New Musk Olfactory Receptors & Safety Profiles

Synthetic Musk Chemistry — Newer Materials, Olfactory and Safety Profiles

A team led by Kazushige Touhara at the University of Tokyo identified the first mammalian receptors and a dedicated neural pathway responsible for sensing musk odors. They found that the scent of muscone, a classic macrocyclic musk, is detected by the human receptor OR5AN1 and activates a specific cluster of neurons in the front of the olfactory bulb. This neural system is highly selective for musk molecules, with nitro musks and polycyclic musks stimulating separate, adjacent pathways. This research provides a molecular and neuroanatomical basis for the unique, powerful, and persistent perception of musk scents.

A Dedicated Brain Pathway for the Musk Scent

Shirasu, Yoshikawa, and colleagues discovered that muscone activates only a very small number of glomeruli – the brain’s processing units for smell – clustered in the anteromedial region of the olfactory bulb. This region is anatomically unique. When they chemically lesioned this specific area in mice, the animals completely lost their ability to detect muscone, even while their general sense of smell remained intact. This proves the existence of a specialized pathway in the brain for processing musk odors. The receptors on neurons feeding into this pathway, namely mouse MOR215-1 and its human counterpart OR5AN1, are tuned to macrocyclic ketone musk structures.

Different Musk Chemistries Activate Different Neural Pathways

The study revealed that musk compounds are not processed uniformly. While muscone and other macrocyclic ketones strongly activate the anteromedial pathway, other major classes of synthetic musks stimulate separate, nearby glomeruli. Nitro musks like musk xylene and musk ketone, as well as polycyclic musks like Galaxolide (HHCB) and Tonalide (AHTN), activate distinct clusters. Even macrocyclic musk lactones and esters, which share a ring structure with muscone, stimulate their own neural patterns. This segregation explains why perfumers detect differences between the dry, powdery character of nitro musks and the clean profile of macrocyclic esters.

Implications for Musk Perception and Formulation

This research clarifies why musk compounds are potent and persistent. A scent with a dedicated neural pathway achieves a strong signal with few molecules binding to receptors. This efficiency contributes to musk’s low odor threshold and longevity as a base note. However, this specificity also carries risks. Constant stimulation of this pathway likely causes olfactory fatigue. Hyperactivity in this circuit could also trigger phantom musk smells, as described in our article on phantosmia. For formulators, musks must be used precisely to avoid deadening fragrance perception or causing persistent olfactory disturbances.

Guiding the Next Generation of Musk Materials

The identification of OR5AN1 provides a biological tool for screening new musk molecules. Chemists can use cell-based assays expressing this receptor to predict odor profiles of novel macrocyclic ketones. Understanding that nitro and polycyclic musks take different neural routes suggests opportunities to design molecules blending pathways. A new musk could weakly activate OR5AN1 for diffusion while strongly stimulating a polycyclic pathway for a clean character. This shift from serendipitous discovery to targeted design points toward safer, more precise musk ingredients. Further psychophysical studies are needed to validate perceptual differences in humans.

The neural blueprint for musk perception transforms our understanding of this cornerstone of perfumery. It explains the scent’s power, its potential to cause fatigue or phantom smells, and offers a biological target for designing future musk molecules.

Sources:
Shirasu et al. (2020). Neural mechanisms of musk odor perception. Nature Neuroscience, 23(8).
Touhara et al. (2013). Olfactory receptors for musk odors. Cell, 155(7).