Test 2 Flashcards
Function of endocrine system
To mediate bodily processes (balance and homeostasis)
Hormone
A chemical released by a cell or gland in response to external or internal signals, which travels to a distal site where it affects other cells.
Endocrine hormone
Hormone released into the bloodstream
Exocrine hormone
Hormone secreted into a duct and then into blood or from cell to cell via diffusion (paracrine signalling)
Autocrine signalling
When hormone stimulates the very cell that released it
Steroid hormones
Includes corticoid and sex hormones
Glucocorticoids
Class of steroid hormones that bind to glucocorticoid receptors
Peptide hormones
Hormones made up of amino acid chains. These include vasopressin, growth hormone, insulin, ghrelin, etc.
How do you assess the relationship between a hormone and behaviour in mice?
Assessed with KO mice/ blocking specific receptor/ surgery to reduce hormone naturally and examine the consequences. You can then give the mouse hormone replacements to see if that reverses the effects
Assessing the relationship between hormones and behaviour in humans
- We can assess individuals with diseases that involve hormone disruption.
- We can assess individual differences of hormone levels
- We can determine whether a variant of a gene is associated with a decrease in levels of hormone/disturbances of a hormone receptor and then relate that to a behaviour.
Describe the HPA axis
1) Stress activates hippocampus or activates the amygdala which in turn activates the hypothalamus
2) Hypothalamus activation results in CRH and AVP release
3) CRH stimulates ACTH release from the anterior part of the pituitary gland. ACTH is then released into the bloodstream
4) ACTH reaches the adrenal glands (located on top of kidneys) and stimulates cortisol release.
5) Cortisol affects its many targets: muscles, adipose tissue, pancreas and regions of the brain (hypothalamus and hippocampus).
6) When cortisol reaches the brain, it regulates the system by inhibiting its release of CRH and effectively stopping the stress response.
Impacts of cortisol
- Increase blood sugar through breakdown of glucose in liver and muscle
- Metabolize fats, carbs and proteins
- Limits overactivation of the immune response
What do mineral corticoids do?
They stimulate active NA+ reabsorption and passive water reabsorption, thus increasing blood volume and blood pressure.
How does the body cope with chronic stress/activation of the HPA axis
Through various adaptations which occur in response to a chronic stressor so that the cortisol response is less pronounced.
Do adaptations occur slow or fast if the chronic stressor is the same on every account?
It occurs fast.
Do adaptations occur slow or fast if the chronic stressor is intermittent/unpredictable?
It occurs slow.
Is adaptation event specific or occurs generally?
Adaptions are seen to be event/cue specific. If a novel stressor is introduced, a normal stress response ensues.
What are some of the downfalls to adaptations in response to chronic stress?
- After stress, vulnerability to common cold in increased.
- Inflammation from down-regulated receptors can contribute to development of diseases such as type 2 diabetes or heart disease.
Prenatal stressor events effect on offspring
Stressing a pregnant rat increases the level of corticosterone in the rat and the fetus. This can result in many biological cascades, like change in strux of stress-sensitive brain regions. This can in-turn lead to various pathologies in the offspring such as attention and learning deficits, increased chance of anxiety depression and schizo.
How do previous stressful experiences effect the HPA axis?
HPA functioning seems to be downregulated in individuals who have encountered previous abuse/trauma. This makes sense because if HPA axis was exaggerated at every aversive stimuli, then the system would encounter allostatic overload.
How is CRH implicated in more than the HPA response
- It could promote 5HT release through the regulation of neurons in the raphe nucleus.
- Could increase forebrain norepinephrine release through infusion in the locus coeruleus.
Fear
A directed emotion that is elicited in response to stimuli that have been paired with an aversive stimuli
Anxiety
Elicited by diffuse stimuli (general environmental context) or it can reflect a free-floating emotion, or one that is felt in anticipation of a threatening event.
What part of the amygdala do systemic stressors influence?
They influence central amygdala activity
What part of the amygdala do psychogenic stressors influence?
They influence medial amygdala activity
What part of the amygdala do fear eliciting stimuli increase CRH?
Increased CRH at various regions INSIDE the amygdala
What part of the amygdala do anxiety eliciting stimuli increase CRH?
Increase CRH in the outer regions of the amygdala specifically the Bed Nucleus of the Stria Terminalis (BNST)
Bed nucleus of stria terminalis
- Output pathway that runs from the amygdala to the hypothalamus
- Neurons in this region are important in governing responses to spatially or temporally distant challenges.
CRH receptor subtypes
CRH1 and CRH2
Leptin
Hormone that reduces food intake.
- It is produced by adipocytes and can influence HPA axis activity.
- Influences the release of some NTs (DA, 5HT) which in turn affects reward seeking behaviours (in terms of food).
Ghrelin
Hormone that increases food intake (as well as neuropeptide Y).
- Levels increase before mealtime
- Stimulates orexin (food craving hormone).
Bombesin (BB)/Neuromedin B(NMB) and gastrin
Release peptide (GRP) act as satiety signals (to reduce food intake)
Insulin
Regulates fat and carb metabolism
- Takes glucose from blood and stores as glycogen inside of tissues.
- Inhibits NPY release which decreases food intake.
Eating hormones implication in stress
- Depressive like behavioural disturbances provoked by chronic stressor could be antagonized by leptin administration
- BB-like peptides can promote anxiety, BB receptor antagonist had the opposite effect.
- Following sufficiently protracted stressor experience, effectiveness of insulin could be decreased.
Sex hormones and stress
- Estradiol (estrogen) can act as a brake on the HPA axis
- Progesterone may result in disturbed negative glucocorticoid feedback.
Effect of chronic cortisol on brain
It can increase signals in the amygdala and decrease function of the hippocampus. The hippocampus is responsible for turning off the HPA axis so this can result in decrease ability to control stressful situations.
As stress increases, hunger ________
decreases.
What is the CRH1 receptor associated with?
The CRH1 receptor is associated with anxiety, primarily affects the psychological aspects of anxiety
What is the CRH2 receptor associated with?
It is also associated with anxiety but tend to be associated with the physiological aspects of anxiety such as increased heart rate, respiration, pupil dilation, etc.