THE STRESS RESPONSE Flashcards

Question

What are the neuroplastic responses to stress?

Answer 1

Atrophy of regions with inhibitory influences on HPA & ANS responses to acute stress and hypertrophy of excitatory regions

Answer 2

• Hippocampus & mPFC • Retraction of apical dendrites & reduced dendritic spine density (sites of excitatory glutamataergic input) in response to chronic restraint. • Decreased GR expression Net: chronic GC elevations (decreased GC feedback); impaired memory & reward

Answer 3

Hypertrophy/up-regulation in regions with excitatory influences on HPA & ANS responses to acute stress • Basolateral amygdala (psychogenic stress/HPAA) - Increased dendritic branching & stress excitability • Central amygdala (systemic stress/ANS activation) - Increased CRH expression and release • Hypothalamic PVN: Increased CRH & AVP expression & release • Decreased GR expression Net: increased excitability to novel stress (GCs & emotionality) & decreased reward

Answer 4

stress ultimately signal via the hypothalamic parvocellular PVN to restore homeostasis

Answer 5

• Hippocampus Contextual, episodic & spatial memory; down-regulation of stress response. Primarily activated by psychogenic stress: terminates HPAA response – regulates duration rather than magnitude [GR] decreases autonomic tone • Amygdala Emotion, fear, anxiety, aggression, up-regulation of stress response. Central Amygdala activated by systemic > psychogenic stress; activates ANS > HPAA via projections to NTS Prefrontal cortex decision making, working memory, controls impulsivity, down-regulation of stress response. It is primarily activated by psychogenic stress. Activation of prelimbic & dorsal regions terminates HPA response and reduces ANS response [GR]. Infralimbic regions initiate ANS & HPA responses via projections to NTS.

Answer 6

Prefrontal cortex decision making, working memory, controls impulsivity, down-regulation of stress response. It is primarily activated by psychogenic stress. Activation of prelimbic & dorsal regions terminates HPA response and reduces ANS response [GR]. Infralimbic regions initiate ANS & HPA responses via projections to NTS.

Answer 7

Neural - CRH and AVP neurones posses ionotropic glutamate and alpha – 1 adrenoceptors (n-ad), which are stimulatory, and GABAa receptors (inhibitory)

Answer 8

Rat. Measure corticosterone release after an injection of LPS versus a vehicle. Also induce hypo glycaemia, - Effects of hypoglycaemic stress on expression of CRH mRNA in the parvocellular PVN of the rat.

Answer 9

– Effect of repeated restraint stress for 1 h per day on expression of CRH and VP heteronuclear RNA levels in the medial parvocellular PVN of the rat. After repeated stress there is down-regulation of CRH mRNA. After repeated stress there is NO down-regulation of AVP mRNA

Answer 10

Experiment: Protocol: – Random exposure to variety of mild stressors, e.g. novel environment, tilted cage, noise, wet bedding, strobe lighting – Key features is the unpredictability of the nature and timing of the stress and the lack of ‘control’ the animal has of the situation. – Compared to control, increased ACTH, Corticosterone, prolactin, increased adrenal gland weight and no change in thymus weight Increase in number of cells expressing CRH mRNA. NB: these increases reflect increases in glutamatergic and noradrenergic inputs Note that chronic variable stress does not increase the number of cells expressing AVP but does increase the amount of mRNA per cell

Answer 11

medullary preganglionic neurones of the intermediolateral cell column of the SC

Answer 12

e.g. activation of NTS, then nucleus ambiguus & dorsal motor nucleus of the vagus nerve

Answer 13

Slower onset (mins), more protracted than ANS response

Answer 14

Primarily activated by psychogenic stress Activation of prelimbic & dorsal regions terminates HPAA response and reduces ANS response [GR] infralimbic regions initiate ANS & HPA responses via projections to NTS

Answer 15

Central Amygdala activated by systemic > psychogenic stress; activates ANS > HPAA via projections to NTS Medial & basolateral amygdala activated by psychogenic > systemic stress to up-regulate HPAA via interactions with PVN-projecting neurons Think - involved in fear.

