(+) pump.

Krokinobacter eikastus rhodopsin 2 (KR2) is the first light-driven Na(+) pump discovered, and is viewed as a potential next-generation optogenetics tool. Since the positively charged Schiff base proton, located within the ion-conducting pathway of all light-driven ion pumps, was thought to prohibit the transport of a non-proton cation, the discovery of KR2 raised the question of how it achieves Na(+) transport. Here we present crystal structures of KR2 under neutral and acidic conditions, which represent the resting and M-like intermediate states, respectively. Structural and spectroscopic analyses revealed the gating mechanism, whereby the flipping of Asp116 sequesters the Schiff base proton from the conducting pathway to facilitate Na(+) transport. Together with the structure-based engineering of the first light-driven K(+) pumps, electrophysiological assays in mammalian neurons and behavioural assays in a nematode, our studies reveal the molecular basis for light-driven non-proton cation pumps and thus provide a framework that may advance the development of next-generation optogenetics.

Caenorhabditis elegans: a model to understand host-microbe interactions.

Host-microbe interactions within the gut are fundamental to all higher organisms. Caenorhabditis elegans has been in use as a surrogate model to understand the conserved mechanisms in host-microbe interactions. Morphological and functional similarities of C. elegans gut with the human have allowed the mechanistic investigation of gut microbes and their effects on metabolism, development, reproduction, behavior, pathogenesis, immune responses and lifespan. Recent reports suggest their suitability for functional investigations of human gut bacteria, such as gut microbiota of healthy and diseased individuals. Our knowledge on the gut microbial diversity of C. elegans in their natural environment and the effect of host genetics on their core gut microbiota is important. Caenorhabditis elegans, as a model, is continuously bridging the gap in our understanding the role of genetics, environment, and dietary factors on physiology of the host.

OFF-responses of interneurons optimize avoidance behaviors depending on stimulus strength via electrical synapses.

Optimization of the types and timing of avoidance behaviors depending on the intensity of a noxious stimulus is essential for survival; however, processing in the central nervous system and its developmental basis are largely unknown. Here, we report that Caenorhabditis elegans preferentially selects one of three different types of avoidance behaviors depending on the strength of the noxious stimulus. We screened 210 neuronal transcription factors using a combination of optogenetics and RNA interference methods and identified 19 candidates required for avoidance behaviors. One candidate, gene lin-32 (abnormal cell LINeage 32), which encodes an atonal homolog, is required for the neural fate determination of AIB interneurons and functions by regulating the expression of electrical and chemical synapse genes, namely, inx-1 (innexin 1) and AMPA-type ionotropic glutamate receptor glr-1. When examined by Ca imaging, AIB showed an OFF calcium increase to the noxious stimulus. The OFF calcium increase was provoked only by strong stimulation, suggesting a role for optimization of the avoidance behavior. However, lin-32 mutants showed an impaired AIB OFF calcium increase, concomitant with a reduced occurrence of the dynamic avoidance behavior called the "omega turn". The AIB neural responses may be transferred to downstream inter/motor neurons projecting to the neck muscles via electrical synapses comprising inx-1. Finally, we found a correlation between powerful contractions of the neck muscles and omega turns. Thus, the central regulation of the magnitude and timing of activation of the AIB interneurons optimizes the probability of omega turn depending on the stimulus context.

Neuron ID dataset facilitates neuronal annotation for whole-brain activity imaging of C. elegans.

BACKGROUND: Annotation of cell identity is an essential process in neuroscience that allows comparison of cells, including that of neural activities across different animals. In Caenorhabditis elegans, although unique identities have been assigned to all neurons, the number of annotatable neurons in an intact animal has been limited due to the lack of quantitative information on the location and identity of neurons. RESULTS: Here, we present a dataset that facilitates the annotation of neuronal identities, and demonstrate its application in a comprehensive analysis of whole-brain imaging. We systematically identified neurons in the head region of 311 adult worms using 35 cell-specific promoters and created a dataset of the expression patterns and the positions of the neurons. We found large positional variations that illustrated the difficulty of the annotation task. We investigated multiple combinations of cell-specific promoters driving distinct fluorescence and generated optimal strains for the annotation of most head neurons in an animal. We also developed an automatic annotation method with human interaction functionality that facilitates annotations needed for whole-brain imaging. CONCLUSION: Our neuron ID dataset and optimal fluorescent strains enable the annotation of most neurons in the head region of adult C. elegans, both in full-automated fashion and a semi-automated version that includes human interaction functionalities. Our method can potentially be applied to model species used in research other than C. elegans, where the number of available cell-type-specific promoters and their variety will be an important consideration.

