Kato, Saul et al. (2011) International Worm Meeting "Temporal processing of olfactory information in C. elegans chemosensory neurons."

Cho, Christine, Bargmann, Cornelia, Abbott, L. F., Xu, Yifan, Kato, Saul

[International Worm Meeting, 2011]

Natural behaviors require sensory processing over a wide range of timescales. For example, the nematode Caenorhabditis elegans can track odor concentrations within a second for gradient climbing, escape a noxious stimulus within seconds, and evaluate the quality of its environment over many minutes. All of these behaviors are initiated by specific chemosensory neurons. What mechanisms support chemosensation at different timescales? To address this question we characterized the responses of three C. elegans sensory neurons, AWC, ASH and ASI, to rapidly fluctuating pseudo-random odor sequences. Precise control of input sequences was achieved by switching of laminar liquid streams within a microfluidic chip. All three neuron classes generate highly reliable calcium responses with distinct temporal selectivities. We applied reverse correlation techniques to extract the temporal filtering properties of each neuron. AWC can track odors at a sub-second time scale, consistent with its role in assessing gradient changes during chemotaxis, and the rapid response requires a specific G protein subunit. The ASH neuron acts as a slower integrator of nociceptive signals, including high osmolarity. Surprisingly, ASI also responded to the ASH stimulus, acting as a slow differentiator that subtracts stimulus history over the past few seconds from prior stimulus history. Both AWC and ASH operate in dual regimes with slow (~minute-long) odor responses superimposed on their rapid responses. Our results suggest that C. elegans chemosensory neurons are selective both for chemical identity and for specific temporal signatures.

Kato, Saul et al. (2015) International Worm Meeting "Global brain dynamics generate the holistic motor command pattern in C. elegans."

Kato, Saul, Zimmer, Manuel, Kaplan, Harris, Schrodel, Tina

[International Worm Meeting, 2015]

Due to technical limitations, prior studies in C. elegans have not typically considered distributed coding principles observed in other nervous systems. Instead, identified neurons have been described as dedicated encoders of specific sensory inputs or motor outputs in a context of separable, linear and mostly feed-forward sensory-to-motor pathways. This viewpoint is hard to reconcile with the largely horizontal and recurrent character of the neuronal wiring diagram. Moreover, the circuit elements in these studies overlap, suggesting that processing of various sensory modalities and computation of behavior may be performed by a common system. Here, using a single-cell resolution, brain-wide Ca2+-imaging approach developed by our group, we find that neural population dynamics exhibit a widely shared, low-dimensional component with a cyclical state space trajectory, indicative of a continuous attractor manifold. Next, by calcium imaging in free-moving worms, we find that the activities of key neurons correlate to both high level motor state as well as analog movement parameters such as speed, and that these activities map onto the state space trajectory in a well-ordered manner: trajectory bundles can be mapped to motor command states and decisions between alternate behaviors are readily observable at bundle branch points. Moreover, an analog parameter like speed drive is discernible by the position on the manifold. We argue that this dynamical organization assembles action sequences of discrete motor states and at the same time encodes graded metrics of motor intent. This study establishes, for the first time in any animal, a real-time mapping between neural and behavioral dynamics on a single-trial basis. Using chemical genetics, we find that network dynamics persist when decoupled from output by pre-motor interneuron inhibition. Moreover, manifold topology is robust and provides a framework for a sensory input, which modulates the probability of branch traversal, to produce stimulus-evoked behavioral transitions. Both results indicate that population state structure is stably maintained by intrinsic dynamics. This work shows that many neuron classes participate in a pervasive low-dimensional signal which holds the high-level motor command sequence. In mammals, cortical population dynamics produce functionality in a distributed manner; e.g. in macaque motor cortex, goal parameters are encoded across the neural population and movement is produced by collective dynamics. The character and function of the collective neural dynamics we observe suggests that despite profoundly differing neuroanatomy, the principles of C. elegans and mammalian brain function are far more similar than previously suspected.

