Bio etiology depression

Biological Level of Analysis
In Depression
Serotonin Hypothesis
Catecholamine Hypothesis
• Suggested by Joseph Schildkraut in 1965
• Depression is associated with low levels of
• Serotonin Hypothesis – depression
Janowsky et al. (1972)
• Participants given drug called ‘physostigmine’
• Within minutes, profoundly depressed, selfhate, and suicidal wishes
• Mood change artificially, disturbance in
• Drugs increasing noradrenaline reduce
depression symptoms
• Delgano and Moreno (2000) – depression may
influence the production of neurotransmitters
• Rampello et al. (2000) – MDD patients imbalance
of noradrenaline, serotonin, dopamine,
acetylcholine – contradicted by Burns (2003)
• Lacasse and Leo (2005) – the brain is too complex
to consider only one reason behind depression
So far..
• Only one of the theories
• Research is less on the neurotransmitter, more
on the process as a whole
Cortisol Hypothesis
• Cortisol: hormone responsible for the stress
• Belongs to stress hormones called
glucocorticoids (plays role in fear and anxiety
• Patients with MDP have high levels of cortisol,
indicating possible link
Over-secretion of cortisol may be linked to other
High levels of cortisol may:
• lower serotonin receptors
• Lowers dopamine levels
• Weaken the function of receptors for
Relationship between stress and
• It cannot be concluded that there is a
causational or correlational relationship
• However high levels of cortisol are associated
with depressive symptoms
• Drugs that normalizes cortisol levels help
decrease depression symptoms
Effects of Depression
Long term depression may lead to structural
• Decrease of glucorticoid receptors in the
hippocampus and prefrontal cortex of suicidal
• Cushing’s syndrome results in excessive
production of cortisol
• Genetic predisposition/ vulnerability may
explain depression
Nurnberger and Gershon (1982):
• 7 twin studies
• Average concordance rate for MZ twins: 65%
• DZ twins: 14%
Duenwald (2003): 5-HTT gene: serotonin pathways
responsible for controlling mood, emotions,
aggression, sleep and anxiety
Caspi et al (2003):
• Correlation between gene and depression does
not indicate causation
• Genetic factors moderate responses to
environmental factors

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