Venkatachalam, Vivek et al. (2015) International Worm Meeting "Pan-neuronal imaging in roaming animals."

Wang, Xian, Tabone, Christopher, Zhen, Mei, Klein, Mason, Chisholm, Andrew, Srinivasan, Jagan, Greenwood, Joel, Clark, Christopher, Samuel, Aravinthan, Alkema, Mark, Mitchell, James, Ji, Ni, Venkatachalam, Vivek

[International Worm Meeting, 2015]

We present an imaging system for panneuronal recording in crawling C. elegans. A spinning disk confocal microscope, modified for automated tracking of the C. elegans head ganglia, simultaneously records the activity and position of ~100 neurons that co-express cytoplasmic calcium indicator GCaMP6 and nuclear localized RFP at 10 volumes per second. We developed a behavioral analysis algorithm that maps the movements of the head ganglia to the animal's posture and locomotion. Image registration and analysis software automatically assigns an index to each nucleus and calculates the corresponding calcium signal. Neurons with highly stereotyped positions can be associated with unique indexes and subsequently identified using an atlas of the worm nervous system. To test our system, we analyzed the brainwide activity patterns of worms subjected to thermosensory inputs. We uncover a strikingly sparse representation of thermosensory perception involving two neurons (AFDL and AFDR), and a broadly distributed representation of the motor state across the nervous system. Our imaging setup and analysis pipeline, panneuronal imaging in roaming animals, or PANERA, provides a new platform to establish functional maps of sensory to motor transformation in behaving C. elegans and Drosophila larva.

Torkashvand, Mahdi et al. (2021) International Worm Meeting "Interneuron Control of Diapause Entry"

Venkatachalam, Vivek, Chai, Cynthia, Sternberg, Paul, Torkashvand, Mahdi

[International Worm Meeting, 2021]

To maximize fitness, animals integrate various external stimuli to sculpt their physiological and behavioral responses throughout development. Under adverse environmental conditions, C. elegans larvae can choose to enter an alternate stress-resistant diapause state. C. elegans constitutively secretes dauer larvae-inducing pheromone, which serves as a proxy for high conspecific density. This information about local competition is integrated with other inputs to assess the environment's suitability for future reproductive growth. Although the roles of sensory neurons have been studied, little is known about the function of other neuron classes in this developmental paradigm. Here, we show that the AIA interneurons integrate pheromone cues from multiple sensory neuron classes and propagate this information via neuropeptidergic pathways to regulate the diapause entry decision. Pre- vious studies have shown that FMRFamide-like neuropeptide flp-2 null mutants are significantly more likely to enter diapause compared to wild-type animals. A flp-2 GFP reporter expressed in AIA, and AIA-specific flp-2 cDNA expression is sufficient to rescue the flp-2 mutant diapause entry phenotype. We also show that chemogenetic inhibition of AIA recapitulates the flp-2 mutant phenotype. AIA is the major postsynaptic partner of the glutamatergic ASK and ADL pheromone-sensing neurons. To investigate the link between the AIA ac- tivity and input signals from these pheromone sensing neurons, we used a microfluidic device to deliver crude pheromone extract in a controlled environment. While ASK and ADL are activated by acute pheromone pre- sentation, we find that AIA is inhibited likely through glutamate-gated chloride channels. To further confirm the dependency of the flp-2 expression on the AIA activity, and that the inhibition of AIA during the L1 larval stage initiates the diapause entry, we've performed periodic imaging of activity in AIA as worms proceed through development in microchambers subject to either dauer-inducing or reproductive chemical environments. Us- ing this platform, we show that AIA is quiescent under dauer-inducing conditions but active under reproductive growth conditions. Identification of a key stimulus integrator in this developmental decision provides an opportunity to further probe its underlying computational processes.

Stumbur, Stephanie et al. (2021) International Worm Meeting "C. elegans regulates its behavior via serotonergic signaling to find food and hydrogen peroxide protection."

McGowan, Natalie, Serkin, William, Sevedolmohadesin, Maedeh, Venkatachalam, Vivek, Stumbur, Stephanie, Apfeld, Javier, Schiffer, Jodie

[International Worm Meeting, 2021]

Hydrogen peroxide is a pervasive chemical weapon used by many species to damage their prey or to protect themselves from their pathogens. Cells rely on conserved defense mechanisms, including catalases, to avoid the damage that hydrogen peroxide inflicts on their macromolecules We recently discovered that C. elegans represses those defenses in response to sensory perception of E. coli, the nematode's food source in the lab, because E. coli can deplete hydrogen peroxide from the local environment and thereby protect the nematodes1. Here, we investigated the extent to which C. elegans can tell the difference between bacteria that provide hydrogen peroxide protection and bacteria that do not. To address that question, we determined the extent to which hydrogen peroxide modulates the behavior of C. elegans in food lawns of wildtype E. coli and mutant E. coli unable to degrade hydrogen peroxide. In the absence of hydrogen peroxide in the environment, C. elegans did not exhibit a preference between these two bacteria stains. However, in the presence of hydrogen peroxide, C. elegans remained on the wildtype bacteria lawn but was much more likely to leave the lawn of the bacteria that do not degrade hydrogen peroxide. This nematode behavior was conserved when we used catalase-positive and catalase-negative bacterial strains from the natural C. elegans microbiome, suggesting that this decision-making occurs in the natural environment. To determine how C. elegans senses and responds to bacteria and environmental hydrogen peroxide, we measured calcium dynamics in ciliated sensory neurons. We identified several neuronal classes that respond to hydrogen peroxide in a bacteria-dependent manner. In addition, genetic analysis showed that serotonin signaling regulates this nematode behavior. Our findings demonstrate that the cross-kingdom interactions between C. elegans and bacteria in their microbiome determine the nematode food-leaving behavior via serotonergic signaling, enabling nematode populations to find safety from hydrogen peroxide. 1. Schiffer JA et al. (2020). Caenorhabditis elegans processes sensory information to choose between freeloading and self-defense strategies. eLife.

