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BIOLOGICAL EXPLANATIONS. Bio chemical changes. Genetic inheritance. Metabolic & hormonal changes. MAOI’S. In the 1950’s, using Monoamine oxidising inhibitors for TB, they discovered that patients were remarkably euphoric. Yippee, I’m ill!.

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Bio chemical changes

Genetic inheritance

Metabolic & hormonal changes


  • In the 1950’s, using Monoamine oxidising inhibitors for TB, they discovered that patients were remarkably euphoric

Yippee, I’m ill!

Qu. Therefore, what neurotransmitters are likely to be involved with mood?

  • Monoamines are = ?

  • Serotonin – Noradrenaline – Dopamine

  • catecholamine" hypothesis

  • Schildkraut (1965)believed that too high a level of noradrenaline led to mania and too little to depression. 

Qu. What happens if you change the level of one monoamine?

  • Prange, 1974

  • A deficit in serotonin ‘permits’ (not causes) the symptoms of depression.

  • Changes in serotonin levels affect the nature and intensity of the symptoms.

  • If monoamine activity is increased = mania

  • If monoamine activity is decreased = depression

Kety, 1975 – Permissive Amine Theory

  • Both Serotonin and noradrenaline levels change in mood disorders.

  • It is serotonin that controls the levels of noradrenaline.

  • High levels of serotonin keep levels of noradrenaline constant which prevents mood swings.

  • There is a serotonin deficit in depressives = is genetic.

  • Qu. Therefore, according to this theory, what happens if there are low serotonin levels?

Kety, 1975 – Permissive Amine Theory





Qu. What if Serotonin levels drop to a very low level?

Supporting evidence for the permissive amine theory?

  • Teuting et al (1981)

  • Examined the urine of depressed patients

  • Found by-products that suggest lowered levels of both serotonin and noradrenalin.

Supporting evidence for the permissive amine theory?

  • McNeal & Cimbolic (1986)

  • Examined the cerebo -spinal fluid of depressed suicidal patients

  • Found reduced amount of by-product.

  • Suggests low level of serotonin in the brain

Qu. If this theory is true, what would happen if you take drugs to increase serotonin levels?

  • Drugs treatments that concentrate on raising serotonin levels (SSRI’s) do improve the depressed mood in the majority of patients

  • Newer anti-depressants (like Effexor) are actually targeted at both serotonin and noradrenaline, and are even more effective in treating depression.

Qu. Can this theory explain gender differences in prevalence rates?

  • Diksic et al (1997)

  • Found that men make 52% more serotonin than women.

  • Qu. Conclusion?

  • This could make men far less prone to depression than women.

Qu. Any criticisms of theory?

  • 1. Not all depressives show reduced levels of these neurochemicals.

  • Qu. Would these benefit from drug treatments?

  • No, not all patients benefit from drugs treatments.

  • Qu. What does this imply about the causes?

  • Are other biological factors involved?

  • Cortisol, oestrogen, diet?

Qu. Any criticisms of theory?

  • Deakin & Graeff (1991)

  • 2. Even following recovery from depression the deficits in serotonin and noradrenalin levels still remain.

  • Qu. What does this imply?

  • Another neurochemical involved perhaps?

Qu. Any criticisms of theory?

  • 3. Anti-depressives such as MAOIs (monoamine oxidase inhibitors) increase the levels of noradrenalin and serotonin within minutes. 

  • However, they have no effect on mood for many weeks (normally two weeks).

  • This suggests that they are not working simply by increasing the levels of chemical in the brain.

  • Qu. What does this imply about the cause?


Depression is a complex issue

We don’t really understand the full interaction between neurotransmitters.

Other biological factors are clearly involved.

Genetics & Depression

Qu. How do you ‘prove’ a genetic argument for any behaviour?

Twin studies:

McGuffin et al, 1996



Bertelsen 1977



Qu. Problems?



Genetics & Depression

Family concordance rates

Gershon 1990



Wender 1986


70% if adopted

Gen Pop


Qu. Problems?

Essay Preparation

  • Biological Aetiologies

  • Using PPt and handout group A01 and AO2 material for Neurotransmitter Explanations

  • Do the same for genetic explanations

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