In
recent studies, it has been established that a subset of microvillous olfactory
neurons are derived from a population of stem cells known as the neural crest,
and in light of olfactory neurons having regenerative capabilities, we may have
found the fountain of youth through smell.
What are olfactory neurons and where do they come from?
First
off, olfactory neurons are specialized sensory detectors for smell. We also
have sensory neurons for sight, pain, and pressure. All of the neurons in the
brain are similar to the roller coasters at Six Flags Great America; if they
were interloped together in a space amounting to only one football field. Each
roller coaster has it’s own pathway and arrives at a destination different than
its neighbors, but nonetheless they all function in perfect synchronization.
This is similar to how the olfactory, optical, and other sensory neurons are organized
in the brain.
Now
imagine trying to trace a single roller
coaster or neuron back to the boarding station, or in this case origin in the
brain. It may seem like an impossible task, but in the paper, Sox-10 Dependent Neural Crest Origin of
Olfactory Microvillous Neurons in Zebrafish, Ankur Saxena and his
colleagues explain to us how they discovered that olfactory neurons do not
all come from one place. According to Saxena et al, it was commonly believed
that all of the olfactory sensory neurons formed from a single place known as the
olfactory placode. But through the use of photoconversion using protein Sox-10
labeled neural crest cells, they were able to track the neural crests from the dorsal neural tube, into olfactory epithelium, and finally as they
differentiated into microvillus neurons. (Saxena et al.) In addition, they used tracking with laser
ablation to prove that the neural crest derived cells are necessary in the
formation of microvillus olfactory neurons, and proved that the up regulation
of Sox-10 protein was necessary for this differentiation. This was ground
breaking, in that it revolutionized our understanding of development, and
because olfactory neurons have regenerative potential, further inspection, of
the lineage of these cells can provide insight into how the regenerative
processes work.
I Smell Discoveries
Similarly,
Alex Stone, in his New York Times article, Smell
Turns Up in Unexpected Places, further illustrates the regenerative
capabilities of olfactory neurons. Stone and the scientists he interviewed,
take us out of the brain, and into the body. Olfactory nerves are a part of a larger
picture, known as the peripheral nervous system. The job of the peripheral
nervous system is to send sensory information from all over the body back to
the brain. Since olfactory neurons can
branch out into the rest of the body, we now have good reason to believe that
that there are odor receptors outside of the nose. Dr. Hanns Hattt, of Ruhr
Univeristy Bochum in Germany has found that there are smell receptors in our
skin, similar to those found in our nose. (Stone)
It
sounds crazy to believe that our skin can smell, but other researchers have
found comparable results. Grace Pavlath of Emory University, found evidence of olfactory
receptors in our skeletal tissue. Her results further explain how, if the
receptors are marinated in synthetic fragrance, they promote muscle
regeneration.
The Fountain of Youth
Although,
healing through smell sounds impossible, Pavlath and Hath might not be entirely
wrong. Despite remarkable work in
embryology, Saxena et al, also explained to us how microvillus neurons from
olfactory epithelium can detect nucleotides, pheromones, and amino acids! It
sounds weird that a odor receptor, can detect an amino acid when it also
functions in smell. We detect smell because a ligand, will bind to specific
receptor, which will trigger a series of metabolic cascades to tell the brain
that what you are smelling is a rose An olfactory receptor is a type of G-
coupled protein. A G-protein can be activated by many sources and further
stimulate a multitude of metabolic functions. Scent molecules, nucleotides,
and amino acids are only some of the ligands that we know to activate olfactory
receptors. As the peripheral nervous
system, extends throughout the body, it is plausible for us to have smell
receptors scattered in our muscular tissue. It is further possible that the
activation of a certain g-protein can activate a pathway towards metabolic
function that results in growth. Stone further claims that there is genetic
evidence for nearly every organ to have olfactory receptors.
The
fact that Saxena, established that olfactory sensory neurons are also derived
from stem cells further confirms the capability of these neurons to regenerate.
All of this work is mind blowing to the point that we could have smell induced
healing medicine. Since human tests results show that we heal 30% faster in the
presence of Sandalore, it may be that we have found the fountain of youth in
smell. (Stone)
Bibliography:
Stone, Alex. "Smell Turns Up in Unexpected Places."
The New York Times. The New York Times, 13 Oct. 2014. Web. 04 Mar. 2016.
Saxena,
Ankur, Brian N. Peng, and Marie E. Bonner. Sox-10 Dependent Neural Crest
Origin of Olfactory Microvillous Neurons in Zebrafish. Elife.elifesciences.org.
N.p., 19 Mar. 2013. Web. 04 Mar. 2016.
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