Webb, John et al. (2019) International Worm Meeting "Information theory rules out the body cascade model of C. elegans locomotion."

Webb, John, Kato, Saul

[International Worm Meeting, 2019]

How the nematode C. elegans moves in a serpentine fashion is still unknown despite a detailed anatomical knowledge, connectome and genetic access to each of its 302 neurons. Two main models exist for C. elegans locomotion: a body cascade model where the back and forth undulations of the head set up an oscillatory pattern that propagates down the body via lateral connections between neuromuscular units and biomechanical linkage, and an alternative active posture model where the sinusoidal body posture along the entire body is effected by active neuromuscular control not solely deriving from lateral neuromuscular signaling from the head to tail. We recorded high resolution videos of worms crawling on an agar surface and extracted time series of the centerline postural angle for each of 13 body segments. As expected, the time series appeared to be a series of phase-lagged noisy sinusoids. We computed the peak cross-correlation between each body segment angle to the anterior-most segment angle-for a simulated worm under the body cascade model, this function monotonically decreases as function of segment number. However, we found a strong breaking of monotonicity in our experimental data, arguing against a strict body cascade model. We then performed mutual information analysis between segment pairs, and found a strong deviation from monotonic information loss. This deviation from monotonicity was further evidence against the strict body cascade model, as a consequence of the data processing inequality theorem. We then performed the same analysis for backwards locomotion and swimming versus crawling behaviors and again found a breaking of monotonicity, although at a different body segments, suggesting a different pattern of neural control. Finally, we performed our analysis on various mutant worms tracked through the Open Worm Movement Database. Overall, our analysis results resembled N2 worms for all analyzed genotypes, though unc-37 and egl-8 displayed reduced strength of the mid-body increases in peak cross-correlation and mutual information, suggesting a loss of central coordination. We conclude that worms employ centrally driven active postural control to locomote in addition to lateral neuromuscular signaling. Thus, basic information theory applied to animal behavior can yield insights into models of neurobehavioral control.

Bubnis, Gregory et al. (2019) International Worm Meeting "A multi-feature probabilistic atlas for automatic cell identification in whole-body C. elegans recordings."

Kato, Saul, Bubnis, Gregory, DiFranco, Matthew, Ban, Steven

[International Worm Meeting, 2019]

We have advanced a collaborative machine learning system to solve the challenging problem of identifying cells in C elegans from still or video volumetric microscopy. The distinguishing features of this approach versus prior approaches include: (1) use of a statistical model of cell features that is iteratively improved, (2) generation of probabilistic guesses at cell ID rather than single best-guesses for each cell, (3) tracking of joint probabilities of features within and across cells, and (4) ability to exploit multi-modal features, such as cell position, morphology, reporter intensities, and activity. We have developed a generative spring-mass model to simulate sequences of cell imaging datasets with variable cell positions and fluorescence intensities. We explore various probability models of increasing sophistication, and we have developed a novel, effective algorithm for Bayesian label matching, part of a class of generally intractable combinatorial optimization problems. We find that atlases that track inter-cell positional correlations give higher labeling accuracies than those that treat cell positions independently. Tracking an additional feature type, fluorescence intensity, boosts accuracy relative to a position-only atlas, demonstrating that multiple cell features can be leveraged to improve automated label predictions. We demonstrate use of this open-source system on whole body still and video volumetric imaging in adult hermaphrodite C. elegans, for both single fluorophore and multi-fluorophore expressing worm strains.

Chalasani, Sreekanth H. et al. (2009) International Worm Meeting "AWC sensory neurons release two neurotransmitters to regulate exploratory behavior upon removal from food."

