Why do wet dogs shake themselves dry? The neurological reasons explained

Why do wet dogs shake themselves dry? The neurological reasons explained

When a dog shakes water from its fur, the action is not simply a random movement—nor a deliberate attempt to drench someone nearby.

This instinctive reflex is seen in many furry mammals, including mice, cats, squirrels, lions, tigers and bears. This movement helps animals remove water, insects or other irritants from hard-to-reach places. However, there is a complex and previously mysterious neurological mechanism behind these shaking movements.

Recently, researchers identified the neural circuit that triggers the characteristic "wet dog" shake in mice - this involves a specific class of tactile receptors and neurons that connect the spinal cord to the brain. Their results were published November 7 in the journalSciencepublished 1.

“The touch system is so complex and rich that it is able to distinguish a drop of water from a crawling insect or the tender touch of a loved one,” explains Kara Marshall, a neuroscientist at Baylor College of Medicine in Houston, Texas. “It is truly remarkable to link a very specific subset of touch receptors to this familiar and understandable behavior.”

Sensitive skin

The hairy skin of mammals is equipped with over 12 types of sensory neurons, each with a unique function to detect and interpret different sensations. A team led by Dawei Zhang, a neuroscientist then at Harvard University in Cambridge, Massachusetts, focused on a type of ultrasensitive touch receptors known as C-fiber low-threshold mecanoreceptors (C-LTMRs), which are wrapped around hair follicles.

In humans, these receptors are associated with pleasant sensations of touch, such as a gentle hug or a soothing stroke. However, in mice and other animals they have a protective function: they warn the animals of the presence of something on their skin, be it water, dirt or a parasite. When these stimuli bend the hairs on the skin, they activate the C-LTMRs, says Marshall, "expanding the skin's sensitivity beyond just the surface."

To get lab mice to shake their fur like wet dogs, the researchers applied drops of sunflower oil to the mice's hind necks. Almost all animals shook off these drops within ten seconds. The team then genetically modified some of the mice to remove most of their C-LTMRs. These animals showed a 50% reduction in shaking movements when drops of oil fell on their necks compared to unaltered control mice.

The researchers also wanted to examine how signals from C-LTMRs travel through the nervous system to orchestrate the wet dog shaking. They traced the route to a group of neurons in the spinal cord; this connects to an area in the brain known as the parabrachial nucleus, which is involved in processing pain, temperature and touch.

By using optogenetics, a technique that allows neurons to be programmed to turn on and off in response to light, the researchers blocked the activity of the spinal cord neurons. These mice had a 58% reduction in shaking movements compared to control mice. Blocking activity in the parabrachial nucleus also produced similar results. The mice scratched, groomed themselves, and moved normally, suggesting that the neural circuitry is specific to wet dog shaking.

Specialized circuit

The discovery opens up new possibilities for future research. “The wet dog shake is a very coordinated motor response,” says Thomas Knopfel, a neuroscientist at Baptist University in Hong Kong, who adds that the study is a good starting point for exploring how the brain sends commands to control movements. “The wet dog shake in many animals is caused by psychedelic drugs,” he explains. The response to psychedelics is related to serotonin receptors, which also play a role in pleasant touch. “This provides inspiration for further work to understand the connections.”

Zhang says future research could also examine whether overactive C-LTMRs contribute to conditions such as twitch skin syndrome in cats, which involves sudden skin ripples and excessive twitching, or other forms of skin hypersensitivity in humans.

1. Zhang, D. et al. Science https://doi.org/10.1126/science.adq8834 (2024).

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