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Causes and Consequences of the Stress Response

Causes and Consequences of the Stress Response. HUMANS in NATURE 2010. Stressors and Coping Responses. The organism possesses a remarkable sense of biological priorities

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Causes and Consequences of the Stress Response

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  1. Causes and Consequences of the Stress Response HUMANS in NATURE 2010

  2. Stressors and Coping Responses • The organism possesses a remarkable sense of biological priorities • Mechanisms that helped cope with stressors -- fragments of motor patterns and autonomic reflexes -- have been cobbled together by evolution (“bricolage”). • Stressor is a real or perceived challenge to an organism’s ability to meet its real or perceived needs.

  3. Real or perceived NEEDS that must be met: • Physiology( Homeostasis) (Food comes first, then morals. -Bertolt Brecht) • Safety(security, order, protection) • Sociality( acceptance, “acceptance”) • Esteem(better reproductive opportunities status, prestige;) • Self-Actualization(reproduction; direct or indirect fitness; “personal fulfillment”) -apologies to Maslow

  4. Coping . . . • STRESSORS are internal or external changes which by challenging an organism’s ability to meet its needs evokes a coordinated coping response • . . . constrained by a threshold for detectionof the change, for attentionbased on real or perceived relevance, andcapacity to respond at any particular level once the challenge is detected.

  5. COPING RESPONSES: constraints of the system • Input (stress can change the sensitivity of sense organs (e.g., Gandelman 1983); resolve competitive parallel afferent pathways,) • Integration(receptive field modulation; stress can affect arousal, selective attention (e.g., Archer 1973, R.J. Andrew 1972); differential regional sensitivity to hormones or neurotransmitters (e.g., Amy Arnsten 2000); control of microcirculation (e.g., Palmer 1986) • Output (resolve competitive parallel efferent paths to action; energetic reserves and the ability to mobilize them)

  6. COPING RESPONSES: constraints of the system When a challenge to a need is apparent: • the AUTONOMIC NERVOUS SYSTEM (key in maintaining homeostasis) • Evokes AFFECT (perceived emotion) which ENERGIZES specific MOTIVATIONAL STSTEMS (many external expressions of this … it can be seen in behavior) • REALLOCATES ENERGY to meet the need (internal, if sustained can damage organism)

  7. COPING RESPONSES: stress sensitive hormones • Sympathoadrenomedullary (SAMS) response (adrenal medullary /chromaffin response to sympathetic activation) • Hypothalamic-pituitary-adrenal (HPA) axis activation(CRF, ACTH, adrenal glucocorticoids) • Opioids(endorphin, enkephalin; affects perception of pain and reproductive axis) • Prolactin (affects reproductive axis) • Angiotensin, Melanotropin?

  8. COPING RESPONSES: problems of interpretation • Bi-phasic (“paradoxical”) responses(responses can be diametrically opposed depending on absolute levels of hormone (e.g., Gandelman 1983) or presence of facilitating hormones (e.g., stress can facilitate classical conditioning [Shors et al. 1992] in males but not in females [Wood & Shors 1998]) • Extra-trophic effects(e.g., CRF canenhances effects of novelty, affect learning,(see Koob 1991); ACTH can suppress aggression (see Brain et al 1971); MSH affects motivation, attention (Stratton & Kastin 1973; Kastin et al. 1971)

  9. COPING RESPONSES: hierarchically arrayed • The most ancient (evolutionarily conservative) responses are invoked first (adrenal medullary /chromaffin response to sympathetic activation) (fear –subcortical limbic areas; pleasure --cortical limbic) • As each response’s adaptive scope is exceeded, successive mechanisms deploy (local, neuroendocrine [CRF, ACTH, glucocorticoids], behavior) • Behavior is the final option (invoked when “lower” responses capacity is exceeded or they would be would be too “expensive”)

  10. THE GENERAL ADAPTATION SYNDROME (GAS): three stages: 1 ALARM REACTION: sudden exposure to stimulus to which organism is not adapted; • Shock phase: initial and immediate (e.g.: tachycardia, loss of muscle tone; decr temp and blood pres) • countershock phase: rebound involving incr adrenal cortical involvement & • relatively rapid SAMS (Sympatho-Adrenomedullary System) response predominates (norepi & epi)

  11. THE GENERAL ADAPTATION SYNDROME (GAS): three stages: 2 STAGE OF RESISTANCE: "organism's full adaptation to the stressor and the consequent improvement or disappearance of symptoms. At this stage, however, there is a concurrent decrease in resistance to most other stimuli.” • the HPA (hypothalamo-pituitary-adrenal axis) response predominates (ACTH and CS) closely interacting with the sympathetic response)

  12. THE GENERAL ADAPTATION SYNDROME (GAS): three stages: 3. STAGE OF EXHAUSTION: coping responses cannot sustain their response if stressor is sufficiently severe and prolonged; • "diseases of adaptation" may arise; • symptoms that disappeared during the stage of resistance may reappear; • death possible.

  13. COPING RESPONSES: not only emergencies ! • Elements of the stress response can be invoked whenever there is a mismatch (unmet expectations, cognitive dissonance; (Goldstein 1990)) • Stressors can be cumulative(acute, sequential, episodic, or sustained stressors all make demands on the system) • The level of response is related to perceived prospects for success (e.g., learned helplessness; active versus passive coping identified with specific columns within the periaquaductal gray (Paradiso et al. 1999))

  14. COPING RESPONSES:delicately balanced alternatives ! • “Fight or flight” (the classic stress alternatives to imminent aggressive threat –not only in animals with a cerebral cortex!) • “Flee or freeze”(lizards can apparently calculate prospects for survival based on external threat , internal resources, and environmental possibilities) • “Green or brown” (the Anolis carolinensis dermal chromatophore –the “chromomotor model”)

  15. SURVEY: stress-sensitive behavior • Detection, Arousal and Attention(steroids affect sensory thresholds, EPI intensifies; acute CS enhances salience) • Activity(CRF facilitates in familiar habitat, inhibits in unfamiliar habitat) • Exploration(CRF and ACTH enhances effects of novelty, CS facilitates) • Learning and memory( EPI, CRF, MSH facilitate acquisition) • Cognition( catecholamine modulation; taking prefrontal cortex “offline” (Arnsten))

  16. SURVEY: stress-sensitive behavior • Feeding( CS stimulates or inhibits depending on circulating levels) • Aggression(ACTH suppresses, CS increases or decreases depending on circulating levels) • Social Dominance(CS increases submissiveness) • Reproduction( ACTH, CS, opiods, and prolactin impair HPG axis) • Dysfunctional behavior(stereotypies, neuroses, psychoses)

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