Stress and the Brain Flashcards
What is the definition of stress?
A change in autonomic, endocrine or other behavioral functions that serves to maintain homeostasis.
The change occurs in response to an actual or perceived threat to homeostasis.
What is the impact of chronic stress on the systems that mediate the stress response?
Chronic bodily response to stresssors can result in the dysregulation of the systems that are designed to mitigate the effect of the stressor –> cause or exacerbate disease
What areas of the brain are active in a person who is alert safe and attentive vs. someone who is stressed?
Non-stressed person - prefrontal cortex provides top down regulation of behavior, thought and emotion. A moderate amount of NE is released which strengthens the PFC and weakens the amygdala
High levels of catecholamines in brain weaken PFC function and strengthen affective responses of amygdala and habitual responses of basal ganglia. The stress response is activated by the amygdala which activates catecholamine centers in the brainstem under psychological stress. This produces a viscious cycle that promotes primitive circuits in control of behavior.
What area of the brain produces CRF?
Paraventricular nucleus
Describe how the amygdala and hippocampus regulate the HPA.
What are the effects of chronic stress on the neurons in the hippocampus, amygdala and prefrontal cortex?
- Decrease in dendrites on neurons of hippocampus and PFC (reduced hippocampal volume)
- Increase in dendrites on neurons of amygdala (increased amygdala volume)
- Since dendrites have receptors for NT, this implies decreased potential for activation of hippocampus and PFC and increase potential for activation of amygdala
Is the damage that is done to cells in the hippocampus by stress and glucocorticoids permanent?
No
Chronic stress does lead to glucocorticoid induced reduction of BDNF, which is brain derived neurotrophic factor. BDNF supports brain health, plasticity, and is antiapoptotic. Reduction of this factor in stress leads to hippocampal neuron atrophy.
Antidepressants have been shown to increase the amount of BDNF again and return hippocampal neurons to their state before the stress induced damage.
Describe the extrahypothalamic production and secretion of CRF.
The central nucleus of the amygdala can also make CRF. It does so in response to stressful stimuli. When it makes CRF, it secretes it locally as a neuropeptide and not as a hormone. It stimulates the bed nucleus of the stria terminalis, the PVN of hypothalamus, and the Locus coeruleus while inhibiting the raphe nucleus. The end result is behavior that is similar to those seen in stress and depression.
Describe the differences between the CRF 1 and CRF 2 receptors in the brain.
CRF 1 in limbic system –> when activated produces anxiety effects of stress
CRF 2 in other parts of brain –> when activated may reduce anxiety like behavior
When the amygdala secretes CRF to the bed nucleus of the stria terminalis, what behavior does that illicit?
Mediates chronic anxiety
What is the difference in the fear response produced by the amygdala vs. the bed nucleus of stria terminalis?
Amygdala = phasic, adaptive fear
BNST = sustained fear, due to sustained reslease of CRF
- In addition to rises in cortisol, acute and chronic stress lead to rises in what 2 other neurotransmitters?
- What effect does this have on the brain?
- What effect does this have on behavior?
- Norepinephrine and dopamine
- Impairs cognitive functioning of PFC and strengthens non-PFC cognitive areas (limbic system)
- Weakens ability of PFC to provide intelligent,inhibitory regulation of behavior, while strengthening the habitual behaviors mediated by subcortical structures
The locus coeruleus is part of what other system in the brain?
Ascending arousal (reticular formation)
- How does physchological stress lead to a change in behavior where a person relies less on the prefrontal cortex for dealing with the situation and more on subcortical structures of the limbic system, like the amygdala and nucleus accumbens?
- What role does glucocorticoids play in this response?
- Psychological stress stimuli activate the amygdala –> amygdala activates locus coeruleus and ventral tegmental area to release NE and dopamine, respectively –> high levels of NE and dopamine impair the rational function of the PFC and weaken it’s control over behavior and emotions –> simultaneously high levels of NE and dopamine strengthen the affective and habitual responses of the amygdala and nucleus accumbens –> a person’s response to stress becomes more emotional and less rational
- The presence of glucocorticoids that ares also produced by the adrenal cortex during the stress response enhance the actions of NE and dopamine in the brain
