Biological Level of Analysis

In Depression

Serotonin Hypothesis

Catecholamine Hypothesis

• Suggested by Joseph Schildkraut in 1965• Depression is associated with low levels of

noradrenaline• Serotonin Hypothesis – depression

Janowsky et al. (1972)

• Participants given drug called ‘physostigmine’• Within minutes, profoundly depressed, self-

hate, and suicidal wishes• Mood change artificially, disturbance in

neurotransmission?• Drugs increasing noradrenaline reduce

depression symptoms

Arguments

• 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 system

• Belongs to stress hormones called glucocorticoids (plays role in fear and anxiety reactions)

• Patients with MDP have high levels of cortisol, indicating possible link

Over-secretion of cortisol may be linked to other neurotransmitters

High levels of cortisol may:• lower serotonin receptors• Lowers dopamine levels• Weaken the function of receptors for

noradrenaline

Relationship between stress and depression

• 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 changes

• Decrease of glucorticoid receptors in the hippocampus and prefrontal cortex of suicidal victims

• Cushing’s syndrome results in excessive production of cortisol

Genetics

• 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