The effect of light therapy on serotonin uptake capacity in patients s
uffering from winter depressions (seasonal affective disorders) was ex
amined indirectly by using [H-3]paroxetine binding to determine the nu
mber of platelet serotonin transporters. In patients who responded to
light therapy the number of platelet serotonin transporters decreased
significantly following treatment. In contrast, patients who did not r
espond to light therapy were found to have a relatively low number of
serotonin transporters prior to treatment, and the number did not chan
ge significantly following treatment.