Even the simplest creatures look extraordinarily complex when you look below the surface. Fortunately, hydra makes this part easier.
Rice’s electrical and computer engineer Jacob Robinson and senior author and alumnus Krishna Badhiwala of the university’s Brown School of Engineering take advantage of the animal’s transparency to do the toughest, manipulating small creatures remarkably resistant in every way possible to learn how they feel to touch.
Their full review of hydra in the open access journal eLife, in collaboration with biologist Celina Juliano and graduate student Abby Primack of the University of California at Davis, is a small step towards understanding neural networks in all living creatures.
Hydra vulgaris, freshwater cnidarians that resemble miniature jellyfish polyps, expand and contract as they navigate their environment, but can also be enticed to do so by giving them a kick. elbow. The Rice lab has developed highly specialized equipment over the past decade to do this, temporarily forcing animals in the channel of a microfluidic device to capture simultaneous images and data that detail their muscle and neural responses.
There, the hydra can be physically pushed with controlled force to cause it to contract. For the new study, the researchers genetically engineered the hydra to express a green fluorescent protein when associated neurons are activated, then removed sets of these neurons – and even parts of the body – to see how the networks react when they bite animals.
Their goal was to build a model of how internal states and external stimuli shape the behavior of an organism with highly dynamic neural architecture.
“We need to establish the fundamentals of how animals like hydra work, in terms of neurobiology, so that we can then start making comparisons with really diverse animals,” said Robinson, a member of the Neuroengineering Initiative of Rice. “I could see that in five or 10 years there would be a lot of really interesting questions that we can answer now that we have laid some of the groundwork.”
Hydra neurons are concentrated in the buccal region (adjacent to the tentacles) and the aboral region (around the “foot”), but researchers have identified two distinct types of neurons: “mechanically responsive” neurons and “mechanically responsive” neurons. Previously discovered “contraction burst”. – distributed in all the bodies. This helped explain the different firing patterns they discovered, depending on whether the hydras contract spontaneously or are triggered mechanically.
Researchers have also found that the oral and aboral regions play a role in spontaneous contractions. The oral region, aka the hypostoma, is larger; because it appears to coordinate the motor response, they learned that removing the hypostome significantly reduced a hydra’s response to the sting entirely.
The aboral region, aka peduncle, appears to contain a high concentration of motor neurons involved in contraction, as evidenced by the calcium networks that activate from the foot upward when triggered either by the hypostome or by pushing a “headless” hydra.
Most interesting was the evidence that when the hydra either suppressed one network or the other or was literally cut in half, the remaining neurons took over to maintain at least rudimentary function and / or regenerate the lost pieces.
“When we first started studying the hydra, we wanted to understand as much as possible about how it works, how it works, and how it differs from other animals,” said Robinson. “One of the things we didn’t know was the specific types of neural structures. Hydra in particular has a distributed nervous network, and we wanted to know if particular regions of the animal process information centrally, or if all neurons are a bit the same. “
It turned out that the oral and aboral networks are quite distinct in the way they control different aspects of the hydra. “But it seems there is redundancy and processing of sensory information, which we also see in other animals,” he said. “This idea of redundancy is really important for the survival of animals, so we see it popping up a lot of times wherever we look.”
While the hydra’s radial nervous systems are fundamentally different from the networks of bilateral creatures like mammals, there are similarities in how all of these systems share the workload when they have to.
“I like to think of it this way: let’s look at all the crazy things nervous systems can do that evolved from the same starting point,” said Robinson. “It can allow us to identify fundamentals that are harder to find in rodents and humans, where they might be obscured by other things that we have developed over time.”
Robinson said neuroscientists who look beyond traditional small model organisms – rodents, worms, zebrafish and fruit flies – will be most interested in the hydra’s findings. “There is a recognition that we really need to diversify our choices of animals that we study,” he said.
There are also implications for scientific initiatives beyond the animal kingdom. “The fact that this particular type of nervous system can fully recover makes me think that there are principles related to what makes a network stable,” said Robinson. “These could be applied to stabilize power grids or the internet, inspired by nature.”
Robinson is an associate professor of electrical and computer engineering and bioengineering at Rice. Juliano is Assistant Professor of Molecular and Cellular Biology at UC Davis. The National Science Foundation (1829158, 1250104), the National Institutes of Health (R21AG067034) and the Keck Center of the Gulf Coast Consortia supported the research.