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Forced-swimming test, irritable bowel syndrome, gut flora and behaviour, neuroplasticity, immune system and the gut, birth and bacteria

The forced-swimming test

Puts rats in water containers too deep for them to reach the bottom with their paws and measures the length of time that they keep swimming until they give up. Used in studies that try to observe the effectiveness of antidepressants for example. When given a cocktail of good gut bacteria, the rats swim significantly longer than without, but when the vagus nerve is severed, they didn't swim longer anymore.

The thalamus is the brain's bouncer, it filters the sensory information and decides what will be sent to the conscious brain. For example, if you will be able to recognise curtains that have been changed is decided there. When the gut is unhealthy, feelings of unease also pass onto the brain.

People with Irritable Bowel Syndrome have a higher incidence of anxiety or depressive disorders.

This may be caused by micro-inflammations, bad gut flora or undetected food intolerances.

Stress can damage the gut, because it reduces the blood supply to the gut, producing less mucus there via signals passed through the sympathetic nervous system. This weakens the gut walls, which sends distress signals to the brain.

Glut flora can also affect behaviour in mice. Timid and exploratory strains of mice were put on antibiotics to wipe out their gut flora, and then there were fed each other's gut bacteria. They showed behavioural characteristics atypical of their own strain, and similar to those from which their gut bacteria originated from.

Stress when eating, such as being told to finish all your food when you are young, activates nerves that inhibit the digestive process, which means we extract less energy from our food, we take longer to digest it, and put the gut under strain.

Neuroplasticity and depression

After the age of 25, nerves start to fire mostly in well-rehearsed patterns. it is harder to learn and change. Thought patterns such as "I am worthless" have taken firm root. If antidepressants increase neuroplasticity, they may work by loosening negative thought patterns.

The side effects on the gut of antidepressants such as prozac are diarrhoea, constipation and nausea, they are caused because the same neural receptors in the gut are also being affected.

95% of the serotonin we produce is manufactured in gut cells, where it enables nerves to stimulate muscle movement, and is a signalling molecule. So affecting gut serotonin can affect the brain too and vice versa.

Where the "self" originates

1) The insula receives information about feelings from the entire body. Each piece of information is like a pixel, all pixels form a picture of a cold, hungry, us sitting on a table for example.

2) The purpose of our brain is to create movement. The insula's map is used to plan meaning for movement

3) The brain is an organ of the body. The insula creates an image of the body, also containing the brain. That must therefore include the areas for social empathy, morality and logic, our perceptions of the environment, and our memories from the past.

Our gut's microbiome can weigh up to 2kg.

80% of our immune system is located in our gut - that is because there are so many bacteria there.

The bacteria are located on the mucous membrane of the gut - preventing them from getting too close to the cells of the gut wall.

Here, immune cells can get acquainted with many previously-unsown species where they don't pose a danger to the body. So when they later encounter them elsewhere, they can react very quickly.

So the immune system in the gut must:

1) suppress its defensive instincts

2) still weed out the bad bacteria

Sometimes there are communication breakdowns, and the immune cells are wrongly trained to distinguish between bacterial cells and body cells, and may attack the body, as in the cases of scarlet fever, type I diabetes.

Usually immune cells are trained in the gut before they are allowed to enter the bloodstream.

They encounter many different pathogens there: if the cells cannot clearly distinguish between a foreign body and our own cells, and nee dot stop and prod, they will never graduate into our bloodstream.

Some cells like red blood cells have markers on their surface very similar to bacteria.

Immune cells are trained to recognise the specific markers of their won body's cells and not to attack them: these are the blood group markers. However, if another blood group's blood is transfused, with these other protein markers, it will be attacked as though it is bacteria. The immune system will make clumps of these red blood cells.

Babies can theoretically receive any blood group transfusion, because their immune cells are not trained yet, however they are given their mother's blood group, in case immune cells from her body are in theirs.

Colonisation resistance: Harmless bacteria occupying spaces that could otherwise we taken up by harmful species.

10% of our cells are human, microbial cells compose 90% of us by number.

In the uterus, we are sterile.

The vagina has the first bacteria we come into contact with. The vagina itself is covered in acidic mucous produced by the bacteria there. This limits the types of bacteria that can survive in that environment, and as they coat the emerging baby, the bacteria that can come into contact with the baby to is selected. These helpful microbe and some that come from the skin of the mother and the hospital are those which will start to train the immune system immediately.

It takes about three years for the gut flora to stabilise. This depends on our environment, what we touch, lick and play with.

Breastmilk also provides many gut flora members. It also contains antibodies to help the child's immune system.

Children born with a C-section have a higher chance of developing allergies and intolerances because of the random gut flora they get to have. Poor nutrition, too much antibiotics, excessive cleanness, too much exposure to bad bacteria can cause a bad start to gut bacteria and hence the immune system too.

Babies contain more active genes for digesting milk.

Guts of obese people more carbohydrate breakdown genes.

Older people have fewer bacteria to deal with stress.

Every microbe contains genes for protein and carbohydrate breakdown and vitamin production.


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