A Gustatory Neural Circuit of Caenorhabditis elegans Generates Memory-Dependent Behaviors in Na+ Chemotaxis.

Animals show various behaviors in response to environmental chemicals. These behaviors are often plastic depending on previous experiences. Caenorhabditis elegans, which has highly developed chemosensory system with a limited number of sensory neurons, is an ideal model for analyzing the role of each neuron in innate and learned behaviors. Here, we report a new type of memory-dependent behavioral plasticity in Na+ chemotaxis generated by the left member of bilateral gustatory neuron pair ASE (ASEL neuron). When worms were cultivated in the presence of Na+, they showed positive chemotaxis toward Na+, but when cultivated under Na+-free conditions, they showed no preference regarding Na+ concentration. Both channelrhodopsin-2 (ChR2) activation with blue light and up-steps of Na+ concentration activated ASEL only after cultivation with Na+, as judged by increase in intracellular Ca2+ Under cultivation conditions with Na+, photoactivation of ASEL caused activation of its downstream interneurons AIY and AIA, which stimulate forward locomotion, and inhibition of its downstream interneuron AIB, which inhibits the turning/reversal behavior, and overall drove worms toward higher Na+ concentrations. We also found that the Gq signaling pathway and the neurotransmitter glutamate are both involved in the behavioral response generated by ASEL.SIGNIFICANCE STATEMENT Animals have acquired various types of behavioral plasticity during their long evolutionary history. Caenorhabditis elegans prefers odors associated with food, but plastically changes its behavioral response according to previous experience. Here, we report a new type of behavioral response generated by a single gustatory sensory neuron, the ASE-left (ASEL) neuron. ASEL did not respond to photostimulation or upsteps of Na+ concentration when worms were cultivated in Na+-free conditions; however, when worms were cultivated with Na+, ASEL responded and inhibited AIB to avoid turning and stimulated AIY and AIA to promote forward locomotion, which collectively drove worms toward higher Na+ concentrations. Glutamate and the Gq signaling pathway are essential for driving worms toward higher Na+ concentrations.

Accurate Automatic Detection of Densely Distributed Cell Nuclei in 3D Space.

To measure the activity of neurons using whole-brain activity imaging, precise detection of each neuron or its nucleus is required. In the head region of the nematode C. elegans, the neuronal cell bodies are distributed densely in three-dimensional (3D) space. However, no existing computational methods of image analysis can separate them with sufficient accuracy. Here we propose a highly accurate segmentation method based on the curvatures of the iso-intensity surfaces. To obtain accurate positions of nuclei, we also developed a new procedure for least squares fitting with a Gaussian mixture model. Combining these methods enables accurate detection of densely distributed cell nuclei in a 3D space. The proposed method was implemented as a graphical user interface program that allows visualization and correction of the results of automatic detection. Additionally, the proposed method was applied to time-lapse 3D calcium imaging data, and most of the nuclei in the images were successfully tracked and measured.

A role for Ras in inhibiting circular foraging behavior as revealed by a new method for time and cell-specific RNAi.

BACKGROUND: The nematode worm Caenorhabditis elegans, in which loss-of-function mutants and RNA interference (RNAi) models are available, is a model organism useful for analyzing effects of genes on various life phenomena, including behavior. In particular, RNAi is a powerful tool that enables time- or cell-specific knockdown via heat shock-inducible RNAi or cell-specific RNAi. However, conventional RNAi is insufficient for investigating pleiotropic genes with various sites of action and life stage-dependent functions. RESULTS: Here, we investigated the Ras gene for its role in exploratory behavior in C. elegans. We found that, under poor environmental conditions, mutations in the Ras-MAPK signaling pathway lead to circular locomotion instead of normal exploratory foraging. Spontaneous foraging is regulated by a neural circuit composed of three classes of neurons: IL1, OLQ, and RMD, and we found that Ras functions in this neural circuit to modulate the direction of locomotion. We further observed that Ras plays an essential role in the regulation of GLR-1 glutamate receptor localization in RMD neurons. To investigate the temporal- and cell-specific profiles of the functions of Ras, we developed a new RNAi method that enables simultaneous time- and cell-specific knockdown. In this method, one RNA strand is expressed by a cell-specific promoter and the other by a heat shock promoter, resulting in only expression of double-stranded RNA in the target cell when heat shock is induced. This technique revealed that control of GLR-1 localization in RMD neurons requires Ras at the adult stage. Further, we demonstrated the application of this method to other genes. CONCLUSIONS: We have established a new RNAi method that performs simultaneous time- and cell-specific knockdown and have applied this to reveal temporal profiles of the Ras-MAPK pathway in the control of exploratory behavior under poor environmental conditions.

