nose

We have known for decades how what we see, what we hear and what we touch works. Science has been mapping these senses for a century, so that each sensory signal has a known direction, a path traced from the organ to the brain. A couple of examples: this retinal map either east of the cochlea. There was one pending subject: smell. Not because no one had looked for it but because the olfactory system has enormous complexity: more than a thousand different types of receptors and twenty million neurons in the nose of a mouse. A biological chaos that a Harvard research team has managed to draw a map. What the map says. The scientific team has discovered that olfactory neurons are not distributed randomly in the nasal cavity, but rather form a spatial code based on overlapping stripes organized by the type of receptor and distributed from the upper to the lower part of the nose. This pattern is practically identical in all the animals studied, so it is a conserved and reproducible biological architecture. The most surprising thing is that this banding arrangement is a mirror of the map of the olfactory bulb in the brain. That is, there is topographic continuity: the position of a neuron in the nose determines exactly which area of ​​the brain it will send its signal to. This means that the brain “reads” odors based in part on the geographic location of the cell that detected the molecule. havard Why is it important. Because it is the missing piece to understand neuroplasticity and the regeneration of smell. In practice, because the loss of smell currently lacks effective treatments: by knowing the original design of the system, researchers can now understand why connections fail after trauma or a viral infection, something that revealed COVID-19. If the architecture of the system is not understood, regeneration goes blindly. As Sandeep Robert Datta, a neurobiologist at Harvard’s Blavatnik Institute and principal investigator of the paper, points out, without understanding this map, attempts to develop new treatments are doomed to failure. Context. Mammalian olfaction is a complex system. In the case of the mouse, it has 20 million olfactory neuronseach expressing one of more than a thousand different receptor types. To get an idea, human color vision is only supported by three types of photoreceptors. This complexity meant that for decades science tended to associate the distribution of receptors randomly. Linda Buck and Richard Axel discover olfactory receptors in 1991 it earned them the Nobel Prize in medicine in 2004but that told us what detected the odors, not where or how they were organized. The good news is that with the advances in molecular biology today it is possible to analyze individual cells in their original position using techniques such as spatial transcriptomics. How have they done it. The Harvard team analyzed approximately 5.5 million neurons from more than 300 mice by combining two techniques: single-cell sequencing to know which receptor each neuron expresses and spatial transcriptomics to know exactly where it is located in the tissue. The study also identified the mechanism that builds that map: retinoic acid. By manipulating the chemical gradients of retinoic acid during embryonic development, they observed that the stripes of these receptors shifted, confirming that this acid functions as a kind of molecular GPS that tells each neuron where to position itself and which receptor to express. Yes, but. The first major limitation of the study is evident: it was done in mice, so as the research team itself acknowledges, they still do not know if the same organization applies to humans. Although the olfactory system of mammals is mostly conserved, humans have significantly fewer functional receptors (approximately 350 compared to more than 1,000 in the mouse) and a different nasal anatomy, so the existence of these stripes in humans still needs to be validated experimentally. Furthermore, although the map explains the wherestill does not fully explain the because of that specific order. We do not know if the stripes are grouped by the chemical structure of the odors or by their biological relevance, for example the smell of food versus odors of danger. Resolving what logic obeys that order is the next big challenge. In Xataka | We have been wondering for decades why Neanderthals became extinct. So we’re studying your nose In Xataka | Nasal strips are back in fashion in sports. Science has already passed judgment on them Cover | Angela Roma and Data Lab