Download Are Subordinates Always Stressed? A comparative analysis of rank

Are Subordinates Always Stressed?
A comparative analysis of rank differences in cortisol
levels among primates
Abbot et al., 2003
Kyle Nash
May 12th, 2009
Agenda
1. Stress and HPA axis review
•
from Kloet, Joels & Holsboer, 2005
2. Abbott et al., 2003
•
•
•
•
Intro
Method
Results
Conclusion
3. Discussion
What is Stress?
• Process: Stimulus  Response
• Stressor:
– Stimulus that threatens animal’s physiological
homeostasis (Kloets et al., 2005)
– Physical vs. Psychological (Real vs. Predicted)
• Stress Response:
– Active maintenance of physiological homeostasis
– Sympathetic (Fight or Flight) & HypothalamicPituitary-Adrenocortical (HPA) systems
Fight or Flight Response
Stressor
Sympathetic
Nervous
System/
Catecholamines
‘Fight or Flight’
Brain
‘Limbic’
Stressor
Stem
System
(e.g. LC)
PVN
http://www.biology.ucr.edu/people/faculty/
Garland/HPA_axis.jpg
Corticosteroid Receptors
• Two types – Both respond to corticosteroids
• Minerocorticoid Receptor (MR):
– Appraisal, initial stress response
– Important in gene transcription activity
– More sensitive corticosteroids (10x)
• Glucocorticoids Receptor (GR):
– Terminates stress response for recovery (i.e. decrease
CRH production)
– Increased sensitivity to corticosteroids during stress
– High density in PVN, aminergic & limbic pathways
– Promotes stressor-related memory storage
MR x GR
Chronically Stressed Animal
• Prolonged and/or repeated exposure to stressor (i.e. prolonged increase in
corticosteroids) can have maladaptive consequences
– Hypertension, type-II diabetes, ulcers, etc.
• Chronic stress  Neuroendocrine change
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–
–
–
–
hippocampal (CA3) atrophy, reduced proliferation (MR)
GRs and MRs downregulated
Diminished Denate Granule cell turnover rate
Reduced 5-HT receptor function
Reduced LTP/Facilitated LTD
• Produce a Stress-typology
• ‘Coping’ can disrupt maladaptive changes
– offspring of ‘caring’ rat mothers, higher hippocampal GR gene expression and
decreased anxiety-related behaviour
• Stress experience (stressors and coping) and genetic background cause
long-term changes
Summary
• Stressors activate sympathetic and HPA
systems
• Glucocorticoids regulate stress response
through MR and GR interaction
• Prolonged stress  physiological problems
and neuroendocrine funtioning
• Individual differences in genetics and
experience important in stress response
Rank and Stress
• Stress levels may be higher in subordinates
– Low access to resources, physical and social
stressors, low ‘coping’ opportunities
• Certain subordinate primates
– elevated glucocorticoids and catecholimines
– higher blood pressure
– Stress-related pathologies
• Not consistent for all primates
Abbot et al., 2005
• Conflicting results on rank and stress
• Purpose
– Survey researchers (quasi-meta-analysis)
– Rank, Sex, Species  Stress
– Looked at both physical/psychological factors
Method
• Questionnaire: 6 Domains, 17 questions
I.
What is it like to be a dominant individual in this
society?
II. What is it like to be a subordinate individual in this
society?
III. What are the typical routes by which ranks change?
IV. What is the nature of revolutionary change in
hierarchies?
V. The role of kinship.
VI. Non-agonistic factors relevant to the stress-response.
• 0 (Not at all) – 3 (Highly applicable)
Method: Sample
4 Old world (e.g. Rhesus)
3 New World (e.g. Marmoset)
• Subordinates: indicated by expert of each sample
• Analyses: by species and sometimes sex
• 10 groups in total, large variance in group dynamics
Method
• DV: Relative Cortisol
– Basal levels
– Circulatory or urinary
– Relative to dominant monkeys, controls for
species differences
• i.e. 100% = equal cortisol levels
Analyses
• Two types of analysis
1. Multiple Regression with independent contrasts
– Flips variables from dependent (i.e. similar species) to
independent
– After data collection, excluded questions based on
• missing values (5)
• High r’s with other questions or Low r’s with cortisol (4)
• 8 total questions
2. Data Tree - decision algorithm from response
variability predicted
– Different excluded values
– Used 4 questions from 8 (above) in regression
Tree-Based Method – Single Branch
• (1) If Question 1A is >X, then this predicts relative cortisol
levels = Y1% (branch 1).
• (2) If Question 1A is <X, then this predicts relative cortisol
levels = Y2% (branch 2).
• Overall Tree = Minimum Branches for Maximum Predictive
Power
Q 1A
Y1
Y2
Final Q’s Multiple Regression
• 1A: How much of a role does aggression play in the attainment of
dominance?
• 2A: How frequently are subordinates subject to stressors?
• 2B: How available is social support for subordinates?
• 2F: Overall, how much should subordinate status be thought of as
an undesirable state actively imposed by more dominant animals?
• 3A: Do animals rise in the hierarchy through strenuous challenge of
the status quo?
• 4A: How often do such “revolutions” occur?
• 5A: How important is kinship in understanding interactions among
these animals?
• 6A: Are there circumstances in which one has to invoke a
physiological adaptation to subordinate status, rather than a
response to agonistic behavior, to make sense of the profile of a
particular stress hormone?
• Two significant predictors, 2A and 2B
Results: 2A - Social Stressors
2B - Social Support
Final Q’s for Tree-Based Analysis
• 2A: How frequently are subordinates subject
to stressors?
• 2B: How available is social support for
subordinates?
• 3A: Do animals rise in the hierarchy through
strenuous challenge of the status quo?
• 5A: How important is kinship in understanding
interactions among these animals?
Discussion
• Subordinates do not always express higher levels of
cortisol
• Important factors:
– Stressors frequency
– Social support
– Relevance of kinship
• Possible neuroendocrine mechanisms
– Increased stressors  decreased GRs  diminished
negative feedback in stress response  cortisol
– Outlets (social support) diminishes cortisol levels
– Kinship variable could predict both stressor frequency and
social support quality
Problems
• Relative measure of cortisol
• consider the cortisol levels for dominant monkeys
• Questionnaire
• Exclusions were largely subjective
• Authors were respondents
Discussion
• Other important factors?
– Other outlets or displacement behaviours?
– Simple stressor disruption?
– i.e., allowing rats access to a running wheel decreases
the magnitude of the glucocorticoid response to shock
• Coping mechanisms: MRxGR?
– Stops GR downregulation?
Coping?
Social Support?
• Stressor controllability inhibits behavioural
response
References
• Unless otherwise noted, figures and tables from
Abbot et al., 2003.
• Sapolsky, R.M., Krey, L., McEwen, B., (1984).
Stress down-regulates corticosterone receptors in
a site-specific manner in the brain. Endocrinology,
114, 287–292.
• Kloet, Joels, & Holsboer, (2005). Stress and the
brain: From adaptation to disease. Nature
Reviews: Neuroscience, 6, 463-475.
• http://www.biology.ucr.edu/people/faculty/Garla
nd/HPA_axis.jpg