These moths smell with their wings and their noses

Amazing stuff! I wish I could smell with my finger tips. Just kidding!

"Like most insects, the wings of tobacco hawk moths (Manduca sexta) are covered in tiny hairs. These microscopic strands help insects taste and stay stable in flight. But the tobacco hawk moth’s wing hairs do something researchers haven’t documented in any other insect: they help the animal smell ..."

From the abstract:

"In addition to their primary olfactory organs, the antennae, insects can smell using other parts of their bodies.

In this study, we examined the olfactory capabilities of the wings of the tobacco hawkmoth, Manduca sexta (Lepidoptera: Sphingidae). Using scanning electron microscopy, we identified an average of 21–32 sensory bristles along the margins of each wing. In addition to raised sockets that indicate mechanosensory function, we observed a subapical pore and numerous wall pores.

These pores are signs of chemosensory function, suggesting that the wings can detect chemicals upon contact or in gaseous form.

Gene expression analysis revealed the presence of genes encoding chemosensory receptors, such as gustatory receptors (GRs) and ionotropic receptors (IRs), including IR76b, the co-receptor of amine-sensing IRs, and IR8a, the co-receptor of acid-sensing IRs.

Genes encoding several odorant receptors (ORs) were also expressed in the wings; however, expression of the gene encoding ORCo, the obligatory OR co-receptor, was not detected.

Electrophysiological recordings revealed that only the volatile amines pyrrolidine and piperidine elicited responses from the wings.

Protein modeling and molecular docking simulations identified members of the Lepidoptera-specific IR7d clade as encoding candidate receptors for these compounds. These are characteristic alkaloids found in solanaceous plants, which tobacco hawkmoths prefer for laying eggs.

Together, these findings demonstrate that the wings of M. sexta function as accessory olfactory organs that may influence oviposition choice."

These moths smell with their wings | Science | AAAS

Noses on the wing: the olfactory capacity of hawkmoth wings (open access)

Fig. 1 Sensilla on the wing margins of Manduca sexta.

Scientists Create First-Ever map of smell receptors in the nose

Amazing stuff!

"At a glance

• Scientists have created the first detailed map of smell receptors in the nose, catching up with similar achievements in sight, hearing, and touch.
• The map reveals that smell receptors are highly organized into tight bands based on type.
• The findings provide foundational knowledge needed to develop better therapies for loss of smell.

...

Yet from a scientific perspective, “olfaction is super-mysterious,” ... with basic biological understanding lagging behind that of vision, hearing, and touch. ...

Working in mice, ... team have now created the first detailed map of how the thousand-plus types of smell receptors in the nose are organized.

They discovered that unlike what scientists had long believed, the neurons expressing these receptors have a high degree of spatial organization: They form horizontal stripes based on receptor type from the top of the nose to the bottom. ..."

From the highlights and abstract:

"Highlights

• ∼1,100 olfactory receptors adopt stereotyped spatial distributions in the epithelium

• Epithelial space coherently regulates the graded expression of ∼250 genes

• Precursor spatial identities bias olfactory receptor choice

• Receptor positions in the nose are aligned with their axonal targets in the brain

Summary

Although topographical maps organize many peripheral sensory systems, mouse olfactory sensory neurons (OSNs) are thought to randomly choose which one of ∼1,100 possible olfactory receptors (ORs) to express, with spatial organization in the olfactory epithelium limited to a handful of broad anatomical “zones” that modestly restrict OR choice.

Here, we reveal that each OR is instead expressed at a unique mean dorsoventral position, thereby instantiating a stereotyped receptor map in the olfactory epithelium.

OSN dorsoventral identities are encoded by a coherent gene expression program, which includes key transcription factors and axon guidance molecules; use of this program reflects a dorsoventral gradient in retinoic acid signaling, translates each physical location into a spatially appropriate distribution of potential OR choices, and aligns receptor maps in the nose and brain.

Spatial order in the olfactory system, therefore, arises from a continuously varying transcriptional code that precisely organizes the many discrete channels responsible for smell."

Scientists Create First-Ever ‘Smell Map’ | Harvard Medical School "A detailed diagram of smell receptors in the nose fills in missing details of how olfaction works"

A spatial code governs olfactory receptor choice and aligns sensory maps in the nose and brain (open access)

Graphical abstract

Figure 2 Each OSN subtype occupies a unique region of the epithelium

A new clue to how the skin detects physical touch

Amazing stuff!

