Mitral cells receive information from olfactory receptor neurons and, in turn, help transfer the information to the brain where it’s translated into odors, new and old. Photo courtesy of Charles Greer, Yale University
Odor of magnitude
Thanks to roughly 5 million olfactory receptors, humans are capable of detecting thousands of odors. On a smell chart, that puts us down among the stinkers. A rabbit, for example, has roughly 20 times more receptors and a bloodhound more than 220 million.
Yet even our comparatively diminished sense of smell is nothing to sniff at. Though hypotheses about how we smell date back to the first century B.C. and the Roman philosopher Lucretius, researchers are only now beginning to really tease out the olfactory process.
One of the enduring mysteries has been where olfactory neurons – the only neurons capable of regeneration through adult life – come from. In a new study, researchers at the California Institute of Technology have an answer: They derive from neural crest stem cells – multipotent, migratory cells unique to vertebrates that give rise to multiple structures and tissues in the body, such as facial bones and smooth muscle.
That’s contrary to previous hypotheses, which have proposed olfactory nerve cells originate from the same embryonic cells that, it’s believed, produce eye and ear sensory neurons.
The findings aren’t just fundamental science. They may have therapeutic benefits, such as helping in the development of new treatments for conditions like anosmia, or the inability to smell.
“Olfactory neurons are unique in their renewal capacity across species, so by learning how they form, we may gain insights into how neurons in general can be induced to differentiate or regenerate,” said Marianne Bronner, professor of biology and corresponding author on the study. “That knowledge, in turn, may provide new avenues for pursuing treatment of neurological disorders or injury in humans.”