Answer 16

Primarily activated by psychogenic stress terminates HPAA response – regulates duration rather than magnitude [GR] decreases autonomic tone

Answer 17

Through reciprocal connections. Brainstem NTS to PVN. and from dorsolateral parvocellular connection to brainstem.

Answer 18

Initially there is adrenal NA and GC, homeostasis restored (dips then goes up again). Then defence and adaptation sustained and optimal (curve plateaus at peak). Then adaptive responses ceases - illness and death. He thought exhaustion is a failure to cope but this model is now outdated. Now thought to be excessive exposure to stress mediators.

Answer 19

Allostasis – ‘The process by which bodily functions change, in response to environmental challenges e.g. stressors: ‘The ability to achieve stability through change’

Answer 20

Stress – Activates allostatic responses. For stability to be achieved , allostatic responses must be switched off.

Answer 21

Failure of habituation such as public speaking (load constantly fluctuating), or inabillity to switch off such as blood pressure (remains high)

Answer 22

Must be perceived as stressful. 1) Primary appraisal – the initial evaluation when the situation is irrelevant, relevant but not perceived as a threat or stressful. 2) Secondary appraisal - evaluation of the capabilities of the individual to deal with the situation. Activates ANS, HPA and behaviour

Answer 23

- Is linked more to the male phenotype - Involves learned behavior and experiential, eg the effect of culture (the murder rate is higher in the Southern states than the Northern) - Innate programming in utero - Brain is hard wired to react to certain stimuli - But is it valid in 21st century? Suddenly examined, unlikely to fight or flee. Flight may now be drugs of abuse, social withdrawal, TV watching/ gaming

Answer 24

When there are no mechanisms to deal with fight or flight and leads to depression

Answer 25

Tend or befriend - Tend : women protect and care for their children - Befriend : women seek out and receive social support - Exclusion study – increased cortisol and increased affliative behaviour - Frightening maternal behaviour – females more likely to approach - Sports competition – female bonding versus male focus

Answer 26

The female response is thought to be driven by OXYTOCIN, which tends to diminish the production of ACTH and thus the stress response. OESTROGEN has a positive effect compared to TESTOSTERONE’S negative.

Answer 27

1) Commonly the HPA axis through parameters such as BP, obesity, HT, T2DM, CVS, hippocampal atrophy 2) Urinary cortisol – pulsatile release and huge variability in what’s normal, so not best measure 3) Cardiovascular. Risk Factor; Increased mortality, cardiovascular disease, cognitive functioning. 4) Metabolic. Risk Factor; Increased mortality, cardiovascular disease, cognitive functioning. 5) Inflammation. Risk Factor; Increased mortality, cardiovascular disease, cognitive functioning. 6) Behavioural. Self reported questionaires. Stress increases with all major diseases. 7) Brain markers

Answer 28

Biological cost of stress This occurs when stress uses some of the resources that are normally allocated to other tissues. Stress can divert energy normally required for other functions, for example stunting growth in children.

Answer 29

- Excessive wear and tear in tissues activated by chronic stress such as the hippocampus - Dysregulation due to diverted energy resources - Direct inhibitory effect of stress hormones on certain systems.

