Biological explanation for schizophrenia: Dopamine hypothesis

Post mortems

A biochemical explanation of schizophrenia, suggests an excess of the neurotransmitter dopamine may be responsible for schizophrenia.

PET scans and animal studies

Evaluation

Evidence comes from drug studies, post mortems, pet scans and animal studies

Dopamine increase in the mesolimbic pathway -> positive symptoms


Dopamine increase in the mesocortical pathway -> negative symptoms

Post mortems

Falkai et al (1988)

  • Autopsies found people with schizophrenia have larger than usual number of dopamine receptors
  • Increase of DA in brain structures and receptor density
    • DA production is abnormal for schizophrenia

PET scans

Recent research

Seeman (2013)

  • Schizophrenics may have higher number of DA receptors - 6% increase
    • These receptors have a higher infinity to dopamine, they're more likely to bind to the neurotransmitter when it is present in the synapse

Animal studies

Lindstroem et al (1999)

  • L-Dopa (radioactively labelled chemical) given to 10 schizophrenics and 10 with no diagnosis
  • Taken up quicker with schizophrenic patients, receptors more sensitive to the drug
    • They produced more DA than the control group

Randrup and Munkvad (1966)

  • Raised dopamine levels of rats by injecting them with amphetamine
  • Change in behaviour, more stereotyped, aggressive and isolated
    • Resulted in psychotic behaviour characteristics of schizophrenics
  • This research sparked the dopamine hypothesis

Strengths

Weaknesses

1. Amphetamines produce symptoms similar to those of excess dopamine

  • Some evidence comes from effects of drugs such as amphetamines causing excess dopamine, resulting in symptoms of psychosis, which are similar to positive symptoms of schizophrenia
  • But excess dopamine has a stimulant effect (e.g overconfidence and high alertness), which are symptoms of mania rather than schizophrenia

1. PET scans show blocking dopamine receptors doesn't always remove symptoms

  • Drugs that block dopamine don't reduce schizophrenia symptoms who have had the illness for 10 years + (even if the block is 90% effective)

2. People with schizophrenia are more sensitive to dopamine uptake

  • Scanning shows if those with schizophrenia are given amphetamines there is a greater release of dopamine than if people without schizophrenia are given the drug
  • Suggests those with schizophrenia are more sensitive to excess dopamine than others
  • Carlsson (2000)

2. Blocking dopamine receptors takes a few days work

  • Anti-schizophrenic drugs block the dopamine receptors almost immediately but calming effects aren't noticed for several days
  • Suggests something other than excess dopamine causes psychotic symptoms

3. Phenothiazines block dopamine receptors and reduce schizophrenic symptoms

  • A group of drugs including chlorpromazine, given to people with schizophrenia
  • Alleviates symptoms and block dopamine receptors
  • If receptors are blocked, less dopamine will be taken up so the effects of excess dopamine are avoided

3. Social and environmental factors are involved

  • Seem to trigger schizophrenia, so a biological explanation isn't sufficient
  • Perhaps stressful events in life may trigger production of excess dopamine
  • Link between social class and schizophrenia --> third explanation