Albrecht, Dirk, Bargmann, Cornelia I., Chalasani, Sreekanth H., Kato, Saul

[International Worm Meeting, 2009]

Animals increase their pirouette frequency in response to removal from food stimulus for a period of 15 min. The AWC and ASK sensory neurons and the AIB interneurons stimulate pirouettes immediately after removal from food, while the AIY and AIA interneurons inhibit pirouettes (Wakabayashi et al 2004, Gray et al 2005). We have found that AWC sensory neurons become active in response to removal of stimulus, releasing two neurotransmitters (glutamate and a neuropeptide NLP-1). The released glutamate acts to activate AIB and inhibit AIY interneurons, promoting reversals (Chalasani et al 2007). In contrast to glutamate, AWC-released NLP-1 acts on AIA interneurons to suppress reversals, suggesting that reversal frequencies are regulated by at least two opposing signaling systems. AWC calcium responses are modulated in these neurotransmitter mutants, suggesting that feedback pathways affect AWC neuronal activity. References: Chalasani, S. H., Chronis, N., Tsunozaki, M., Gray, J. M., Ramot, D., Goodman, M. B., and Bargmann, C. I. (2007). Dissecting a circuit for olfactory behaviour in Caenorhabditis elegans. Nature 450, 63-70. Gray, J.M., Hill, J.J., and Bargmann, C.I. (2005). A circuit for navigation in Caenorhabditis elegans. Proc. Natl. Acad. Sci. 102, 3184-3191. Wakabayashi, T., Kitagawa, I., and Shingai, R. (2004). Neurons regulating the duration of forward locomotion in Caenorhabditis elegans. Neurosci. Res. 50, 103-111.

JJ Ewbank et al. (1999) International C. elegans Meeting "We do it, bees do it, even educated fleas do it, (plants as well), but how do worms fight infections?"

JJ Ewbank, P Bulet, JA Hoffmann, D Ferrandon

[International C. elegans Meeting, 1999]

Over the last few years, insights into the antimicrobial defenses of the fruit fly Drosophila melanogaster have revealed remarkable parallels between insect and mammalian innate immunity (1). Relatively little is known about the immune responses of C. elegans . In Drosophila , an infection provokes the rapid sysnthesis of powerful antimicrobial peptides and opsonising proteins (2). While seven distinct anti-microbial peptides have been identified in flies, thus far, only two have been characterised from C. elegans , encoded by abf-1 and abf-2 on C50F2 (3; see also 4). Searching for conserved peptide motifs has yielded two further family members, abf-3 and abf-4 , (on F54B8 and Y38H6C, respectively) the study of which we are undertaking. Further, we are using MALDI-TOF mass spectrometry to investigate whether other antimicrobial peptides are induced upon infection of C. elegans . In Drosophila , the expression of anti-fungal peptides is controlled by the Toll pathway (5). A search of the genome reveals that C. elegans possesses structural homologues of most of the components of this signalling cascade (for Toll, pelle, tube, cactus, on cosmids C07F11, K09B11, F45G2 and C04F12, respectively). As a first step, we are using Northern analysis to determine whether this putative pathway is implicated in worm defense mechanisms. The results of these investigations will be presented. 1. Medzhitov and Janeway, 1998, Curr Opin Immunol, 10, 12-5 2. Hoffmann and Reichhart, 1997, Trends in Cell Biology, 7, 309-316 3. Kato, 1997, International Worm Meeting abstract 296 4. Kato and Komatsu, 1996, J. Biol. Chem., 271, 30493-30498 5. Lemaitre et al., 1996, Cell, 86, 973-983

Kuramochi, Masahiro et al. (2015) International Worm Meeting "Calcium imaging and computational simulation for the spatio-temporal dynamics of the neural coding in a C. elegans chemotaxis circuit."