"... While scientists have long known that a protein called PIEZO2 acts as a key sensor for touch, it remained unclear why PIEZO2 is specialized for the localized mechanical forces experienced by sensory neurons, whereas its close relative PIEZO1 responds to broader mechanical stresses such as those generated when cells stretch, as occurs in blood vessels. 

Now, a new study  ... clarify how PIEZO2 detects specific types of force and explain why evolution may have selected it as the body’s primary sensor for light touch. This work may guide future exploration into sensory disorders linked to PIEZO2 mutations. ...

Although PIEZO1 and PIEZO2 appear nearly identical in molecular models, they behave very differently in living cells. PIEZO2 is especially important in the somatosensory nervous system, the network of nerve cells that detects touch. These cells are highly sensitive to small indentations, like a light tap on the skin. By contrast, PIEZO1 responds more readily to general membrane stretch, such as when a cell is pulled or swollen, rather than poked at a specific point.

To investigate the difference, the research team used minimal fluorescence photon flux (MINFLUX) super-resolution microscopy ... Whereas other imaging techniques, including cryogenic electron microscopy (cryo-EM), have captured detailed but static images of frozen PIEZO proteins that serve as references for overall shape, MINFLUX allows scientists to track the positions and movements of proteins in cells with nanometer-scale precision. ..."

From the abstract:

"PIEZOs are mechanically gated ion channels that transduce force into electrochemical signals.
PIEZO1 responds to diverse stimuli including membrane stretch2 and shear stress, whereas 

PIEZO2 is generally tuned to detect cellular indentation. The functional specialization of PIEZO2 is proposed to underlie its distinct physiological roles, including mediating the sense of touch. How PIEZO2 achieves this selectivity despite its close structural similarity to PIEZO1 is unclear.
Here we combine single-molecule MINFLUX fluorescence nanoscopy with electrophysiology to link the conformational states of PIEZO2 to channel gating in intact cells. We find that PIEZO2 is intrinsically more rigid than PIEZO1, and that disparate mechanical stimuli paradoxically evoke opposite conformational and gating responses in each channel.

These unique gating properties arise in part from a connection to the actin cytoskeleton, and we identify filamin-B (FLNB) as a molecular tether that is required for this interaction. This complex alters how force is transmitted to PIEZO2 and confers heightened sensitivity to and selectivity for cellular indentation. PIEZO2 and FLNB are co-expressed in somatosensory neurons and colocalize within tens of nanometres at the end organs of cutaneous mechanosensory afferents. These findings help to explain why PIEZO2 is a specialized mechanosensor and provide a molecular blueprint for understanding how cells decode diverse mechanical stimuli across tissues and organ systems."

A new clue to how the body detects physical force | Scripps Research

The molecular basis of force selectivity by PIEZO2 (open access)

Fig. 1: The divergent structural mechanics of PIEZO1 and PIEZO2 in a cell membrane.

Can humans learn to listen like an owl with ears shaped like an owl?

Amazing stuff!

"Thanks to their incredibly sensitive hearing, barn owls can hunt down rodents and other tiny prey even on the darkest of nights. One ear is positioned slightly higher than the other, allowing these nocturnal predators to precisely locate sounds in both the vertical and horizontal planes. By rapidly integrating information from both ears, the bird’s brain can construct a three-dimensional map of auditory space.

Humans, by contrast, have symmetrical ears and lack such mental maps. Even so, we’re fairly good at localizing sounds and readily adapt to changes in ear shape and hearing sensitivity that affect the way we perceive spatial cues. ...

To find out, scientists fitted human listeners with custom-made asymmetrical ear molds and tested their ability to localize different types of sound. Study participants wore the molds continuously for up to 5 weeks, only taking them off to sleep. The wearers’ ability to localize sounds in the horizontal plane was largely unaffected, the team reports in a bioRxiv preprint. But the participants had a much harder time determining the vertical position of sounds. This ability did improve over time, but adaptation was limited, suggesting that the human brain can only partially remap spatial dimensions. ..."

From the abstract:

"The brain computes sound location from auditory spatial cues. Humans and barn owls can localize sounds with high accuracy, yet they rely on fundamentally different cue configurations shaped by their ear anatomy and neural circuitry.

In humans, symmetrical ears provide interaural time and level differences for horizontal localization, while vertical localization depends primarily on high-frequency, monaural spectral cues generated by the pinnae.

Barn owls, by contrast, possess asymmetrical ears and use binaural cues to localize sounds in both azimuth and elevation. Because auditory pathways are assumed to be tuned to the statistics of species-specific cues, it remains unclear whether humans can localize sounds using barn-owl-like spatial information.

