October 8, 2013
Brain Cell Neurons Tell Us If We Like Or Dislike Smells
April Flowers for redOrbit.com - Your Universe Online
Some smells are instantly attractive to us. For example, think of the smell of baking bread. With no other cues, visual or tactile, that smell can draw you into the nearest bakery. In contrast, some smells -- like fresh fish -- are not that appealing, unless perhaps you haven't eaten in three days.
For scientists who are trying to address the increasingly acute problem of obesity, the question of how this works and what underlying biological mechanisms account for our unconscious ability to determine how attractive or repulsive a particular smell seems is an important one. The processes underlying food selection and preferences need to be understood.
A new study from Cold Spring Harbor Laboratory (CSHL) revealed a set of cells in the fruit fly brain that responds specifically to food odors. The researchers found the degree to which these neurons respond when the fly is presented different food odors – apple, mango, banana – predicts "incredibly well how much the flies will 'like' a given odor," says Jennifer Beshel, PhD, a postdoctoral investigator in the laboratory of CSHL Professor Yi Zhong, PhD. The findings of their study were published in the Journal of Neuroscience.
"We all know that we behave differently to different foods – have different preferences. And we also all know that we behave differently to foods when we are hungry," explains Dr. Beshel. "Dr. Zhong and I wanted to find the part of the brain that might be responsible for these types of behavior. Is there somewhere in the brain that deals with food odors in particular? How does brain activity change when we are hungry? Can we manipulate such a brain area and change behavior?"
The researchers investigated the response of neurons expressing a peptide called dNPF -- which is the fly analog of appetite-inducing Neuropeptide Y, found in people -- to a range of odors. They found the flies only responded to food odors. The fly neurons responded more to these same food odors when flies were hungry. The team found the amplitude of their response could predict how much the flies would like a given food odor -- for example, move toward it -- with great accuracy by simply looking at the responses of the dNPR-expressing neurons.
When these neurons were "switched off," the team was able to make flies treat their most favored odor as if it were just air. If, however, these neurons were remotely turned on, the flies would suddenly approach odors they have previously tried to avoid.
As Dr. Beshel explains, "The more general idea is that there are areas in the brain that might be specifically involved in saying: 'This is great, I should really approach this.' The activity of neurons in other areas in the brain might only take note of what something is – is it apple? fish? -- without registering or ascribing to it any particular value, whether about its intrinsic desirability or its attractiveness at a given moment."
Image Below: Circled green spots are the cell bodies of two dNPF neurons, one in each hemisphere of the fruit fly brain. The degree to which these cells respond to specific food odors corresponds with how much a fly likes or dislikes those odors, as reflected in behavior. Credit: Zhong lab - CHSL