Kuramochi, Masahiro, Doi, Motomichi

[International Worm Meeting, 2015]

To understand the neural information processing navigating animal behaviors, integration of the in-vivo observation of neuronal activity and the computational modeling using observation data is quite useful. This strategy gives us important information to characterize the spatio-temporal dynamics of the activity in each single neuron and their roles on information processing through synaptic integration. Recent studies have succeeded to apply the integrated analysis into C. elegans sensory neurons [Kato et al., 2014]. We have focused on a C. elegans chemosensory circuit and are conducting an integrational analysis to understand the neural information processing during salt-chemotaxis behavior. By using calcium-sensitive fluorescent proteins, in this study, we monitored the activities of the ASE salt-sensing neurons and their postsynaptic interneurons, and using these data, we have developed a novel simulation model to estimate their activities in-silico.The calcium-sensitive fluorescent proteins GECO were expressed in either ASE neurons or their postsynaptic neurons such as AIY, and the transgenic animals were stimulated by the decrease or increase of NaCl concentration. To monitor and collect the patterns of neuronal activities close to worm's living conditions, we applied various types of stimuli to the transgenic animals, such as long or short duration of stimulation, tiny or large concentration change, and the rapidly-flickering concentration change. These imaging analyses imply several characteristics about one of the salt-sensing ASE neurons ASER. First, the ASER neuronal activity is described by a leaky integrator which includes an exponential decay occurred after initial activation process. Second, the activity of the ASER neuron has a nonlinear relationship with the concentration change of NaCl. Thirdly, the ASER can response reliably to rapidly-flickering stimuli as the temporal dynamics observed in the AWC neuron [Kato et al., 2014]. For the computational modeling of the ASER neuronal activity, we have developed a kind of 'leaky integrate-and-fire model', in which neuronal cells are described as multi-compartments. We confirmed that this model reproduces the neuronal activity of the ASER neuron in agreement well with imaging data. Our integrated strategy will help to understand how neurons are responded and how these responses do contribute to the spatio-temporal dynamics of the postsynaptic neuronal activity, as worms sense various types of stimulation.

Saifuddin, Mashel Fatema et al. (2021) International Worm Meeting "Olfactory memory consolidation requires the TRPV channel OSM-9 in sensory neurons of the circuit."

Miller, Julia, L'Etoile, Noelle, Chandra, Rashmi, Chen, Alec, Benedetti, Kelli, Gallegos, Maria, Dunn, Raymond, Zhang, Bo, Kaye, Julia, Saifuddin, Mashel Fatema, Kato, Saul

[International Worm Meeting, 2021]

Memory is one of the most important abilities of the brain. It is defined as an alteration in behavior as a consequence of an experience. For example, the C. elegans nematode will downregulate its chemotactic response to the innately attractive odor, butanone, if the odor is not paired with food. Through repeated, spaced training with this odor in the absence of food, C. elegans will maintain this memory for a prolonged period of time. Although transient receptor potential (TRP) channels are classically thought of as primary sensory receptors, it was reported that the OSM-9/TRPV5/TRPV6 (TRP vanilloid 5/6) channel is required for single exposure learning. Here we describe a new role for osm-9 in consolidation of memory that is induced by repeated, spaced training. In this paradigm, osm-9 mutant animals learn as well as wild-types, but are unable to consolidate the memory. Though sleep is required for memory consolidation, loss of the TRPV channel OSM-9 does not affect sleep. This indicates that the TRP channel promotes memory in a process that acts outside the sleep pathway. We investigate the endogenous expression pattern of OSM-9 and show that it is not expressed in the butanone-responsive AWC olfactory sensory neuron. Instead, it is expressed in the paired AWA olfactory neuron, the ASH nociceptive neurons, the OLQ and two other unidentified sensory neurons which are most likely ADF and ADL as they express osm-9 mRNA. Because OSM-9 acts in sensory neurons that do not participate in butanone sensation, this indicates that the circuit participates in olfactory memory consolidation.

Scholz, Monika et al. (2019) International Worm Meeting "Predicting locomotion from whole-brain neural dynamics in freely moving animals."

