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Posted On Jul 10, 2016

Updated On Jun 25, 2025

How Probiotics Can Influence Behavior

Behavior

The GI microbiota is known to play a role in the maintenance of health and we also know that there is an association with disturbances in the gut microbiome and various diseases. In a past webinar, Dr. E'Lise Christensen - a veterinary behaviorist - shared some interesting information on how changes in the GI flora (and use of probiotics) can lead to changes in behavior! This is a transcription of an excerpt from that webinar:

I'm speaking - from a veterinary behaviorist's perspective - on probiotic use, and there are many reasons that veterinary behaviorists may reach for probiotics. The main reason being that the intestinal tract has many outposts, actually, where neurons can be influenced by the different bacterial concentrations in the gut. So, when we look at the research that's been done - in conjunction with our anecdotal evidence from the patients that we see with anxiety disorders, impulse control problems, and aggression - we often find that we have a comorbidity or additional problems with gastrointestinal distress. This is particularly obvious in dogs.

Consider that animals have a stress organ - for instance, a cat's stress organ might be their urinary bladder. When cats get agitated they can have changes in the bladder mucosa and bladder wall and wind up with clinical signs associated with the urinary tract. In veterinary behavior we wind up seeing these patients because the cats are urinating outside of the litterbox. Similarly, in dogs, we can see a phenomenon called stress colitis or diarrhea. Diarrhea associated with anxiety or panic is fairly common in dogs when they are placed into an unfamiliar environment or, perhaps, when separated from their families. Examples are animals that go to a kennel, or that end up in a boarding facility, or if the family moves and they have this underlying stress, anxiety, or panic attacks.

So, whenever we have a patient that has clinical signs of stress colitis or that has an underlying anxiety disorder coupled with other gastrointestinal signs - such as nausea or vomiting, a decreased appetite, and excessive lip licking in the context where we do not suspect nausea – because remember, there are behavioral reasons for lip licking that are not necessarily associated with nausea - or discomfort about eating, I’m considering probiotics. Certainly, any sign of food aversion or a dog that has rapidly acquired a new food aversion would be another instance in which I would be thinking about adding a probiotic.

What's really interesting about this is that in multiple species – and much of the research on this has focused on germ-free mice or specific pathogen-free mice but - there has been a lot of research and clinical interest on the gut-brain axis. The bacteria in the gut can actually influence the brain because of neuronal
outposts around the GI tract. In addition, when we have an inflammatory process in the intestines we see an increased permeability that can lead to neurotransmitter alterations and chemical changes that can then be relayed to the central nervous system. This is basically how bacteria in the GI tract - on a very simple level - can influence behavior.

So, there is a lot of interesting research into the gut brain axis and the effect of improving the microbiome by altering the concentrations of the different bacterial species. Doing so can actually change how neurotransmitters are produced or the response to them in the brain. We have some indication that issues with the microbiota may modulate serotonin and GABA. Serotonin is the neurotransmitter that we often address when we are looking to help animals with generalized anxiety, impulse control problems, or even general aggressive behavior to a number of different triggers. The other thing that we want to think about is the GABAnergic potential of these microbiota, and what we can find is that we can actually create some triggering of GABA by metabolism of glutamate. So, GABA is the major neuroinhibitory neurotransmitter in the brain, and the cool thing is that's the same neurotransmitter that we modulate when we use medications like valium, Xanax, klonopin, and even some of the anticonvulsants.

We are looking to improve our patient’s neurotransmitter system in a way that helps them get a better quality of functioning with less suffering. So, if we can find something that has few or no side effects and that has a good shot at improving our patient’s overall anxiety and normalizing the hypothalamic-pituitary-adrenal axis - like the microbiome potentially can - we really want to capitalize on that. So, we know that shifts in the microbiome can influence stress-related behaviors. We also know that this complicated interaction between the commensal microbiome, the probiotics that we may administer, and the pathogenic bacteria that may be in the gut (but maybe not at clinically significant levels until something else happens that destabilizes it or significant numbers of pathogenic bacteria get introduced) – that the interaction between those three groups of bacteria is what can activate these neuronal pathways and CNS signaling systems. So, it's really common for those of us in veterinary behavior – who have patients with clinical signs of anxiety and potential issues with the gut - to consider that relationship and include probiotics in a multimodal treatment plan.