Leeches may unlock spinal-cord secrets

Leeches and the human brain both contain the chemical dopamine.

Scott Doane

In 2005, 4.1 million people worldwide suffered from Parkinson’s disease, and that number could grow to 8.7 million in 2030, according to the American Academy of Neurology.

But one small discovery at the University might lead to bigger things.

Researchers used leeches and found that dopamine, a chemical that’s also in the human brain, may activate segments of the spinal-cord that lead to locomotion in humans.

This finding could lead to treatments for Parkinson’s disease or spinal-cord injuries in the distant future.

Professor Karen Mesce of the department of entomology and neuroscience began studying the effects of dopamine on locomotion two years ago.

Using leeches gave researchers insight into what the human spinal cord might look like, Mesce said. Like the spinal cord, leeches are broken down into individual segments and their nerve cells are easily accessible.

Dopamine acts like the conductor of an orchestra, she said. It activates certain nerve cells while others shut off.

“They’re operating like an orchestra that’s playing a complex piece of classical music,” she said. “Dopamine makes sure that all the players in the orchestra are doing what they need to do at the right time.”

Mesce and graduate student Joshua Puhl first dissected individual collections of nerve cells from a leech and put them in a dish, she said. Tiny electrodes were placed in it to record nerve activity and dopamine was fused into the nerve cells.

They compared the recordings of those individual nerves to recordings and video tape of an entire moving leech and found that the nerve activity was the same.

“It’s very complicated,” Mesce said. “Probably hundreds of neurons are being activated, but the dopamine is what’s beautifully choreographing all of these activity relationships.”

Puhl said he felt fortunate to be part of a project that produced such important results.

“We’ve uncovered far more possibilities than a small army of grad students could address at once,” Puhl said.

Even with this research, a treatment for Parkinson’s disease is still years away, said Dr. Walter Low, a professor of neurosurgery who has done Parkinson’s research.

“There’s a long way to go,” Low said. “A leech is not a perfect model of the mammalian central nervous system.”

Mesce said they used leeches as a model for the spinal cord, but they still don’t understand what human spinal cord circuits are like.

“We don’t know how the human circuitry is organized yet,” Mesce said. “Our findings can instruct us how they might be organized.”

Doing this research in an animal closer in anatomy to humans could possibly be the next step, Low said. However, he said these were significant findings.

“It gives insight into the role dopamine plays and how it can activate these motor programs,” Low said.

Puhl said every contribution to science works toward a greater good.

“As researchers work on small portions, every study is important in some way, especially if it gives other people ideas,” he said.