Effect of 5-hydroxytryptophan on H-reflex recovery curves in normal subjects and patients with affective disorders

The effect of the serotonin precursor DL-5-hydroxytryptophan (5-HTP) on the Hoffmann reflex recovery curve (HRRC) was studied in normal subjects and patients with affective illness. 5-HTP significantly decreased the HRRC in normal controls and in depressed and manic patients receiving treatment with lithium or antidepressants. 5-HTP increased the HRRC in unmedicated depressed and manic patients. These results provide further evidence for a serotonergic abnormality in the affective disorders.