Lecture 17 - Stress and Motivation Flashcards
Depression
Abnormal stress and fear substrates
very undertreated
-reduced input from PFC to subcorticol structures
-less dampening on HPA axis (PVN)
-hyperactive HPA = stress response
-chronic elevated cortisol damaging to body
Stress
Anything that shifts homeostasis –> daily occurence
- state of homeostatic dysregulation produced by aversive stimulus
- release epinephrine and activate HPA axis
Fear
Perception of threat
-considered at one end of arousal-stress continuum
Homeostasis
process by which stable internal milieu maintained in face of challenges
- set point, sensor to detect deviations, mechanism for returning to set point
- important for acute changes
Allostasis
process by which system deals with changes in SET PT
- positive feed back loops due to compensatory changes
- opponent process causing change in set point
- chronic, repeated, extreme changes to set point
Factors determining stress effect
Chronicity
Perceived controllability
Stressor physical vs. psychological
HPA axis
hypothalamus-pituitary-adrenal axis
- fight or flight from cortisol and epinephrine
- neuroendocrine system mediating stress response
- transiently activated in response to stress
- cortisol preps body for stress, helps produce glucose
- neg feedback direct to PVN and hippocampus
- moderate glucocorticoids aid in learning/memory
- high glucocorticoids are neurotoxic to hippocampus
Paraventricular nucleus
PVN of hypothalamus initiates response to acute stress
- multimodal sensory inputs to PVN
- releases corticotropin releasing hormone
- affects Locus coeruleus (arousal, awareness activation)
- affects Ant. Pit via portal system –> ACTH –> Cortisol
- affects dorsal motor X (decrease parasympathetic tone)
- possibly affects lateral T1-L2 (increase sympathetics)
PFC dampens PVN activity from psych stress
CRF system
Corticotropin-releasing factor (separate from HPA)
- unique and independent population of neurons in central nuclei of amygdala that also produces CRF
- amygdala transiently activated when afraid or stressed
- psych stress recruits CRF production in amygdala
- enhance learning/memory associated with acute stress
Excessive stress
contributes to depression and other psychiatric illness by allostatically altering systems that regulate normal adaptive stress/fear responses
-chronic stress causes hippocampal atrophy (decreases normal neurogenesis)
Learned helplessness model
3 mice
1. control
2. able to stop stressful stimuli (stops both 2. and 3’s)
3. feels stimuli but dependent on 2 to stop
#3 mouse has depression
CRF
Corticotropin-releasing factor
- widespread localization of CRF and receptors in forebrain for coordinated stress response
- CRF elevated in depressed patients
- major regulator of stress/fear
- activates HPA axis
- activates LC-NE (autonomic response)
- elicits anxiety and fear resposne from amygdala
