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“So far, almost all studies of gut neurotransmitters were conducted in adult animals or human subjects, where a specific gut cell type called enterochromaffin cells produce neurotransmitters,” said Dr. Zeng. “However, we discovered that this isn’t the case in the newborn gut where most of the serotonin is made by bacteria that are more abundant in the neonatal gut.”
Had no idea serotonin has other uses. Watch, the gut be responsible for modern wide spread depression.
Probably not directly responsible but there is a strong link between them in the gut-brain axis, the effects are likely bidirectional
Yes, that's a theory being explored currently.
The gut brain connection, more explicitly the microbiota, is directly tied into anxiety and depression. This is a major reason broad spectrum antibiotics should only be used when absolutely necessary plus a well round diet is vital!
More mind blowing is the recent research showing Fecal Transplants helping with Autism. It's been demonstrated microbiota dysbiosis when young is associated with developing Autism, and Fecal Transplants allow for a healthly microbiota to replace the one in disarray.
Here's a research paper digging into the depression and anxiety apects if you're interested: Gut Microbiota in Anxiety and Depression - Unveiling the Relationships and Management Options https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10146621/
Hm, so it's not the mere exposure to bacteria that does the immune system training. Chemicals produced by bacteria are needed for the training on other things to be correct.
It's not chemicals but unique cellular patters (like flagella, peptidoglycan, and LPS to name a few) which are recognized as not being apart of self. Training occurs before B and T Cells ever see a foreign pathogen. It occurs in the bone marrow for B Cells and in the Thymus for T Cells. The biggest aspect of training is not recognizing pathogens but actually not binding to self. This is what helps to prevent autoimmunity. Only a small percent of B and T Cells pass this training as their B and T Cell receptors are made entirely at random. So, even if a B or T Cell passes training, there's a chance it'll never be used as it doesn't bind to a single pathogen epitope. Basically the production of our adaptive immune response is super energy intensive due to soo many cells failing training, plus another portion that pass not being useful for the pathogens we encounter. However, this process is also the reason a small percentage of folks were immune to COVID before ever encountering the virus thanks to the random nature of B and T Cell receptor formation. The immune system is super intriguing and it's 100% my favorite subject to study!