Why does a wet dog shake himself off?

A dog whose fur is wet shakes its body noisily to shake off the water droplets. Why do they act like that? A new study reveals that secrets are hidden in the unique neural circuitry of furry mammals. This is the content reported by the scientific journal Nature based on a paper by researchers at Harvard University published in Science on the 7th (local time).

This instinctive reflex is shared by many furry mammals, including mice, cats, squirrels, lions, tigers, and bears. This behavior helps the animal remove water, insects, or other irritants from hard-to-reach places. However, the specific neurological mechanism at work was shrouded in mystery.

Through a study on mice, researchers led by Dawei Zhang (neuroscientist) at Harvard University’s Howard Hughes Medical Institute discovered a specific type of touch receptor that causes the ‘wet dog shake behavior’ and a neural circuit that connects the spinal cord and brain. “The tactile system is so complex that it can distinguish between water droplets, crawling insects, and the gentle touch of a loved one,” said Kara Marshall, a neuroscience professor at Baylor College of Medicine in the US who reviewed the paper. “It has a very specific subgroup of tactile receptors. “This is an amazing study that was solved by linking it to such familiar and understandable movements.”

The hairy skin of mammals is densely packed with more than a dozen types of sensory neurons. Each has its own unique ability to detect and interpret various senses. The researchers focused on ultra-sensitive tactile receptors called ‘C-group neurofibrillary low-threshold mechanoreceptors (C-LTMR)’ that surround hair follicles.

In humans, these receptors are involved in detecting pleasant tactile sensations, such as a gentle hug or stroking. However, in rats and other animals, the skin acts as a protection, alerting them to the presence of water, dust, and parasites. When these stimuli cause the hairs on the skin to bend, C-LTMR is activated, Professor Marshall explained.

The researchers sprayed droplets of sunflower oil on the back of the rats’ necks to make them shake their fur like wet dogs. Almost all mice shook off the oil droplet within 10 seconds. The researchers then removed C-LTMR from some mice through genetic manipulation. When these animals were exposed to oil droplets, they showed a 50% decrease compared to control mice that had not been genetically modified.

The researchers also uncovered a neural circuit that coordinates wet dog brushing behavior. C-LTMR signals pass through neurons in the spinal cord and are connected to the parabrachial nucleus or parabrachial nucleus of the midbrain, which is involved in processing pain, temperature, and tactile information.

The researchers blocked the activity of spinal nerve cells using optogenetics, a technology that manipulates nerve cells to turn them on and off in response to light. Then, the rats showed a 58% decrease in shaking behavior compared to the control rats. Blocking the activity of the parabrachial nucleus also showed similar results. Nevertheless, they showed that the neural circuit connecting the spinal cord and parabrachial nucleus via C-LTMR was specific to the induction of the ‘wet dog brushing behavior’ in that the rats showed normal behavior of scratching, grooming, and moving their fur.

These findings will pave the way for future research into the mechanisms that trigger pleasant tactile responses and various skin sensitivities. “The movement of brushing a wet dog is a very coordinated motor response,” said Thomas Köppel, a neuroscience professor at the Hong Kong Baptist University. “This study is a good starting point for research into how the brain sends commands to control movement.”

Professor Köppel said, “In many animals, the wet dog whisking behavior is triggered by hallucinogens. The response to hallucinogens is related to serotonin receptors, which also influence pleasant touch.” He said the study was “a lot of inspiration for connecting these dots.” Jang explained that this could lead to further research into whether overactive C-LTMR also contributes to conditions such as spastic skin syndrome in cats, which causes sudden skin ripples and excessive twitching, or to other types of skin hypersensitivity in humans.

The paper can be found at the following link: