Laura Ward
Pet Nutritionist
rewardingpetnutrition.com
info@rewardingpetnutrition.com
Anxiety in dogs
Anxiety, defined as a “preparatory response made in anticipation of threatening stimuli or scenarios”, is an adaptive response which many canine behavioural issues can be linked to. A 2020 Finnish study estimated that 72.5% of dogs exhibited anxiety behaviours of some extent. These behaviours include noise sensitivity, fear, excessive activity, compulsive behaviour, aggression, and separation-related behaviours. This alone is stressful for dogs, as well as their humans, but studies show that dogs with anxiety are also more likely to have a shorter lifespan and are more prone to disease. Anxiety behaviours can also play a part in dogs being given up for adoption or even euthanized.
There is a lack of research into how the microbiome and gut health can impact anxiety in dogs, but there are few studies combining with studies in humans and rodents which discuss this.
The gut brain axis
There is two-way communication between the gut microbiome and the central nervous system. This is fascinating, but when we think of how eating junk food makes us feel sluggish or how stress upsets our stomach this shouldn’t be a big surprise. This two-way communication is comprised of several different mechanisms including neural, metabolic, endocrine, and immune-mediated signalling pathways.
Microbiome Interactions
Metabolites
The microbiota uses fibres which reach the colon to produce energy, whilst also creating metabolites. These metabolites, for instance short-chain fatty acids, are beneficial to gut health. Metabolites can also reach the brain and have other roles throughout the body. A study found that supplementing short chain fatty acids restored brain function in rodents and markedly improved stress behaviours.
Neural pathways
Effects of the microbiome can be detected by the nervous system, through their effects within the gut. Metabolites are sensed by the vagus nerve, which the central nervous system then responds to.
Endocrine routes
Gut microbiota influence hormone production and regulation pathways. Tryptophan is mainly produced within enterochromaffin cells of the gut and neurons of the enteric nervous system. Tryptophan plays a key role in sleep, cognition, anxiety, and mood, amongst other applications.
Gut microbiota have a significant role in the regulation of Dopamine and it’s precursor, norepinephrine, as well as GABA (gamma-aminobutyric acid). Changes in GABA regulation link with stress and anxiety. GABA administration and regulation of GABA receptors relate to reduced anxiety symptoms in rodents.
Communication between the gut microbiome, neural mechanisms and behaviour is strongly suggested through data, but studies are required to thoroughly test this.
Hypothalamus
The hypothalamus is an area of the brain which is responsible for regulating many areas of the body through homeostasis*, which also includes response to stress factors. There is a complex feedback system to the hypothalamus to balance this homeostasis*, which includes the gut microbiome. Some gut bacteria could increase the activity of the hypothalamus, and stress can affect the gut microbiome populations and the gut wall permeability.
*Homeostasis is a self-regulation of the body to maintain the equilibrium and optimal conditions. This includes temperature, blood sugar, and so many more.
Immune mediated mechanisms
The development of the immune system and it’s functioning is impacted by gut bacteria, as are cognitive function and behaviour. Cytokines and chemokines are a mechanism of regulation. Studies of pro-inflammatory states have found that cytokines and chemokine production is affected, particular cytokine patterns are associated with anxiety disorders.
Cytokines within the brain also have the potential to influence neurotransmitters such as dopamine, affect hormone production and even neural tissue development. Inflammatory cytokines can play an important role in neurodegenerative mood disorders and development.
Microbiome Effects on Memory and Cognition
A study has found connections between the gut microbiome and cognitive performance in dogs. Populations of particular types of gut bacteria were seen to be linked to performance during a memory test and also age. Dogs are thought to experience cognitive decline with age in the same way as humans when affected by Alzheimer’s disease, and the microbiome effect seen in both dogs and humans is consistent.
Dietary effects on Anxiety
A canine study found that dietary supplementation of omega 3 fatty acids and particular fibre and polyphenol sources were associated with changes to the gut microbiome population and beneficial changes to anxiety related metabolites. This suggests that nutrition can modulate the gut microbiota to improve the profile of metabolites linked to anxiety.
Changes to the levels of tryptophan metabolites was seen, which is of interest as previous studies supplementing tryptophan to dogs found a reduction in dominance and territorial aggression and reduced teeth baring, snapping biting and nosing in Sled Dogs.
Summary
Although more research is needed to more thoroughly understand the intricacies of the relationship between the gut microbiome and the brain, we can already see how the health of the microbiome affects the brain, and vice versa. It is evident that the gut microbiome plays an important role in many pathways which affect cognition and brain health, confirming that maintaining the health of the gut and microbiome is a necessity for health of the rest of the body.
References
1. Sacoor C, Marugg JD, Lima NR, Empadinhas N, Montezinho L. Gut-Brain Axis Impact on Canine Anxiety Disorders: New Challenges for Behavioral Veterinary Medicine. Vet Med Int. 2024 Jan 23;2024:2856759. doi: 10.1155/2024/2856759. PMID: 38292207; PMCID: PMC10827376. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10827376/)
2. Mills D. S., Mueller H. W., McPeake K., Engel O. Development and psychometric validation of the Lincoln canine anxiety scale. Frontiers in Veterinary Science . 2020;7:p. 171. doi: 10.3389/fvets.2020.00171. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10827376/#B3)
3. Salonen M., Sulkama S., Mikkola S., et al. Prevalence, comorbidity, and breed differences in canine anxiety in 13,700 Finnish pet dogs. Scientific Reports . 2020;10(1):p. 2962. doi: 10.1038/s41598-020-59837-z. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7058607/)
4. Kubinyi E, Bel Rhali S, Sándor S, Szabó A, Felföldi T. Gut Microbiome Composition is Associated with Age and Memory Performance in Pet Dogs. Animals (Basel). 2020 Aug 24;10(9):1488. doi: 10.3390/ani10091488. PMID: 32846928; PMCID: PMC7552338.
5. Ephraim E, Brockman JA, Jewell DE. A Diet Supplemented with Polyphenols, Prebiotics and Omega-3 Fatty Acids Modulates the Intestinal Microbiota and Improves the Profile of Metabolites Linked with Anxiety in Dogs. Biology (Basel). 2022 Jun 28;11(7):976. doi: 10.3390/biology11070976. PMID: 36101356; PMCID: PMC9312346.