We addressed this by fitting human listeners with asymmetric ear molds that disrupted normal spectral cues and introduced elevation-dependent interaural level differences, while preserving interaural time differences. Participants wore the molds during daily life and were tested on sound localization using broadband, high-pass, and low-pass noise.

Acute exposure to the molds severely degraded elevation localization, while horizontal localization remained largely unaffected. With prolonged exposure, elevation localization improved, but adaptation was limited. Crucially, improvement was strongest for broadband sounds. Because broadband sounds uniquely provide access to both low-frequency interaural time differences and high-frequency interaural level differences, this pattern indicates that listeners learned to use binaural cues to infer sound elevation.

These findings demonstrate that the human auditory system can partially adapt to extreme barn-owl-like outer-ear acoustics. Binaural cues can be repurposed to support elevation localization, with effective learning requiring access to complementary spatial cues."

ScienceAdviser

Learning to localize sounds like a barn owl

Figure 1. Acoustic spatial cues in humans and barn owls.

Elephant trunk whiskers exhibit material intelligence, revealing the secret behind an amazing sense of touch

Amazing stuff!

"... The 1,000 whiskers that cover an elephant's trunk have unusual material properties that highlight where contact happens along each whisker, giving elephants an amazing sense of touch that compensates for their thick skin and poor eyesight. ..."

"To the point

• Sense of touch despite thick elephant skin: Researchers have discovered that the hairs on elephants' trunks are responsible for their extraordinary sense of touch. 
• Special material properties: Elephant sensory hairs have a stiff base and a soft tip, which enables them to precisely feel objects and recognize where contact is made. These properties are similar to the whiskers of cats and differ from the completely stiff sensory hairs of rats and mice. ...
• Applications in robotics: The findings will be used in the development of robot-assisted sensor technologies that mimic the stiffness gradient of elephant tactile hairs.

..."

From the editor's summary and abstract:

"Editor’s summary

Mammals such as cats and rats use whiskers to help sense their environment. In rats, the short whiskers and long whiskers resonate at different frequencies, helping rats map out their surroundings as the keratin-based fibers contact the edges and surfaces of nearby objects.

Elephants also have whiskers, which line the length of their trunks. Schulz et al. used micro–computed tomography imaging, electron microscopy, mechanical testing, and finite element analysis to map out the structure and properties of these whiskers.

At the base of the trunk, the whiskers are thick, circular, porous, and stiff, but they progress toward being thin, ovular, dense, and soft toward the tip, which contrasts with whiskers found in most other mammals. This combination of structure and form helps magnify the signals transmitted to the trunk. ...

Structured Abstract

INTRODUCTION

Animals have evolved a diverse array of sensing systems that help them traverse complex terrain, locate food, and detect predators. Many terrestrial and aquatic mammal species use specialized sensory hairs, known as whiskers, as active tactile sensory organs to monitor their environment. A follicle surrounds each whisker’s base with mechanoreceptors that respond to physical whisker stimulation and thereby extend the animal’s sense of touch. Most research focuses on how the geometry and/or neuromechanics of the whisker-follicle structure affect tactile sensitivity. This study analyzes variations in intrinsic whisker properties, including how porosity and stiffness change along the whisker.

RATIONALE

The boneless elephant trunk is covered with about 1000 whiskers that expand the sensory volume of this highly dexterous appendage. These whiskers do not possess the innervated local muscles that allow the characteristic “whisking” behavior commonly seen in rats and mice, and they cannot regrow, so we hypothesized they may also differ in other fundamental ways. This study applies several precise measurement approaches to characterize the geometry, porosity, and stiffness of Asian elephant (Elephas maximus) whiskers and uses mechanical simulation to show how the captured characteristics may affect trunk touch.

RESULTS

We measured the geometry, porosity, and material stiffness from the base to the tip of elephant whiskers and entered these properties into our open-source, customizable finite element model that allows whisker properties to vary longitudinally. This simulation was then used to compare elephant whiskers with rat whiskers, which exhibit uniform material stiffness along their length. By contrast, elephant whiskers showcase three independent functional gradients. The geometry of elephant whiskers shows a tapered ovular cross section, facilitating bending as the trunk extends between obstacles. Elephant whisker porosity is characterized by a network of hollow tubules in the inner cortex; this horn-like microstructure at the base merges into a dense whisker tip.

