What you taste may not seem new to you but it probably is, at least to your taste buds. Every 10 days or so, the little sensory cells on your tongue die and are replaced and reconnected to nerves in a system so seamless you never notice.
The taste system is providing one Medical College of Georgia researcher with an interesting model for nerve regeneration that could lend insight into repairing much larger nerve damage such as that from spinal cord injuries.
Although it has not received the interest and grant funding of more vital senses such as sight and hearing, the taste system does provide unique insights into other important body systems such as the immune system, MCG researcher Lynnette P. McCluskey says. Taste, in fact, is a family passion - Dr. McCluskey's husband, David, is a chef who recently opened Fresh Thyme Cafe in Surrey Center.
"I can get pretty scientific about my work," Mr. McCluskey said from his restaurant. "Say the way you make mashed potatoes. If you're crushing a cell wall, your mashed potatoes are going to be a little more gummier and goopier than if you're slicing a cell wall. Things like that."
Dr. McCluskey's work is an example of how some long-held beliefs about the body are being abandoned in the search for new approaches to stubborn problems such as repairing nerve damage. Part of that is a new understanding of how the immune system and the nervous system may interact, she said.
"The big myth, which is still in textbooks, is that the immune system doesn't affect the nervous system and especially in the brain," Dr. McCluskey said. "For a long time, people thought that chemicals secreted by immune cells only affected other immune cells ... But we're starting to realize that these two systems have really important interactions."
The taste system, with its constant turnover of taste buds, provides an interesting place to test those interactions.
"How do these neurons hook up to these particular receptor cells and become functional and turn over the connections so that you never notice any difference in taste?" Dr. McCluskey said.
And how does it react to damage?
Working with rats, Dr. McCluskey cut the nerve on one side of the tongue, which kills off the receptor cells on that side. When the nerve grew back in just a few days, the receptor cells reappeared.
She also found that nerves can be manipulated.
By limiting contact with sodium, Dr. McCluskey found that when the receptors on the severed side returned, they had a low response to sodium. Surprisingly, the receptors on the other side of the tongue, connected to a completely separate undamaged nerve, became overly responsive to sodium, Dr. McCluskey said. There was no obvious pathway for those receptor cells to communicate, which made her suspect that the immune system is involved.
"We know that leukocytes (cells from the immune system) can move through local tissue and can be carrying signals from one side to the other," Dr. McCluskey said.
The cells could be attracted by the damage and also could be releasing chemical messengers called cytokines and nerve growth factors that stimulate regeneration, Dr. McCluskey said.
The role of inflammation and immune response in the nervous system also has seen a turn-around in thinking in recent years, said David Hess, the chairman of the Department of Neurology at MCG.
"I think there has been a change in the pendulum in the last probably five years in neuroscience where now people are looking at the possible good of inflammation, looking upon it as a double-edged sword where maybe the specific situation, the area of the nervous system and the timing is critically important," Dr. Hess said.
Certain types of immune cells, such as macrophages and monocytes, secrete those beneficial chemical agents. How they can be manipulated for nerve repair is an exciting area of study, Dr. Hess said.
"Looking at the immune system that way is very cutting-edge in neuroscience right now," Dr. Hess said.
Dr. McCluskey said the next step is to clarify what immune system cells are available to interact with the taste system and what kind of impact they can have on nerve regeneration.
"Once we know the rules behind this, what do we do to the immune system?" Dr. McCluskey said. "How do we control that so that we provide a beneficial environment for regenerating nerves? I think it holds a lot of promise for recovery from neural injury."
Reach Tom Corwin at (706) 823-3213 or firstname.lastname@example.org.
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