1. "Stress" is a general, imprecise term that refers to either a stressor or the response to stress. Stressors (the cause), such a treat, cold exposure, or fear, elicit a response (the effect), such as increased epinephrine (E) or glucocorticoid release.
2. One example of an immediate (=acute) response to a stressor is Cannon's "fight or flight" syndrome involving activation of the amygdala which drives the sympathetic nervous system to release E from the adrenal medulla. Epinephrine in turn causes increased heart rate, increased blood flow to the heart, redirection of blood flow to the muscles, glycogen and fat catabolism, and activation of the reticular activating system.
3. The long term (=chronic) response to a stressor acts via the amygdala to release Corticotropin Releasing Factor (CRF) from the hypothalamus which then increases Adrenocorticotropin (ACTH) secretion from the anterior pituitary. ACTH increases activity of both the adrenal medulla (E) and cortex (Corticosterone, B). E and B enhance 1) glucose and glycogen synthesis at the expense of lipid and protein catabolism, 2) pain suppression, and 3) an anti-inflammatory response.
4. Seyle proposed the General Adaptation Syndrome (GAS) which states that long-term response to stress acts through increased adrenal function and consists of three phases: alarm, resistance, and exhaustion. Following exhaustion survival is less likely. Some question the validity of the GAS concept.
5. Long term response to a stressor has been studied in some natural populations and has been implicated in social dominance, overpopulation, and migration. But most data are correlational, rather than cause and effect.
LECTURE OUTLINE
OBJECTIVES
1. To define "stress", stressor, and stressor response.
2. To establish the roles of the brain, pituitary, sympathetic nervous system,
and adrenal gland in the immediate and long-term response to a stressor
3. To discuss the contributions and limitations of the Seyle’s General
Adaptation Syndrome
4. To evaluate the role of a stressor in laboratory and natural populations
I. INTRODUCTION TO STRESS
A. Stress is a term that is often misused
1. Stressor and Stress Response are cause and effect
B. Example of Stress Response: Gazelle attacked by a lioness
2. Immediate responses and long-term responses
II. NEURAL AND HORMONAL INTEGRATION OF STRESS
A. The brain and the stress response
1. Amygdala
2. Immediate response: Sympathetic nervous system and adrenal medulla
3. Long-term respones: Adrenal cortex
B. Structure and function of the adrenal gland
1. Anatomy of the adrenal cortex and the adrenal medulla
2. Hormones of the adrenal cortex and adrenal medulla
C. Adrenal Medulla and the immediate response
1. Cannon's Fight or Flight Response: Sympathetic Nerves (NE)
and Epinephrine (E)
2. Actions of adrenal medulla
* increases heart rate and blood pressure
* increased lipolysis and blood sugar
* vasodilation of heart vessels and respiratory passages
* increases breakdown of glycogen stores
* stimulates Reticular Activating System
D. Adrenal Cortex and the long-term response
1. Regulation of the adrenal cortex (CRH, ACTH, and Corticosterone)
2. Corticosterone (B) Actions
* increases glycogen synthesis
* breaks down lipid and protein
* inhibits glucose uptake, except in brain
* Anti-inflammatory (in large amounts)
* Suppresses immune response
E. Summary of stress timetable
1. Two loops are involved (sympathetic and glucocorticoid)
F General Adaptation Syndrome (GAS) of Seyle
1. GAS--A non-specific response to any stressor involving the
sympathetic nervous system, adrenal gland, ADH, and the
renin-angiotensin system
a. Summary of GAS
2. GAS time course (Alarm, Resistance, and Exhaustion)
3. Recent criticisms of GAS
a. Response to a stressor is often specific, not non-specific
Example: Responses to cold, immobilization, and pain
b. How could GAS be an adaptive response?
III. STRESS AND SOCIAL DOMINANCE
A. Introduction
1. Review of aggression in territorial species and dominance
hierarchies in social species
B. Social dominance and stress in lab populations
1. Stress and B are tightly correlated in rats
C. Social dominance and stress in natural populations
1. Stress and B are not tightly correlated
a. Possible reasons
IV. STRESS AND SALMON MIGRATION
A. Stress and Salmon Migration--Role in olfactory memory
1. Migrating salmon exhibit increased cortisol
2. GC receptors are concentrated in olfactory/memory sites
V. STRESS AND REGULATION OF POPULATION SIZE
A. Introduction to Population Cycles
1. Example: Lemming population cycles
B. Christian's studies on natural populations of Sika Deer
C. Andrew's Lemming studies
