If you have ever been close to a dog after it has gone for a swim, you have probably been sprayed with water flinging from its fur. We now know the brain pathway that causes animals to rapidly wiggle themselves dry – a phenomenon known as the wet dog shake.
At least 12 different types of nerve cells help hairy mammals like mice and dogs feel physical sensations, such as temperature changes or touch. Yet it wasn’t clear which of these neurons sense irritating substances that animals want to shake off.
To pinpoint the culprit, at Harvard University and his colleagues placed a drop of cold sunflower oil on the back of the necks of 20 mice to elicit wet dog shakes. Twelve of the mice had been bred to have impairments in sensory neurons that respond to mechanical forces, such as pressure or stretch, meaning they couldn’t feel physical touch. The rest of the rodents had impairments in neurons that detect cold temperatures, so they could feel the pressure but not the chill of the oil droplet.
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Mice that couldn’t feel touch didn’t try to shake off the oil droplet, but mice without neurons for cold temperatures did. This suggests sensory neurons that respond to mechanical touch – not temperature – trigger wet dog shakes.
The team then placed an oil droplet on 17 different mice that didn’t have any sensory impairments and monitored the activity of six different types of neurons that respond to mechanical touch. This revealed that three types of neurons activate during wet dog shakes.
Using a technique to switch cells on and off with light known as optogenetics, the researchers then activated each of these neuron types and found that one, called C-LTMRs, reliably produced wet dog shakes. Further experiments showed these neurons relay information to a brain region called the parabrachial nucleus, which triggers the animals to rapidly shake.
Together, these findings map out the brain circuitry that causes hairy mammals to shimmy themselves dry. at the Salk Institute for Biological Studies in California suspects the same pathway also plays a role in itchy sensations. He says if that is the case, developing treatments that target this brain pathway could help treat chronic itching in people.
Science