Answer 30

Cohort – High functioning 70-79 year olds Baseline: Higher AL Lower baseline functioning, poorer cognitive performance and weaker physical performance After 3 years: Higher AL Greater declines in cognitive and physical functioning and augmented risk of incident cardiovascular disease (CVD) indepen- dently of socio-demographics and baseline health status. (NB No individual biomarkers significantly explained these outcomes, supporting the utility of a multi-systemic composite approach) After 7 years: Higher AL Threshold effect revealed Greatest risk of cognitive and physical declines and risk of CVD. Most importantly, higher AL was related to increased risk of all-cause mortality

Answer 31

Low cortisol. Addisons and CAH. In cortisol secreting tumours, ACTH is reduced

Answer 32

Inflammatory suppression involves direct interactions of the glucocorticoid receptor with AP-1 and NF-κB

Answer 33

Sex steroids and glucocorticoids however not aldosterone as much

Answer 34

In Congenital adrenal hyperplasia you do not have 21-hydroxylase (*) meaning that you cannot produce cortisol or aldosterone. Can synthesise some forms but these are salt wasting. However, the pathways to produce androgens is still viable as well as increased precursors and overactive from the increased ACTH meaning that females can get secondary sexual characteristics. The increased ACTH from the lack of negative feedback from the absent cortisol.

Answer 35

* Rapid onset: Reduces the release of AVP/CRH and ACTH from preformed stores * Slow onset: Reduces the synthesis of AVP/CRH and ACTH and thus the amount of hormone available for release

Answer 36

• At 0 mins, give either saline or cortisol to rats, then after 75 minutes give either saline or IL-1b. Much reduced response if give cortisol first. This can also be seen by either doing a sham operation or removing the adrenal glands. Adx causes increased parvocellular AVPmRNA PVN and CRH Talk about what happens when you give exogenous glucocorticoids to patients.

Answer 37

Mediated principally by intracellular receptors, MR and GR Some rapid onset effects may also involve membrane-bound receptors.

Answer 38

* Low affinity * Glucocorticoid selective * Widespread – found in most cells

Answer 39

* High affinity * Binds to glucocorticoids and mineralocorticoids equally * Discrete locations: pituitary gland, hypothalamus distal nephrons, colon, sweat gland, hippocampus and vascular smooth muscle

Answer 40

High affinity receptors – therefore detect low (non-stress) levels of corticosterone in the blood. Unless protected by 11βHSD2 are saturated at high physiological (stress) levels of GCs Expressed in the pituitary gland, hypothalamus, hippocampus and probably also other brain areas. Immunohistochemical localisation of the mineralocorticoid receptor in the murine brain . High affinity receptors – therefore detect low (non-stress) levels of corticosterone in the blood. Unless protected by 11βHSD2 are saturated at high physiological (stress) levels of GCs Expressed in the pituitary gland, hypothalamus, hippocampus and probably also other brain areas. Hippocampal receptors are not ‘protected’ by 11βHSD2, therefore readily accessible to circulating GCs Evidence suggests that MRs, particularly hippocampal MRs, have an important role in regulating CRH/AVP and ACTH secretion in basal, non-stress conditions at the nadir of the circadian rhythm.a

Answer 41

Low affinity receptors Do not detect low GC levels (nadir of the circadian rhythm) Are sensitive to circadian and stress-induced elevations in GCs Widely distributed, abundant in all areas associated with GC feedback Sensitivity increased by 11βHSD1 Primary mediators of GC feedback

Answer 42

In the bloodstream, cortisol is bound to CBG however only the free form enters the cell.

Answer 43

By transactivation (increase in the rate of gene transcription) or transrepression or NON-GENOMICACTIVATION OF KINASE CASCADE

Answer 44

- GR are nuclear receptors - Cortisol (F) accesses cell GR in cytoplasm - Found as complex with heat shock proteins (chaperones) - When F binds, chaperones dissociate - Receptor dimerised translocated to nucleus - In the nucleus, associates with co-activators or co-repressors - Activated receptor acts as a transcription factor- directly binds to DNA - Activated receptor targets the promoter of specific target genes

Answer 45

With heat shock protein

Answer 46

``` Transactivation – β-adrenoceptors – PNMT – GLUT-4 – PEPCK – Other metabolic genes – Annexin 1 and other anti-inflammatory molecules, e.g. IқB ```

Answer 47

``` Transrepression – CRH – AVP (parvocellular) – POMC (pituitary) – NFқB – Pro-inflammatory cytokines – COX-2 – iNOS PEPCK is involved with regulating processes such as gluconeogenesis in the liver. INOS is in inflammatory cells and produces ROS. ```

Answer 48

- Receptor doesn’t dimerise - Activated receptor binds and interacts with other TFs such as AP1 TF - Receptor translocated to nucleus and binds to other TFs, not DNA itself. So changes activity of other TFs. - Prevents the action of other TFs, and reduce proteins they are producing, so downregulates target gene expression.