Susoy, Vladislav et al. (2019) International Worm Meeting "Mapping circuit-wide neuronal dynamics to a complex goal-directed behavior in C. elegans."

Venkatachalam, Vivek, Hung, Wesley, Zhen, Mei, Susoy, Vladislav, Samuel, Aravinthan, Whitener, Joshua, Wu, Min

[International Worm Meeting, 2019]

A central question in neuroscience is how brain circuits generate animal behavior. Addressing this question would benefit from knowing the system-wide activity patterns during complex, naturalistic tasks, along with synaptic and cellular features of all relevant neurons. We use the mating behavior of C. elegans males as such a paradigm. The mating behavior is an important self-motivated task, consisting of multiple steps with different temporal dynamics. Using customized microscopes build in our laboratory, we performed simultaneous continuous recordings of the activity of all neurons in the male mating circuit over the entirety of mating, while simultaneously tracking the animal's behavior. We have performed in-depth analyses of seven datasets, lasting 5-10 minutes each, that capture a wide range of mating sub-behaviors. Traces of neuronal activity were extracted for more than 60 identified neurons per dataset. Using these recordings in combination with cell-specific interventions, we were able to assign new specific functions to numerous neurons, as well as follow the progression of neuronal responses from sensory inputs to motor outputs. We have identified and confirmed multiple neurons involved in distinct mating steps including searching, scanning, turning, vulva location, excretory pore detection, insemination, and resting. By integrating the neuronal activity time series across experiments, we inferred an underlying functional network. By comparing the functional network with the known anatomical network of synaptic connectivity, we were able to assess the computational significance of electrical and chemical synapses and the sign and strength of interactions between synaptic partners. Our work creates a framework for a complete predictive model of a complex naturalistic behavior from underlying neuronal and circuit activity and connectivity patterns.

Ji, Ni et al. (2015) International Worm Meeting "AIY, a one neuron locus for sensorimotor integration."

Samuel, Aravinthan, Alkema, Mark, Ji, Ni, Venkatachalam, Vivek, Lim, Maria, Rodgers, Hillary, Clark, Christopher, Zhen, Mei, Kawano, Taizo

[International Worm Meeting, 2015]

For an animal to navigate its habitat, the nervous system of the animal must constantly integrate sensory input with feedback from its motor state. Corollary discharge, a phenomenon where signals from the motor circuitry are relayed to upstream circuit components, has been implicated in sensorimotor integration in a variety of animal behaviors. However, the mechanism by which corollary discharge or motor feedback contributes to complex navigational behavior such as thermotaxis is not well understood.To elucidate the loci for sensorimotor integration in C. elegans, we used volumetric imaging to simultaneously track many neurons in the thermosensory and the motor circuitry in animals that freely navigate a spatiotemporal temperature gradient. We observed that the AIY interneurons, which have long been known to play a key role in thermosensory signaling, exhibit activity patterns that correlate with both the thermosensory input as well as the motor behavior of the animal. Through cell ablation and genetic and optogenetic manipulations, we confirmed that the motor-related signal in AIY is corollary discharge in nature. In particular, we identified a series of premotor interneurons that are involved in relaying the motor-related signal to AIY. Through quantitative behavior analysis, we observed that animals with a disrupted corollary discharge pathway exhibit specific deficits in thermotaxis. Finally, we constructed a computational model that explains how the corollary discharge pathway contributes to a biased-random-walk strategy utilized by C. elegans during thermotaxis. Our study reveals a new mechanism by which individual neurons integrate sensory and motor signals to organize navigational behavior. .

Calvo, Ana C. et al. (2013) International Worm Meeting "The AIB interneuron is required for thermotaxis."

Hawk, Josh, Samuel, Aravinthan D.T., Venkatachalam, Vivek, Cook, Nathan, Colon-Ramos, Daniel A., Calvo, Ana C.

[International Worm Meeting, 2013]

The nematode Caenorhabditis elegans moves towards the cultivation temperature when placed in a thermal gradient, tracking isotherms once this temperature is reached. AFD is the principal thermosensory neuron and is required to perform all modes of thermotactic behavior. But how one neuron can drive the distinct sensorimotor transformations that underlie movement down or up gradients towards the cultivation temperature vs. isothermal tracking near the cultivation temperature is not understood. To study this question, we explored the downstream synaptic pathways from AFD. AFD has direct synaptic output to only two interneurons, chemical synapses to AIY and electrical synapses to AIB. While AIY role in thermotaxis has been widely studied and its inactivation is known to cause a constitutive cryophilic movement (movement towards colder temperatures), little is know of the AIB role. Using a genetic approach based on reconstituted caspases, we have ablated the AIB interneuron and found that these animals display no preference to move up or down the gradient. Moreover, AIB ablated worms show an increased isothermal tracking behavior: they track isotherms at temperatures where wild type animals show cryophilic or thermophilic behavior. Mutants that lack the gap junction between the AFD and AIB neurons (inx-1) exhibit a similar tracking behavior as the one seen in AIB ablated animals. Taken together, these results suggest that electrical and chemical synaptic pathways from the AFD neuron are differentially used to perform distinct modes of thermotaxis.