Regulation of experience-dependent bidirectional chemotaxis by a neural circuit switch in Caenorhabditis elegans.

The nematode Caenorhabditis elegans changes its chemotaxis to NaCl depending on previous experience. At the behavioral level, this chemotactic plasticity is generated by reversing the elementary behaviors for chemotaxis, klinotaxis, and klinokinesis. Here, we report that bidirectional klinotaxis is achieved by the proper use of at least two different neural subcircuits. We simulated an NaCl concentration change by activating an NaCl-sensitive chemosensory neuron in phase with head swing and successfully induced klinotaxis-like curving. The curving direction reversed depending on preconditioning, which was consistent with klinotaxis plasticity under a real concentration gradient. Cell-specific ablation and activation of downstream interneurons revealed that ASER-evoked curving toward lower concentration was mediated by AIY interneurons, whereas curving to the opposite direction was not. These results suggest that the experience-dependent bidirectionality of klinotaxis is generated by a switch between different neural subcircuits downstream of the chemosensory neuron.

Automated detection and tracking of many cells by using 4D live-cell imaging data.

MOTIVATION: Automated fluorescence microscopes produce massive amounts of images observing cells, often in four dimensions of space and time. This study addresses two tasks of time-lapse imaging analyses; detection and tracking of the many imaged cells, and it is especially intended for 4D live-cell imaging of neuronal nuclei of Caenorhabditis elegans. The cells of interest appear as slightly deformed ellipsoidal forms. They are densely distributed, and move rapidly in a series of 3D images. Thus, existing tracking methods often fail because more than one tracker will follow the same target or a tracker transits from one to other of different targets during rapid moves. RESULTS: The present method begins by performing the kernel density estimation in order to convert each 3D image into a smooth, continuous function. The cell bodies in the image are assumed to lie in the regions near the multiple local maxima of the density function. The tasks of detecting and tracking the cells are then addressed with two hill-climbing algorithms. The positions of the trackers are initialized by applying the cell-detection method to an image in the first frame. The tracking method keeps attacking them to near the local maxima in each subsequent image. To prevent the tracker from following multiple cells, we use a Markov random field (MRF) to model the spatial and temporal covariation of the cells and to maximize the image forces and the MRF-induced constraint on the trackers. The tracking procedure is demonstrated with dynamic 3D images that each contain >100 neurons of C.elegans. AVAILABILITY: http://daweb.ism.ac.jp/yoshidalab/crest/ismb2014 SUPPLEMENTARY INFORMATION: Supplementary data are available at http://daweb.ism.ac.jp/yoshidalab/crest/ismb2014

Roles for class IIA phosphatidylinositol transfer protein in neurotransmission and behavioral plasticity at the sensory neuron synapses of Caenorhabditis elegans.

Growing evidence suggests that sensory neuron synapses not merely pass, but actively encode sensory information and convey it to the central nervous system. The chemosensory preferences of Caenorhabditis elegans, as manifested in the direction of chemotaxis, are reversibly regulated by prior experience at the level of sensory neurons; the attractive drive is promoted by diacylglycerol (DAG) signaling, whereas the counteracting repulsive drive requires PtdIns(3,4,5)P(3) signaling. Here we report that the two opposing drives require a class IIA phosphatidylinositol transfer protein (PITP), PITP-1, which localizes to the sensory neuron synapses. In pitp-1 mutants, attraction behavior to salt is reduced, whereas conditioned repulsion from salt is eliminated: the mutants inflexibly show weak attraction behavior to salt, irrespective of prior experience. To generate flexible behavioral outputs, attraction and repulsion, PITP-1 acts in the gustatory neuron ASER and likely regulates neurotransmission from ASER, as pitp-1 mutations do not affect the ASER Ca(2+) response to sensory stimulus. Furthermore, full attraction to salt is restored in pitp-1 mutants by expression of the phosphatidylinositol transfer domain alone, and also by mutations of a DGK gene that cause accumulation of DAG, suggesting that PITP-1 serves for DAG production via phosphatidylinositol transport and, hence, regulates synaptic transmission. In addition to gustatory behavior, olfactory behaviors and osmotic avoidance are also regulated by PITP-1 in the sensory neurons that detect each sensory stimulus. Thus, PITP-1-dependent phosphatidylinositol transport is essential for sensory neuron synapses to couple sensory inputs to effective behavioral responses.

