New York City -- Under the lens of the microscope, the portraits of the brain cells are like an aquatic creature with multiple tentacles for receiving messages from one's senses. The brain cells make sense of otherwise invisible smells like the aroma of a flower or the stink of rotten food. The brain cells' red and green streaks reveal cells in a mouse lab's brain center called the olfactory bulb.
This olfactory bulb comprises hundreds to thousands of segregated clusters named glomeruli. Each glomeruli interacts specifically with thousands of smell chemicals that can breathe from the floating air.
The single glomerulus signal-carrying projections or axons from the sensory cells in the nose have converged.
The Rise of Neuroscientific Mystery
From its own set of olfactory neurons, each glomerulus receives signals that will randomly spread in an animal's nose, yet all tuned to detect the smell in the same way.
A group of researchers in the 1990s claims that each of the subsets of the olfactory neurons contains a different shaped receptor protein that latches differently into a small molecule. This research was based on Doctor Richard Axel from the Zuckerman Institute.
From then, it presents quite the neuroscientific mystery: how can each randomly located, odor-detecting cell in the nose manage to send signals to a single glomerulus within the olfactory bulb?
Putting this into an illustration, 50 friends who were originally separated in random locations in a city making their way to the same house without having the address. But somehow, these friends know where to go.
According to the latest published study in Cell Journal, Doctor Stavros Lomvardas, Principal Investigator from the Zuckerman Institute, explains the vital insight into how the olfactory system achieves its wiring precisions to be in hand. Doctor Lomvardas and MD-PhD candidate Hani Shayya created a team that will find out what they suspect, that the central organizing process in the mouse between the smell sensory cells and the glomeruli aims at the brain's olfactory bulb.
The axons of sensory cells in a single glomerulus within a mouse brain’s olfactory bulb are labeled in red and green in this photo illustration.
Solving The Neuroscientific Mystery
The Columbia University-led team's main discovery resides in the form of each receptor's protein as it assumes its unique three-dimensional shape within a tubular component of the cell called the endoplasmic reticulum (ER).
The protein's form is determined by the different sequences of its amino acid components. The team has found that these amino acid sequences impose a measurable level of stress on the ER, or putting into a simple illustration, a sock containing numerous objects inside. The levels of ER stress serve like a dial setting, but further studies are needed to confirm.
The setting triggers a gene-orchestrated process in which the sensory cells direct their axons to aim at the glomeruli within the olfactory bulb. The subset of sensory cells with the same-shaped receptor proteins ends up projecting its axon to the same glomerulus. Without receptor-glomerulus mapping, a flower could end up smelling like rotten food or vice versa.
Dr. Lomvardas, a professor of neuroscience and biochemistry and molecular biophysics at Columbia University's Vagelos College of Physicians and Surgeons, described the research outcome as "mind-blowing." He then said in the paper, "This system found a way to create a genetically encoded, hard-wired means of transforming randomly-chosen receptor identity to a very precise target in the olfactory bulb."
He then mentioned that Alzheimer's, Parkinson's, and other neurodegenerative illnesses involve olfactory deficits during early disease development. Shayya, on the other hand, pointed to another tantalizing possibility. Unless the olfactory neurons are not alone in the ER, stress organizes its wiring with downstream neurons. "If it turns out that all neurons do this, this discovery could help us understand much more about the brain," Shayya said.
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