Calling All Chemosignals

Chemical communication between female rats exists and is complex

Jun 2023, phys.org

https://phys.org/news/2023-06-chemical-communication-female-rats-complex.html

I'm just here because today I learned that mice urine and rat urine are very different:

At this point, MUP (major urinary proteins) enter into play. MUPs are key in the transmission of odors through marks, yet function differently in mice (found in the urine with which they mark) as opposed to rats (whose marks contains sebaceous secretions, in addition to urine).

But the research found that a variety of these scent marking proteins came from the clitoral glands of the females, and we didn't know that before. ... the combination of urine and the secretion from the clitoral glands is necessary for the marks of the females to arouse interest in other females.

via University of Córdoba, University of Liverpool: Guadalupe Gómez-Baena et al, Unraveling female communication through scent marks in the Norway rat, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2300794120

https://dx.doi.org/10.1073/pnas.2300794120

Post Script: Scent marking in rats has been studied in depth when it comes to males, but, in the case of females,  there's a knowledge gap.

Image credit: AI Art - British Grandma on the Phone - 2024

Hand odor can reveal a person's sex, study shows

Jul 2023, phys.org

https://phys.org/news/2023-07-odor-reveal-person-sex.html

Statistical analysis and mass spectrometry analyze the volatile scent compounds present on the palms of 60 individuals - half male and half female predicted a person's sex with a 96.67% accuracy rate.

via Florida International University: Multivariate regression modelling for gender prediction using volatile organic compounds from hand odor profiles via HS-SPME-GC-MS, PLoS ONE (2023). DOI: 10.1371/journal.pone.0286452

https://dx.doi.org/10.1371/journal.pone.0286452

Post Script: On Handshakes and Animal Behavior, 2021

http://www.limbicsignal.com/2021/08/on-handshakes-and-animal-behavior.html

Living With Friends

Above we see a microscopic view of the Paenibacillus bacteria, found in coffee machines and where coffee is prepared. It's been used as a probiotic for both chickens and bees, and might have something to do with the idea that coffee is good for your health. 

But that's just coffee. Onto the real story -- nobody lives alone, and that includes even those of us who don't live with other people. We're talking about the vast array of microbes that share our domestic biome with us. They outnumber us by the billions (uncountable really) and could have a strong influence on our health, maybe even our behavior (looking at you Toxoplasmosis), all by way of the mediating effects between our microbiome and our immune system. And they smell. Not all of them, but where there's life, there's smells. It's our own domestic ecology of smells.  

Each one of us affects the microbiome we live with, depending on who we are, what we eat, what we do for work and in our spare time, how we clean, how often and how thoroughly we clean, ad infinitum. The home is a dynamic place, and very different from a scientific laboratory, in almost every way, and so we don't have a good idea of what's happening in our homes, not on a biological basis, and not even on a chemical basis. 

And then came the HOME house, the HOME Chem model house, a chemical-lab-house, put together by 60 scientists from 13 universities in Austin, Texas circa 2020. They do regular-house things and measure the chemical profile of the air inside the home over time while they cook, clean, eat, sleep. It might sound mundane, but it's the first time we're getting real world indoor air quality data from the domestic frontier.

Most air quality data comes from outside air. We haven't been thinking about the indoor air for very long, and much less resources and scientific inquiry have been devoted to it. The HOME project gives us the first glimpse of what's really happening to our indoor environment while we live there.  

With roommates, it's all about chemistry, molecularly speaking

Jun 2022, phys.org

https://phys.org/news/2022-06-roommates-chemistry-molecularly.html

An experimental test home was erected in Austin, Texas during the summer of 2018. The house was designed for ordinary use and included bathrooms, a kitchen, gathering and work areas. Overnight stays were prohibited, but 45 study participants, plus visitors, spent time in the house, occupying it for approximately six hours per day for 26 days, during which they performed scripted activities, such as cooking, cleaning and socializing.

The house was deep cleaned with a bleach solution. Nonetheless, researchers said traces of molecules associated with humans were still present. After almost of month of human occupation, the house was alive with molecular and microbial abundance and diversity, albeit unevenly distributed.

