The stress axis Flashcards
What is the function of the hypothalamus?
Ancient, conserved, central regulator of homeostasis
What are the main nuclei in the hypothalamus?
Paraventricular nucleus (PVN)
Arcuate nucleus (Arc)
Ventromedial nucleus (VMN)
Where do the neurons in the Arc and VMN nuclei develop from?
Progenitors that either:
1) Transiently express shh
2) Respond to shh
What neurons are in the Arc nucleus?
What do these neurons do?
PomC+ neurons
Make precursor protein (Pomc) that is made into many hormones - some that impact on CRH
–> Makes ATCH
What neurons are in the VMN?
What do these neurons do?
SF1+ neurons
Help to regulate the maturation of steroidal hormones –> form active hormones
Where do the neurons in the PVN develop from?
What neurons are born in the PVN?
EARLY where Shh is REPRESSED in progenitors
CRH/CRF neurons
What is useful about the hypothalamus in simpler vertebrates?
SAME organisation of hypothalamus and the SAME neurons in the SAME nuclei SAME neurotransmitters and neurohormones
Can investigate problems happening in humans
Why need very high numbers of model organisms to do behavioural work?
Why is the zebrafish a good model for the hypothalamus?
Many VARIABLES in behaviour
Zebrafish - good model can link genetics to behaviour (screen MANY fish)
What neurons are important in the production of the stress hormone and therefore the regulation of stress?
- Pomc neurons (arc)
- SF1 neurons (VMN)
- CRH neurons (PVN)
Where do the CRH neurons project to?
What happens here?
Medial eminence
HPA axis:
1) End feet release CRH - taken up by the portal capillaries –> pituitary gland
2) In PG - regulates an endocrine cell –> release ACTH (adrenocorticotrophic hormone)
3) ACTH acts on the ADRENAL GLANDS –> release cortisol
What are the CRH neurons responsible for?
CRH released in response to stress
What is the main stress hormone?
Where is it released from?
Cortisol
Released from the adrenal gland when stimulated by ACTH
What is the DISC1 gene?
Results of this gene?
Deleted in Schizophrenia 1
High risk of mental illness
When was DISC1 identified?
Through genetic analysis of an inbred family with high-risk of mental problems:
- Each sibling/cousin had inherited a copy of the allele where this gene was deleted
What is the first question must ask if there is a phenotype resulting from a deleted gene?
WHERE is the gene NORMALLY expressed?
WHY lack of function –> mental illness
Where is DISC1 normally expressed?
How can see this?
Normally in the hypothalamus, with expression overlapping with cells expressing Fgf+ and Shh+ (early progenitors)
SPECIFIC to the hypoT - not in the rest of the body
Seen in zebrafish using IN SITU HYBRIDISATION
Why is it hard to determine what the DISC1 protein does?
Likely to interact with many proteins due to its structure:
- Large protein
- Globular domain at N terminus
- Alpha-helix domain
- Coiled coil domains
How was a disease model of DISC1 created in the zebrafish?
Create 2 lines of zebrafish mutants (with different point mutation in the globular domain - N terminus)
Fish are homozygous viable but DO NOT make the DISC1 mRNA/protein
Why were 2 zebrafish transgenic lines made in the disease model for DISC1?
To increase confidence in results
How are the WT and DISC1 mutant fish different to each other?
How can this been seen?
DISC1 mutants:
- Not as many progenitors and progenitors differentiate PREMATURELY (Interferes with the balance of stem/progenitor/differentiated cells)
- Hypothalamic neurons (especially ones involved in stress regulation) differentiate abnormally
Seen using ISH of zebrafish mutants/WT
How does DISC1 interfere with progenitor levels?
We are not sure
How do the hypothalamic neurons of the zebrafish DISC1 mutant differentiate abnormally?
Pomc+ (Arc) neurons REDUCED
Sf1+ (VMN) neurons INCREASED
Crh+ (PVN) neurons INCREASED
What do the differences between the WT and the DISC1 mutant fish show?
Imbalance in early progenitors has a KNOCK-ON effect and leads to the ABERRANT DIFFERENTIATION of HYPOTHALAMIC NEURONS that are involved in STRESS REGULATION
How can we measure an output to see if the difference in neurons has an impact on the physiology and/or behaviour of the fish?
1) Behavioural analysis
2) Assays - look at endocrine function
