Grenache DG et al. (1993) Worm Breeder's Gazette "Differential Effects of Dauer-Defective Mutations in L1-Specific Surface Antigen Switching"

Politz SM, Grenache DG

[Worm Breeder's Gazette, 1993]

DIFFERENTIAL EFFECTS OF DAUER-DEFECTIVE MUTATIONS ON L1- SPECIFIC SURFACE ANTIGEN SWITCHING. David G. Grenache and Samuel M. Politz, Department of Biology and Biotechnology, Worcester Polytechnic Institute, Worcester, MA.

Luo, Linjiao et al. (2010) Worm Breeder's Gazette "Making linear chemical gradients in agar"

Luo, Linjiao, Greenwood, Joel, Kim, Daniel, Soucy, Edward, Samuel, Aravinthan

[Worm Breeder's Gazette, 2010]

Fang-Yen, Christopher et al. Worm Breeder's Gazette "Agarose immobilization of C. elegans"

Wasserman, Sara, Fang-Yen, Christopher, Sengupta, Piali, Samuel, Aravinthan D. T.

[Worm Breeder's Gazette]

Chen, Sway P. et al. (2011) International Worm Meeting "How larvae wiggle: functional analysis of the L1 larva locomotory circuit."

Tang, Anji, Chen, Sway P., Wen, Quan, Samuel, Aravinthan D. T.

[International Worm Meeting, 2011]

At all developmental stages, C. elegans navigates its environment by generating and propagating sinusoidal bending waves along its body. The neural circuit controlling the locomotory behavior, however, changes significantly at the late L1 larval stage [1]. Neuroanatomy shows that almost no cholinergic motor neurons innervate the ventral body wall muscles in the L1 larva, raising the question of how the larva is capable of normal locomotion. Here we hypothesize that ventral body wall muscles in the L1 larva contract by default. During the dorsal muscle contracting phase, DB cholinergic motor neurons activate DD GABAergic motor neurons and cause periodic relaxation of the ventral muscles. This hypothesis is supported by two experimental observations. First, we examined the swimming behavior of GABA-deficient mutant unc-25 in the L1 stage and found that the tail consistently curved to one side. Second, we found that wild-type worms expressing GFP in VNC neurons consistently curved to the ventral side after being paralyzed by ivermectin, a drug that silences the motor circuit but has no effect on muscles. Further optogenetic and calcium imaging experiments will be carried out to quantify and relate motor neuron and muscle activity in the free-moving larva. Our approach will build toward a detailed mechanistic model of L1 locomotion. Hopefully, comparison of L1 and adult worm locomotion will shed light on conserved principles of rhythmic motion in general. 1.White, J.G., et al., The structure of the ventral nerve cord of Caenorhabditis elegans. Philos Trans R Soc Lond B Biol Sci, 1976. 275(938): p. 327-48.

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.

Leifer, Andrew et al. (2011) International Worm Meeting "Shining light on behavior: An optogenetic dissection of neural circuits in freely behaving C. elegans."

Wen, Quan, Samuel, Aravinthan, Clark, Christopher, Leifer, Andrew, Fang-Yen, Christopher, Alkema, Mark

[International Worm Meeting, 2011]

Optogenetics provides a promising new platform for conducting behavioral neuroscience investigations in the nematode Caenorhabditis elegans. The ability to precisely manipulate neural activity in individual neurons in a moving worm allows one to pinpoint the contribution of individual neurons to animal behavior. Previously we developed a high-resolution optogenetic illumination system capable of delivering arbitrary light patterns to targeted cells in a freely moving C. elegans (Leifer and Fang-Yen et al, Nature Methods, 2011). The system, called CoLBeRT, uses a high speed camera and custom computer vision software to monitor the motion of an unrestrained worm. As the worm swims or crawls, the system instructs a digital micromirror device to reflect patterns of blue or green laser light onto specific cellular targets expressing Channelrhdopsin-2 or Halorhodopsin. The system has sufficient accuracy and resolution to stimulate individual mechanosensory neurons while a worm swims. Here we have expanded the CoLBeRT system's capabilities to dissect the motor circuit, mechanosensory circuit and investigate the roles of command interneurons. The system is now able to generate illumination patterns with arbitrary amplitude waveforms and we have adapted the system to work with microfluidic devices. We have used the system to differentiate models of wave propagation in the motor circuit, to study habituation in the mechanosensory circuit and to begin an exploration of the command interneurons. Preliminary evidence suggests that stimulation of the command interneuron AVA modulates the worm's backward velocity.

Fang-Yen, Christopher et al. (2009) International Worm Meeting "The worms crawl in, the worms crawl out: An analysis of C. elegans locomotory gaits."

Wen, Quan, Samuel, Aravinthan, Kawai, Risa, Fang-Yen, Christopher, Wyart, Matthieu, Chen, Sway, Chklovskii, Dmitri

[International Worm Meeting, 2009]

C. elegans exhibits very different locomotory patterns when swimming in fluids and crawling on a solid substrate. Compared with crawling, swimming is characterized by a longer wavelength and higher frequency of undulations. We are interested in understanding how a single circuit composed of command neurons, motor neurons, and muscles is capable of supporting these two locomotory gaits. We estimate that when crawling on moist surfaces, worms are held by capillary forces up to 100,000 times greater than the viscous forces experienced during swimming. To investigate in more detail the effect of this mechanical loading on locomotion, we immerse worms in solutions of varying viscosity and measure their wavelength, frequency, and curvature by machine vision algorithms. We show that worm exhibit a continuous transition from swimming to crawling behavior as viscosity is increased from that of water to a value 5 orders of magnitude larger. Worms in fluids of intermediate viscosity exhibit locomotory patterns intermediate between swimming and crawling. Swimming and crawling can therefore be seen as low-load and high-load limits of a continuum of locomotory patterns. We show that our results can be understood in terms of a biomechanical model of C. elegans locomotion in which the swimming to crawling transition is associated with a transition between elastic-dominated and viscous-dominated dynamics. Next we analyze the behavior of worms undergoing spatial transitions between swimming and crawling behaviors, such that mechanical loading varies over the length of the worm. The analysis of such transitions gives insights into the generation and propagation of the sinusoidal bending wave, and the mechanisms of modulation of locomotory gaits. We show that the worm behavior follows neither strictly local nor strictly global modulation, but rather can be described by a set of rules governing the generation and propagation of undulatory waves.

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.

Politz SM et al. (1992) Parasitol Today "Caenorhabditis elegans as a model for parasitic nematodes: a focus on the cuticle."

Philipp M, Politz SM

[Parasitol Today, 1992]

The phylum Nematoda consists of over half a million species of worms that inhabit astoundingly diverse environments. Nematodes can live as obligatory parasites of plants and animals, or alternate a parasitic with a free-living life style. The fact that the vast majority of species are strictly free living often surprises parasitology students, for obviously the highest research priorities in this field have involved parasites of medical, veterinary and agricultural importance. Here Samuel Politz and Mario Philipp contend that some basic questions concerning the biology of the parasite cuticle can be investigated more easily and in greater depth in the free-living nematode Caenorhabditis elegans than in the parasites themselves.

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. .