What Stresses Us?
Types of Stressors
- Job interview
- Death in family
- Disease diagnosis
Psychological stressors most highly activate the HPA system.
- Sympathetic (adrenaline)
- Hypothalamic-pituitary-adrenal system
- Brain activity
Stressors elevate circulating levels of HPA
Cortisol level is (the best?) measure of stress:
- BUT, it is not a perfect measure
- Not all stressors clearly elevate cortisol
- Cortisol can increase without stress
- System can become dysregulated with prolonged exposure
Cortisol is a good measure of the effect of relatively short-term psychological stressors, when other factors affecting HPA activity are controlled.
Handling control “Base”
- Alone home
- Alone novel
- Dog novel
- Person novel
Dogs entering animal shelters are confronted with an array of psychological stressors (e.g., novelty, uncertainty, separation from attachment figures). On entering the shelter, cortisol is higher on Day 1 than in pets at home.
Why should high cortisol levels matter?
- Welfare of dogs
- Long-term effects on behavior
- Potential health effects
White blood cells are elevated on 1st day in shelter and continue to rise.
Can human interaction reduce the cortisol response?
- Human interaction is a key factor for improving the welfare of dogs in shelters.
- Human-dog interaction can counteract stress.
- Human interaction prevents enhanced cortisol elevation.
Specific human interaction in the shelter reduces cortisol response to:
- additional stressor (venipuncture)
- additional stressor at a later time (novelty)
Presence of a human, regardless whether they ignore, pet or play with the dog, stress response is reduced for the shelter dogs. Suppressed immune systems from high CORT levels of dogs in shelters means there is a potential illness risk throughout entire shelter.
- loss of control
- social separation
CORT levels differ depending on the kind of life the dog has and medical conditions.
Key ingredient: human interaction away from the main kennel area significantly reduces stress.
Relinquished dogs didn’t find human petting as reassuring (per cortisol tests) as strays.
Circulating levels of the primary stress hormone, cortisol, are about three times higher than observed in pet dogs sampled in their owner’s homes.
As little as 15 minutes of interaction between humans and dogs can reduce the circulating cortisol response.
Multiple sessions continued to produce effects, and dogs entering the shelter as strays appeared more susceptible to stress than dogs released by their owners.
Part 1 – Introduction Into The Biology Of Stress
Miles Orchinik, PhD
Is Stress A Headache?
- Yes, but it produces a lot of another physical annoyances (pain, heart beat, insomnia).
- But it is also more than a headache.
- Chronic and severe stress can cause a number of conditions.
- Affects mental and physical health – PTSD, heart disease, arthritis, asthma, and more.
- Research study on monkeys by Uno andSapolsky
- Stressed vs normal monkeys – hypocampus was very physical different.
- Abnormal response – no one is ever that stressed, but impressive result
Consequences of Stress
- Stress related illnesses in US cost us about 100 billion dollars annually.
- Our response to stressors is what makes us sick – the stressors don’t make us sick.
- Every vertebrate has the same response to stress.
- Stress is a label, but it doesn’t describe what is actually happening physically and mentally.
A stressor is a perceived threat to homeostasis – a stimulus. The stress response is an attempt to restore homeostasis. The stress response is the release of stress hormones.
Homeostasis is a property of living organisms to regulate their internal environment in order to maintain stability. Blood pH is an example. If the pH changes from “normal” levels, the body adjusts to return it to normal through a physiological reflex.
A stressor is perceived by the brain, it is processed, and triggers the stress response (fight or flight). Behavior response helps us survive threat.
Stress Response is a physiological response known as HPA axis. The HPA axis is when the hypothalamus releases CRH, the Pituitary gland then releases the ACTH (a neuroendocrine cascade of chemical releases and reactions), the then the Adrenal cortex releases cortisol (corticosterone). This cascade of reactions supplies the body with the necessary tools to evade a perceived threat.
There is also a daily rhythm of cortisol release. Levels peak just before onset of activity (for example, just before waking up).
Stress can be related to reproduction. It can be a threat to one’s ability to reproduce because threats can affect long term success. For example, taking an exam is stressful because can determine your success and ability to reproduce with your desired mate in the long run.
Role of Cortisol
Lion vs. Zebra Chase: Prey and predator both have a stress response during hunt. Cortisol redirects response (energy) towards dealing with the threat.
- Increase in glucose in the blood stream which generates energy to escape/move (lion needs energy to catch zebra, zebra needs to move to escape)
- Increases glucose in the body.
- Increases sympathetic system.
- Decreases parasympathetic system response to turn off unnecessary functions for immediate survival.
- Stress related behaviors increase to escape the threat.
- Alertness increases.
- Once the threat is gone, negative feedback of the HPA axis to turn off stress response.
Part 2 – Importance Of Contexts When Studying Stress
Context matters when determining stressors in an environment. One study by Romero, Reed, and Wingfield in 2000 discovered that tropical birds were more affected by weather changes than arctic birds. Bad weather did not produce a stress response in arctic birds.
Predictability is important in stress. One species of birds stressed about weather changes that were unpredictable. The other species of birds unpredictable weather was predictable and did not stress them out.
Some highly stressful events are predictable (like one’s parents becoming elderly), so there must be other things that contribute. Controllability is important, even when things are predictable.
Example: In a study where rats were put in a wire cage and shocked. The rats that had the ability to control the shock which meant evading the shock were significantly less stressed than rats who had no control. The stressor was the same, but the stress responses were different.
- Ability to escape it with control reduced stress.
- Those that could not control the shock had compromised immune systems.
“CORT is not always anti-reproductive. Neuroendocrine context is important.” Miles Orchinik
Most vertebrates are highly resilient with stress.
Stress as a child can create “abnormal” responses to stress in adulthood. The prefrontal cortex doesn’t act “normally” in adulthood.
Nurture vs. Nature: One’s stress response depends on the environment one grew up in. Birth mother does not matter as much as the nurturing environment one grew up in as a young child. The environment in which they are raised influences their physiological response to stress as adults. (Kim, P. et al., 2013, PNAS)
Is stress a killer?
- Stress increases mortality but only among those who perceived that stress affected their health.
- If they didn’t think it affected them, they did not die at any different rate.
(Keller, A. et al., 2012, Health Psychology)
Anti-Stress Hormone – Oxytocin
The gaze of a dog increases oxytocin levels in dog and the human – increases the bond. (Nagasawa, M. et al., 2015, Science)
Take-Home Concepts To Consider
- Stress is critical in survival and reproduction.
- Stressors produce context specific effects. Context is incredibly important when analyzing the stress.