Answer 49

For gene expression

Answer 50

When cortisol binds to its receptor and receptor phosphorylation occurs that influences protein transcription. The non genomic activation of membrane bound receptors is rapid which induces a complex kinase signaling cascade that eventually leads to: • K+ extrusion • Blockade of Ca2+ entry This is for the rapid effects

Answer 51

* GCs exert rapid effects on CRH/AVP and ACTH secretion which inhibit the release of hormone from pre-formed stores * They also exert effects which are slow in onset which reduce the synthesis of CRH/AVP and POMC.

Answer 52

11bHSD, MDRP, Neutrophil elastase that works on the proportion of free and bound cortisol

Answer 53

Neutrophil elastase was identified in neutrophils (sites of infection and inflammation). Breaks down the binding protein that cortisol binds to. Get recruitment of neutrophil to area to activate stress response, helps also to increase the cortisol at a LOCAL level through neutrophil elastase. CBG has an exposed loop that is cleaved and decreases affinity of binding globulin for cortisol, meaning more cortisol • GC availability is thus increased in inflamed tissues, facilitating an anti-inflammatory effect to maintain homeostasis.

Answer 54

• Probably not important in steroid feedback in normal physiological situations as there should be no local inflammation in the HPA axis. • However, may be important in conditions of brain/pituitary injury where there is a local inflammatory response – the consequent increase in local GC levels would enhance steroid feedback

