Cellular porthole connects odors to brain

February 24, 2005

A cellular "porthole" known best for its role in the digestive system apparently has a major role in helping the brain sense odors, Johns Hopkins scientists report in the Feb. 17 issue of Neuron. The porthole, which lets chloride into cells, is also critical in digestion, hearing, balance, and fertility.

The researchers suggest that digestive system cells and odor-detecting cells use the same chloride porthole, or ion transporter -- the former to facilitate secretion of digestive juices, and the latter to communicate information about scents to the brain.

Although scientists have long known that odor-sensing cells require lots of charged chloride atoms, or ions, to relay odor signals to the brain, they did not know how cells keep levels of chloride high inside of the cells. Now Hopkins researchers have shown that these high chloride levels in odor-detecting cells depend on the same transporter, known as NKCC1, used in many other types of cells as well.

"It's not unusual for the body to use the same machinery to solve different problems," notes one of the lead authors, Jonathan Bradley, Ph.D., a postdoctoral fellow in neuroscience. "Chloride is a kind of jack-of-all-trades that cells can hijack to do what they want."

Odor-detecting nerve cells are long and thin, extending from the tissues lining the nose where odors are sensed all the way to the brain. When you smell cookies baking, odor molecules bind to these cells, triggering a series of molecular "gates" on the cell surface to open. The open gates let charged ions, including chloride, move in and out of the cell, creating differences in charge between the inside and outside of the cell. Such differences allow electrical signals to travel to the brain, telling you that home-made cookies are nearby.

Bradley and co-author Johannes Reisert, Ph.D., suspected NKCC1 might be involved in this process precisely because of the transporter's known importance in regulating chloride in many other tissues. Since NKCC1 appears in other cell types, and because odor-detecting nerve cells neurons need large amounts of chloride to sense odors, Reisert and Bradley hypothesized that NKCC1 was responsible for maintaining high chloride levels in odor-sensing cells too.

To test their idea, the researchers exposed individual odor-detecting nerve cells from mice to odor molecules. Unlike normal cells, those without functional NKCC1 had no detectable chloride movement, indicating that the NKCC1 transporter was indeed responsible for the necessary chloride current.

Bradley and Reisert also discovered that the porthole was located on an unexpected region of the odor-detecting cell. However, its location on these cells corresponds to its location on cells that line the digestive tract -- reinforcing the idea of "borrowed" machinery.

"At first we were surprised to find this location of the transporter," says Bradley, "but in hindsight it makes sense -- both types of cells need to keep chloride high in order to do their jobs, and the transporter's location helps them."

Now that the chloride-controlling machinery in the nose is known, scientists can probe details of chloride's involvement in sending information to the brain, the researchers say. Bradley and Reisert suspect that having lots of chloride available in odor-detecting cells may help the brain discriminate between different smells.

"The involvement of chloride might also make the cells' response to odor more robust and reliable," says Reisert, also a postdoctoral fellow in neuroscience.

The researchers plan to study the behavior of mice without NKCC1 and are now attempting to clone and characterize the chloride transporter to get a better sense of how chloride is required for odor detection.
-end-
These studies were funded by the Howard Hughes Medical Institute. The authors on the paper were Reisert, Jun Lai, King-Wai Yau and Bradley, all from Johns Hopkins.

On the Web: http://www.neuron.org/

Johns Hopkins Medicine

Related Brain Articles from Brightsurf:

Glioblastoma nanomedicine crosses into brain in mice, eradicates recurring brain cancer
A new synthetic protein nanoparticle capable of slipping past the nearly impermeable blood-brain barrier in mice could deliver cancer-killing drugs directly to malignant brain tumors, new research from the University of Michigan shows.

Children with asymptomatic brain bleeds as newborns show normal brain development at age 2
A study by UNC researchers finds that neurodevelopmental scores and gray matter volumes at age two years did not differ between children who had MRI-confirmed asymptomatic subdural hemorrhages when they were neonates, compared to children with no history of subdural hemorrhage.

New model of human brain 'conversations' could inform research on brain disease, cognition
A team of Indiana University neuroscientists has built a new model of human brain networks that sheds light on how the brain functions.

Human brain size gene triggers bigger brain in monkeys
Dresden and Japanese researchers show that a human-specific gene causes a larger neocortex in the common marmoset, a non-human primate.

Unique insight into development of the human brain: Model of the early embryonic brain
Stem cell researchers from the University of Copenhagen have designed a model of an early embryonic brain.

An optical brain-to-brain interface supports information exchange for locomotion control
Chinese researchers established an optical BtBI that supports rapid information transmission for precise locomotion control, thus providing a proof-of-principle demonstration of fast BtBI for real-time behavioral control.

Transplanting human nerve cells into a mouse brain reveals how they wire into brain circuits
A team of researchers led by Pierre Vanderhaeghen and Vincent Bonin (VIB-KU Leuven, Université libre de Bruxelles and NERF) showed how human nerve cells can develop at their own pace, and form highly precise connections with the surrounding mouse brain cells.

Brain scans reveal how the human brain compensates when one hemisphere is removed
Researchers studying six adults who had one of their brain hemispheres removed during childhood to reduce epileptic seizures found that the remaining half of the brain formed unusually strong connections between different functional brain networks, which potentially help the body to function as if the brain were intact.

Alcohol byproduct contributes to brain chemistry changes in specific brain regions
Study of mouse models provides clear implications for new targets to treat alcohol use disorder and fetal alcohol syndrome.

Scientists predict the areas of the brain to stimulate transitions between different brain states
Using a computer model of the brain, Gustavo Deco, director of the Center for Brain and Cognition, and Josephine Cruzat, a member of his team, together with a group of international collaborators, have developed an innovative method published in Proceedings of the National Academy of Sciences on Sept.

Read More: Brain News and Brain Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.