biochemistry

• the dopamine hypothesis

  research suggests that faulty levels of dopamine in the brain can cause symptoms of schizophrenia.
• the dopamine hypothesis

  dopamine is an excitatory neurotransmitter, increasing the rate of impulses between neurons
• too much dopamine has been linked with positive symptoms [type 1 schizophrenia]
• too little dopamine has been linked to negative symptoms [type 2 schizophrenia]
• evidence to support the dopamine hypothesis:

  1. anti-psychotic drugs work by blocking dopamine receptors and reducing dopamine activity. these have proven very effective in reducing positive symptoms such as hallucinations, delusions and paranoia
  2. giving someone drugs sthat create a sudden increase in dopamine activity [e.g. LSD or amphetamines] can bring on schizophrenia symptoms
  3. L - Dopa has been shown to alleviate negative symptoms by raising dopamine levels
• how did Davis updaate the dopamine hypothesis?

  high levels of dopamine are not found in all schizophrenics and modern anti-psychotics have little dopamine blocking activity but still work

  He suggestee that it is high levels in the mesolimbic dopamine system that is associated with positive symptoms. while high levels of dopamine in the mesocorticol dopamine system are associated with negative symptoms
• what is the mesolimbic pathway?

  [reward pathway]

  its located in the midbrain. it controls motivation for rewarding. stimuli facilitates reinforcement and reward-related motor function learning, and may plat a role in the perception of pleasure
• what is the mesocortical pathway?

  another dopamine pathway that is essential for the normal cognitive function of the prefrontal cortex [part of the frontal lobe], and is thought to be involved in cognitive control, motivation and emotional response. this pathway is thought to be associated with the negative symptoms of schizophrenia
• Randrup

  gave rats amphetamines, which increase dopaminergic activity, and created schizophrenia like symptoms.

  Randrup then reversed the effects by giving them neuroleptics which inhibit the release of dopamine

  this supports the hypothesis
• postmortems and the dopamine hypothesis

  postmortems on schizophrenic sufferers found excess dopamine in the limbic system, supporting the hypothesis
• research against the dopamine hypothesis

  1. other neurotransmitters have also been identified as potentially being involved in schizophrenia, including serotonin and glutamate. gene mapping supports this
  2. newer anti-psychotic drugs work on serotonin rather than dopamine activity and are proving equally as effective. suggesting serotonins role in schizophrenia
  3. some people have schizophrenia [positive symptoms] but have normal dopamine levels, up to 1/3 of sufferers. anti-psychotics then have no impact