contemporary study: carlsson et al (2000)

• aim

  to review studies into the relationship between levels of NT & SZ (dopamine & glutamate) - 2 existing explanations of what might be responsible for SZ

  • hyperdopaminergia (high levels of dopamine)
  • hypoglutamatergia (low levels of glutamate)
• procedure - groups of studies

  literature review which involved reviewing 33 previous studies on NT levels in patients with SZ - groups of studies looked at:

  1. brain scan studies in SZ looking at dopamine activity in the brain
  2. use of recreational drugs known to induce psychotic symptoms (e.g: PCP linked with psychosis, amphetamines which increase dopamine levels)
• what are PET scans

  • involve injecting the patient with a radioactive tracer carried by the blood to the brain which concentrates around brain structures that are active
  • scan detects radioactivity and converts digital image of brain, highlighting areas in yellow and red
• procedure - researchers evidence

  • researchers drew on evidence from studies into effectiveness of drugs used to treat SZ and mechanism of action it has on the brain to see which NT are associated with SZ
  • researchers discussed what kind of drugs can be produced without side effects to improve quality of life and improve compliance rates as patients complained about side effects
• findings - drug use

  • amphetamine (increasing effects of dopamine) users - increases SZ like symptoms
  • PCP - linked to creating SZ like symptoms as it antagonies glutamate receptor NMDA receptors so PCP reduces action of glutamate in the brain which result in psychotic symptoms in users even more than amphetamine users
• findings - glutamate

  • low levels of glutamate is linked to psychotic symptoms as glutamate is related in both positive/negative symptoms of SZ
  • low levels in the cerebral cortex = negative symptoms of SZ & low levels in the basal ganglia = positive symptoms
• findings - thalamus

  thalamus filters out information from sense - glutamate is dominant but if glutamate levels are low, thalamus cannot filter so leads to hyperarousal leading to positive symptoms of SZ
• findings - effective treatments

  studies shown that clozapine (reducing psychotic symptoms) has antidopaminergic (blocks activity of dopamine) and antiserotonergic (blocks activity of serotonin) functions so reduces level of both NT
• conclusion

  • carlsson suggested that SZ may have different subtypes that could be caused by different NT such as glutamate not just dopamine
  • means there are implications for drug treatments as drug needs to be carefully targeted at particular NTs
  • further research still needed to develop drugs that treat SZ and avoid severe side effects
• strength

  • draws from a large pool of 33 studies as secondary data to come up with results and conclusion
  • carlsson has a large sample size & dataset of patients of a rare MH disorder and allows studies to be collated & increase diversity of sample size so increasing generalisability of conclusions that multiple NT are linked to SZ
  • findings of the causes and suggestions for treatments of SZ is applicable to SZ patients and their therapists
• weakness (counterpoint)

  • secondary data collected may include studies that have used old classification systems (e.g: DSM 3 to diagnose patients)
  • means results may not be true for updated classification systems
  • therefore, not valid for MH disorders at present time
• strength

  • study could lead to development of new drugs - real life application
  • carlssons emphasis on serotonin & glutamate has pointed pharmaceutical businesses to consider serotonin antagonists and glutamate agonists to reduce symptoms of SZ
  • study can lead to new drugs with little side effects & high compliance rates to treat SZ
• weakness

  • study not generalisable to humans
  • many of the studies used in review were based on animal research, such as animals being given NMDA antagonists
  • results from some of the studies may not be generalised to humans as our brain structures and NT are not identical