A porous base provides functional benefits of mass reduction and impact resistance, similar to the horns of bighorn sheep.

Our stiffness analysis shows that elephant whiskers transition from a stiff base (modulus of elasticity = 2.99 GPa) to a soft, resilient tip (0.0706 GPa), a shift of two orders of magnitude, although elephant body hair has approximately constant stiffness from base (2.20 GPa) to tip (1.15 GPa). The stiffness gradient of elephant whiskers provides two key benefits over homogenous whiskers: reduction of base stress during large deflection and amplification of signal differences along the whisker length, strengthening the encoding of contact location.

CONCLUSION

The geometry, porosity, and stiffness gradients of Asian elephant whiskers seem tuned to augment tactile sensing. Their tapered ovular geometry increases interaction with textures and allows preferred bending directions; the shift from a porous base to a dense tip reduces mass, increasing the whisker’s resonant frequency and reducing breakage; and the transition from a stiff base to a soft tip increases tip deflection and facilitates contact encoding along the whisker. The physical intelligence of these three functional gradients found together in elephant whiskers expands our understanding of touch and could inspire new approaches in artificial tactile sensing."

Elephant trunk whiskers exhibit material intelligence, revealing the secret behind an amazing sense of touch

Elephant trunk whiskers exhibit material intelligence (original news release)

Functional gradients facilitate tactile sensing in elephant whiskers (no public access)

Functionally graded keratin facilitates tactile sensing in elephant whiskers (preprint, open access)

... with a 3D-printed replica of an elephant's trunk hair, which helped the research team understand how a transition in material stiffness facilitates contact sensing in the tactile hairs of elephants and cats.

An artificial tongue for spiciness using skim milk powder

"Variety's the very spice of life, That gives it all its flavor!" (from a poem by William Cowper's 1785)

"... Scientists have previously developed artificial tongues that measure sweet and umami flavors, so researchers wanted to alter the technology for spicy foods by using the milk protein casein, which binds to capsaicin, the active compound in spicy peppers. They added skim milk powder to a flexible, opaque, tongue-shaped gel that conducted an electrical current; when the technology touched capsaicin, as well as pungent compounds in garlic, onion, horseradish, and ginger, the current changed and signaled their presence.

To validate their fake tongue against real ones, the researchers exposed their gel and a panel of taste testers to eight peppers and eight spicy foods. The tongue’s electrical responses matched the taste testers’ spiciness rankings and measured capsaicin concentrations from undetectable-by-humans to painful. ..."

"... So, researchers made an artificial tongue to quickly detect spiciness. Inspired by milk’s casein proteins, which bind to capsaicin and relieve the burn of spicy foods, the researchers incorporated milk powder into a gel sensor. The prototype, reported in ACS Sensors, detected capsaicin and pungent-flavored compounds (like those behind garlic’s zing) in various foods. ...

As a proof-of-concept, the researchers tested eight pepper types and eight spicy foods (including several hot sauces) on the artificial tongue and measured how spicy they were by changes in electrical current. A panel of taste testers rated the spiciness of the same items. Results from the artificial tongue and the tasting panel matched well. ..."

From the abstract:

"Artificial tongues have been extensively studied to detect the five basic tastes like humans. Spiciness, or pungency, is essential for food selection for both humans and animals. However, it is challenging to fully mimic human tongue-like performance for spicy taste.

Inspired by the fact that milk can relieve the pungent taste on the tongue, we introduced a soft gel-based artificial tongue as a flexible chemiresistive sensor for pungency detection.

When exposed to pungent compounds, it leads to the formation of hydrophobic complexes and conformational changes that decrease the ionic conductivity. The artificial tongue enables pungent compounds to be detected over a wide range (0.0001–1 wt %) with high sensitivity (0.259 wt %–1) and fast response times (<10 s).

Moreover, our artificial tongue can detect the pungency degree in a variety of spicy foods and condiments with intertranslatable ionic currents. Our work could enable both pungent compound detection and spicy sensation estimation, making a powerful platform for future applications involving movable humanoid robots and portable spicy taste monitoring devices."

ScienceAdviser

Artificial tongue uses milk to determine heat level in spicy foods

A Soft and Flexible Artificial Tongue for Pungency Perception (no public access)

Graphical abstract

Investigator Charles Zuker and his team explore How We Taste Sweetness

Good news! That is funny! Zucker is the German word for sugar! Sometimes a name presents a calling (not to be confused with name calling). 😊

"... have unveiled the structure of the human sweet receptor, adding fundamental insights into taste detection and our understanding of the taste system, and paving the way for modern-day confectioners to reduce the amount of sugar in consumer products – all without sacrificing sweetness. ...

