Heidi Day, Ph.D.Asst. Research

Professor

Psychology Dept.& Center forNeuroscience

The term “stress” and its associated physiological effects was originally defined by Hans Selye (1940’s) in recognition of a “generalized” alarm system in response to illness and surgery in humans.

One current definition of a stress response is:“A non-specific physiological reaction caused by the

perception or detection of aversive or threatening situations that may jeopardize some homeostatic functions.”

Stressful situations can be divided into 2 categories:

1. Psychological/Emotional Stressors

2. Systemic Stressors

Different brain regions may be involved, particularly in the initial response.

A Three-System View of Stress

Behavior

HPA axis(Hypothalamic-

Pituitary-Adrenal) Autonomic

Stress and the Autonomic Nervous System

Sympathetic neurons of the autonomic nervous system become more active (involuntary), release norepinephrine and very quickly cause a wide array of physiological responses.e.g. increase heart rate, dilate bronchioles, dilate pupils, relax bladder, inhibit saliva, inhibit digestion, piloerection, increase sweat, increase glucagon release from liver.

Stress and the Autonomic Nervous System

The sympathetic nervous system also innervates (has nerve input to) the adrenal medulla. Secretory cells of the adrenal medulla release epinephrine (adrenaline) and norepinephrine (noradrenaline) that then act as hormones, and also increase heart rate etc. This is also a relatively fast response.

Stress and the Hypothalamic Pituitary Adrenal Axis

The anterior pituitary releases adrenocorticotropic hormone (ACTH), which elicits the release of glucocorticoids (cortisol) from the adrenal cortex.Relatively slow and long lasting response (peaks after ~ 30 min. and returns to baseline after ~ 2 hours). Virtually all cells have receptors for glucocorticoids.

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This is an endocrine or hormonal response

Psychological versus Systemic Stressors

Psychological/Emotional Stressors: Limbic System Involved

Systemic/Physical Stressors (e.g. blood born pathogens or poisons, immune stressors, hemorrhage): Limbic system not involved.

1. circumventricular organs (areas of the brain that do not have the blood brain barrier)

2. somatosensory system3. autonomic nervous systemResponses are similar e.g. increase in glucocorticoids

AnteriorPituitary

ACTH

AdrenalCortex

Glucocorticoids

Vagus nerve

Interleukin-1

hypothalamus brainstem

Is Stress Bad for You?

Acute stress Responses are ADVANTAGEOUS:

• increases in heart rate and blood pressure to bring more blood to muscles

• mobilization of energy resources (production and release of glucose for use by muscles)

• inhibition of inflammatory responses• Inhibition of sexual functions and sex steroid

production and release

• But the response needs to be turned off rapidly. Dr. Bob Spencer (Psych) works on glucocorticoid negative feedback.

Chronic stress responses are DISADVANTAGEOUS:

• hypertension & heart disease• cancer• gastrointestinal ulcers• diabetes• inhibition of growth • Infertility• drug abuse and relapse• suppression of the immune system (eg increased

susceptibility to colds and infections, decreased response to vaccination: movie)

• damage to the brain (Hippocampus: movie)

Incidence of hypertension in various age groups of air traffic

controllers at high-stress and low-stress airports

Percentage of caregivers and control subjects whose wounds had healed as a function of time after a biopsy was performed

Percentage of subjects with colds as a function of an index

of psychological stress

***MOVIES***

Reducing the effects of Stress:Stress Resistance Versus Stress Resilience

Current knowledge is very hazy!

We know that stress can be bad for your health, and that some interventions (e.g. feeling in control, exercise) seem to prevent some of the deleterious effects of stress. We don’t know how these interventions help.

1. Stress Resistance: A stressor has a smaller psychological and physiological effect.

2. Stress Resilience: A stressor has the same physiological effect, but despite this, the consequences are not as bad.

E.g. Despite high levels of glucocorticoids, hippocampal atrophy is not as bad.

Feeling in Control

Many situations are “perceived” as stressful by some people, not others.

The perceived control over a situation, even if it is an illusion, can prevent some of the negative effects of stress – to have the perception of control is called a coping response.

Animals and humans that display coping responses generally have reduced incidence of cardiovascular problems, gastric ulcers and psychological problems.

Dr. Steve Maier (Psych) works on stress controllability – the prefrontal cortex is very important

Model: Inescapable versus Escapable Shock

Groups:1. Control/baseline: Placed in apparatus, but no shock2. Escapable Shock: 100 tail shocks, active wheel to control shock termination3. Inescapable Shock: 100 identical tail shocks, inactive wheel. (Spins, but does not turn off shock)

Important: The Inescapable and Escapable animals are YOKED, so they receive exactly the same physical stress, but one has CONTROL, and the other does not.

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Control Inescapable Stress

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Test Day: Escape latencies in a shuttle box:Time how long it takes to escape a mild foot shock by “shuttling” from one side of the box to the other and

back again. A short time (small number) is better!

True or False:

“Exercise can “burn off” natural chemicals that build up during

stress”

(Quote from pamphlet in Recreation Center)

Other Strategies toCope with Stress

Voluntary exercise in rats decreases the

release of ACTH and corticosterone

following low intensity stress

(Dr. Heidi Day)

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Voluntary exercise facilitates adaptation to stress(Dr. Serge Campeau)

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Voluntary exercise prevents the learned helplessness seen after inescapable stress in rats

Dr. Monika Fleshner (IPHY)

Some People Who Study “Stress” on Campus

Heidi Day (Psych)Limbic System ResponsesEffect of Exercise

Serge Campeau (Psych)Neural Circuits in Psychological StressStress Adaptation; Exercise

Steve Maier (Psych)Coping: Uncontrollable vs. Controllable StressDrug Abuse and Stress

Bob Spencer (Psych)Glucocorticoid Negative FeedbackHPA axis

Monika Fleshner (IPHY)Exercise and the Stress Resistant BrainExercise and Immunity

GET INVOLVED!! BURST, UROP, URAP, Work Study

Other things you can do to decrease the negative effects of stress

Imagine happy or peaceful scenes; Meditate

Healthy eating

Relaxation, Meditation, Biofeedback

Social interaction, optimism, humor