L2 HPA axis Flashcards
The hypothalamus contains the _______ ______ (PVN) which contains _____ ______ hormone (CRH) neurones. The hypothalamus releases CRH which acts on the _____ _____. The _____ _____ produces __________ ______ (_ _ _ _) which acts on adrenal glands to produce ______. _____ liberates energy and glucose stores to prepare for fight/flight.
Paraventricular nucleus Corticotrophin releasing hormone (CRH) Pituitary gland Pituitary gland Adrenocorticotrophic hormone (ACTH) Cortisol Cortisol
So…
Stress causes ______ to release _ _ _ which acts on the ______ which releases _ _ _ _ which acts on the _______ ______ to produce ______ which binds _________ receptors and ________ receptors which then has a negative feedback.
Hypothalamus CRH Pituitary ACTH Adrenal glands Cortisol Mineralocorticoid and glucocorticoid
Cortisol has physiological effects e.g.
1) Anti _____ and auto ____ effects which puts a brake on the immune system
2) Actions on reactivity to _____ in blood e.g. effects on arterioles and BP
3) Maintains concentrations of _____ involved in metabolic homeostasis
4) Enhances ______ permeability
5) ______ proteins to fat to provide energy
6) Inhibits _____ and r_______
7) Catabolism of cells of immune system, bone, muscles to provide substrates for _______________.
Hence chronic exposure to stress = reduction in bone density, immune func and reproductive fertility
1) Anti inflammatory and autoimmune
2) Adrenaline
3) Enzymes
4) Vascular
5) Catabolises
6) growth and reproduction
7) Gluconeogenesis
HPA axis has a role in anxiety and depression:
- Elevated cortisol is a feature of MDD and psychotic depression
- In healthy individuals there is a _____ feedback in HPA axis to _____ the amount of ____ produced but in chronic stress and MDD this is switched off and cortisol levels are unregulated.
- This is demonstrated by the _______ _______ test.
Negative
Reduce
Cortisol
Dexamethasone suppression
Successful depression treatment with ____ restores the HPA axis ______ feedback
SSRIs
Negative
Cortisol acts as a _____ feedback regulator of HPA axis at several levels:
- Reduces ____ and _____
- Does this by switching off _____ ____ and ______.
Negative CRH ACTH Anterior pituitary Hypothalamus
The _____ _____ test can test for dysregulation of the HPA axis. No suppression of _____ secretion in test is a biomarker for depression. Give dexamethasone around 11pm and test cortisol in morning around 8am - measure and if reduced cortisol then _____ successful.
Dexamethasone suppression
Cortisol
Treatment
How does cortisol negative feedback work?
1) Cortisol acts on _____ _____ ______ receptors in ________ and _____ _____.
2) Cortisol binding to the __ causes it to ______ to the nucleus
3) This activates _____ _____ by binding _______ _______ ______ (GREs) in genes
4) These TFs repress gene expression so leads to reduced ____
5) Less ____ means less cortisol secretion from adrenals so NEGATIVE FEEDBACK
Cytosolic inactivated glucocorticoid Hypothalamus Anterior pituitary GR Translocate Transcription factors Glucocorticoid recognition elements ACTH ACTH
In MDD you lose the negative feedback effect of cortisol so levels of cortisol increase - this can be shown by the _______ _______ test.
If after dexamethasone administration the levels of cortisol do not decrease, then there may be a 1ry defect in _______ ______ or 2r defect in ______ release.
Dexamethasone suppression test
Glucocorticoid receptor e.g. desensitised receptors
ACTH
Can use cortisol _______ inhibitors:
e.g. Ketoconazole, metyrapone
BUT although Metyrapone inhibits ______ synthesis it is not _____ and also inhibits a number of other steroid hormone processes so helps depressed patients but has intolerable side effects.
Can use selective inhibitors of ______ which inhibits the enzyme that converts __-______ to _____ (this is more _____ and doesn’t affect ______ synthesis.
Synthesis Cortisol Selective CYP11B1 11-deoxycortisol to cortisol Specific Aldosterone
Using cortisol biosynthesis inhibitors is useful in tackling the excess cortisol BUT some cortisol is needed for motivation. So would need a ______ dose of cortisol too.
Maintenance
Glucocorticoid receptors are _______ regulators.
There is the ______ receptor and the _______ receptor.
The GR: is type , NR3C (nuclear receptor 3 family _)
It has a higher affinity for _____ than _____. and is activated by ___ levels of glucocorticoid
The MR: is type , NR3C (nuclear receptor 3 family 2)
It has a higher affinity for ______ than _____. and is activated by ____ levels of glucocorticoid.
Transcriptional Glucocorticoid Mineralocorticoid 2, NR3C1 (nuclear receptor 3 family 1) Cortisol than aldosterone High
1, NR3C2 (nuclear receptor 3 family 2)
Aldosterone than cortisol
Basal
Glucocorticoid antagonists e.g. ________
_____ is an anti______ licensed in UK for termination of pregnancies BUT also affects depression related behaviours.
It blocked GR receptors so reduces ______ of ACTH and reduces ____ levels as a result.
Study by Wilson et al 2010, showed that rats given _____ in a _____ _____ ____ demonstrated less periods of ______ and more _____ (antidepressant effect). Antidepressant effect seen in patients after a follow up a few weeks after treatment.
BUT only really useful in _____ depression.
Mifepristone Mifepristone Antiprogestin transcription Cortisol Mifepristone Forced swim test Immobility Swimming Psychotic
Depressed pts have increased ___ axis activity, elevated ___ in CSF and increased ___ MRNA expression in ___ compared to nondepressed pts
Antidepressants can decrease ___ concentrations in CSF of healthy and depressed pts
HPA CRH CRH PVN (paraventricular nucleus) CRH
CRH has an agonist binding/activation region (___) a _____ region and a receptor binding/activation region (____) - both ends combine with ______ to activate it.
- NH2
- CRFBP
- COOH
- Receptor
