Serotonin transporter binding is reduced in seasonal affective disorder following light therapy

Abstract

Objective To investigate the effects of light therapy on serotonin transporter binding (5‐ HTT BP ND ), an index of 5‐ HTT levels, in the anterior cingulate and prefrontal cortices ( ACC and PFC ) during winter in seasonal affective disorder ( SAD ). 5‐ HTT BP ND fluctuates seasonally to a greater extent in SAD relative to health. We hypothesized that in SAD , 5‐ HTT BP ND would be reduced in the ACC and PFC following light therapy. Methods Eleven SAD participants underwent [ 11 C] DASB positron emission tomography ( PET ) scans to measure 5‐ HTT BP ND before and after 2 weeks of daily morning light therapy. Results The primary finding was a main effect of treatment on 5‐ HTT BP ND in the ACC and PFC (repeated‐measures manova , F (2,9) = 6.82, P = 0.016). This effect was significant in the ACC ( F (1,10) = 15.11 and P = 0.003, magnitude of decrease, 11.94%) and PFC ( F (1,10) = 8.33, P = 0.016, magnitude of decrease, 9.13%). 5‐ HTT BP ND also decreased in other regions assayed following light therapy (repeated‐measures manova , F (4,7) = 8.54, P = 0.028) including the hippocampus, ventral striatum, dorsal putamen, thalamus and midbrain ( F (1,10) = 8.02–36.94, P < 0.0001–0.018; magnitude −8.83% to −16.74%). Conclusions These results demonstrate that light therapy reaches an important therapeutic target in the treatment of SAD and provide a basis for improvement of this treatment via application of [ 11 C] DASB PET .