One Biological Explanation for Uni-polar Depression Flashcards
what is the biological explanation of uni-polar depression (upd) ?
neurochemical
who came up with the monoamine depletion hypothesis ?
Joseph schildkraut (1965)
what did schildkraut argue ?
upd is caused by low levels of the monoamine neurotransmitters
what are the monoamine neurotransmitters ?
1) serotonin
2) dopamine
3) noradrenaline
what is serotonin ?
a chemical created by the body that works as a neurotransmitter. it is responsible for managing moods.
what is noradrenaline ?
it is a catecholamine hormone and neurotransmitter with multiple roles including maintaining concentration.
what are receptor sites ?
areas on the post-synaptic neuron that allow neurotransmitters to lock onto the membrane
what is down-regulation ?
it is a homeostatic mechanism where the brain produces less of something in response to an increase.
where in the brain are monoamine neurotransmitters known to regulate functions ?
the brain’s limbic system (the emotional centre that form connections with other areas of the brain, like the frontal cortex):
- amygdala
- hypothalamus
- hippocampus
what did the original hypothesis focus on and what was wrong with it ?
it focused only on serotonin (low levels of serotonin causes depression) - this ignored the substantial evidence for the role of noradrenaline
what was the developed monoamine depletion hypothesis called and what did it claim ?
the permissive hypothesis - states that it is the balance of serotonin and noradrenaline that causes depression (serotonin usually controls the level of noradrenaline but low levels of serotonin ‘permits’ noradrenaline levels to drop too - causing depression)
overall, what does the permissive hypothesis state ?
serotonin is a necessary condition for depression but not sufficient on its own.
why was the monoamine depletion hypothesis quickly challenged and why?
because it was too simplistic - drugs were developed that had antidepressant properties that didn’t increase levels of monoamine neurotransmitters, suggesting there was more causing depression than these alone
what does the receptor sensitivity hypothesis argue ?
that depression is caused by changes in the sensitivity of post-synaptic receptors
what usually occurs with receptors when there is a depletion of neurotransmitters ?
up-regulation - neurons compensate for the reduction in neurotransmitter stimulation by increasing the sensitivity of receptors and -over the long term - producing more of them
instead of up-regulation, what happens in depression ?
down-regulation - serotonin and noradrenaline post-synaptic receptors become even more sensitive (supersensitivity) to the reduced stimulation than normal
what does BDNF stand for ?
brain-derived neurotrophic factor
what is BDNF ?
a chemical that ‘feeds’ neurons the nutrients they need to survive, grow and function efficiently
what does BDNF play a key role in ?
neuronal plasticity
what is neuronal plasticity ?
the ability of the brain to form new synapses
what are the conditions of BDNF in people with upd ?
they have low levels of BDNF in the hippocampus and prefrontal cortex
what is BDNF’s close relationship with symptom severity ?
the lower the levels of BDNF, the more severe the symptoms (negative correlation)
what has the BDNF hypothesis allowed researchers to find and how ?
a link between depression and stress - this is because the gene for BDNF may be ‘switched-off’ under stress
when the BDNF gene is ‘switched-off’, what can this lead to ?
it can lead to the neurons that are fed by BDNF being left vulnerable to atrophy (shrinkage) or apoptosis (cell death) - both of which are observed in depression