Microbes in charge

Imagine this: you have just won ten million dollars in the lottery, or you have just eaten the most delicious, warm, chocolate brownie. In these situations, our brains produce chemicals called neurotransmitters, which give us these great feelings of pleasure and happiness. Now, imagine this: you're about to sit an exam. In this situation, our brains, instead, produce different chemicals, making us feel stressed and anxious. Our emotions control the highs and lows of life. I have always heard that the brain inside all of us controls everything that we feel, think and do.

However, I've always found it strange that every feeling, thought, and behaviour is controlled by a three-pound, soggy lump of cells inside our heads, until I learned about gut microbiota. We each have a second brain, which controls as much of our physical and mental functions as the brain in our heads, and plays a role in preventing diseases. This second brain is our gut microbiota. However, we have completely underestimated their role as the second brain. I learned this first through the intriguing story of the rat. If the rat becomes colonised with the microbe Toxoplasma gondii, a fascinating thing happens: they lose their fear of cats. The cat's smell was chosen as a measure. The infected rat preferred the areas that had the smell of cats. So, the microbes take control of the brain and change the way you think. 

In another study, a research group at University College Cork in Ireland fed Lactobacillus rhamnosus, a good bacteria—or 'probiotic' you can usually find in yoghurt—to one of two groups of mice. The probiotic mice were much more likely to succeed in the face of adversity tests than those not treated with the probiotic. They repeated a similar study in humans, with the probiotic-fed humans displaying improved resilience to negative emotions compared to those without the probiotic.

As I mentioned earlier, neurotransmitters are these chemicals that can change how we think, behave, and feel. As it turns out, neurotransmitters are also produced in our gut, 50% of the dopamine and 90% of serotonin (nature's antidepressant): two neurotransmitters that drastically affect your mood, happiness and pleasure. According to some studies, dopamine also plays a role in memory and learning, so gut microbiota controls how you think and behave and is also involved in cognitive functions like memory and learning. 

Let’s now turn to mental health! One study by Venket Rao studied 39 individuals with chronic fatigue syndrome (a syndrome characterised by severe anxiety, depression, and long-term exhaustion), split the individuals into two groups. The first group received a bacterial strain for two months while the other group received only a placebo. The group that received the bacterial strain showed a significant decrease in anxiety with respect to the other group.

Noticeably, there is a vital link between the gut microbiota and the immune system.  70-80% of immune cells are present in the gut. Additionally, studies have shown that Germ-free mice have fewer immune system structures in their intestines than wild-type mice. These immune structures in the gut are referred to as the gut-associated lymphoid tissues (GALT) and Peyer's patches. Another study explored the gut microbiota of 42 patients affected by Rheumatoid Arthritis and 10 healthy controls. They observed that rheumatoid arthritis patients have a higher population of Lactobacillaceae family and the Lactobacillus genus, and fewer Faecalibacterium, a butyrate producer. Butyrate is the fuel source for our intestinal cells to produce mucin, which then repairs the intestinal lining and mucosal membrane and reduces inflammation. 

Our gut and brain are physically and biochemically connected in several ways. First, our intestines are physically linked to our brain through the vagus nerve, which sends signals in both directions. Interestingly, even if this is cut off (severed), our intestines can continue to function fully without a connection to the brain, suggesting they have a mind of their own. Secondly, our brains are made up of a hundred billion neurons, which continuously send messages to tell our bodies how to work and behave. Well, interestingly, our guts have a hundred million neurons. 

Our gut microbiota, the unsung hero behind our feelings, thoughts, immune system and behaviour - proving that sometimes, it's not just all in our heads, but in our "guts" too!

Written by Prabha Rana

Related articles: The gut microbiome / The dopamine connection

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