There is growing evidence that two neurotransmitters - dopamine and glutamate - are abnormal in people with psychotic illness, including schizophrenia. Among many other things, these chemicals play a role in cognitive functions, such as memory, learning, and problem-solving.
A new study in Biological Psychiatry is now the first to examine the relationship between these two brain chemicals by measuring both in the same individuals.
Dr. James Stone and colleagues studied people with sub-threshold psychotic symptoms, who were at very high risk of undergoing transition to full-blown psychotic illness, using two brain imaging techniques - magnetic resonance spectroscopy, which allows measurement of glutamate in the brain, and [18F]DOPA positron emission tomography, which gives a measure of dopamine neuron activity.
""By combining neuroimaging approaches, we may get new insights into the disturbances in brain circuits that contribute to the emergence of psychosis and the full schizophrenia syndrome from the less developed symptoms of the at-risk state," commented Dr. John Krystal, Editor of Biological Psychiatry.
They found that in these individuals, lower glutamate in hippocampus, a major structure in the brain involved in memory, was associated with increased dopamine activity. This was in keeping with earlier animal models, and with clinical studies of hippocampal and striatal function in psychosis.
According to Dr. Stone, "the findings support the hypothesis of an abnormal relationship between the dopamine and glutamate neurotransmitter systems in individuals with psychosis, and suggest that the development of drugs targeting glutamatergic transmission may be useful in the early treatment of psychosis."
The findings also suggest that this abnormal glutamate-dopamine relationship may be a risk marker for later transition to a psychotic disorder.
New brain biomarker could enable early diagnosis of psychosis