When hairy mammals feel something on their back, they will emit “wet dog vibes.” If you’ve ever been within the splash zone of a dog that just got out of the pool, you’ve likely been at the receiving end of its effect. We’ve all seen it, but the neural mechanisms that underpin the behavior have remained something of a mystery—until now.
While it’s fun to watch the silly faces dogs make when they do this, this shaking behavior also serves an important purpose as it can help them rid their bodies of irritating and potentially harmful pollutants. Therefore, understanding how it occurs can inform how and why it has been evolutionarily conserved in so many furry mammals.
We think that C-LTMRs may also be involved in tickling sensations.
Dr Dawei Zhang
Mice are another species that exhibit wet dog oscillations, and so a team of scientists used them as a model to explore the neurobiological underpinnings of the behavior. Their research identified a type of light-touch-sensitive mechanoreceptor in the skin that mediates the evolutionarily conserved behavior, involving the Piezo2 protein and C-fiber low-threshold mechanoreceptors, or C-LTMRs.
You can induce a wet dog shake in a mouse by putting drops of oil on its back, but to determine the mechanisms behind the behavior, the team had to get more technical. One approach they used involved using optogenetics, which allows scientists to control specific neurons using light. By using light in this way, they found that they could induce a wet canine shiver in mice, even when no drop of oil was placed on their backs. They also used ablation, which involves removing or deactivating neurons—and when the team removed the C-LTMRs, the mice stopped shaking as much.
The main role of C-LTMRs is to innervate the hair follicles of the substrate for furry mammals, and they are involved with pleasant affective touch (aka why good guys like pets so much). The same mechanoreceptors also appear to serve a functional role when something sticky sticks into a furry mammal’s back, sending a signal to spinoparabrachial neurons that then relay the message to the brainstem.
We know this because when the team inhibited the synapses of the spinoparabrachial neurons, they couldn’t get a wet dog shake from the mice using optogenetics. OR the actual physical points of the oil. The same disruption was seen when they inhibited excitatory neurons in the part of the brainstem that was at the receiving end of the spinoparabrachial neurons’ messages.
Now, we humans may not be covered in fur, but it’s possible that this neurobiological pathway may be behind our biggest Achilles heel: the dreaded tickle.
“When C-LTMRs were first discovered in cats, the scientist Zotterman (published in 1939) found that C-LTMRs continued to respond/fire after the stimulus (stroking the cat’s furry skin) had ceased, while many other sensory neurons stopped firing when the stimulus stopped,” first author Dawei Zhang of the Program in Neuroscience at Harvard University told IFLScience. “This is consistent with the persistent sensation of tickling in humans even after the stimulus has ceased and led him to hypothesize that C-LTMRs convey tickling sensations.”
“In our experiments, we observed that wet shaking of dogs was often associated with scratching behavior in rats. When we removed the C-LTMRs, in addition to a reduction in WDS, we also saw a reduction in scratches. Therefore, we think that C-LTMRs may also be involved in tickling sensations.
A fascinating insight into the animals that shake it, then, and in the future the team may turn their sights to those that don’t seem to do the wet dog shake.
“It would be interesting to explore how these sophisticated motor outputs are generated by the nervous system, beyond understanding only the sensory aspect,” Zhang added. “It would also be intriguing to understand why some animals do not perform wet dog shakes – whether this is due to differences in sensory, motor or other parts of the nervous system.”
The study is published in the journal Science.