Are Subordinates Always Stressed?A comparative analysis of rank differences in cortisol

levels among primates

Abbot et al., 2003Kyle 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) & Hypothalamic-

Pituitary-Adrenocortical (HPA) systems

Fight or Flight Response

Stressor

Sympathetic Nervous System/

Catecholamines

‘Fight or Flight’

http://www.biology.ucr.edu/people/faculty/Garland/HPA_axis.jpg

PVN

Stressor

Brain Stem (e.g. LC)

‘Limbic’ System

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– 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 questionsI. 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 analysis1. 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

Y2Y1

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?

• Stressor controllability inhibits behavioural response

Coping? Social Support?

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/Garland/HPA_axis.jpg