Biological Responses to Stress

1
Biological Responses to Stress

• Classic response fight or flight (FOF)
• Two components to FOF response
• Activation of sympathetic nervous system
• Activation of hypothalamic-pituitary-adrenal
  (hpa) axis
• Sympathetic component
• Activation of adrenal medulla
• Release of epinephrine (adrenaline) and
  norepinephrine (noradrenaline)
• Increased heart rate, metabolic rate, blood
  pressure
• Sympthathetic component short term response to
  stress

2
HPA Axis

• Long-term response to stress
• Hypothalamus releases corticotropin-releasing
  factor (CRF)
• CRF stimulates pituitary secretion of
  adrenocorticotropin hormone (ACTH)
• ACTH stimulates release of cortisol from adrenal
  cortex
• Cortisol causes elevation in blood glucose
  levels, suppresses inflammatory and immune
  responses

3
FOF Response

• Nature of stressor determines whether organism
  will fight or flee
• Vast majority of research on FOF response
  conducted in males
• Prior to 1995, 17 of studies on neuroendocrine
  basis for FOF conducted in females
• Reasons cited for exclusion cyclical variations
  in reproductive hormones
• Evidence supporting FOF in females is inconsistent

4
Formulation of Tend and Befriend Theory

• Based on premise that successful stress responses
  subject to laws of natural selection
• Must allow survival of mother and offspring
• fight would put offspring in jeopardy
• Confined to situations requiring defense
• flight impossible while pregnant, caring for
  offspring

5
Tend and Befriend

• What responses are observed in female animal
  kingdom?
• tending behaviors
• Quieting, caring for offspring
• Blending into environment
• befriending behaviors
• Creation of social networks for resources,
  protection
• Possible hormonal basis those involved in mother
  / infant bonding
• Oxytocin, endogenous opiates, others

6
FOF differences in females

• Why dont females fight?
• Possible role of androgens
• Organizational , activational effects
• Possible role for socialization
• Why dont females flee?
• Possible counteracting effect of oxytocin (OT)

7
OT and FOF Response

• Rodent studies
• OT decreases sympathetic activity
• OT reduces fearfulness, enhances sedation,
  relaxation
• Effects are more pronounced in females
• OT response to stress is greater in females
• Androgens inhibit OT release in response to
  stress
• Estrogen enhances the anxiolytic effects of OT

8
OT rodent experiments

• In response to acute stress, females
• Show fewer behavioral indications (freezing)
• Show slower withdrawal latencies to heat,
  mechanical stimuli
• Higher ambulation scores on open field tests
• Administer exog. OT
• Decrease blood pressure (more in females)
• Decreased pain sensitivity
• Decreased corticosteroid levels

9
Review questions

• Describe physiological basis of FOF response
• Effects of sympathetic n.s. activation
• Activation of hpa axis
• Describe behavioral animal studies that suggest
  FOF doesnt describe typical female responses to
  stress.
• How do the majority of female animals respond to
  stress?
• What are tending behaviors?
• Befriending behaviors?
• Why might these behaviors be a result of natural
  selection?
• Why is OT thought to be the biological basis for
  these sex diffs in stress responses?

10
Human evidence for tend and befriend vs. FOF

• Activation of sympathetic n.s. and hpa axis
  occurs in response to stress in both sexes
• Lack of data re FOF behaviors in men vs. women
• Evidence for sex differences in tending
  responses to stress
• Parental responses to stressful work day

11
Tend and befriend vs. FOF

• LOTS of evidence for human sex differences in
  befriending due to stress
• 25 out of 26 studies have shown gender diffs
  (many at plt0.0000001 level)
• Examples of studies
• affiliative behaviors of subjects in response
  to heat or noise stress
• Female mobilize more social support in times of
  stress (family, work-related, interpersonal,
  financial, others)
• Maintain more same-sex close relationships
• Report more benefits of same-sex relationships

12
Biological correlate?

• Studies in breastfeeding vs. non-breastfeeding
  women
• Calmness
• sociability
• Studies in nonlactating women
• Maintain OT levels gt less anxiety in
  interpersonal relationships
• Higher OT gt reduced cortisol responses to stress
  (lab challenge)