FFrom the biggest tigers to the smallest mice, most furry creatures share the common problem of how to dry off without a bath towel. Many have developed a similar strategy: a vigorous full-body shaking motion that researchers have dubbed “wet dog shakes.” Although somewhat ridiculous, this behavior can be important for survivalhelping the pet dry off quickly so it can conserve body heat and precious calories.¹

Now, a research team led by a neurobiologist from Harvard University David Ginty identified the somatosensory machinery that mediates this behavior. In a study published today (November 7) in ScienceGinty and his team discovered that a type of mechanoreceptor called the C-fiber low-threshold mechanoreceptor (C-LTMR) helps trigger this behavior in response to various stimuli.² Results reveal a novel function for C-LTMRs, which are associated with emotional touch And pain modulation in mice and humans.^3.4

The researchers found that many types of stimuli evoked wet-dog shaking in mice: They performed the behavior when wet, but also in response to minor irritants, like a droplet of oil or a whiff of water. air, applied to the back of the neck. To confirm their suspicions that the dog’s wet jerks were mediated by mechanosensation, as opposed to the mild cold sensation that is also caused by humidity or puffs of air, the researchers removed the Piezo2 gene, which encodes an ion channel crucial for touch detection. As they predicted, the lack of Piezo2 Essentially eliminated shaking behavior in response to water or oil droplets.

Mice and humans have different types of mechanosensory neurons that each respond to different types of touch. The researchers measured how these neuronal populations responded to the application of an oil droplet and found that three types of low-threshold mechanoreceptors were the most responsive. Of these, only C-LTMRs consistently caused wet dog tremors when optogenetically stimulated. Conversely, when the researchers ablated most of the C-LTMR, the oil droplet-induced trembling behavior was significantly reduced, while the mice otherwise maintained normal locomotor behavior. .

Finally, the researchers traced the pathway that carried these sensory signals from the skin to the brain. Previous anatomical studies have demonstrated that C-LTMRs collect tactile information from the skin and transmit it to the other end of the cell, located in the dorsal horn of the spinal cord (in a cross-section of the spinal cord, it there is a butterfly-shaped region of gray matter composed largely of cell bodies; the dorsal horn is the upper wing of the butterfly). From there, the researchers followed the signal across the synapse to spinoparachial neurons, which carried the signal down the spinal cord to the parabrachial nucleus (PBN), a region of the brainstem responsible for transmitting signals. sensory information to the rest of the brain. When the researchers removed the ability of spinal cord neurons to communicate with the PBN, or when they silenced the PBN itself, tremor behavior decreased, confirming the importance of the spinoparabrachial pathway in mediation of wet dog tremors.

Although humans have access to bath towels and therefore do not need to dry them, they have similar types of mechanoreceptors. In humans, these C mechanoreceptors are thought to encode pleasant contact; they can help modulate pain and will likely play a role in the assessment of social touch.^{5 to 7} Thus, understanding the functions of these mechanoreceptors could lead to new knowledge about pleasure and pain.