Gut bacteria can change the neurotransmitters (brain chemicals) in the body, because certain gut bacteria thermselves manufacture certain neurotransmitters. Some probiotics have a great effect in reducing anxiety. Another way gut bacteria works to reduce anxiety is by sercreting certain chemical messengers called cytokines that change the immune system/nervous system response. This is called psychoneuroimmunology. 
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Lactobacillus Rhamnosus and GABA
GABA is a great neurotransmitter. It is the OFF switch of the nervous system and patients with anxiety often do not have enough GABA, or they have too much other excitatory neurotransmitters. GABA helps a person settle down, feel calm, feel safe and stop the fight and flight response. Certain prescription medications that affect the GABA pathway include Klonopin, Xanax, Valium, and Gabapentin. But these medications are often addictive and have unwanted side effects. It’s best that your body makes it’s own GABA. The probiotic Lactobacillus rhamnosus makes GABA. L rhamnosus can be a GABA making machine in the body if a patient has enough of this strain in their gut.
An animal study shows that treatment with L rhamnosus decreased activity in the hippocampus, amygdala and local coeruleus.
1. The hypocampus is associated with long term memory, spacial relationship, and behavioral inhibition. Excessively active activity such as over firing in the hypocampus or inflammation can affect the above
2. The amygdala associates the 5 senses with emotions. Overactive function may ingrain more traumas such as in PTSD or excessive negative emotional associations with events, smells, sights, people etc.
3. The local coeruleus is the part of brain involved in stress and panic. It Secretes adrenaline.
Lactobacillus rhamnosus also reduced the stress response associated with cortisol. Therefore supplementation with L. rhamnosus is promising for supporting the body in making more GABA via the bacteria producing it.
Lactobacillus rhamnosus and Inflammation
Too much inflammation in the brain is not good and can contribute to anxiety. We are not referring to the type of inflammation like a concussion, but chronic oxidative stress to the nervous system. Patients with higher levels of inflammation in the body such as those with autoimmune diseases, allergies, aches and pains are more likely to also have more inflammation in their nervous system. Anxiety, depression, and memory loss are definite symptoms that indicate an increased inflammatory response in the brain.
Think of increased inflammation in the brain as increased firing of neurons. Think of an electric cord with too much electricity going through it that it blows the fuse. GABA helps to slow down this rapid firing and regulate it back down to normal.
A study shows that Lactobacillus rhamnosus inhibits the inflammatory response by increasing IL-10 levels. IL-10 is an anti-inflammatory cytokine and helps to shut down the T cell response after infections or stressors. If there is not enough IL-10, inflammation can extend long after it is needed, resulting in chronic inflammation. L. rhamnosus probiotic can help support healthy levels of IL-10.
Psychobiotics
Lactobacillus Rhamnosus is a psychobiotic. A psychobiotic is a live organism (probiotic) that when ingested in a certain amount produces a health benefit in patients suffering from psychological disorders. How does this work? The gut bacteria influence the vagus nerve which communicates with the brain. The vagus nerve is the longest cranial nerve, exiting the brain and reaching all the way to the intestinal tract. This nerve channels the communication between the brain and the gut. I use a product, Ultra Flora Women's by Metagenics with my patients which contains L. Rhamnosus.