Not surprisingly, the kitchen and toilet were hotspots of molecular and microbial diversity, though numbers fluctuated with surface cleaning and sanitation. "It appears that, even when a subset of chemistry is removed because of the cleaning, it is only temporary and/or partial, as the sum total of cleaning and human activities overall results in an increase in accumulation of richer chemistry," the authors wrote.

via University of California San Diego, Colorado State (Delphine Farmer), and University of Colorado: Alexander A. Aksenov et al, The molecular impact of life in an indoor environment, Science Advances (2022). DOI: 10.1126/sciadv.abn8016

https://dx.doi.org/10.1126/sciadv.abn8016

Image credit: Paenibacillus bacteria found where coffee was prepared - Prof. Eshel Ben-Jacob Wikimedia - 2022

Here's more links on HOME:

https://indoorchem.org/

https://phys.org/news/2020-02-window-home-flush-chemicals-air.html

https://phys.org/news/2022-09-indoor-air-quality-exposure-cooking.html

And here's some information on how bad we are at perceiving air quality indoors:

• Teachers did not accurately perceive mechanical ventilation sufficiency
• Air quality and temperature are conflated
• Dramatic difference in IAQ perception (but not quality) in summer vs winter
• Occupants misperceive temperature as a proxy for indoor air quality; they think cooler air is better, and confuse warm air with "stuffy, stale" air
• Teachers in classrooms with worse ventilation were more satisfied with classroom temperature
• Occupants don't understand how the systems work, and think incoming cold air in winter is a defect, for example (when in fact it is the system adding fresh air to the mix); they then say the system isn't working, and therefore they must have bad IAQ; they also think the only time the system brings fresh air is when the AC is on, which is the complete opposite of what's happening

Source: Pistochini T, Mande C, Modera M, et al. Improving Ventilation and Indoor Environmental Quality in California K-12 Schools (CEC-500- 2020-049). Sacramento, CA: California Energy Commission; 2020. https://www.energy.ca.gov/publications/2020/improving-ventilation-and-indoor-environmental-quality-california-schools

The Smell of Fear

Protecting gardens and crops from insects using the 'smell of fear'

Aug 2021, phys.org

https://phys.org/news/2021-08-gardens-crops-insects.html

They're using methoxypyrazines, such as isopropyl methoxypyrazine, isobutyl methoxypyrazine and sec-butyl methoxypyrazine. Methoxypyrazines smell like "green, herbaceous, vegetative, green peppers, freshly cut grass, and asparagus." 

But for aphids, methoxypyrazines smell like ladybugs. Aphids hate ladybugs. And farmers hate aphids. 

On a related note, the smell of cut grass is a defense mechanism for grass to tell other grass that it's being attacked, and to "brace yourselves." The next time you smell it, you can think of the sound of grass screaming.  

via American Chemical Society: Smell of fear: Harnessing predatory insect odor cues as a pest management tool for herbivorous insects, ACS Fall 2021.

https://www.acs.org/content/acs/en/pressroom/newsreleases/2021/august/protecting-gardens-and-crops-from-insects-using-the-smell-of-fear.html

Smelling Sickness

The Annual Report from the Monell Center is out, and I'd like to copy a few interesting bits over the coming weeks.

The Monell Center in Philadelphia specializes in taste and smell research, and their first piece of news is about volatile signals for disease. We know that illnesses makes us smell different. Body odor comes from our distinct metabolic byproducts, and when our metabolism is disrupted, by a disease for example, it smells different. Dogs know this, and so does Alexandra Horowitz who wrote the book Being a Dog: Following the Dog Into a World of Smell (2016).

We can smell it too. Bruce Kimball, PhD, sensory neuroscientist Johan Lundstrom, PhD, and collaborators at the Karolinska Institute in Sweden reported that people can detect acute inflammation in others just by the smell of their urine.

But what we didn't know it actually changes the way others smell, just by being around us. Chemical ecologists Bruce Kimball, PhD, and Stephanie Gervasi, PhD, partnered with behavioral biologist Gary Beauchamp, PhD, to show that body odors of otherwise healthy people can change in an environment shared by sick-smelling people (or animals, according to the experiment).

Don't forget that the olfactory system is such a primitive part of us. It doesn't just go back to our animal ancestors, but even further. Plants don't see, and they don't hear.* But they can smell. Not the way we would consider smell, but they can sense chemicals in their environment, and those chemosignals can instigate immune response all by themselves. When a nearby plant is attacked by bugs, for example, they emit an olfactory alert to that their neighbors detect, and then beef-up their own chemical defense systems (by emitting bug-repellant vapors).

If you think about it, we're doing the same thing, only it's not us, it's the primitive chemosensory part of us. It detects potential threats in our environment, via the olfactory alerts from others, and rearranges our immune system accordingly.

Good to know, thanks Monell.

*Although you could say that plants "see" because they have some kind of photoreceptor that can tell where the light is and how much is there, etc.

Notes:

Monell Annual Report 2018-2019

Monell Center, Philadelphia PA

Code Smell

There's the thing in computer programming called Code Smell, and it refers to the finding of a problem in the code, like a funny smell in the code that indicates where the bugs are coming from.

