Stress and Mood Disorders Flashcards
What does the stress response do?
- Mobilise energy stores
- Increase blood flow to brain and muscles
- Decrease blood flow to digestive and reproductive systems
- No energy wasted on growth, reproduction, and healing
- Ignore pain
Metabolic Stress response
Insulin is suppressed but glucagon is released. This causes the release of glucose and energy
Catecholomines and glucocorticoids are also released.
Long term response is weakness and fatigue
Suppression of the HPA axis - Feedback of cortisol on the PVN
- Cortisol binds to glucocorticoid receptors
- This triggers release of endocannabinoids
- These inhibit release of glutamate from pre-synaptic terminals onto PVN
Suppression of the HPA axis - Hippocampus
- Indirect inhibition
- Contains many mineralocorticoid receptors
- Intermediate-term feedback: returns psychogenic stress response back to baseline
Pituitary Gland
Beta-endorphins is released from the pituitary gland as a hormone to suppress pain. Also releases vasopressin
Cardio-vascular stress response
Vasopressin recovers more water in the kidneys leading to an increase in blood volume.
Sympathetic nervous system causes increased heart rate and vasoconstriction, which in turn increases blood pressure.
Long term leads to coronary heart disease
Major Depression symptoms
- Depressed mood
- Sleeping problems
- Fatigue
- Change in appetite
- Lethargy
- Feelings of worthlessness
Depression and the HPA axis
Dysregulated HPA axis is common in affective disorders
Both pathological increases and decreases in cortisol can lead to depressive symptoms
Chronic stress is a major risk factor for depression
Chronic Stress
Amygdala –> HPA Axis –> cortisol
Glucocorticoids (cortisol) –> Locus Coeruleus –> noradrenergic projections –> amygdala
How do glucocorticoids damage the hippocampus?
They reduce adult hippocampal neurogenesis and shrink dendritic arbors. They also reduce glucose uptake and in the long run kill hippocampal neurons.
All this leads to smaller hippocampal volume
Other effects of chronic stress
- Depletion of noradrenaline from locus coeruleus
- Depletion of serotonin from Raphe Nuclei
- Depletion of dopamine from Ventral Tegmental Area to nucleus acumen and prefrontal cortex
Sleep in Major Depressive Disorder
Shorter REM and short sleep latency (fall asleep straight away).
Can be caused by some anti-depressants that suppress REM sleep.
Lowering mood with sleep
Phase shift between endogenous circadian rhythm and externally imposed sleep-wake cycle can lead to lower mood/depression
Depression and circadian cycle
Circadian cycle is often advanced with depressed patients. Going to sleep with circadian clock, then slowly shifting the clock may help with depression.
Bright Light Treatment
Seems to have positive effects for non-seasonal depression. Could be related to the advanced circadian clock.
Evidence of connection between melanopsin-containing RGCs and vIPOA