3D - The gut-brain axis

Question 1

define Gut (also known as the gastrointestinal tract)

Answer 1

the gastrointestinal tract or long tube that starts at the mouth and ends at the anus

Question 2

role of the gut

Answer 2

• The gut is responsible for processing food, absorbing nutrients, and excreting waste
• The gut is made up of multiple components
• Within your gut, there are many living microorganisms that help maintain gut health and functioning.
  -These microorganisms are known as the gut microbiota

Question 3

define gut microbiota

Answer 3

all of the microorganisms that live in the gut

Question 4

define gut microbiome

Answer 4

all of the genes of the microorganisms that live in the gut

Question 5

the health of the gut

Answer 5

• can change based on the types and amounts of microorganisms present in the gut
• When the gut microbiota is imbalanced, meaning there is not enough ‘good’ bacteria and too much ‘bad’ bacteria, it is called gut microbiota dysbiosis
• In contrast, when the gut microbiota is balanced, it is called gut microbiota symbiosis
• Typically, a diverse gut microbiota results in better gut health
• the composition of microorganisms in the gut can change

Question 6

the factors influencing the types and amounts of microorganisms in the gut include

Answer 6

• type of diet
• levels of stress
• age
• genetics
• levels of physical activity
• Medication

Question 7

define gut-brain axis

Answer 7

the bidirectional connection between the gut and the brain through the enteric and central nervous systems

Question 8

define enteric nervous system

Answer 8

the network of nerves in the gut and is a subdivision of the autonomic nervous system

Question 9

define central nervous system

Answer 9

a major division of the nervous system comprising the brain and spinal cord, which receives and transmits neural messages to and from the peripheral nervous system

Question 10

GBA explanation

Answer 10

• communication can occur in both directions, from brain to gut and gut to brain
• It involves looking at the connection between the gut and the brain, and how they may interact and influence each other
• Nerves within the ENS communicate with nerves in the CNS, therefore reflecting the relationship between the gut and the brain

Question 11

role of the ENS in the GBA

Answer 11

• the ENS controls the digestive system and is directly connected to the CNS
• The ENS coordinates the rhythmic muscle contractions that move material along the digestive tract; it also regulates gastric acid secretion, changes in local blood flow and the release of gut hormones; and it interacts with the immune system.
• the connections between the enteric nervous system and the brain contain both afferent (sensory) nerves and efferent (motor) nerves
• the bidirectional communication that occurs between the CNS and the ENS happens via the vagus nerve and gut microbiota

Question 12

define vagus nerve

Answer 12

a nerve that connects the brain (central nervous system) to organs within the autonomic nervous system, via nerve fibres that directly link organs such as the lungs, heart, oesophagus and intestinal tract
- It originates in the brain stem and extends to the colon

Question 13

The vagus nerve is responsible for bidirectionally conveying information between the gut and the brain and it connects:

Answer 13

• The brain to the gut: 10–20% of the vagus nerve, communicates message such as salivation and secretion of gastric acid when we smell or anticipate food
• The gut to the brain: 80–90% of the vagus nerve fibres, communicates messages such as pain, discomfort and feeling hungry or full
• The vagus nerve controls many crucial bodily functions, including mood, immune response, digestion and heart rate.

Question 14

gut microbiota explanation

Answer 14

• These microbes digest the components of our food to provide their own nutrition while also simultaneously providing us with energy and nutrients.
• They are also involved in the production of neurochemicals, which can influence brain function

Question 15

gut microbiota and the ENS

Answer 15

• Gut microbiota are also involved in the production of some neurotransmitters, which can affect the concentrations of related neurotransmitters in the brain.
• Interestingly, certain microbiota in the gut are involved in regulating the production, storage and release of neurotransmitters by neurons in the ENS.
• This can have effects within the ENS itself as well as enabling fast signals to be transmitted to the brain via the vagus nerve.
• Ultimately, it is neurotransmitters that allow the bidirectional communication between the CNS and ENS to occur.

Question 16

Why are gut microbiota important?

Answer 16

• The health of your gut can change based on the types and amounts of gut microbiota present
• More “good” bacteria = good gut health
• More “bad” bacteria = poor gut health
• In addition, a greater diversity of gut microbiota can result in greater gut health
• A healthy diet = healthy and diverse gut microbiota = greater ability to cope with stress

Question 17

Connecting gut microbiota to the brain

Answer 17

• In the walls of the intestines, there are neurons that can detect chemicals produced by bacteria, influencing release of neurochemicals such as serotonin
• Serotonin will signal the vagus nerve to send a neural signal to the brain
• This can then influence behaviours and functions controlled by the brain, for example: appetite, sleep, mental health

Question 18

Stress, gut microbiota and nervous system function

Answer 18

• stress causes changes in gut microbiota and deficiencies in certain bacteria, which have been linked to anxiety and depression
• specific gut microbiota associated with stress have been shown to increase anxiety related behaviours
• stress exposure early in life or in adulthood can change an organism’s microbiota composition
• the types and variety of microbe populations we have in our gut can shape our stress responsiveness
• treatment with healthy microbiota can reduce anxiety-like behaviour and reduce stress responsiveness in humans and mice
• chronic stress and increased levels of cortisol can have a profound impact on our gut microbiota as well as our psychological processes and behaviour

Question 19

The gut-brain axis in psychological processes and behaviour

Answer 19

• Due to the bidirectional gut-brain connection, the gut can send messages to our brain.
• Therefore, the gut can impact our psychological processes and behaviour.
• Research on the gut-brain axis has suggested there are potential links between the gut and experiences of stress, the presence or absence of mental illness, learning, memory, body weight, and behaviour.
• The composition of gut microbiota can impact psychological processes and behaviour.
• Often, a diverse gut microbiota is associated with greater levels of overall health, therefore having more positive influences on psychological processes and behaviour

Question 20

emerging research

Answer 20

emerging research has been done through:
- germ-free animal studies
- comparing microbiota composition in humans
- exploring gut-related diseases and their impacts on cognition and emotion

Question 21

Germ-free animal studies

Answer 21

• Germ-free animals are animals that have had microorganisms from their gut microbiota removed.
• Germ-free animal studies compare certain behaviours and psychological processes in germ-free animals with non-germ-free animals
  The role of GBA in psychological processes and behaviour include:
• significant changes in anxiety-like behaviour and anxiety responses in germ-free mice
• poorer memory function in germ-free mice
• increased secretion of stress hormones in germ-free mice

Question 22

Microbiota composition in humans

Answer 22

• the composition of gut microbiota can influence the likelihood of experiencing:
• autism spectrum disorder
• mental disorders, including depressive disorders, anxiety disorders, and psychotic disorders
• cognitive decline

Question 23

Gut-related diseases

Answer 23

• individuals with gut-related diseases and their experiences of anxiety, depression, and other cognitive and/or emotional problems
• Two of these gut-related diseases that have been discussed in research are irritable bowel syndrome and inflammatory bowel disease
• Therefore, experiencing a gut-related disease may increase the likelihood of experiencing a mental illness