So it's like, Here I am, having written a book on the language of smell, read every book in the Library of Congress on the subject, hundreds and hundreds of scientific articles, and thousands of web documents, and would you look at that? Never heard of it.

It gets better because apparently “developing your code nose” is a worthy pursuit for any programmer.

They aren't bugs per se, but more like a weakness in the code that increases the risk of a bug. Duplicated code, for example, gives off a code smell.

Further, there is a distinction made between Code Smell and Language Smell. One is for the way the code works and the other is for that actual language used in the code. In this case it’s called language smell, not code smell.

Almost Truth

When you search ‘breath of fresh air’ and every picture has people with their arms open wide. (What’s up with that?) image source

Mice can smell oxygen

Dec 2016, phys.org

There seems to be this debate, or perhaps I should just call it confusion, over whether or not we can smell non-organic molecules like ammonia, chlorine, or sulfur. From what I can get out of people who are professionals in chemistry, smell science, or what have you – we cannot smell these things.

When we smell the ‘chlorine in the pool,’ we are actually smelling chlorine as it mixes with other organic molecules to make chloramines (and the so the smell of chlorine, which most would consider clean and disinfected, is actually the smell of a dirty pool, because the cleaning agent chlorine is mixing with all the organic garbage poop molecules in the pool). “Sulfur” is the smell of sulfur mixed with other organic molecules. Some people say we can smell ammonia, but I bet it’s the same situation.

While we’re talking about it, “metal” is not the smell of metal but the smell of something, an organic something (like our sweaty hands), interacting with the metal.* (I have a smell in my vocabulary called ‘metal mold’ and although I’m not sure what it is, its smell is powerful and unmistakable...and it's on my fire escape sometimes.)

So when I hear this – "mice can smell oxygen" – I have a feeling it’s not as it seems. And sure enough the truth reads like this:

They don’t smell oxygen itself, but the “levels of oxygen in the air.” They also don’t use odor receptor genes to do this; they are chemosensitive genes, but not odor receptor genes. And also, in humans, these genes are non-functional (called pseudogenes or junk genes), so we can’t generalize this to humans, only mice.

Can we say that mice “smell” oxygen? That’s like almost the truth, almost a fact. They can sense it. And if we consider chemosensation to fall under olfaction, just for simplicity sake, then sure, they can. That’s how almost truth works, isn’t it? And for the record, this is one of the reasons Hidden Scents is subtitled …’the age of approximation.’ The very thing that is so commonplace in studying or simply experiencing the world of olfaction is fast becoming the norm in how we interact with the Noosphere, the total collection of facts and knowledge.

*Credit to author Alexandra Horowitz; I got this from her book Being a Dog, it just came out in 2016, and is absolutely fascinating.

The Universal Language of Chemosignals

source: What Do Plants Talk About

Not only can plants “see” light and “hear” vibrations, they are now known to smell parasitic worms. These nematodes communicate with each other using pheromones (specifically ascarosides), which in turn regulate the worm’s development and behavior. We might think of it as wi-fi.

The chemical signal is excreted (or transmitted) from one worm, and received by another. Plants, using that natural tendency of all living things to be clever, hack into the nematode wi-fi network, and use that information to regulate their own behavior and development. When you watch roots grow in timelapse, you realize they're just like worms, wiggling through the ground, looking for nutrients. Only they're not looking, they're smelling.

This should be a reminder to us that the thing we call Smell is a primitive form of communication used by all living things. Plants don't have brains, so they don't smell like we do. But they do have memories, and even autobiographies. We would call this ontological history – these are interactions stored in the ever-changing DNA of the plant. Experience is passed on to subsequent generations.

The first organisms lived in a chemical world. And although they may have been sensitive to light particles and waves of vibration, they were also a receiver of chemical signals. And of the lot, the chemo-signals were the most complex and required the most sophisticated translation. Our brains – real human brains – grew through evolution out of the olfactory bulb. We may associate the advanced cortical functions of our mind with other, higher senses like vision and audition, but that whole thing is undergirded by the primitive nose- brain. “We think because we smell.” (Diane Ackerman, A Natural History of the Senses, 1990)

Our impossibly complex brains can't really fathom what it means for a plant to smell until we come to understand our own chemically-encrypted selves.

Chemo-signal pattern recognition has come a long way, and it’s a history worth looking into.

Bed Bug Signal

The shed skin of bed bugs time-releases smell compounds that signal to other bed bugs where a good spot to bed down is located. They call it pheromones, but to me, that just makes the whole thing sound even funnier.

Shed skins of bed bugs emit pheromones that could help combat infestations of the insect

July 2016, phys.org