Gut brain axis

Question 1

Communication through the GBA

Answer 1

It is bidirectional between the CNS and enteric nervous system, linking emotional/cognitive CNS centres with the peripheral intestinal functions.

Also includes the HPA axis. Cortisol from the HPA can act on the gut.

Vagus nerve innervates the gut, communication through these neurones. The brain can then influence the variety of cells in the GIT.

Question 2

Gut microbiota determinants and products

Answer 2

Made up of many bacterial species, and determined by diet and antibiotic exposure.

Many of the NTs are synthesised largely in the gut, e.g., 90% of 5-HT from the gut.

The microbiota contribute to the production of GABA, melatonin, histamine, and ACh. nitrate and nitrite from the diet generate NO.

Initial microbiota acquired at birth, and is shaped by environmental and intrinsic factors.

It is flexible throughout life and can adjust to new environments

influenced by age, diet, environment, antibiotics, prebiotics, exercise, mode of delivery and stress (HPA-mediated)

Question 3

Ways the products of the gut microbiota can act on the body. (how they distribute themselves to targets)

Answer 3

They can directly act on enteroendocrine cells (to release GIT hormones), be taken up into the blood, or can act on the vagus nerve afferents that connect to the brain.

The location, and type of bacteria present in the GIT all changes the GBA functions.

Question 4

Examples of gut bacteria

Answer 4

Good:

Bifidobacteria: keeps bad bacteria levels in check, aids immune response, and produces vits

E. coli: produces vit K2, and keeps bad bacteria levels in check

Lactobacilli: produces vits, immunity, and anticarcinogenic

Bad:

Campylobacter: cause degradation of the mucus: diarrhoea and ulcers

Enterococcus faecalis: common cause of post-surgical infections

Clostridium difficle: causes diarrhoea and colitis

Question 5

GBA in neurotoxic signalling and GBA in ASD and AD

Answer 5

Campylobacter jejuni infection was seen to increase nuclear c-Fos protein in the brain.

Cytokines from immune cells have effect on CNS signalling.

Leaky gut in ASD enables bacterial migration: linked to amyloid-beta peptides -> increases cytokines release.

Higher fat diets seen to exacerbate AD phenotypes. increased lipopolysaccharides seen in AD. sees increased amyloid-B deposition and increased microglial activation

Question 6

Beneficial GBA bacteria

Answer 6

oxytocin produced by lactobacillus reuteri. L reuteri increases social behaviour

Bifidobaterium longum upregulates BDNF - reduces anxiety/depression

bactericides fragilis improves anxiety, repetitive and communicative behaviours.

Bacteroides fragilis ameliorates ASD-related abnormalities in an offspring that underwent maternal immune activation

Question 7

Pre- and pro-biotics

Answer 7

e.g., yoghurt, kefir, miso, some beers.

Has some effects on the expressio of certain gut microbiota.