Neurobiology of Stress

Question 1

stress

Answer 1

• A threat, real or implied, to homeostasis

- Can help survival, unless it’s chronic

Question 2

how was stress first identified?

Answer 2

• 13th century infant language experiments by King Frederick caused extreme stress, but people didn’t understand it at the time
• 1930’s: Hans Selye coined the term stress (originally “general alarm reaction”): “the non-specific response of the body to any demand for change”

Question 3

eustress

Answer 3

“good” stress – defined by
how one perceives the stressor (e.g.
responding with hope/vigor)

Question 4

Selye’s experiments

Answer 4

• Injecting ovarian extracts into rats to try and find new hormones
• • Symptoms: adrenal cortex enlargement, atrophy of immune tissues, gastrointestinal ulcers
• Injected other stuff (ex. Pituitary, kidney, spleen, formalin, etc.) and got same symptoms
• Stressors he studied: “exposure to cold, surgical injury, production of spinal shock, excessive muscular exercise, or intoxication of drugs”

Question 5

General Alarm Reaction stages

Answer 5

1. 6-48 hours after injury; Atrophy of organs, loss of muscle tones, fall of body temp, erosions in digestive tract
2. > 48 hours after injury; adrenals enlarge, body growth ceases, gonads atrophy, lactation stops (adaptation can occur, with organs returning to normal)
3. > 3 months: Loss of resistance -> exhaustion

Question 6

Hans Selye

Answer 6

• coined the term stress
• figured out 3 stages in general alarm reaction
• suggested controversial link between stress and illness
• Dedicated his career to understanding the neuroendocrine mechanisms involved in disease

Question 7

why were Selye’s suggestions about stress and illness controversial?

Answer 7

• It was difficult to give a precise, universally applicable definition to stress
• Primitive methodologies to validate scientific ideas

Question 8

homeostasis vs. allostasis

Answer 8

• Homeostasis: stability of physiological systems that maintain life (systems essential for life must be maintained within a range optimal for current life history stage)
• Allostasis: the active process by which the body responds to daily events and maintains homeostasis (achieving stability through change)

Question 9

glucocorticoids

Answer 9

• steroid hormones (produced by endocrine glands, immediately released, not water-soluble, require “chaperones” to move through bloodstream)
• Can affect almost every cell in the body; major functions in metabolism, development, cognition, immune function, and stress
• large category -> subcategories include cortisol (humans) and corticosterone (rats)

Question 10

mechanisms underlying activation of HPA axis

Answer 10

Hypothalamus releases CRH -> acts on pituitary gland -> releases ACTH -> acts on adrenal gland -> releases glucocorticoids

Question 11

PVN (Paraventricular nucleus)

Answer 11

• 2 types of neurons
• • Magnocellular neurons: oxytocin & vasopressin
• • Parvocellular neurons: CRH (Corticotrophin-Releasing Hormone)

Question 12

stressor

Answer 12

• Anything that knocks an organism out of homeostatic
  balance
• Events that are threatening to an organism and which elicit
  physiological and behavioural, in addition to that imposed by
  the normal life cycle

Question 13

pituitary gland

Answer 13

• “the master gland”
• produces hormones that control the production
  of hormones in other glands

Question 14

adrenal gland (structure and function

Answer 14

• Cortex = outer layer; medulla = inner layer

- produces cortisol -> when ACTH is released, it acts on various enzymes to produce cortisol

Question 15

glucocorticoid receptors (2 types)

Answer 15

• Type 1: Mineralocorticoid receptor (MR) (first ones bound, like the baseline fullness of a hotel)
• Type 2: glucocorticoid receptor (GR) (second ones to bind, fills up extra empty spaces like hotel guests at a conference)
• Widely distributed in the CNS and periphery

Question 16

negative feedback

Answer 16

• the diminution of an effect by its own influence on the process giving rise to it, as when a high level of a particular hormone in the blood may inhibit further secretion of that hormone
• Change in controlled variable eventually leads to that variable being restored to normal (allostasis)
• Ex. thermostat

Question 17

glucocorticoid’s actions: acute stress

Answer 17

• Increased heart rate & blood pressure
• Mobilization of energy
• Suppression of digestion, growth, and reproduction
• Modulation of immune system
• Sharpening of cognition

Question 18

glucocorticoid’s actions: chronic stress

Answer 18

• Fatigue, myopathy
• Stress-induced cardiovascular disease
• Ulceration, obesity
• Psychogenic dwarfism
• Amenorrhea, loss of libido, and impotency
• Increased disease risk
• Deficit in memory, neuronal death

Question 19

stress and hippocampus

Answer 19

• Chronic exposure to corticosterone causes a loss of hippocampal neurons in a similar amount to losses observed in normal aging
• Chronic stress impairs spatial learning (ex. Rats in water maze – inhibited ability to find platform)

Question 20

mice and corticosteroid binding globulin

Answer 20

Mice with less globulin are more susceptible to illnesses

Question 21

influence of artificial selection on stress response of Siberian foxes

Answer 21

Hormone and neurotransmitter changes -> low stress response

Question 22

primate social hierarchy on stress system

Answer 22

• Subordinate males: higher cortisol levels with exposure to stressors (higher blood pressure, increased anxiety, impaired immune function, etc.) -> much higher risk of disease
• Dominate males: low cortisol levels
• These results translate to humans as well: people in lower-ranking positions at their work call in sick more and are more prone to illness than higher-ranking people

Question 23

Sapolsky’s baboons

Answer 23

• Studied a troop of baboons, some ate contaminated garbage, wiping out alpha males
• Years later, he saw that the troop was less aggressive, even though there was only one alpha male left who had been exposed to this epidemic
• This shows that the new members and new alpha males were learning that being less aggressive was the way to behave

Question 24

social isolation on stress system

Answer 24

• Increases chances for immune disorders
• Supresses immune response
• Induces anxious-depressive-like behaviour
• Impacts progression of disease
• Influences our perception of pain
• Regardless of this, social isolation is still used in jail (Associated with increased suicide rates, psychiatric illness, increased recidivism rates)

Question 25

trans-generational stress: Dutch famine

Answer 25

Women who were pregnant during Dutch famine gave birth to kids with more intense stress responses