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Squishy hydra's simple circuits ready for their close-up · Daniel Vercosa, now an engineer at Intel Corp. Robinson is an assistant professor of electrical and computer engineering

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Page 1: Squishy hydra's simple circuits ready for their close-up · Daniel Vercosa, now an engineer at Intel Corp. Robinson is an assistant professor of electrical and computer engineering

Squishy hydra's simple circuits ready fortheir close-up26 July 2018

A hydra is pulled into a pipette in preparation forinsertion into a microfluidic chamber. Credit: Jeff Fitlow

Just because an animal is soft and squishy doesn'tmean it isn't tough. Experiments at Rice Universityshow the humble hydra is a good example.

The hydra doesn't appear to age – and apparentlynever dies of old age. If you cut one in two, you gethydrae. And each one can eat animals twice itssize.

These beasties are survivors, and that makes themworthy of study, according to Rice electrical andcomputer engineer Jacob Robinson.

Robinson and his team have developed methodsto corral the tiny, squid-like hydrae and perform thefirst comprehensive characterization ofrelationships between neural activity and musclemovements in these creatures. Their resultsappear in the Royal Society of Chemistry journalLab on a Chip.

The researchers used several methods to revealthe basic neural patterns that drive the activities offreshwater hydra vulgaris: They immobilized the

animals in narrow, needle-laden passages, droppedthem into arenas about one-tenth the size of a dimeand let them explore wide-open spaces. Theyexpect their analysis will help them identify patternsthat have been conserved by evolution in largerbrain architectures.

Robinson is a neuroengineer with expertise inmicrofluidics, the manipulation of fluids and theircontents at small scales. His lab has developed anarray of chip-based systems that let scientistscontrol movements and even sequester biologicalsystems – cells and small animals – to study themup close and over long periods of time.

The lab has studied all of the above with its custom,high-throughput microfluidics systems, with wormsrepresenting the "animal" part.

But hydrae, which top out at about a half-centimeterlong, come in different sizes and change theirshapes at will. That presented particular challengesto the engineers.

"C. elegans (roundworms) and hydrae havesimilarities," Robinson said. "They're small andtransparent and have relatively few neurons, andthat makes it easier to observe the activity of everybrain cell at the same time.

"But there are enormous biological differences," hesaid. "The worm has exactly 302 neurons, and weknow exactly how it's wired. Hydrae can grow andshrink. They can be cut into pieces and form newanimals, so the number of neurons inside canchange by factors of 10.

"That means there's a fundamental difference in theanimals' neurobiology: Where the worm has tohave an exact circuit, the hydrae can have anynumber of circuits, reorganize in different ways andstill perform relatively similar behaviors. Thatmakes them really fun to study."

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Page 2: Squishy hydra's simple circuits ready for their close-up · Daniel Vercosa, now an engineer at Intel Corp. Robinson is an assistant professor of electrical and computer engineering

The microfluidics platform let the lab sequester asingle hydra for up to 10 hours to studyneurological activity during distinct behaviors likebody column and tentacle contraction, bending andtranslocation.Some of the hydrae were wild, whileothers were modified to express fluorescent orother proteins. Because the best way tocharacterize a hydra is to watch it for about a week,the lab is building a camera-laden array ofmicrofluidic chips to produce time-lapse movies ofup to 100 animals at once.

Rice University electrical and computer engineer JacobRobinson peers into a chamber of hydra cultivated in hislab for testing. Credit: Jeff Fitlow

"If you look at them with the naked eye, they just sitthere," Robinson said. "They're kind of boring. But ifyou speed things up with time-lapse imaging,they're performing all kinds of interesting behaviors.They're sampling their environment; they're movingback and forth."

Electrophysiology tests were made possible by thelab's development of Nano-SPEARs, microscopicprobes that measure electrical activity in theindividual cells of small animals. The needlesextend from the center of the hourglass-shapedcapture device and penetrate a hydra's cellswithout doing permanent damage to the animal.

Nano-SPEARS don't appear to measure activity ofneurons inside the animal, so the researchers usedcalcium-sensitive proteins to trigger fluorescent

signals in the hydra's cells and produced time-lapsed movies in which neurons lit up as theycontracted. "We use calcium as a proxy for electrical activity inside the cell," Robinson said."When a cell becomes active, the electricalpotential across its membrane changes. Ionchannels open up and allow the calcium to comein." With this approach, the lab could identify thepatterns of neural activity that drove musclecontractions.

"Calcium imaging gives us spatial resolution, so Iknow where cells are active," he said. "That'simportant to understand how the brain of thisorganism works."

Manipulating hydrae is an acquired skill, accordingto graduate student and lead author KrishnaBadhiwala. "If you handle them with pipettes,they're really easy, but they do stick to pretty muchanything," she said.

"It's a little difficult to jam them into microfluidicsbecause they're really just a two-cell-layer-thickbody," Badhiwala said. "You can imagine thembeing easily shredded. We eventually got to thepoint where we're really good at inserting themwithout damaging them too much. It just requiressome dexterity and steadiness."

Credit: Rice University

With this and future studies, the team hopes toconnect neural activity and muscle response tolearn about similar connections in other membersof the animal kingdom.

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Page 3: Squishy hydra's simple circuits ready for their close-up · Daniel Vercosa, now an engineer at Intel Corp. Robinson is an assistant professor of electrical and computer engineering

"C. elegans, drosophila (fruit flies), rats, mice andhumans are bilaterians," Robinson said. "We allhave bilateral symmetry. That means we shared a common ancestor, hundreds of millions of yearsago. Hydrae belong to another group of animalscalled cnidarians, which are radially symmetric.These are things like jellyfish, and they have amore distant ancestor.

"But hydrae and humans shared a commonancestor that we believe was the first animal tohave neurons," he said. "From this ancestor cameall the nervous systems that we see today.

"By looking at organisms in different parts of thephylogenetic tree, we can think about what'scommon to all animals with nervous systems. Whydo we have a nervous system? What is it good for?What are the things that a hydra can do that wormsand humans can also do? What are the things theycan't do?

"These kinds of questions will help us understandhow we've evolved the nervous system we have,"Robinson said.

Co-authors are Rice graduate students DanielGonzales and Benjamin Avants and alumnusDaniel Vercosa, now an engineer at Intel Corp.Robinson is an assistant professor of electrical andcomputer engineering.

More information: Krishna N. Badhiwala et al.Microfluidics for electrophysiology, imaging, andbehavioral analysis of Hydra, Lab on a Chip (2018).DOI: 10.1039/C8LC00475G

Provided by Rice UniversityAPA citation: Squishy hydra's simple circuits ready for their close-up (2018, July 26) retrieved 1 February2019 from https://phys.org/news/2018-07-squishy-hydra-simple-circuits-ready.html

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