Life Lines by Dr. Dolittle

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Humans do it, cats do it, dogs do it…why can’t rodents or rabbits do it?

Image of a Zucker rat by Joanna Servaes – via Wikimedia Commons

Did you know that rodents and rabbits are not able to vomit? This was certainly news to me. So, I had to find out more…

First, let’s talk about the difference between retching and vomiting. During retching (or dry heaves), the diaphragm and abdominal muscles contract, which helps increase pressure within the stomach (and prepare the contents for expulsion). Vomiting also involves contractions of the diaphragm, abdominal as well as intercostal muscles and likewise increases the pressure in the stomach and chest cavity to expel the contents of the stomach. Both retching and vomiting are controlled by the brainstem.

A study published in 2013 compared 3 groups of animals from the order Rodentia: mouse-like rodents (rats, mice, beavers, voles), Ctenohystrica rodents (guinea pigs and nutria), as well as squirrel-like rodents (mountain beavers) in comparison to animals that are known to vomit such as cats, ferrets, and musk shrews. Although the animals were exposed to agents known to cause vomiting in other species (copper sulfate, veratrine, or apomorphine – each of which acts in a different way to trigger vomiting), none of the rodent species even so much as retched after exposure. Anatomical comparisons revealed that the rodent diaphragm was less muscular and their esophagus was longer than animals that are well-known for their vomiting reflexes. These features may make it more difficult to vomit, but do not really explain the total lack of a vomit reflex. Further study of the rodents showed that the animals may be missing the neural wiring in the brainstem that is necessary for activating the vomiting reflex.

The research team should have included my cat in their positive control group. He has a rather impressive vomiting reflex that is like clockwork after he eats…or as I am just climbing into bed. Why couldn’t he be just a bit more like a rodent?

But, then again, my cat’s strong vomiting reflex (although utterly disgusting) serves to protect him from clogging up his gastrointestinal tract with hairballs. I guess that is a good thing as some animals, like rabbits can develop fatal hairballs as they lack the vomiting reflex too.

Source:

CC Horn, BA Kimball, H Wang, J Kaus, S Dienel, A Nagy, GR Gathright, BJ Yates, PLR Andrews. Why Can’t Rodents Vomit? A Comparative Behavioral, Anatomical, and Physiological Study. PLoS ONE. 8(4): e60537, 2013.doi:10.1371/journal.pone.0060537

Categories: Comparative Physiology, Feline, Illnesses and Injuries, Pets

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