Neuroendocrine challenge tests: assessment of 5-HT function in anxiety and depression.

5-Hydroxytryptamine (5-HT, serotonin) has been implicated in the aetiology and pathophysiology of many psychiatric disorders over the last twenty-five years. The f'mding that drugs which altered 5-HT function improved depression, together with evidence of decreased levels of 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid (CSF), suggested that 5-HT might play some part in the aetiology of affective disorders (Coppen, 1967). Post-mortem findings of reduced 5-HIAA and/or 5-HT, and increased numbers of 5-HT 2 receptor binding sites in the brains of suicide victims have lent further support (Meltzer and Nash, 1988). However, the results from these studies remain conflicting (Deakin, 1988) and consistent evidence for the indoleamine hypothesis of depression is still lacking (Cowen and Anderson, 1991).