Stress: Causes, Chemicals, Consequences

1. Stress:Causes, Chemicals, Consequences

2. Just What Exactly Is Stress? • Initially identified by Selye as “noxious agents.” • Became known as stress syndrome. Source: www.alnoorhospital.com/uploadedfiles/common/stress/jpg

3. Three Stages of Stress • Stage 1: The alarm reaction in which the body prepares itself for “fight or flight.” • Stage 2: Since the first stage cannot be sustained, there is a general resistance to the stress which is established. • Stage 3: If the stress is continued for a long period of time, then eventual exhaustion results (the body’s response to prolonged “wear and tear”).

4. Stress includes both internal and external factors. • Factors involve the “nonspecific response of the body to any demand."

5. The “Fight or Flight” Response • Perceive extreme danger or distress • Neurons (nerve cells) in brain send entire body into “high gear” • Responsively prepare for “fight or flight” Source: www.saludparati.com/entres.htm

6. Challenged by physiological, psychological, and environmental changes (stressors) • Failure to accommodate to changes can lead to exhaustion Source: www.bet.com/Health/Archives

7. Remember Neurons? • specialized cells of which nerve tissue is composed • have the ability to send “messages” to each other through the release of chemical substances called neurotransmitters • electrical in nature, maintaining polarity through electrical gradients established by ions on the inside and outside of their cell membranes. • send electrical signals (action potentials) by depolarizing.

9. Neurons labeled with fluorescent proteins Source: Joshua Sanes, Harvard University. Lecture:”Neurons: how they look and what they do.7/11/2005

10. How Do Neurons Communicate? • Neurons do not physically touch each other. • Neurons communicate with one another through various neurotransmitters released from synaptic vesicles at the synaptic cleft • The synaptic cleft separates one neuron from another. Source:http://www.miracosta.cc.ca.us/home/sfoster/neurons/animation.gif.

11. Perceptions… http://www.youtube.com/watch?v=6tLqh1qYvV4

12. Perception of Pain Fear/ Helplessness PAIN Sleep deprivation Anxiety

13. “Good” and “Bad” Pain “A” Fibers: • Signal “good pain” • Serve as injury warning • Release glutamate “C” Fibers: • Signal more diffuse, chronic pain • Pain sources include tissue damage and cancer • Release “substance P” Source: http://office.microsoft.com/clipart

14. A Computer-Brain Analogy • Remember when the older computers didn’t have enough memory (RAM) to support more complex programs? • Continual bombardment of the brain by stress signals results in the inability to process and respond adequately to such signals. Source: http://office.microsoft.com/clipart

15. Homeostasis, the state of internal constancy or equilibrium necessary to maintain physiological health is… • disrupted by stress! Source: http://spwb.com/articles/anti-aging/stress.gif

16. Disturbance of Homeostasis • Our bodies react to environmental changes (stressful or otherwise) by producing hormones and neurotransmitters. • These chemical substances are the messengers and mediators of the nervous system and endocrine system. • Stressful events cause the release of adrenalin and hormones (e.g., cortisol) from the adrenal medulla and cortex, respectively.

17. Brain integrates and coordinates bodily responses • Physiological and behavioral stress responses result in adaptation • Over time “load” accumulates and can cause disease, even death Source: www.sciencebob.com/lab/bodyzone/brain/html

18. Ex. Psychology and physiology… • In a 1977 study published in the New England Journal of Medicine, researchers showed diminished degradation of plasma cortisol and low plasma triiodothyronine (active hormone controlling metabolic rate) in young women suffering from anorexia nervosa.

19. Population Crowding Causes Stress in Deer • In the early 1920’s, a pair of deer was placed on a 150-acre island in Chesapeake Bay. • The deer population grew until the density reached about one deer per acre. • Then the deer began to die off (in the absence of known predators) despite the presence of adequate food and water. Source: www.whiskersinn.com/sale/images/3%20deer.jpg

20. The Post-mortem Findings • areas of atrophy in the liver tissue, marked decrease in liver glycogen, and hypoglycemia. • evidence of small (petechial) brain hemorrhages and both congestion and hemorrhage of the adrenal glands and kidneys. • These findings suggested what later was identified as adrenal stress syndrome.

21. Stress in Minnesota Jack Rabbits • In a 1939 study also reported in The Bulletin of the Atomic Scientists, Minnesota Jack Rabbits demonstrated rise and fall in population densities but when death rates and densities were high, they frequently entered into convulsive seizures or comatose states. • Liver and adrenal pathology, as well as hypertension and hypoglycemia associated with adrenal stress syndrome, were observed. Source: http://homestudy.ibea.com/wildlifeID/043jackrabbit.htm

22. Population Density and Behavior (Norway Rats) • In 1962, John Calhoun (of the National Institutes of Health) observed high mortality rates in confined wild Norway rats when population densities were high as a result of stress-induced behavioral changes. Source: http://www.ratbehavior.org/Aggression.htm

23. Population Density and Behavior (Norway Rats) • Calhoun conducted several experiments involving both a quarter-acre enclosure and 6’ x 6’ interconnecting pens. • Calhoun made the following observations: Source: http://office.microsoft.com/clipart

24. Behavior changes in females • Pregnancies were often aborted through miscarriage. • Considerable disruption of normal pre- and postpartum maternal behavior (i.e., failure to build proper nests, nurse offspring and transport litters) occurred. • Up to 25% of estrus females were so vigorously pursued by males that they did not survive.

