There is a network of neurons lining the gut, and it's so extensive that some scientists refer to it as a second brain. We know that the neurotransmitters work to help handle digestion, but the story is much bigger than that. It turns out that the gut-brain and the brain in the skull have conversations so-to-speak and the gut-brain helps to determine mental state. This second brain can control digestion independently of the brain in the skull, and rather than information going from the skull-brain to the gut (as was always thought), it turns out that the gut-brain sends information to the "main" brain.
Scientists believe that a big part of our emotions are actually influenced by the nerves in the gut. The enteric nervous system uses more than 30 neurotransmitters, just like the brain. Consider that 95 percent of the body's serotonin is found in the bowels, so if you've been wondering why stress can affect the bowel, you may have just come closer to the answer. As regards serotonin as a mediator of the gut-brain connection: “One role of the gut-brain axis is thought to be as protection against disagreeable substances, where a rapid response may be critical. If you ingest a toxin or something that is detrimental, then these cells, because they are chemosensors, will respond and may send signals to induce vomiting or diarrhea, for instance” http://mobile.the-scientist.com/article/49713/gut-feeling
There is a clear association between changes in the microbiota and cognitive behavior. Intestinal dysbiosis, as modeled using GF mice (containing no microbiota), bacterial infection with an enteric pathogen, and administration of probiotics, can modulate cognitive behavior including learning and memory. This chapter will highlight recent findings in both human and animal studies indicating how changes in the composition and diversity of the microbiota can impact behavior and brain physiology in both disease states and in health. Cognitive behavior can not only be affected in cases of intestinal disease, but also manifests changes in extra-intestinal disease conditions. https://www.ncbi.nlm.nih.gov/pubmed/24997042
Changing the way a dog feels emotionally has exciting opportunity to shape/change behaviour.
Undernutrition and Overnutrition of the host alters the microbiome
These are defined as selectively fermented ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus also being a benefit to the host organism.
These are most frequently defined as live microorganisms, which when consumed in adequate amounts confer a health benefit on the host.
The microbiota on mucosal surfaces, especially the GI tract, in dogs is complex. The composition varies from site to site and there is some evidence that changes in the composition of the microbiota/microbiome are associated with certain diseases. However, analysis of the canine GI and faecal microbiota composition, its function, production of metabolites and immunological properties is far from complete, even though data on the microbiome are accumulating. https://onlinelibrary.wiley.com/doi/full/10.1002/vms3.17 Accordingly, overall knowledge of the best characteristics of a canine microbial commensal or probiotic is patchy and most assumptions about their best properties are derived from human studies.
Can probiotics survive when antibiotics are given?
“….significantly reduce the time to resolution of clinical signs and the number of dogs receiving metronidazole in a study of acute idiopathic diarrhoea” Acute diarrhoea in dogs in which probiotics have been administered include stress-associated (e.g. kennelling stress), antibiotic-induced and idiopathic diarrhoea Dysbiosis is associated with IBS, and central nervous disorders (those that can cause muscle tremors, bobbing of the head, twitching paws; paralysis, seizures, cramping… think Scotty Cramp which is associated with a disorder of melatonin.