In 2001, Zuker’s laboratory discovered the genes that encode the sweet receptor. When we enjoy our favorite candies and desserts, these foods taste sweet solely because they activate this receptor.  ...

to cut back on the amount of sugar and calories in products, food and beverage makers could simply use less sugar and add a modulator to their product ..."

From the highlights and abstract:

"Highlights

• Two GPCR subunits assemble to recognize sweet ligands

• The TAS1R2 subunit binds the ligands and couples to the G protein

• A common binding pocket recognizes sucralose and aspartame

• 3D variability analysis shows coordinated structural changes between the subunits

Summary

In humans, the detection and ultimately the perception of sweetness begin in the oral cavity, where taste receptor cells (TRCs) dedicated to sweet-sensing interact with sugars, artificial sweeteners, and other sweet-tasting chemicals.

Human sweet TRCs express on their cell surface a sweet receptor that initiates the cascade of signaling events responsible for our strong attraction to sweet stimuli. Here, we describe the cryo-electron microscopy (cryo-EM) structure of the human sweet receptor bound to two of the most widely used artificial sweeteners—sucralose and aspartame.

Our results reveal the structural basis for sweet detection, provide insights into how a single receptor mediates all our responses to such a wide range of sweet-tasting compounds, and open up unique possibilities for designing a generation of taste modulators informed by the structure of the human receptor."

Scientists Unveil the Structure of the Receptor Responsible for How We Taste Sweetness | HHMI

The structure of human sweetness (open access)

Graphical abstract

Figure S2 Cryo-EM data processing workflow, related to STAR Methods

Charles Zuker

Rats use ultrasound to boost their fine sense of smell for dynamic social interactions

Amazing stuff!

"... For decades scientists have recorded rodents vocalizing at ultrasonic frequencies, which is believed to be a form of communication and might help them find mates. It might even be a kind of laugh, since they also do it when researchers tickle them, according to one of the most endearing studies of recent years.

In a new study, scientists ... have identified another potential, unexpected benefit of rodents’ ultrasound pulses. The animals could use these sounds to stir up particles in the air around them, which they can quickly inhale to boost their already strong sense of smell. ...

The researchers were first inspired to investigate the idea by previous studies into how rodents navigate their environment. It was found that the animals would usually sniff the air immediately after making each ultrasound vocalization (USV). ..."

"... Vibroacoustics, or artificially produced ultrasonic vibrations, cause airborne particles to cluster, leading Mercado to suggest that rodents are using USVs to create odor clusters enhancing the reception of pheromones (chemical signals), thus making it easier for the vocalizer to detect and identify friends, strangers, and competitors. ..."

From the highlights and abstract:

"Highlights

• Rodent vocalizations could contribute to a unique mode of active olfactory sensing.

• Ultrasonic vocalizations may affect how rodents smell by clustering inhaled odorants.

• Coordinating sniffing with sound production might enhance reception of pheromones.

Abstract

Chemosensation via olfaction is a critical process underlying social interactions in many different species. Past studies of olfaction in mammals often have focused on its mechanisms in isolation from other systems, limiting the generalizability of findings from olfactory research to perceptual processes in other modalities. Studies of chemical communication, in particular, have progressed independently of research on vocal behavior and acoustic communication. Those bioacousticians who have considered how sound production and reception might interact with olfaction often portray odors as cues to the kinds of vocalizations that might be functionally useful. In the olfaction literature, vocalizations are rarely mentioned. Here, we propose that ultrasonic vocalizations may affect what rodents smell by altering the deposition of inhaled particles and that rodents coordinate active sniffing with sound production specifically to enhance reception of pheromones. In this scenario, rodent vocalizations may contribute to a unique mode of active olfactory sensing, in addition to whatever roles they serve as social signals. Consideration of this hypothesis highlights the perceptual advantages that parallel coordination of multiple sensorimotor processes may provide to individuals exploring novel situations and environments, especially those involving dynamic social interactions."

Rats use ultrasound to boost their sense of smell, suggests new study

‘Use the force,’ Mickey: Study suggests that ‘Jedi’ rodents remotely move matter using sound to enhance their sense of smell (original news release) "It’s so far off the scale of what we know … it almost seems like magic,’ says University at Buffalo researcher Eduardo Mercado III"

Do rodents smell with sound? (no public access)