Disturbance of brain biochemistry, especially involving monoamine transmitters, appears to be present in most psychiatric disorders, although it cannot be assumed that a chemical abnormality is the cause of the disorder rather than its result. Direct studies on the brains of living patients are limited for both practical and ethical reasons. Indirect techniques of investigation include the following:

• Post-mortem brain studies. These require brains to be harvested and frozen within a few hours of death. Findings may be influenced by recent medication, and the condition that caused the death, as well as by the psychiatric disorder of interest.

• Analysis of cerebrospinal fluid (CSF), blood, or urine for precursors or metabolites of neurotransmitters. The findings are affected by many factors such as diet and exercise, and may not give an accurate reflection of concentrations in the brain itself.

• Pharmacological studies. Inferences about the biochemical defect present in a particular disorder may be made from studies, performed on patients or on animals, of the properties of drugs that are effective in treating that disorder.

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