Answer 55

``` – NADPH – Widespread, liver, CNS, vascular SM, adipose – Km (nM) • cortisol - 17,000 (low affinity) • cortisone - 200 • dexamethasone –negligible ```

Answer 56

cortisol - 50 (high affinity) cortisone - negligible dexamethasone 150

Answer 57

KO 11BHSD1: you actually INCREASE the levels of corticosterone. Reducing negative feedback as there is less cortisol produced through 11bhsd1 so more ACTH stimulating. KO also increases cortisol during stress. ESPECIALLY DURING RESTRAINT STRESS

Answer 58

Type 1 augments delivery to receptor and state ko results whereas type 2 protects MR so less likely to play a role and in protecting foetus

Answer 59

Important role in the blood barrier, limiting drug access by promoting exportation of the drug from the cell. Also found in many other cell types in the body, including brain neurones and pituitary cells Dexamethasone is a powerful substrate Cortisol and corticosterone are weaker substrates

Answer 60

Forced swim Stress on ABC KO mice: have reduced ACTH and no difference cortisol. This is because more cortisol can access the brain and thus the negative feedback is greater. There is impaired rise in circadian rhythm due to impaired negative feedback→ plays a role in circadian rhythm. There is reduced CRH and POMC in the hypothalamus/pituitary

Answer 61

• There are Dose-dependent effects of dexamethasone on decreasing plasma ACTH and corticosterone ABC-B1 (i.e. mrdp) knockout mice compared to wild type. Summary: increases the sensitivity of the axis to dexamethasone

Answer 62

Neonatal endotoxin (ENDO) treatment reduces GR expression in in the rat brain in adulthood. Early stressors in life change subsequent responses to stress. Maniuplation in early life has significantly reduced gr expression in three key brain areas. This means that there is less negative feedback→ Neonatal endotoxin treatment augments CRH and AVP expression in the pPVN in the adult rat. There is also an increased response under stress. There is a decreased inhibitory effect of dexamethasone.

Answer 63

1. Corticosterone inhibits ACTH release from anterior pituitary within ten mins, and treatment with cyclohexamide does not stop this inhibition (stops translation) 2. Stress-induced ACTH release in adrenalectomised rats does not return rapidly to baseline (as it does in sham operated animals, but it is suppressed by GC administration. 3. GC treatment inhibits CRH-induced ACTH secretion in vivo, even in animals treated with actinomycin-D (inhibits transcription, and so DNA synthesis)

Answer 64

GCs rapidly inhibit CRH release from hypothalamic slices and synaptosomes Administration of GCs within 2 minutes of adx prevents the fall in hypothalamic CRH content Dex treatment decreases electrical excitability in PVN CRH neurones Dex infusion into PVN 5 mins before restraint stress blocks ACTH and cortisol responses. Evidence for membrane bound receptors

Answer 65

* GCs can rapidly inhibit CRH release from PVN neurons by acting on membrane-associated receptors on the CRH neurones * Receptor activation leads to increased retrograde endocannabinoid (eCB) signalling at CB1 receptors at presynaptic terminal which suppresses excitation of presynaptic glutamatergic neurons

Answer 66

• GR is localized to post-synaptic neuronal membranes in PVN (electron microscoopy, immunocytochemistry) • Glucocorticoid suppression of excitation of CRH neurones is absent in PVN GR KOs • Administration of GC conjugated to BSA into PVN suppresses restraint-induced activation of HPA axis. (Localising it and forcing it to stay outside cell, and as cannot get into cell, any effect it has is on membrane-bound receptors) • CB1 receptors are ubiquitous in pre-synaptic terminals (not CRH neurones themselves) • eCBs (synthesized from arachidonic acid metabolites) are rapidly produced in PVN dendrites following GC exposure • CB1 antagonism or KO increases PVN CRH mRNA and plasma ACTH and corticosterone

Answer 67

* Specifically the NTS: Within 30 mins stress (acute & chronic) → GCs suppress preproglucagon (GLP-1; and HPA-stimulatory peptide) mRNA and peptide levels in NTS by destabilizing mRNA pools, without affecting gene transcription. GC inhibit the production of GLP-1 in the NTS, as these GLP-1 producing neurones also stimulate CRH neurones * Influences in limbic brain regions * Annexin 1-mediated actions

Answer 68

GCs provide rapid, non-genomic inhibition of glutamate release from presynaptic terminals GC inhibit the production of GLP-1 in the NTS, as these GLP-1 producing neurones also stimulate CRH neurones. GCs enhances glutamate input and so activates GABA pathways, which have inhibitory input to CRH neurons

Answer 69

Depending on physiological demand and anticipatory signals from the forebrain, GCs may provide feedforward excitation of the HPA axis. Largely mediated through the amygdala, where cortisol has a positive effect on CRH production, or glutamate production which feeds on to the hypothalamus to increase CRH neurone stimulation GCs can upregulate CRH signaling in the amygdala and BST, potentially prolonging GC secretion. GCs may also act on glutamatergic neurons in the ilPFC and BLA to excite PVN CRH neurons via synaptic relays in the hypothalamus

Answer 70

Rapid facilitation of hypothalamic aggression by corticosterone in adrenalectomized rats may explain why stress is a major factor in stimulating aggressive behaviour in humans and rodents Hypothalamic aggression, in turn, was rapidly facilitated by a corticosterone injection in rats in which the natural adrenocortical stress response was prevented by adrenalectomy. Effects not blocked by cyclohexamide The rapidity of both effects points to a fast, mutual, positive feedback of the controlling mechanisms within the time frame of a single conflict. Such a mutual facilitation may contribute to the precipitation and escalation of violent behavior under stressful conditions.

Answer 71

``` Glucocorticoid-regulated Anti-inflammatory Anti-proliferative, pro-apoptotic Neuroprotective Modulator of neuroendocrine function ```

