Biological Explanations of Depression

The Biological explanations of Depression

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  • Created by: Jessica
  • Created on: 09-03-13 17:35
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  • Biological Explanations
    • Cortisol Hypersecretion
      • Cortisol is released when we are suffering from stress. It gives the body a steady supply of blood sugar to help fight or flight
      • Depressed patients often show an increased level of cortisol
      • Strickland et al. found no evidence of increased cortisol levels in a large group of women with depression or in the majority of those who were vulnerable to depression through adverse social or personal circumstances
        • Poses serious problems for an explanation linking elevated cortisol levels to lowered brain serotonin function and to depression
      • O'Keane and Marsh claim that during pregnancy, higher levels of cortisol are necessary for the normal development of the baby
        • However, if cortisol levels are too high this can lead to premature birth, which is the leading cause of infant death and post natal illness
    • Neurotransmitter Dysfuntion
      • Noradrenaline
        • Bunney et al. suggests that a deficiency in noradrenaline can be linked to depression
        • Post mortem studies show that depressed suicide victims reveal increased densities of noradrenaline receptors
          • When a NT is scarce in a synapse, the number of receptors expand to pick up whatever NTs are available
        • Leonard suggest that drugs that lower noradrenaline levels bring about depressive states, while those that increase noradrenaline levels show antidepressant effects
        • Kraft et al. studied 96 patients with major depression, who were treated with SNRI. Patients showed a significantly more positive response
      • Serotionin
        • Link between low levels of serotonin and depression
        • McNeal - Cerebrospinal fluid of depressed and suicidal patients show a reduced amount of a by product of serotonin showing a low level of serotonin in the Brain
        • Ruhe et al. - Patients are given a tryptophan - deficient amnio acid mixture that temporarily decreases serotonin levels in the brain. They experience a brief relapse of symptoms, suggesting that a lowering of serotonin levels results in depression
        • Aan Het Rot et al. suggest that it is possible that a depressive episode alters the serotonin system in such a way that a person becomes more vulnerable to the effects of future changes in serotonin levels
    • Genetic Factors
      • Family Studies
        • Research suggests that around 20% of probands' relatives have depression compared to 10% of the population suggesting there is a genetic link
        • Having a first degree relative puts people at greater risk
      • Twin Studies
        • MZ twins share 100% genes, compared to 50% of DZ, if MZ rates are higher, this indicates a genetic influence
        • McGuffin et al. studied 177 probands diagnosed with depression and looked at their same sex twin
          • The concordance rate was 46% for identical and 20% for faternal.      Strongly suggests a biological link
      • Adoption Studies
        • Wender et al. studied the biological relatives of adopted individuals who had been hospitalised for severe depression
          • Found a much higher incidence of severe depression in the biological relatives of the depressed group than in the biological relatives of a non-depressed control group
      • Genes as diatheses
        • Diatheses-stress relationship suggests that it is an interaction between genetics and environmental factors that leads to depression
        • Can assume that environmental factors will affect those with a genetic predisposition to depression differently to those without the genetic risk
      • Zhang et al. - A mutant gene that starves the brain of serotonin has been found to be 10 times more prevalent in depressed patients than in control individuals
        • The Mutant gene codes an enzyme in the brain which makes serotonin and can result in an 80% reduction of normal serotonin levels in the brain
        • Caron et al. found that this version of the gene was carried by 9 out of 87 depressed patients
      • Even though the concordance rates for genetic depression seem fairly low, this can be explained.
        • People may have a genetic predisposition to mental health disorders rather than depression itself
          • Kendler et al. found that a higher incidence of mental disorders in twins when looking at depression alone
            • Suggests some disorders are a product of genes that underline a number of different disorders
      • Support for this view comes from the evolutionary theory
        • The fact that depression is so widespread among humans suggests that it may have some evolutionary significance


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