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What did Hans Selye do?
- Identified “general adaptation syndrome”, which he later renamed the “stress response”
- This constituted enlarged adrenal glands and lymph node and thymic atrophygastric erosions/ulcers.
- First to suggest that hormones from the adrenal cortex might be important, in addition to the already-known-about hormones from the adrenal medulla
What are the two stress systems?
- The sympathetic-adrenomedullary system
- The hypothalamic-pituitary-adrenocortical system
- Basically sympathetic and parasympathetic response
What are the features of the sympathetic adreno-medullary system?
- Fight or flight response (mostly flight)
- Focussed in the thoracic and lumbar parts of the spinal cord
- Readies us for danger
What are the features of the parasympathetic response?
- Rest and digest
- Mainly focussed in the cranial and sacral regions of the spinal cord
- Maintains bodily function
What are the features of the hypothalmic-pituitary-adrenocortical system
- In response to stress, Corticotropin releasing factor initiates a cascade of events that culminate in the release of glucocorticoids from the adrenal cortex
- These are Cortisol (hydrocortisone) in humans and corticosterone in rats
- Both are produced by the adrenal cortex
What is the process of cortisol production?
- Corticotrophin releasing factor is produced in the hypothalmus
- This reaches the anterior pituitary, which stimulates the release of adrenocorticotrophic hormone, which travels to the adrenal cortex
- This produces cortisol and other hormones, which travel to target hormones to produce the stress response
- Some also travels back to the anterior pituitary (stimulating more release) and the hypothalmus (inhibiting release)
What effects does prolonged exposure to cortisol have?
- Hippocampal shrivelling
- Ulcers to the hippocampus is associated with prolonged, and fatal stress in primates
- Smaller hippocampus heads found in PTSD Gulf war vets
- Impairs declarative function in healthy humans
What effects does one's upbringing have on stress hormone production?
- Neglected monkies show higher plasma adrenocorticotrophic hormone levels, and an increased response to stress both in cortisol production, and its genetic manifestation, with more RNA receptor messengers for cortisol
- Same findings for women with a history of child abuse
How is upbringing linked to epigenetics?
- Epigenetic means heritable effects that don’t alter the DNA sequence, and environmental factors that modify gene functioning
- Offspring of attentive mother mice have increased serotonin production, and demethylation of gene Nr3c1
- This is a promoter (activator) for another gene called NGF1-A, which regulates glucocorticoid activity (more is produced now)
- This is heritable because the offsprings’ own parenting will be affected in turn, and yet no DNA sequence was re-ordered
- This has been found in abused humans, with less demethylation, meaning stress responses can't be inhibited as easily. And this is linked to suicide..
What long term effects can stress have?
- Cognitive decline in rats
- Limited nesting behaviour, worse nursing behaviour, struggles bringing up pups
- Worse at spatial learning