Answer 72

The pituitary and hypothalamus

Answer 73

Annexin I belongs to the annexin family of Ca2+-dependent phospholipid-binding proteins. Annexin A1 both suppresses phospholipase A2 and COX level, thereby BLOCKING EICASANOID PRODUCTION, and inhibits various leukocyte inflammatory events

Answer 74

In resting conditions, human and mouse immune cells such as neutrophils and macrophages contain high levels of annexin A1 in their cytoplasm. Annexin A1 is promptly mobilized to the cell surface and secreted. Annexin A1 promotes neutrophil detachment and apoptosis, and phagocytosis of apoptotic neutrophils by macrophages

Answer 75

In vitro and in vivo analyses show that exogenous and endogenous annexin A1 counter-regulate the activities of innate immune cells, in particular extravasation and the generation of proinflammatory mediators, and this ensures that a sufficient level of activation is reached but not exceeded.

Answer 76

Immunoneutralisation of ANXA1 reverses the inhibitory effects of corticosterone on IL-1B induced ACTH secretion Animals treated with saline and IL-1B have increased ACTH production When corticosterone added, it suppresses IL-1B induced ACTH secretion When ANXA1 antibody added in vivo, ACTH increases, and so corticosterone is ineffective in suppressing IL-1B induced ACTH secretion Therefore annexin mediates GC feedback in these rats

Answer 77

mimicked by ANXA1 inhibited by anti-ANXA1 antisera ANXA1 antisense ODNs

Answer 78

De novo annexin 1 synthesis: A) Dexamethasone increases the expression of ANXA1 in the rat anterior pituitary gland, measured by western blot. Detected at cell surface, close to endocrine cells b)Translocation of annexin 1 from the cytoplasm to the cell surface where it is retained by a Ca2+-dependent manner.

Answer 79

Annexin 1 is localized to folliculostellate cells in the anterior pituitary gland (Not present in the corticotrophs, but collects where folliculostellate cells come into contact with endocrine cells) Increased detection of cell surface ANXA1 in co-cultures of pituitary cell line, AtT20 and pituitary FS-like cell line, TtT/GF cells by immunofluorescence

Answer 80

If you increase the concentration of annexin, increase the binding. If you give enough annexin, can saturate the binding sites. Cell sorting identified annexin 1 binding sites on approximately 80% of the pituitary endocrine cells, including Corticotrophs Somatotrophs Lactotrophs Gonadotrophs

Answer 81

Reversal of the inhibitory effects of Annexin and dexamethasone on forskolin-stimulated ACTH release in vitro by PKC blockade (nhibitor of PKC caused ACTH release to increase, even when ANXA and Dex administered) Dexamethasone administration causes translocation of annexin-1 to cell surface. If you give PKC inhibitor, lose the dexamethasone-induced appearance of annexin 1 on the cell surface of rat anterior pituitary cells (Western blot)→ need protein kinase c Dexamethasone causes increased translocation of GFP-tagged annexin to cell surface: Mutation of serine 27 of annexin 1, no translocation of GFP-tagged annexin 1 to the cell surface in FS cells.

Answer 82

GC binds to GR Upregulates annexin 1, serine phosphorylation, externalization. ABCA1 is important in facilitating this Serine phosphorylated annexin 1 sits outside, in close position to corticotroph cells (FS cells touch corticotrophs) Deliver ANXA1 Subsequent receptor is prpbably FPR that influences exocytosis, therefore ANXA interferes with exocytosis Summary

Answer 83

Stress related pathology Can be due to; Excessive wear and tear in tissues activated by chronic stress Dys-regulation due to diverted energy resources Direct inhibitory effect of stress hormones on specific systems

Answer 84

Reduced hippocampal density in PTSD Vietnam veterans, reduced growth in a abused child, worked cancer survival in depressed patients, worsening of atherosclerosis in stressed

THE STRESS RESPONSE Flashcards

(111 cards)