Activation of lateral preoptic neurons is associated with nest-building in male mice.

Nest-building behavior is a widely observed innate behavior. A nest provides animals with a secure environment for parenting, sleep, feeding, reproduction, and temperature maintenance. Since animal infants spend their time in a nest, nest-building behavior has been generally studied as parental behaviors, and the medial preoptic area (MPOA) neurons are known to be involved in parental nest-building. However, nest-building of singly housed male mice has been less examined. Here we show that male mice spent longer time in nest-building at the early to middle dark phase and at the end of the dark phase. These two periods are followed by sleep-rich periods. When a nest was removed and fresh nest material was introduced, both male and female mice built nests at Zeitgeber time (ZT) 6, but not at ZT12. Using Fos-immunostaining combined with double in situ hybridization of Vgat and Vglut2, we found that Vgat- and Vglut2-positive cells of the lateral preoptic area (LPOA) were the only hypothalamic neuron population that exhibited a greater number of activated cells in response to fresh nest material at ZT6, compared to being naturally awake at ZT12. Fos-positive LPOA neurons were negative for estrogen receptor 1 (Esr1). Both Vgat-positive and Vglut2-positive neurons in both the LPOA and MPOA were activated at pup retrieval by male mice. Our findings suggest the possibility that GABAergic and glutamatergic neurons in the LPOA are associated with nest-building behavior in male mice.

Different modes of stimuli delivery elicit changes in glutamate driven, experience-dependent interneuron response in C. elegans.

Memory-related neuronal responses are often elicited by sensory stimuli that recapitulate previous experience. Despite the importance of this sensory input processing, its underlying mechanisms remain poorly understood. Caenorhabditis elegans chemotax towards salt concentrations experienced in the presence of food. The amphid sensory neurons ASE-left and ASE-right respond to increases and decreases of ambient salt concentration in opposite manners. AIA, AIB and AIY interneurons are post-synaptic to the ASE pair and are thought to be involved in the processing of salt information transmitted from ASE. However, it remains elusive how the responses of these interneurons are regulated by stimulus patterns. Here we show that AIY interneurons display an experience-dependent response to gradual salt concentration changes but not to abrupt stepwise concentration changes. Animals with AIY intact (but AIA and AIB ablated) chemotax towards low salt concentrations similarly to wild-type animals after cultivation with low salt. ASE neurons transmit salt information about the environment through glutamatergic signaling, directing the activity of the interneurons AIY that promote movement towards favorable conditions.

Multiple p38/JNK mitogen-activated protein kinase (MAPK) signaling pathways mediate salt chemotaxis learning in C. elegans.

Animals are able to adapt their behaviors to the environment. In order to achieve this, the nervous system plays integrative roles, such as perception of external signals, sensory processing, and behavioral regulations via various signal transduction pathways. Here genetic analyses of Caenorhabditis elegans (C. elegans) found that mutants of components of JNK and p38 mitogen-activated protein kinase (MAPK) signaling pathways, also known as stress-activated protein kinase (SAPK) signaling pathways, exhibit various types of defects in the learning of salt chemotaxis. C. elegans homologs of JNK MAPKKK and MAPKK, MLK-1 and MEK-1, respectively, are required for avoidance of salt concentrations experienced during starvation. In contrast, homologs of p38 MAPKKK and MAPKK, NSY-1 and SEK-1, respectively, are required for high-salt chemotaxis after conditioning. Genetic interaction analyses suggest that a JNK family MAPK, KGB-1, functions downstream of both signaling pathways to regulate salt chemotaxis learning. Furthermore, we found that the NSY-1/SEK-1 pathway functions in sensory neurons, ASH, ADF, and ASER, to regulate the learned high-salt chemotaxis. A neuropeptide, NLP-3, expressed in ASH, ADF, and ASER neurons, and a neuropeptide receptor, NPR-15, expressed in AIA interneurons that receive synaptic input from these sensory neurons, function in the same genetic pathway as NSY-1/SEK-1 signaling. These findings suggest that this MAPK pathway may affect neuropeptide signaling between sensory neurons and interneurons, thus promoting high-salt chemotaxis after conditioning.