Brain Sense

How your brain makes sense of your senses.

What Nematodes and Sea Slugs Tell Us about Our Brains

Small creatures are perfect research subjects for neuroscientists.

The nematode, C. elegans
One way to study the human brain is to look at the brains of other animals. We aren't all that different, especially on the molecular level. In Brain Sense, I wrote about how the lowly nematode, Caenorhabditis elegans, or C. elegans for short, is revealing the secrets of the sense of touch.

At no more than a millimeter long, C. elegans isn't much to look at and it leads a dull life--by human standards anyway--but it's the darling of touch researchers because it has big, easily accessible neurons--each of which can be studied individually. What's more, its mechanoreceptors (touch-sensitive neurons and their associated cells) are "conserved across evolutionary history." That means your touch sense works pretty much the same as a nematode's.

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In humans, touch is handled by neurons in the skin, joints, and mesenteries (membranes that support organs). Those neurons respond specifically and exclusively to a particular kind of touch, such as light contact, pressure, vibration, or body position. From studies of C. elegans, researchers know that touch changes the structure of channels in the membrane of a touch-sensitive neuron. The change opens the channels' gates, allowing positively charged sodium (Na1+) ions to flood in. The influx of ions changes the relative charges of the cell inside and outside, opening the gate to yet another channel, one that permits calcium ions (Ca2+) to enter. Those chemical changes activate the channel, so it sends an electrical impulse from a touch-sensitive neuron to an interneuron (one that carries messages between neurons). In the nematode, the interneuron ferries the signal to a motor neuron, which, in turn, stimulates a tiny roundworm muscle to contract, causing the animal to move. Signals from touch neurons also travel to opposing motor neurons that inhibit motion, so the animal can move in one direction, with movement in the opposite direction blocked.

John H. "Jack" Byrne, Ph.D., and other UTHealth neuroscientists are using sea snails to learn. Photo credit: R. Clayton McKee

Another star of the neuroscience research lab is the species of sea snail known as Aplysia californica. The mollusk has contributed a lot to our understanding of learning and memory. Neuroscientists at the University of Texas Health Science Center at Houston (UTHealth) published a new report on the Nature Neuroscience website this week. They used the sea snail to test the most effective time sequence for learning. "When you give a training session, you are starting several different chemical reactions. If you give another session, you get additional effects. The idea is to get the sessions in sync," said John H. "Jack" Byrne, senior author and chair of the Department of Neurobiology and Anatomy at the UTHealth Medical School.


Byrne's research team looked at the timing of learning sessions. Two groups of snails received five learning sessions. One group trained in regular 20-minute intervals. The other received learning sessions at irregular intervals as predicted by a mathematical model. The model built on earlier research that identified proteins linked to memory; it predicted when the activity of the proteins might be aligned for the best learning experience.


Five days after the learning sessions were completed, a significant increase in memory was detected in the group that was trained with a schedule predicted by a computer. But no increase was detected in the group with the regular 20-minute intervals. To confirm their findings, researchers analyzed nerve cells in the brain of snails and found greater activity in the ones receiving the enhanced training schedule. "We found that memory could be enhanced appreciably," said Byrne. "We have developed a way to adjust the training sessions so they are tuned to the dynamics of the biochemical processes."


Is there any practical application to research on nematodes and snails? More than you can imagine. C. elegans studies are informing us on everything from muscle atrophy to nicotine dependence; and what researchers are discovering from sea snails may someday help people with learning impairments resulting from aging, stroke, traumatic brain injury, or congenital cognitive impairments.

For More Information:

Brynie, Faith. Brain Sense, Part One: Touch.


Yili Zhang, Rong-Yu Liu, George A Heberton, Paul Smolen, Douglas A Baxter, Leonard J Cleary & John H Byrne. Computational design of enhanced learning protocols. Nature Neuroscience. Published online Dec. 25, 2011.

 

C. elegans photo source: The NIF Blog.

 

 

Faith Brynie, Ph.D, is a scientific and medical writer. She is the author of Brain Sense (Amacom, 2009).

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