Randi, Francesco, Leifer, Andrew, Yu, Xinwei, Shaevitz, Joshua, Linder, Ashley, Scholz, Monika, Sharma, Anuj

[International Worm Meeting, 2019]

How do patterns of neural activity across the brain represent an animal's behavior? Recent techniques for recording from large populations of neurons are providing new insights into how locomotion is encoded in population-level neural activity. Studies from mammalian systems suggest that behavioral information may be more prevalent throughout the brain and may account for a larger fraction of neural dynamics than previously thought. In C. elegans, pioneering studies revealed that the worm's neural dynamics during immobilization exhibit striking stereotyped low-dimensional patterns of neural activity that dominate brain-wide dynamics (Kato et al., 2015). These dynamics are hypothesized to map onto a motor sequence consisting of forward, backward and turning locomotion. One interpretation is that the majority of the worm brain's activity may be involved in encoding these locomotory behaviors. Here we seek to directly measure how patterns of neural activity represent locomotion by recording brain-wide calcium activity in freely-moving animals. We record calcium activity simultaneously from the majority of head neurons in C. elegans during unrestrained spontaneous locomotory behavior (Scholz et al., 2018). We find that a subset of neurons distributed throughout the head encode locomotion. By taking a linear combination of these neurons' activity, we predict the animal's velocity and body curvature and further infer the animal's posture from neural activity alone. The collective activity of these neurons outperforms single neurons at predicting velocity or body curvature. We further attempt to estimate the identity of neurons involved in the prediction. Among neurons important for the prediction are well-known locomotory neurons, as well as neurons not traditionally associated with locomotion. We compare the neural activity of the same animal during unrestrained movement and during immobilization and observe large differences in their neural dynamics. Intriguingly, during unrestrained movement we estimate that only a small fraction of the brain's overall neural dynamics are encoding velocity and body curvature. We speculate that the rest of the brain's neural dynamics may be involved in encoding other behaviors, processing sensory information or maintaining internal brain states. Kato, S., Kaplan, H.S., Schrodel, T., Skora, S., Lindsay, T.H., Yemini, E., Lockery, S., and Zimmer, M. (2015). Global brain dynamics embed the motor command sequence of Caenorhabditis elegans. Cell 163, 656-669. Scholz, M., Linder, A.N., Randi, F., Sharma, A.K., Yu, X., Shaevitz, J.W., and Leifer, A. (2018). Predicting natural behavior from whole-brain neural dynamics. BioRxiv 445643.

Jennifer L. Tenor et al. (2007) International Worm Meeting "A conserved Toll-like receptor is required for Caenorhabditis elegans innate immunity."

Jennifer L. Tenor, Alejandro Aballay

[International Worm Meeting, 2007]

Pathogen recognition through Toll-like receptors (TLRs) is the first step required to mount an appropriate immune response against invading pathogens. The only toll-like receptor, tol-1, in Caenorhadbitis elegans was shown to be required for behavioral avoidance to a particular Gram-negative bacterium, Serratia marcescens (1). Although we did not observe significant differences in behavioral avoidance between wild type and the tol-1(nr2033) mutant to various other Gram-negative pathogens, the tol-1 mutant was hypersusceptible to these pathogens suggesting that TOL-1 may provide protection through other mechanisms. Based on survival assays and microscopy, we found that TOL-1 is essential for protecting the pharynx against the enteropathogenic bacterium, Salmonella enterica serovar Typhimurium. Loss of tol-1 not only led to rapid death of C. elegans but also resulted in rapid accumulation of S. enterica in the terminal bulb of the pharynx. We showed that TOL-1 is required for the proper expression of ABF-2 which is a defensin-like molecule expressed in the pharynx (2) and HSP-16.41 which is also expressed in the pharynx and is part of a family of heat shock proteins required for C. elegans immunity (3). These results indicate that TOL-1 plays a direct role in innate immunity. (1) Pujol et al., 2001; (2) Kato, 2002; (3) Singh and Aballay, 2006.