Schizophrenia - revised dopamine hypothesis (bio)

Mesolimbic pathway

• ventral tegmental area → nucleus accumbens

• regulates salience, fear and reinforcement learning

• too much dopamine along this pathway causes overstimulation and positive symptoms

how does antipsychotic drugs work?

reduces activity in the mesolimbic pathway, which reduces symptoms

what is salience

desire and motivation

Mesocortial pathway

• ventral tegmental area → frontal lobe

• lobe involved in cognitive control, motivation and emotional response

• associated with negative symptoms

Davies et al (1999) (mesocortial)

found too little dopamine in D1 receptors is evidence of negative symptoms of scz.

L-dopa drug

• Used to try and treat parkinsons

• worked by increasing dopamine

• side effects were positive symptoms

• supports the mesolimbic pathway

However atypical antipsychotics work by targeting:

serotonin

Patel et al (2010)

• assessed level of dopamine in schizophrenics using a PET scan

• control group of non-schizophrenics

• found lower levels of dopamine in prefrontal cortex of non-scz.

• Valid as PET scans are scientific

Grottesman et al (1991)

looked at incidence of schizophrenia in cousins, grandchildren, half-siblings, parents, siblings, MZ and DZ twins.

As genetic similarity increased, so did the probability of both individuals having schizophrenia

Difficulty in measuring dopamine

dopamine is measured in cerebrospinal fluid which can only be obtained through lumbar puncture - this is a painful procedure

the participants drug use and diet can affect metabolite levels and make it difficult to assess dopamine levels, and it varies widely from participants

Therefore conclusions are being drawn from uncertain metabolite-based research

Serotonin

Atypical antipsychotics work by blocking the D2 receptor and the Serotonin receptor equally. Therefore the dopamine hypothesis may be reductionist as it places scz on one neurotransmitter when there’s proof of 2

Copolov and Crook (2000)

Using PET scans they were unable to detect differences in the dopamine activity of the brains of individuals with scz and without

May be that scz causes dopamine imbalances, and so may be a symptom (cause or effect)