A WMU researcher and pond dwellers illuminate the nervous system

contact: Paula M. Davis
| WMU News

Dr. John Jellies—also known as "The Leech Guy"—was one of two researchers honored this fall with a Distinguished Faculty Scholar award, the highest annual honor WMU bestows on faculty members.

Read about Jellies' research in this story pulled from the WMU Magazine archives.

Leeches and light

Photo of an illuminated leech

At the end of a lab table clogged with notebooks and instruments, five European medicinal leeches gyrate, squirm or swim in a jar of water.

Dr. John Jellies rolls up the sleeve of a black turtleneck sweater, reaches in and grabs a leech with the ease of one snatching a gummi worm from a candy jar.

But this slimy invertebrate won't just quiver benignly in Jellies' grasp. Using suction cups on its head and tail, it crawls, inchworm-like, across his hand.

What's more, this creature is the type of leech that sucks blood for nourishment (Jellies will tell you that not all leeches do).

But its appetite for blood is of no concern to this professor of biological sciences in whose Haenicke Hall lab these creepy crawlies call home.

To read more from the WMU Magazine, click here.

After all, John Jellies is: The Leech Guy.

He's well earned this moniker after working with leeches for more than 30 years. His lab is full of bubbling aquariums, amplifiers, microscopes and computers, as well as dishes of snails and, of course, hundreds of leeches.

When regarding the leeches in Jellies' lab, you might see a simple, primordial pond dweller. But he sees a creature of beauty and intricacy.

As a scientific researcher, he's interested in how circuits of neurons generate behaviors. He says that studying this requires neurons that one can actually see, listen to and manipulate.

This is where the leech undulates into the picture.

In his view, the leech fits into a sort of scientific "Goldilocks zone" as an animal that is not too simple and not too complicated, but just right for his research questions.

One can gain insights by performing direct experiments on its neurons, he says.

Jellies seeks to unlock the mysteries of the central nervous system through this creature whose anatomy can help answer complex questions about vision, locomotion, light sensing, and other sensory responses and actions.

The 'sheer joy' of discovery

Photo of Dr. John Jellies


As a researcher, Jellies adheres to "a tenacious reliance on experimentalism to obtain answers that expand the narrative of understanding in concrete, generalizable ways," he says, adding: "First, happiness is an understanding of how things work. And second, if you want to know how something works, do the experiment."

Jellies grins and says, "It's mostly mountains of detailed grunt work punctuated by occasional moments of sheer joy."

"There's a high probability of using findings (with the leech) to generalize to other more complex animals— perhaps even humans," he says.

After earning a Ph.D. in neurobiology from the University of Texas at Austin, Jellies accepted a post-doctoral fellowship in the Department of Biology at the University of California at San Diego, obtaining an award from the National Institutes of Health. He used to study the development of neurons and neural circuits that generate behavior in the humble leech.

He came to WMU in 1995, establishing his research program using leeches.

The researcher stops short of applying, wholesale, lessons learned from leeches onto humans. But there are broad-based similarities that are instructive.

For instance, he has done research into the various neural circuits of a leech, drafting detailed maps of the nerves and synapses within the animal and what behaviors they are responsible for.

Photo of Dr. John Jellies holding a well-fed leech

Jellies holding a well-fed leech

The undulating, graceful swimming motion of a leech is actually a complex behavior, from a neuromuscular standpoint, Jellies says. Think about the alternating complex rhythms of walking, jogging or sprinting in human locomotion.

The European medicinal leech has two "brains"—one in the head and the other in the tail—and a central nerve cord connects the two. Jellies notes that if this nerve cord is severed, given time to recover, the animal will eventually regain much of its original ability.

The same does not hold true for humans because our spinal cord is encased in boney vertebrae, Jellies explains.

While this boney structure offers significant protection, he says that it also isolates the sensitive neurons so that that when they are severely traumatized, the effects are significant and the neurons are prevented from growing in this enclosed environment.

"Very different degenerative diseases like traumatic paralysis or Alzheimer's— are among the many different things that can interrupt how neurons talk to each other—I argue that to make progress in understanding them, we must understand at a basic, detailed level how these neural circuits do these almost miraculous things in the first place," Jellies says.

Though experimenting on the leech isn't meant to address specific human diseases like these, learning how a leech's more simple physiology and anatomy works has a lot of relevance, he says.

"After all, how do we understand how a system is failing if we don't understand how it works at a fundamental level in the first place?"

Leeches and light sensing

Photo of a dissected leech

Photo of a dissected leech

Among the many research questions that interest Jellies is how animals integrate multiple stimuli and generate adaptive behaviors in response to them.

Humans do this each moment, using hundreds of stimuli at the same time, even without conscious awareness.

Jellies' most recent research has centered on how leeches behave when exposed to different wavelengths of light.

Just as the leeches Jellies studies outdo humans in their number of brains, the same is true for eyes. The leeches have five pairs of eyes on their head, each containing 50 photoreceptors.

To visualize these photoreceptors, imagine a vase made out of black glass, containing 50 marbles. Each of these vases is attached to an optic nerve that sends a signal to the animal's brain. In addition, there are other photoreceptors that run all along a leech's elongated, undulating body.

As complex as our eyes are, the chemicals that detect light and turn them into an electrical signal have a common origin, Jellies says.

The photoreceptors, rods and cones that make up the intricacy of the human eye also can be found in houseflies, squid and, yes, leeches. And the same genes that "turn on" to build the human eye during development are also found in leeches, worms and dogs, Jellies says.

Though leeches seek prey during daylight hours, overexposure to invisible ultraviolet light can weaken or even kill them.

Jellies hypothesized that in addition to already known responses to visible light, leeches must be able to detect and integrate UV radiation as a visible cue to decide whether to hide, pursue prey or "get out of Dodge," he says.

But this had never been shown.


Photo of leeches in a lab

Through a series of experiments involving the use of small LED light wands that emitted light across both the visible and UV spectra, Jellies showed that leeches would back away from the harmful UV radiation.

To his surprise, UV radiation aimed at the head resulted in a shortening of the body to withdraw, while the same light at the tail resulted in extension, the opposite motor pattern.

Both behaviors make sense in that they removed the leech from the light, but their different movements to accomplish this suggested a high degree of sensory and motor integration, he says.

He was also able to show that at least some photoreceptors on the leech were specifically sensitive to UV radiation, and that one of the higher-level leech neurons dedicated to controlling rapid movement is activated by both visible and UV radiation, setting the stage for looking at how the nervous system integrates various sources of diverse inputs to make decisions. Some neurons even responded to both light and the pressure of physical touching.

His findings were published in the Journal of Experimental Biology.

"We've begun to get a better understand of how input is getting into the central nervous system. There's a lot more to do on that but we have made a start," Jellies says.

"What happens to neurons and synapses during profound responses associated with things like addiction, learning, flinching? To broaden the question: What does the brain do with the input when the signals are coming in?

"We are in the early stages of this, but I think those doing research in vertebrates will be informed by the kinds of things we find out about these deceptively simple (leech) nervous systems that are really pretty complex," Jellies says.

"I hope that what we do has an impact on the human condition in some meaningful ways. Almost all studies of living systems relate to each other, to the fundamental molecular structure of life," he says.

"All animals' nervous systems are built out of basically the same things. We have, with the leech, one of the best systems at the single-cell level for asking the big questions about neurons and brain function. These are exceptionally complex issues, we at least have a prayer of success with this critter."

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