25. Behavior changes in males • Some animals became hyperactive, constantly fighting. • These animals also became hypersexual and lost the ability to discriminate among estrus and non-estrus females, juveniles, and other males. • Some became cannibalistic. • Some became withdrawn, demonstrating no interest in social interaction.

26. Human Population Density • The following slide depicts human population growth in Europe from an estimated number of 20 million people in 400 BC to 728 million in 2000 AD. • Note that in the last three centuries or so, the growth curve becomes progressively exponential or logarithmic.

27. Source: http://wps.prenhall.com

28. Population Density and Stress in Humans • Very few studies directly correlate stress of crowding with changes in the human brain. • Compelling evidence now available to link neurological changes in human brains to prolonged exposure to general stress. Source: www.spokane7.com/…/archive/asp?mon=Jan2004

29. Stress, Hormones, and the Brain • Once perceived, stress activates the hypothalamus of the brain, triggering a cascade of hormones through the hypothalamic-pituitary-adrenal (HPA)axis. • Trigger of the HPA axis results in the release of glucocorticoids (e.g., cortisol) from the adrenal gland.

30. Stress, Hormones and Brain: The Hypothalamic-Pituitary-Adrenal Axis • Some neurons in the hypothalamus produce corticotropin-releasing factor (CRF). • The synapses of these cells make contact with blood vessels, sending CRF to the adenohypophysis (anterior pituitary) • The pituitary then secretes adrenocorticotrophic hormone (ACTH) causing glucocorticoid release by the adrenal cortex. • At the same time the adrenal medulla produces adrenalin. Source:www.aafp.org/afp/20000901/1119_f2.gif. (The American Academy of Family Physicians)

31. What do glucocorticoids (such as cortisol) do? • increase blood glucose for the “fight or flight” reaction and thus have short-term benefits. • Over time, frequent release of these glucocorticoids adversely affects the hippocampus of the brain (the center of numerous glucocorticoid receptors). • Normal levels maintain normal neuronal function in the hippocampus • High levels adversely affect synaptic transmission and actually interfere with glucose uptake by neurons. • Resultant reduction of neural connections may responsively induce memory loss (Seckl, 2005).

32. Daily changes in cortisol in depressed patients Source: Neuroscience Presentation by Paul Arfydio, Harvard University. July 14, 2005

33. Jonathan Seckl’s Conclusions • Both animals and humans may gradually develop a stress-related syndrome involving: • Excess levels of glucocorticoids • Pathological changes in the structure and function of hippocampal cells • Neuronal death (sometimes) • Increased numbers of hippocampal glucocorticoid receptors, making the brain more sensitive to negative feedback control. • This may be one mechanism of action for certain antidepressant drugs.

34. References • Boyer, R.M.,et al. Cortisol secretion and metabolism in anorexia nervosa.NEJM, 294 (4),1977. • Brooks, Crystal. Overcrowding and violence in federal correctional institutions:An empirical analysis. Retrieved from http://dspace.library.drexel.edu. • Bresler, Jack B., ed. Human Ecology. Reading,MA. Addison-Wesley.1966. • Calhoun, John. Population density and social pathology. Scientific American. Feb.,1962.

35. References (continued) • Cox, Thomas. Black Hills State University. Learning and Conditioning Laboratory. PSYC305L. Fall, 2004. Retrieved from http://www.bhsu.edu. • Duane, Mary, et al. Inquiry in science using an animal behavior model. Retrieved from http://www.woodrowwilson.org/teachers/bi/1998/planaria/index.htm. • Hoagland, Hudson. Cybernetics of population control. Bulletin of the Atomic Scientists. Feb.,1964. • Marieb, Elaine N. Essentials of Human Anatomy and Physiology. San Francisco. Addison-Wesley-Longman. 2000.

36. References (continued) • Massachusetts Department of Education. Massachusetts Curriculum Frameworks. Retrieved fromhttp://www.doe.mass.edu/frameworks. • Mayer, Emeran A. The neurobiology of stress and emotions. Participate/Digestive Health Matters.Winter, 2001. • McEwen, Bruce and Teresa Seeman. Allostatic load and allostasis. Retrieved from http://www.macses.uscf.edu/Research/allostatic/notebook/allostatic. August, 1999. • National Institute of Child Health and Human Development. NIH Backgrounder. http://www.nichd.nih.gov. Sept. 9, 2002.

37. References (continued) • National Research Council and National Academy of Sciences. National Sciences Education Standards. Retrieved from http://www.nap.edu/readingroom/books/nses/html/index.html. • Regoeczi, Wendy C. The impact of density: The importance on nonlinearity and selection on flight and fight response. Social Forces. 81, 2002. Retrieved from http://www.ncsociology.org/sociationtoday/v22/crowding.htm. • Seckl, Jonathan R. Glucocorticoids, aging, and nerve cell damage. Retrieved from http://neuroendo.org.uk/index/php/content/view/18/11. June, 2005. • Society for Neuroscience. Brain Facts, a Primer on the Brain and Nervous System. Washington. Society for Neuroscience.

38. References (continued) • Spedding, M. and P. Lestage. Synaptic plasticity and neuropathology: New approaches in drug discovery. MedSci (Paris). 21:1. Jan., 2005. • United States Dept. of Agriculture. Agricultural Research Service. Detecting stress in animals. Agricultural Research. Jan.,2002. • University of Scranton Neuroscience program. “Welcome to the Sheep brain Dissection Guide.” Retrieved from http://www.humboldt.edu.