Researchers find biological clock for smell in mice

December 18, 2006

Biologists at Washington University in St. Louis have discovered a large biological clock in the smelling center of mice brains and have revealed that the sense of smell for mice is stronger at night, peaking in evening hours and waning during day light hours.

A team led by Erik Herzog, Ph.D., Washington University associate professor of Biology in Arts & Sciences, discovered the clock in the olfactory bulb, the brain center that aids the mouse in detecting odors.

The olfaction biological clock is hundreds of times larger than the known biological clock called the suprachiasmatic nucleus (SCN), located at the base of the brain right on top of where the optic nerves cross each other. Cells in both the SCN and the olfactory bulb to each other and environmental cycles of day-night.

"It's been a question for some time whether the SCN functions as the only biological clock," said Herzog. "One wouldn't think that the ability to smell would cycle, but that's what we show."

"I think now that the SCN is like the atomic clock, important for keeping central time, and then there are all of these peripheral clocks - for timing tasks like sleep-wake, vigilance, digestion, olfaction, hearing, touch and vision, though not all yet found. It may be that the peripheral clocks are like individual wristwatches that we must periodically reset."

Perhaps most surprising is the observation that the olfactory bulb clock can run independent of daily rhythms in sleep-wake or the SCN, making it the Big Ben of the mammalian circadian rhythm world.

"It seems to be one of those biological clocks that can keep running itself for a long time, even without the SCN," Herzog said.

Results were published in the Nov. 22, 2006, issue of the Journal of Neuroscience.

Herzog and collaborators Daniel Granados-Fuentes, Ph.D., Washington University postdoctoral researcher, and undergraduate student researcher Alan Tseng, put a little cedar oil on a Q-tip and allowed mice to sniff it for five minutes.

"We then preserved their brains and counted the number of olfactory bulb cells that had been activated by the odorant," Herzog said. "The gene cFOS is a marker for cells that were activated by the stimulus. We recorded the expression of that gene. All of the data came from in vivo measurements." They saw more of those cells light up in the olfactory bulb at night than in the day.

"The olfactory bulb might be more sensitive at night when the creatures are active than when they are resting in the day," Herzog speculated. "This might help them find food or mates when they are hungry for food or for love."

Do the results suggest that women should splash on the Estee Lauder during the night so that men can notice all the more and shun the bottle during the day" "There are anecdotes in the literature about humans liking certain perfumes more during the evening than the morning, and there is some evidence that we also have daily rhythms in olfaction," Herzog said.

Herzog said that it is rare to find someone missing their SCN, so it's tricky to study the human olfactory clock by itself. For this reason, his lab plans to study olfactory behavior in mice.

"We can say that this (olfactory bulb) clock has a functional consequence, and now we're setting up to do olfactory behavior," he said. "We'll ask the mice to tell us when they can smell odors of different concentrations, and we hope to learn more about how and how much the clock modulates their sense of smell, and which cells and genes are needed.

The olfactory bulb biological clock study opens up many questions, a key one of which is: Why are there multiple clocks?

"This idea of multiple biological clocks is new," Herzog said. "We might need now to consider ourselves a clock shop. It appears that disrupting the coordination between these clocks is bad for our health, like in jet lag or shift work."

Washington University in St. Louis

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 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