Dopamine Hypothesis

• What does the dopamine hypothesis state?


  Brains of people with scz have more dopamine than those who don't. Evidence from studies with drugs ( can induce symptoms of scz with drugs), post mortems and PET scans. Neurons that use dopamine fire too often and transmit too many messages or too often- could lead to hallucinations. Certain D2 receptors are known to play key role in guiding attention.
• Falkai et al (1998)?

  Autopsies found people with scz have larger number of dopamine receptors than usual.
• Lindstroem et al (1999)?

  Radioactively labelled chemical L-Dopa. Administered to 10 patients with scz and 10 with no diagnosis. L-Dopa taken up quicker with scz patients- suggests they were producing more DA than control group.
• What were the issues with the OG dopamine hypothesis?

  Giving people drugs which reduce dopamine reduces positive symptoms, but don't seem to affect negative symptoms. Only seems to explain positive symptoms. Oversimplified hypothesis.
• What is the revised dopamine hypothesis for scz?

  Too much dopamine and too little dopamine. Too much dopamine in neurons of mesolimbic pathway causes overstimulation in brain and hallucinations and delusions.
• Davis et al (1991)?


  Too little dopamine in D1 receptors in frontal lobe (part of Mesocortical pathway) is found in scz patients displaying negative and cognitive symptoms.
• What did research in 1950s look at?

  Role of dopamine in Parkinson's disease- neurological condition causing tremors and slow imprecise movements. Drug L-Dopa increased amount of dopamine in brain and reduced Parkinsonian symptoms. However caused behaviours similar to scz, so link between scz and dopamine established.
• J.J Griffith et al (1968)?

  Induced psychosis in non-scz volunteers with dexto-amphetamine( increases dopamine in brain).Found volunteers demonstrated generally abrupt onset of paranoid delusions and demonstrated cold and detached emotional response.
• Seeman and Lee (1975)?


  Research showed impact of antipsychotic drugs on D2 receptor. As D2 receptors primarily found in subcortical regions, limbic system became main focus of dopamine hypothesis.
• Link between mesolimbic pathway and scz?

  Dopamine major neurotransmitter in mesolimbic pathway. Pathway carries signals from ventral tegmental area to Nucleus Accumbens. Too much dopamine from neurons that fire too often or too quickly cause overstimulation and positive symptoms of scz. APs reduce dopaminergic neurotransmission and reduce dopamine activity in pathway and reduce positive symptoms.
• Link between mesocortical pathway and scz?

  Dopamine major neurotransmitter here. Pathway carries signals from ventral tegmental area to frontal lobe. Vital in emotional responses, motivation and cognition.
• Kenneth Davis et al (1991)?

  Too little dopamine (hypofunction) is evident in D1 receptors of frontal lobe of many individuals with cognitive impairments and negative symptoms of scz.
• What is the limbic system?

  Consists of variety of subcortical structures that are engaged in many functions, most notably emotions, memory formation and arousal. Nerve pathways leave from limbic system to many other subcortical structures and also to cerebral cortex.