Why do dogs shake even when they are barely wet?
ITA version ESP version
Many furry mammals perform quick shakes to remove water and irritants from their fur, following a typical pattern of three shakes back and forth. But what is the mechanism that triggers this innate response? Dr. Dawei Zhang and his team from Harvard Medical School asked themselves this question and, in the lab, sought to understand it by using mice as a model.
The first step was to observe if different stimuli on the mice’s skin could trigger the “wet dog shake.” Researchers blew air on the mice, sprayed them with water, and even immersed them briefly in a bath. Surprisingly, a small drop of oil on the neck was enough to trigger the shake, suggesting that a light, annoying touch was the triggering factor.
At this point, the researchers aimed to understand which part of the nervous system “felt” this drop, initiating the shake response. They genetically modified some mice, eliminating specific skin receptors. First, they removed the receptors that perceive temperature changes, noting that the mice continued to shake. Temperature, therefore, was not a decisive factor. Then, they eliminated mechanoreceptors, which respond to tactile stimuli. This time, the mice shook far less than unmodified ones, suggesting that tactile sensitivity was key.
The team then focused on a specific group of mechanoreceptors, the low-threshold C fibers (C-LTMR), located around hair follicles and responsive to light touches. To confirm the hypothesis, the researchers used optogenetics, a technique that activates nerves with light. By stimulating the C-LTMR optically, the mice shook as if wet; blocking them, however, reduced the shake, confirming the role of the C-LTMR.
But the team also wanted to understand where the signals from C-LTMR travelled and which part of the brain processed them to generate the shake response. They traced the path of these signals, discovering they travelled from hair follicles to the spinal cord, and from there to a specific region of the brain called the parabrachial nucleus, which processes sensations like pain and itching. This pathway called the C-LTMR-spinoparabrachial circuit, turned out to be the mechanism behind the “wet dog shake.”
This discovery is significant because C-LTMR represents an evolved defence system that removes annoying stimuli like drops of water or parasites. Thanks to a system of specialized tactile receptors and neural pathways, shaking vigorously is the most efficient way for many mammals to eliminate these irritants.
What about humans? Like other mammals, we have something similar. Our receptors, called C-mechanoreceptors, have adapted to perceive pleasant sensations like caresses and hugs. Yet, many people feel a slight chill when someone lightly touches their neck. This reaction may be a distant “evolutionary memory” of the response that triggers the shake in dogs and other animals. In us, however, this reflex has lost its defensive function, transforming into a response linked to pleasure and social connection.
See you soon, and Good Science!
Source
