21 septiembre 2007

Por qué las cosas huelen

Why Stuff Stinks: Secret Sniffed Out

By Dave Mosher, LiveScience Staff Writer

posted: 21 September 2007 08:36 am ET

Our noses can quickly distinguish a pleasant smell and a stench, but until now the chemical cues that help us make such decisions had not been understood.

Researchers have found that heavier, more spread-out molecules tend to smell worse than lighter, more compact molecules, although exceptions to the rule exist. The finding can be used to predict how good or bad a molecule smells before anyone takes a whiff of it.

Rehan Khan, a neuroscientist at the University of California in Berkeley, thinks evolution selected for pleasantness of smell as a gut reaction to guide us through our environments.

"People can tell you right away whether something smells bad or good, but they're bad at naming the scent," Khan said. "Evolution probably latched onto the most efficient cues, like how the eye uses the wavelength of light to pick out colors."

Khan and his colleagues' findings are detailed in a recent issue of the Journal of Neuroscience.

Molecular breakdown

To find the nose's shortcuts for discerning good smells from bad, Khan and his team looked at more than 1,500 different properties of about 150 molecules, then compared them to professional "smelling assessments" of the substances.

In the end, molecular weight and electron density best correlated with pleasantness. Butanol, for example, is an "electron-dense" and spread-out molecule that stinks like rotting wood, while limonene—a compact but lightweight molecule—smells like citrus.

"We think, evolutionarily, that our bodies have settled on this handful of properties to distinguish good smells from bad ones for a reason," Khan told LiveScience, but admitted that he's uncertain why the brain and nose evolved sensitivity to the molecular properties that they did.

"What we do know is that chemicals perceived as less pleasant are generally not useful to us, and can even be harmful," he said.

Smell this

Putting their new model to the test, Khan and his colleagues predicted how good or bad 27 chemicals not previously assessed by experts smelled across American, Jewish-Israeli and Arab-Israeli cultures.

Khan and his team's model, it turns out, correctly placed about 30 percent of the chemicals in an ordered list of bad-smelling to pleasant-smelling molecules. He explained that the number may appear low, but it's relatively and statistically high given the differences in cultural upbringing and complexity of our smelling abilities.

"When we presented the preliminary results at a conference, a fragrance company said they flat-out didn't believe us," he said. The wary corporation sent his team 20 new molecules for the team to predict the pleasantness of, and when they returned their results, he said the company was "quite surprised."

Professional noses

Khan said the U.S. scent-manufacturing industry, which designs and produces the scents in everyday products such as food, perfumes and candles, is a multi-billion-dollar-a-year business.

But the companies who design and make the compounds rely on highly-trained and expensive professional smellers, called "noses," to assess them.

Khan thinks if his team's model could help design pleasant-smelling chemicals from the get-go and cut back the reliance on human noses.

"We can now use chemistry to predict the perception of the smells of new substances," Khan said. "This may really help to design scents other than by trial-and-error, which is an extremely expensive process."

Cómo percibimos los olores

How We Smell

By Corey Binns, Special to LiveScience

posted: 22 May 2006 08:37 am ET

Your nose is one powerful protrusion. Whether it's a big honker or a little button, if it is working correctly you can sense a skunk from only 0.000,000,000,000,071 of an ounce of offensive spray.

Animals can trace even tinier trails. Male luna moths, for example, track females from 5 miles away.

Such nosiness is important for the survival of almost all creatures: to find food, avoid being eaten, and pick proper mates. It warns us about rotten milk, a burning house, or an unhappy skunk, and can turn our attention to attractive potential dates.

Nosing around

Despite its value, scientists knew little about how we sensed scents before the 2004 Nobel Prize winners took a jab at it.

Know Your Noses

Guess who these famous honkers belong to, then click to see the full pictures. (Hint: None of these is attached to Gerard Depardiu or Pinocchio.)



In 1991, laureates Richard Axel of Howard Hughes Medical Institute and Linda Buck at the Fred Hutchinson Cancer Research Center discovered about 1,000 genes that encode for olfactory receptors inside the human nose. They also found that each receptor is tuned for only a small number of odors.

Researchers recently determined which receptors in a fruit fly detect which specific odors. They plotted each receptor to form an entire map of where the fly senses each scent.

"The results of our analysis allow us to make predictions about which odors smell alike to an animal, and which smell different," said Yale University molecular biologist John Carlson who worked with then-grad student Elissa Hallem, now a molecular biologist at the California Institute of Technology.

Their findings are published in the April issue of the journal Cell.

Take a deep breath

Although we don't yet have a scent map for humans, thanks to Axel and Buck, scientists know how you smell.

Take a deep breath. Air is sucked up into your nostrils over bony ridges called turbinates, which add more surface area to your sniffer. The air travels over millions of olfactory receptor neurons that sit on a stamp-size sheet, the olfactory epithelium, on the roof of the nasal cavity. Odor molecules in the air stimulate and inhibit the receptors.

Each aroma sets off a signal made by the receptors that travels along the olfactory nerve to the olfactory bulb. The olfactory bulb sits underneath the front of your brain. Signals from the bulb tell your brain what reeks.

Humans can recognize 10,000 different odors. However, no two people sense anything the same.


Good weather for smelling

Several factors, including genes, skin type, and diet are related to how smells smell. Even the weather can alter an odor.

  • When we're hungry, our smell sense grows stronger
  • Women have keener whiffers than men and like the smell of a symmetrical man best.
  • At certain times of the month, men say the scent of a woman is more attractive.
  • Our schnozzes are at their worst in the mornings, improving as the day goes on.

Some people endure long-term proboscis problems.

Smell disorders most often stem from injuries to the head and upper respiratory infections. Other causes include hormonal disturbances, dental problems, and exposure to chemicals such as insecticides and solvents can also cause smell disorders. Radiation for treating head or neck cancer can create smelling problems as well.

A nose that's in less than tip-top condition can affect taste buds too. Researchers say 80 percent of the flavors we taste come from what we smell, which is why foods become relatively flavorless when we're plugged up.

19 septiembre 2007

El brócoli y la barrera hematoencefálica

De acuerdo a un estudio aparecido en el Journal of Neuroscience (Jing Zhao, Anthony N. Moore, John B. Redell, and Pramod K. Dash) el brócoli puede ayudar en la protección del cerebro. La conclusión se obtuvo de un estudio realizado con una molécula llamada sulforaphane, que se encuentra presente en el brócoli, que ayuda a incrementar la actividad de la barrera hematoencefálica cuando ésta se encuentra dañada. El estudio se hizo en animales de laboratorio pero pudiese extrapolarse a humanos.

La
función principal de la barrera hematoencefálica es proteger al cerebro al prevenir la entrada de sustancias químicas peligrosas que se encuentren en la sangre. La forma como funciona el sulforaphane es atenuando la pérdida de las proteínas citoprotectivas de la barrera hematoencefálica que son las que mantienen la integridad de la misma. Estas proteínas suelen declinar después de una lesión. El sulforaphane además de disminuir la pérdida de estas proteínas al incrementar la actividad de un factor llamado Nrf2 y los elementos de respuesta antioxidante (ARE), también ayudó a disminuir la pérdida de céulas endoteliales y redujo la incidencia de daños similares por permeabilidad de la membrana y edema cerebral.

Traducido por Rubén Carvajal Santana de http://www.nutraingredients.com/news/ng.asp?n=79886-broccoli-cruciferous-vegetables-superfoods