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Question 1

What are the two types of models to study the microbiota-gut-brain-axis

Answer 1

Germ-free models

Antibiotic models

Question 2

What is a germ free model?

Answer 2

Generated by using c-section to avoid contact between offspring and microbes in the mothers vagina and skin. Hand-raised in an aseptic isolator. Colonies are maintained FG with sterile food, bedding, and water.
Cages and feces are regularly swapped to confirm that no bacteria are present.

Question 3

Advantages and disadvantages of a germ-free model

Answer 3

Advantages:
Mice are free of all microorganisms in all tissues
Allows for exclusive colonization with defined microbes

Disadvantages:
Expensive
Specialized equipment and training
New genotypes must be re-derived
not all experiments feasible
Developmental defects

Question 4

What is an antibiotic model?

Answer 4

Animals raised using a single antibiotic or cocktail of antibiotics

Question 5

Advantages and disadvantages of an antibiotic model?

Answer 5

Pros:
Inexpensive
no specialized equipment needed
Applicable to any genotype

Cons:
Some bacteria still present
Other microorganisms still present
May affect eukaryotic cells
May select for resistant bacteria or promote fungal outgrowth

Question 6

What did figure 5a-d show

Answer 6

They were demonstrating fear extinction in control mice, GF mice, and mice with various types of bacteria. All mice showed fear extinction impairment implying that a diverse set of bacteria is required. They then tested in ex-GF mice who were colonized with a full microbiota at weaning and as an adult. Both showed impaired fear extinction.
They then showed fear extinction if Ex-GF fostered by pathogen-free surrogate mother. They did not show impaired fear extinction. This indicated that fear extinction learning may required signals during a developmental period before weaning.

Question 7

What did figure 5 e and f show

Answer 7

Figure 5 and e attempted to demonstrate that 4 metabolites were required in the development and function of neurons.
They showed the relative abundances of four metabolites in CSF and serum in Control fostered mice, GF mice, and Ex-GF fostered mice.

They claimed that because they were downregulated in GF mice, they were linked to neurological conditions. However the changes were robustly linked to the behavioural changes. Much more data is needed in order to establish a causal relationship