Dog Discoveries

I am Your Dog’s Blood Brain Barrier


What’s more marvelous than a special barrier that protects the dog’s brain from potentially harmful substances? Owners of a sub-population of collies and several other herding breeds, in particular may be well aware of the risks their dogs may be susceptible to due to the way their blood brain barrier is structured, but this is something that certainly may interest owners of any other types of dogs as well. As we marvel at this structure, we can gain more insights on how the blood brain barrier works and gain more information about possible problems. So let’s see what our dog’s blood brain barrier has to say so we can get more acquainted with this structure. So let’s welcome today the dog’s blood brain barrier!

Let Me Introduce Myself!

Hello, you may not know me well, but you sure need to thank me for protecting something as important as your dog’s brain! I might not be popular as the brain, but I sure need a place of honor for ensuring your dog’s brain is shielded from potential dangers. I take no offense if you have never heard about me before, but my job today is just this, introducing myself and letting others become aware of my noble duties.

While time ago, it was suggested that I was present only in an immature form in young animals, today studies have instead indicated that my sophisticated structure is actually already quite operative at birth! I am highly permeable and therefore operative (although selectively) in neonate puppies according to veterinarian Kit Kampschmidt. This means that neonates are more vulnerable to the toxic effects of certain drugs, which is why veterinarians are cautious in medicating those youngsters unless strictly necessary!

Warning, Restricted Area

What’s my day like as a blood brain barrier? My main role is allowing the entry of essential nutrients such as glucose and several amino acids while blocking certain substances from reaching the brain.

To be more precise, I have a network of blood vessels lined with tightly wedged endothelial cells that form a nearly impermeable boundary responsible for restricting the passage of certain substances from the bloodstream to your dog’s brain.

Hey, if you rarely hear about brain infections, it is thanks to me! Indeed, I effectively protect the brain from harmful substances such as toxins and bacteria. At the same though, as mentioned, I must grant access to important sugars and amino acids. These latter successfully gain access courtesy of special transport systems that move them across the barrier and into brain tissue as needed.

When Things go Wrong

As effective as I am in restricting access to the brain, I must admit, I am not invincible. Sometimes cancers or bacteria break me down which allows small compounds that normally wouldn’t come through to gain access. When this happens, this can be bad news. Since my barrier is effective at preventing the passage of foreign substances, I may prevent certain life-saving drugs from reaching the brain.

Antibodies meant to the fight the bacteria are also too large to make it through my barrier, so really only a few selected antibiotics are able to pass. Administering them directly into the cerebrospinal fluid may seem like a good option, but it’s quite a tortuous trip to reach all those tight interstitial passages to the brain.

One good thing though is that when I am inflamed, I become more permeable, which increases absorption of certain antibiotics, but you must be careful too as this also means that the brain becomes more vulnerable to the infiltration of bacteria and viruses!

The Issue with Collies

Owners of collies/collie mixes and other herding dogs are likely aware of the problems associated with giving these dogs the heartworm drug ivermectin. The issue with ivermectin toxicity observed in collies was first noticed in the 1980s. What’s the problem in these dogs?

You see, ivermectin is toxic to pesky parasites, but it is thanks to me that most breeds aren’t affected. As a barrier, I prevent this drug from reaching your dog’s brain, but since parasites do not have a blood brain barrier, this drug affects them without poisoning your dog. You must therefore thank me for allowing this form of “selective toxicity!”

However, it was discovered that a sub-population of collies (along with several other herding breeds, see quote below) had a tendency to accumulate high concentrations of ivermectin in brain tissue which caused them severe neurological symptoms. Why?

Turns out, such dogs lack a functional blood-brain barrier, explains Katrina L. Mealey a board certified veterinarian specializing in internal medicine and clinical pharmacology. The issue is the result of an altered multi-drug-resistance gene (MDR-1) which makes their blood brain barrier more permeable. It’s estimated that about 3 out of every 4 collies in the United States have the mutant MDR 1 gene, explains Dr. Joey, a board-certified veterinarian.

Affected breeds include Australian Shepherds, Collies, McNabs, Longhaired Whippets, Silken Windhounds, English Shepherds, German Shepherd Dogs, Old English Sheepdogs and Shetland Sheepdogs. ~Dr. Marty Becker

Ivermectin at high doses isn’t the only drug these dogs are sensitive to, according to Washington State University, other problem drugs include loperamide (Imodium), acepromazine and several chemotherapy and antiparasitic agents agents.

Fortunately, today there are tests that can screen for multidrug sensitivity. One of them is offered by Washington State University.  The old adage of “white feet, don’t treat” which refers to not treating scotch collies due to the risks associated with their “leaky blood brain barrier”, has now transformed into “white feet, test to see if you can treat” says Patricia Dowling in an article published on CanVet Brand Animal Health Products.

So if you own a collie or other affected breed and are wondering about risks associated with giving certain medications, consult with your vet and ask about getting your dog tested!

Drugs to watch for: The tranquilizer acepromazine; the pain medication butorphanol; the anti-cancer drug doxorubicin, vinblastine and vincristine; the antibiotics erythromycin and rifampin;  the anti-parasitic drugs ivermectin (in high doses), milbemycin, moxidectin and selamectin; and the anti-diarrhea drug loperamide (Imodium).~Dr. Marty Becker

I hope this article may have helped you understand me better! You know, not many people are aware of me and I thought I deserved to at least be acknowledged. The best part is that I am not exclusive to dogs, so today you have also learned something about yourself as well! Thank you for listening and enjoy the rest of your day!

Yours truly,

The Blood Brain BarrierDog Pawprint

Did you know? According to the University of Washington website, the blood brain barrier was discovered more than 100 years ago when a blue dye was injected into the bloodstream of an animal. Curiously, all the structures of the animal’s body turned blue except for the brain and spinal cord.

Disclaimer: The article is not intended to be a substitute for professional veterinarian advice, diagnosis, or treatment. If your dog is sick, please see your vet.


  • Clinical Anatomy & Physiology for Veterinary Technicians, Thomas Colville DVM, Joanna M. Bassert VMD, Mosby Inc.  St Louis, MO, 2002
  • Newborn rabbit blood-brain barrier is selectively permeable and differs substantially from the adult, Braun LD, Cornford EM, Oldendorf WH, J Neurochem. 1980 Jan;34(1):147-52.
  • Pharmacogenetics: It’s not just about ivermectin in collies, Patricia Dowling, Can Vet J. 2006 Dec; 47(12): 1165–1168.
  • Brain, Society for Neuroscience, The Blood-Brain Barrier
  • Vet Street: Multidrug Sensitivity: What You Need to Know

Adrienne Farricelli
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